Release v0.1.5

README.md

@@ -33,7 +33,26 @@ The first backend implementation stores VEVENT data in two layers:
 - normalized fields for API range queries and calendar rendering
 - raw iCalendar property records and generated `text/calendar` output so unsupported VEVENT properties and parameters can round-trip
 
-This is intentionally not yet a network CalDAV server. CalDAV protocol sync, external ETags, REPORT handling, scheduling inbox/outbox behavior, and full recurrence expansion are calendar-owned follow-up work.
+CalDAV sync is implemented as a calendar-owned backend primitive. A CalDAV source
+records the remote collection URL, sync token, ETag/ctag state, username,
+credential reference, sync interval, sync direction, and conflict policy.
+Credentials can be supplied transiently for manual sync, referenced from
+environment variables with `env:NAME`, stored through a platform secret provider
+when one is available, or stored as encrypted calendar-owned credentials.
+
+Inbound sync uses CalDAV `calendar-query` for full sync and `sync-collection`
+when a sync token exists. It imports all VEVENT components in a resource and
+soft-deletes local events when remote resources disappear. Two-way sources also
+write local creates, updates, and deletes back with CalDAV `PUT`/`DELETE` and
+ETag preconditions. If a remote resource changed, the local mutation is rejected
+and the user must sync before retrying. A calendar-owned task,
+`govoplan_calendar.sync_due_caldav_sources`, can run due sources in a worker or
+cron-style scheduler.
+
+This is not yet a full CalDAV network server. Scheduling inbox/outbox behavior,
+CalDAV server endpoints, UI credential management, and full user-facing
+recurrence editing remain follow-up work. The backend now includes a free/busy
+API primitive for scheduling and appointment modules.
 
 ## Development
 

docs/CALENDAR_INTEGRATION_CONCEPT.md

@@ -22,9 +22,11 @@ The first standalone module provides:
 - normalized query fields: start, end, summary, location, all-day flag, status, transparency, classification, calendar ID, UID, recurrence ID, sequence, source, and ETag
 - iCalendar preservation: raw VEVENT properties, parameters, and generated `text/calendar` export
 - API endpoints for listing calendars, creating/updating/deleting events, importing iCalendar, and exporting event ICS
+- free/busy API primitive with recurrence expansion for scheduling and appointment conflict checks
+- calendar-owned CalDAV sync sources with credential references, scheduled due-sync metadata, full/incremental inbound sync, two-way PUT/DELETE writes, and ETag conflict handling
 - WebUI views: month, week, workweek, day, and continuous week-row scrolling
 
-The first implementation is not yet a full CalDAV network server. It is the internal calendar storage and UI foundation on which CalDAV sync, Open-Xchange integration, recurrence expansion, and free/busy endpoints can be built.
+The first implementation is not yet a full CalDAV network server. It is the internal calendar storage, sync, availability, and UI foundation on which Open-Xchange integration, richer recurrence editing, scheduling inbox/outbox behavior, and CalDAV server endpoints can be built.
 
 ## Integration Points
 
@@ -112,8 +114,9 @@ The connector boundary should hand calendar a configured profile and credentials
 ## Follow-Up Work
 
 - Full recurrence expansion for RRULE, RDATE, EXDATE, RECURRENCE-ID, overridden instances, and detached instances.
-- Free/busy endpoint and capability for scheduling, appointments, and resource checks.
-- CalDAV sync adapter with collection sync tokens, ETags, REPORT handling, and conflict resolution.
+- User-facing recurrence editing for RRULE, RDATE, EXDATE, RECURRENCE-ID, overridden instances, and detached instances.
+- UI management for CalDAV credentials, sync status, sync direction, and conflict resolution.
+- CalDAV server endpoints if GovOPlaN should expose calendars to external clients rather than only syncing remote collections.
 - Open-Xchange adapter that maps OX calendars, attendees, resources, recurrence, and free/busy to the internal calendar model.
 - Attendee RSVP workflow and mail/notification bridge.
 - Resource calendars for rooms, equipment, counters, and service desks.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@govoplan/calendar-webui",
-  "version": "0.1.4",
+  "version": "0.1.5",
   "private": true,
   "type": "module",
   "main": "webui/src/index.ts",
@@ -19,7 +19,7 @@
     "LICENSE"
   ],
   "peerDependencies": {
-    "@govoplan/core-webui": "^0.1.4",
+    "@govoplan/core-webui": "^0.1.5",
     "lucide-react": "^0.555.0",
     "react": "^19.0.0",
     "react-dom": "^19.0.0",

pyproject.toml

@@ -4,15 +4,17 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "govoplan-calendar"
-version = "0.1.4"
+version = "0.1.5"
 description = "GovOPlaN calendar module with VEVENT storage and WebUI integration."
 readme = "README.md"
 requires-python = ">=3.12"
 license = { file = "LICENSE" }
 authors = [{ name = "GovOPlaN" }]
 dependencies = [
-  "govoplan-core>=0.1.4",
-  "govoplan-access>=0.1.4",
+  "govoplan-core>=0.1.5",
+  "govoplan-access>=0.1.5",
+  "icalendar>=7.2",
+  "python-dateutil>=2.9",
 ]
 
 [tool.setuptools.packages.find]

src/govoplan_calendar/backend/caldav.py

@@ -0,0 +1,275 @@
+from __future__ import annotations
+
+import base64
+import urllib.error
+import urllib.parse
+import urllib.request
+from dataclasses import dataclass, field
+from typing import Mapping, Protocol
+from xml.etree import ElementTree
+
+
+class CalDAVError(RuntimeError):
+    pass
+
+
+class CalDAVSyncUnsupported(CalDAVError):
+    pass
+
+
+class CalDAVPreconditionFailed(CalDAVError):
+    pass
+
+
+class CalDAVTransport(Protocol):
+    def __call__(self, method: str, url: str, headers: Mapping[str, str], body: bytes | None, timeout: int) -> tuple[int, Mapping[str, str], bytes]:
+        ...
+
+
+@dataclass(frozen=True, slots=True)
+class CalDAVObject:
+    href: str
+    etag: str | None = None
+    calendar_data: str | None = None
+    deleted: bool = False
+
+
+@dataclass(frozen=True, slots=True)
+class CalDAVReportResult:
+    objects: list[CalDAVObject] = field(default_factory=list)
+    sync_token: str | None = None
+    ctag: str | None = None
+
+
+@dataclass(frozen=True, slots=True)
+class CalDAVWriteResult:
+    href: str
+    etag: str | None = None
+    status: int = 0
+
+
+class CalDAVClient:
+    def __init__(
+        self,
+        *,
+        collection_url: str,
+        username: str | None = None,
+        password: str | None = None,
+        bearer_token: str | None = None,
+        timeout: int = 30,
+        transport: CalDAVTransport | None = None,
+    ) -> None:
+        self.collection_url = ensure_collection_url(collection_url)
+        self.username = username
+        self.password = password
+        self.bearer_token = bearer_token
+        self.timeout = timeout
+        self.transport = transport or urllib_transport
+
+    def propfind_collection(self) -> CalDAVReportResult:
+        body = b"""<?xml version="1.0" encoding="utf-8"?>
+<D:propfind xmlns:D="DAV:" xmlns:CS="http://calendarserver.org/ns/">
+  <D:prop>
+    <D:displayname/>
+    <D:sync-token/>
+    <CS:getctag/>
+  </D:prop>
+</D:propfind>"""
+        payload = self.request("PROPFIND", self.collection_url, body=body, depth="0", expected={207})
+        return parse_multistatus(payload)
+
+    def list_objects(self) -> CalDAVReportResult:
+        body = b"""<?xml version="1.0" encoding="utf-8"?>
+<C:calendar-query xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav">
+  <D:prop>
+    <D:getetag/>
+    <C:calendar-data/>
+  </D:prop>
+  <C:filter>
+    <C:comp-filter name="VCALENDAR">
+      <C:comp-filter name="VEVENT"/>
+    </C:comp-filter>
+  </C:filter>
+</C:calendar-query>"""
+        payload = self.request("REPORT", self.collection_url, body=body, depth="1", expected={207})
+        return parse_multistatus(payload)
+
+    def sync_collection(self, sync_token: str) -> CalDAVReportResult:
+        body = f"""<?xml version="1.0" encoding="utf-8"?>
+<D:sync-collection xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav">
+  <D:sync-token>{xml_escape(sync_token)}</D:sync-token>
+  <D:sync-level>1</D:sync-level>
+  <D:prop>
+    <D:getetag/>
+    <C:calendar-data/>
+  </D:prop>
+</D:sync-collection>""".encode("utf-8")
+        try:
+            payload = self.request("REPORT", self.collection_url, body=body, depth="1", expected={207})
+        except CalDAVError as exc:
+            raise CalDAVSyncUnsupported(str(exc)) from exc
+        return parse_multistatus(payload)
+
+    def fetch_object(self, href: str) -> str:
+        payload = self.request("GET", self.object_url(href), body=None, depth=None, expected={200})
+        return payload.decode("utf-8")
+
+    def put_object(self, href: str, ics: str, *, etag: str | None = None, create: bool = False, overwrite: bool = False) -> CalDAVWriteResult:
+        headers = {"Content-Type": "text/calendar; charset=utf-8"}
+        if create:
+            headers["If-None-Match"] = "*"
+        elif etag and not overwrite:
+            headers["If-Match"] = etag
+        elif not overwrite:
+            raise CalDAVPreconditionFailed("Refusing CalDAV PUT without an ETag")
+        status, response_headers, _payload = self.request_raw(
+            "PUT",
+            self.object_url(href),
+            body=ics.encode("utf-8"),
+            depth=None,
+            expected={200, 201, 204},
+            extra_headers=headers,
+        )
+        return CalDAVWriteResult(href=href, etag=response_etag(response_headers), status=status)
+
+    def delete_object(self, href: str, *, etag: str | None = None, overwrite: bool = False) -> CalDAVWriteResult:
+        headers: dict[str, str] = {}
+        if etag and not overwrite:
+            headers["If-Match"] = etag
+        elif not overwrite:
+            raise CalDAVPreconditionFailed("Refusing CalDAV DELETE without an ETag")
+        status, response_headers, _payload = self.request_raw(
+            "DELETE",
+            self.object_url(href),
+            body=None,
+            depth=None,
+            expected={200, 202, 204, 404},
+            extra_headers=headers,
+        )
+        return CalDAVWriteResult(href=href, etag=response_etag(response_headers), status=status)
+
+    def object_url(self, href: str) -> str:
+        return urllib.parse.urljoin(self.collection_url, href)
+
+    def request(self, method: str, url: str, *, body: bytes | None, depth: str | None, expected: set[int]) -> bytes:
+        _status, _headers, payload = self.request_raw(method, url, body=body, depth=depth, expected=expected)
+        return payload
+
+    def request_raw(
+        self,
+        method: str,
+        url: str,
+        *,
+        body: bytes | None,
+        depth: str | None,
+        expected: set[int],
+        extra_headers: Mapping[str, str] | None = None,
+    ) -> tuple[int, Mapping[str, str], bytes]:
+        headers: dict[str, str] = {
+            "Accept": "application/xml,text/calendar,*/*",
+            "User-Agent": "govoplan-calendar-caldav/0.1",
+        }
+        if body is not None:
+            headers["Content-Type"] = "application/xml; charset=utf-8"
+        if depth is not None:
+            headers["Depth"] = depth
+        if self.bearer_token:
+            headers["Authorization"] = f"Bearer {self.bearer_token}"
+        elif self.username and self.password:
+            token = base64.b64encode(f"{self.username}:{self.password}".encode("utf-8")).decode("ascii")
+            headers["Authorization"] = f"Basic {token}"
+        if extra_headers:
+            headers.update(dict(extra_headers))
+        status, response_headers, payload = self.transport(method, url, headers, body, self.timeout)
+        if status not in expected:
+            if status == 412:
+                raise CalDAVPreconditionFailed(f"{method} {url} failed because the remote resource changed")
+            raise CalDAVError(f"{method} {url} returned HTTP {status}")
+        return status, response_headers, payload
+
+
+def urllib_transport(method: str, url: str, headers: Mapping[str, str], body: bytes | None, timeout: int) -> tuple[int, Mapping[str, str], bytes]:
+    request = urllib.request.Request(url, data=body, headers=dict(headers), method=method)
+    try:
+        with urllib.request.urlopen(request, timeout=timeout) as response:
+            return response.status, dict(response.headers.items()), response.read()
+    except urllib.error.HTTPError as exc:
+        return exc.code, dict(exc.headers.items()), exc.read()
+    except urllib.error.URLError as exc:
+        raise CalDAVError(f"{method} {url} failed: {exc.reason}") from exc
+
+
+def parse_multistatus(payload: bytes) -> CalDAVReportResult:
+    try:
+        root = ElementTree.fromstring(payload)
+    except ElementTree.ParseError as exc:
+        raise CalDAVError(f"Invalid CalDAV XML response: {exc}") from exc
+    objects: list[CalDAVObject] = []
+    sync_token = first_child_text(root, "sync-token")
+    ctag = first_child_text(root, "getctag")
+    for response in child_elements(root, "response"):
+        href = first_child_text(response, "href")
+        if not href:
+            continue
+        deleted = False
+        etag = None
+        calendar_data = None
+        for propstat in child_elements(response, "propstat"):
+            status = first_child_text(propstat, "status") or ""
+            prop = first_child(propstat, "prop")
+            if prop is None:
+                continue
+            if " 404 " in status or status.endswith(" 404"):
+                deleted = True
+                continue
+            if " 200 " not in status and not status.endswith(" 200"):
+                continue
+            etag = first_child_text(prop, "getetag") or etag
+            calendar_data = first_child_text(prop, "calendar-data") or calendar_data
+            sync_token = first_child_text(prop, "sync-token") or sync_token
+            ctag = first_child_text(prop, "getctag") or ctag
+        objects.append(CalDAVObject(href=href, etag=strip_weak_etag(etag), calendar_data=calendar_data, deleted=deleted))
+    return CalDAVReportResult(objects=objects, sync_token=sync_token, ctag=ctag)
+
+
+def ensure_collection_url(value: str) -> str:
+    return value if value.endswith("/") else f"{value}/"
+
+
+def strip_weak_etag(value: str | None) -> str | None:
+    if value is None:
+        return None
+    return value.strip()
+
+
+def response_etag(headers: Mapping[str, str]) -> str | None:
+    for key, value in headers.items():
+        if key.lower() == "etag" and value:
+            return strip_weak_etag(value)
+    return None
+
+
+def xml_escape(value: str) -> str:
+    return value.replace("&", "&amp;").replace("<", "&lt;").replace(">", "&gt;")
+
+
+def first_child(element: ElementTree.Element, name: str) -> ElementTree.Element | None:
+    for child in element:
+        if local_name(child.tag) == name:
+            return child
+    return None
+
+
+def first_child_text(element: ElementTree.Element, name: str) -> str | None:
+    found = first_child(element, name)
+    if found is None or found.text is None:
+        return None
+    return found.text.strip()
+
+
+def child_elements(element: ElementTree.Element, name: str) -> list[ElementTree.Element]:
+    return [child for child in element if local_name(child.tag) == name]
+
+
+def local_name(tag: str) -> str:
+    return tag.rsplit("}", 1)[-1] if "}" in tag else tag

src/govoplan_calendar/backend/db/models.py

@@ -94,4 +94,61 @@ class CalendarEvent(Base, TimestampMixin):
     calendar: Mapped[CalendarCollection] = relationship(back_populates="events")
 
 
-__all__ = ["CalendarCollection", "CalendarEvent", "new_uuid"]
+class CalendarSyncSource(Base, TimestampMixin):
+    __tablename__ = "calendar_sync_sources"
+    __table_args__ = (
+        Index("ix_calendar_sync_sources_calendar", "tenant_id", "calendar_id", "source_kind"),
+        Index(
+            "uq_calendar_sync_sources_active_url",
+            "tenant_id",
+            "source_kind",
+            "collection_url",
+            unique=True,
+            sqlite_where=text("deleted_at IS NULL"),
+            postgresql_where=text("deleted_at IS NULL"),
+        ),
+    )
+
+    id: Mapped[str] = mapped_column(String(36), primary_key=True, default=new_uuid)
+    tenant_id: Mapped[str] = mapped_column(ForeignKey("tenants.id", ondelete="CASCADE"), nullable=False, index=True)
+    calendar_id: Mapped[str] = mapped_column(ForeignKey("calendar_collections.id", ondelete="CASCADE"), nullable=False, index=True)
+    source_kind: Mapped[str] = mapped_column(String(30), default="caldav", nullable=False, index=True)
+    collection_url: Mapped[str] = mapped_column(String(1000), nullable=False)
+    display_name: Mapped[str | None] = mapped_column(String(255))
+    auth_type: Mapped[str] = mapped_column(String(30), default="none", nullable=False)
+    username: Mapped[str | None] = mapped_column(String(255))
+    credential_ref: Mapped[str | None] = mapped_column(String(255))
+    sync_enabled: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False, index=True)
+    sync_interval_seconds: Mapped[int] = mapped_column(Integer, default=900, nullable=False)
+    sync_direction: Mapped[str] = mapped_column(String(30), default="two_way", nullable=False)
+    conflict_policy: Mapped[str] = mapped_column(String(30), default="etag", nullable=False)
+    sync_token: Mapped[str | None] = mapped_column(Text)
+    ctag: Mapped[str | None] = mapped_column(String(255))
+    last_attempt_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
+    last_synced_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
+    next_sync_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True, index=True)
+    last_status: Mapped[str | None] = mapped_column(String(30))
+    last_error: Mapped[str | None] = mapped_column(Text)
+    deleted_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True, index=True)
+    metadata_: Mapped[dict[str, Any] | None] = mapped_column("metadata", JSON, nullable=True)
+
+    calendar: Mapped[CalendarCollection] = relationship()
+
+
+class CalendarSyncCredential(Base, TimestampMixin):
+    __tablename__ = "calendar_sync_credentials"
+    __table_args__ = (
+        Index("ix_calendar_sync_credentials_tenant_kind", "tenant_id", "credential_kind"),
+    )
+
+    id: Mapped[str] = mapped_column(String(36), primary_key=True, default=new_uuid)
+    tenant_id: Mapped[str] = mapped_column(ForeignKey("tenants.id", ondelete="CASCADE"), nullable=False, index=True)
+    credential_kind: Mapped[str] = mapped_column(String(30), nullable=False, index=True)
+    label: Mapped[str | None] = mapped_column(String(255))
+    secret_encrypted: Mapped[str | None] = mapped_column(Text)
+    created_by_user_id: Mapped[str | None] = mapped_column(ForeignKey("users.id", ondelete="SET NULL"), nullable=True, index=True)
+    deleted_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True, index=True)
+    metadata_: Mapped[dict[str, Any] | None] = mapped_column("metadata", JSON, nullable=True)
+
+
+__all__ = ["CalendarCollection", "CalendarEvent", "CalendarSyncCredential", "CalendarSyncSource", "new_uuid"]

src/govoplan_calendar/backend/ical.py

@@ -1,239 +1,553 @@
 from __future__ import annotations
 
-from dataclasses import dataclass
-from datetime import date, datetime, time, timezone
+from datetime import date, datetime, time, timedelta, timezone
 from email.utils import format_datetime
 from typing import Any
+from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
+
+from dateutil.rrule import rruleset, rrulestr
+from icalendar import Alarm, Calendar, Event, vCalAddress
+from icalendar.parser import Parameters
 
 
 class ICalendarError(ValueError):
     """Raised when iCalendar content cannot be parsed as a usable VEVENT."""
 
 
-@dataclass(frozen=True, slots=True)
-class ICalendarProperty:
-    name: str
-    value: str
-    params: dict[str, list[str]]
+GENERATED_EVENT_PROPERTIES = {
+    "UID",
+    "DTSTAMP",
+    "DTSTART",
+    "DTEND",
+    "DURATION",
+    "RECURRENCE-ID",
+    "SUMMARY",
+    "SEQUENCE",
+    "STATUS",
+    "TRANSP",
+    "CLASS",
+    "DESCRIPTION",
+    "LOCATION",
+    "CATEGORIES",
+    "RRULE",
+    "RDATE",
+    "EXDATE",
+    "ORGANIZER",
+    "ATTENDEE",
+    "ATTACH",
+    "RELATED-TO",
+}
 
-    def as_dict(self) -> dict[str, Any]:
-        return {"name": self.name, "value": self.value, "params": self.params}
+
+class RawICalendarValue:
+    def __init__(self, value: str, params: dict[str, str]) -> None:
+        self.value = value
+        self.params = Parameters(params)
+
+    def to_ical(self) -> bytes:
+        return self.value.encode("utf-8")
 
 
 def parse_vevent(ics: str) -> dict[str, Any]:
-    lines = unfold_ical_lines(ics)
-    event_lines = component_lines(lines, "VEVENT")
-    if not event_lines:
+    events = parse_vevents(ics)
+    if not events:
         raise ICalendarError("No VEVENT component found")
+    return events[0]
 
-    properties = [parse_content_line(line) for line in event_lines]
-    props = [prop.as_dict() for prop in properties]
-    by_name = group_properties(properties)
 
-    uid = first_value(by_name, "UID")
+def parse_vevents(ics: str) -> list[dict[str, Any]]:
+    try:
+        calendar = Calendar.from_ical(ics)
+    except Exception as exc:  # noqa: BLE001 - normalize parser errors for API callers.
+        raise ICalendarError(f"Invalid iCalendar content: {exc}") from exc
+
+    events = [component for component in calendar.walk("VEVENT") if component.name == "VEVENT"]
+    if not events:
+        raise ICalendarError("No VEVENT component found")
+    normalized_ics = normalize_ics(ics)
+    return [parse_vevent_component(calendar, event, raw_ics=normalized_ics) for event in events]
+
+
+def parse_vevent_component(calendar: Calendar, event: Event, *, raw_ics: str) -> dict[str, Any]:
+    uid = text_value(first_property_value(event, "UID"))
     if not uid:
         raise ICalendarError("VEVENT is missing UID")
-    dtstart_prop = first_property(by_name, "DTSTART")
-    if dtstart_prop is None:
-        raise ICalendarError("VEVENT is missing DTSTART")
 
-    start_at, all_day, tzid = parse_temporal_property(dtstart_prop)
+    dtstart = first_property_value(event, "DTSTART")
+    if dtstart is None:
+        raise ICalendarError("VEVENT is missing DTSTART")
+    start_at, all_day, tzid = temporal_property(dtstart)
+
     end_at = None
     duration_seconds = None
-    dtend_prop = first_property(by_name, "DTEND")
-    if dtend_prop is not None:
-        end_at, _end_all_day, _end_tzid = parse_temporal_property(dtend_prop)
+    dtend = first_property_value(event, "DTEND")
+    duration = decoded_property(event, "DURATION")
+    if dtend is not None:
+        end_at, _end_all_day, _end_tzid = temporal_property(dtend)
         duration_seconds = int((end_at - start_at).total_seconds())
-    elif first_value(by_name, "DURATION"):
-        # Keep full DURATION semantics in raw properties. The first module
-        # stores it but does not yet calculate every RFC 5545 duration form.
-        duration_seconds = None
+    elif isinstance(duration, timedelta):
+        end_at = start_at + duration
+        duration_seconds = int(duration.total_seconds())
 
-    summary = first_value(by_name, "SUMMARY") or "(Untitled event)"
-    organizer = property_party(first_property(by_name, "ORGANIZER"))
-    attendees = [property_party(prop) for prop in by_name.get("ATTENDEE", [])]
-    categories = split_csv(first_value(by_name, "CATEGORIES") or "")
+    properties = component_property_records(event)
+    alarms = [component_alarm_record(alarm) for alarm in event.subcomponents if alarm.name == "VALARM"]
+    standard = standard_property_index(properties)
 
     return {
         "uid": uid,
-        "recurrence_id": first_value(by_name, "RECURRENCE-ID"),
-        "sequence": int_or_zero(first_value(by_name, "SEQUENCE")),
-        "summary": summary,
-        "description": first_value(by_name, "DESCRIPTION"),
-        "location": first_value(by_name, "LOCATION"),
-        "status": (first_value(by_name, "STATUS") or "CONFIRMED").upper(),
-        "transparency": (first_value(by_name, "TRANSP") or "OPAQUE").upper(),
-        "classification": (first_value(by_name, "CLASS") or "PUBLIC").upper(),
+        "recurrence_id": recurrence_id_value(first_property_value(event, "RECURRENCE-ID")),
+        "sequence": int_or_zero(text_value(first_property_value(event, "SEQUENCE"))),
+        "summary": text_value(first_property_value(event, "SUMMARY")) or "(Untitled event)",
+        "description": text_value(first_property_value(event, "DESCRIPTION")),
+        "location": text_value(first_property_value(event, "LOCATION")),
+        "status": (text_value(first_property_value(event, "STATUS")) or "CONFIRMED").upper(),
+        "transparency": (text_value(first_property_value(event, "TRANSP")) or "OPAQUE").upper(),
+        "classification": (text_value(first_property_value(event, "CLASS")) or "PUBLIC").upper(),
         "start_at": start_at,
         "end_at": end_at,
         "duration_seconds": duration_seconds,
         "all_day": all_day,
         "timezone": tzid,
-        "organizer": organizer,
-        "attendees": attendees,
-        "categories": categories,
-        "rrule": parse_key_value_property(first_value(by_name, "RRULE")),
-        "rdate": [prop.as_dict() for prop in by_name.get("RDATE", [])],
-        "exdate": [prop.as_dict() for prop in by_name.get("EXDATE", [])],
-        "attachments": [prop.as_dict() for prop in by_name.get("ATTACH", [])],
-        "related_to": [prop.as_dict() for prop in by_name.get("RELATED-TO", [])],
-        "icalendar": {"component": "VEVENT", "properties": props},
-        "raw_ics": normalize_ics(ics),
+        "organizer": party_record(first_property_value(event, "ORGANIZER")),
+        "attendees": [party_record(value) for value in property_values(event, "ATTENDEE")],
+        "categories": category_values(event),
+        "rrule": recurrence_rule(first_property_value(event, "RRULE")),
+        "rdate": records_for_name(properties, "RDATE"),
+        "exdate": records_for_name(properties, "EXDATE"),
+        "reminders": [alarm_to_reminder(alarm) for alarm in alarms],
+        "attachments": records_for_name(properties, "ATTACH"),
+        "related_to": records_for_name(properties, "RELATED-TO"),
+        "icalendar": {
+            "component": "VEVENT",
+            "schema_version": 1,
+            "properties": properties,
+            "alarms": alarms,
+            "standard": standard,
+            "method": text_value(first_property_value(calendar, "METHOD")),
+            "timezones": calendar_timezones(calendar),
+        },
+        "raw_ics": raw_ics,
     }
 
 
 def event_to_ics(event: Any) -> str:
-    properties = [
-        ("UID", {}, event.uid),
-        ("DTSTAMP", {}, format_ical_datetime(datetime.now(timezone.utc))),
-        ("DTSTART", date_params(event), format_ical_temporal(event.start_at, all_day=event.all_day)),
-    ]
+    return events_to_ics([event])
+
+
+def events_to_ics(events: list[Any]) -> str:
+    calendar = Calendar()
+    calendar.add("version", "2.0")
+    calendar.add("prodid", "-//GovOPlaN//Calendar//EN")
+    calendar.add("calscale", "GREGORIAN")
+
+    method = next((metadata_value(event, "method") for event in events if metadata_value(event, "method")), None)
+    if method:
+        calendar.add("method", method)
+
+    for event in events:
+        calendar.add_component(event_to_component(event))
+    return calendar.to_ical().decode("utf-8")
+
+
+def event_to_component(event: Any) -> Event:
+    component = Event()
+    component.add("uid", event.uid)
+    component.add("dtstamp", datetime.now(timezone.utc))
+    component.add("dtstart", event_temporal_value(event.start_at, all_day=event.all_day, timezone_id=event.timezone))
     if event.end_at is not None:
-        properties.append(("DTEND", date_params(event), format_ical_temporal(event.end_at, all_day=event.all_day)))
-    properties.extend(
-        [
-            ("SUMMARY", {}, event.summary),
-            ("SEQUENCE", {}, str(event.sequence or 0)),
-            ("STATUS", {}, event.status),
-            ("TRANSP", {}, event.transparency),
-            ("CLASS", {}, event.classification),
-        ]
-    )
+        component.add("dtend", event_temporal_value(event.end_at, all_day=event.all_day, timezone_id=event.timezone))
+    elif getattr(event, "duration_seconds", None) is not None:
+        component.add("duration", timedelta(seconds=int(event.duration_seconds)))
+    if getattr(event, "recurrence_id", None):
+        add_recurrence_id(component, str(event.recurrence_id))
+    component.add("summary", event.summary)
+    component.add("sequence", int(event.sequence or 0))
+    component.add("status", event.status)
+    component.add("transp", event.transparency)
+    component.add("class", event.classification)
     if event.description:
-        properties.append(("DESCRIPTION", {}, event.description))
+        component.add("description", event.description)
     if event.location:
-        properties.append(("LOCATION", {}, event.location))
-    for category in event.categories or []:
-        if category:
-            properties.append(("CATEGORIES", {}, category))
+        component.add("location", event.location)
+    if event.categories:
+        component.add("categories", list(event.categories))
     if event.rrule:
-        properties.append(("RRULE", {}, serialize_key_value_property(event.rrule)))
+        component.add("rrule", normalized_rrule_for_export(event.rrule))
     if event.organizer:
-        properties.append(party_to_property("ORGANIZER", event.organizer))
+        component.add("organizer", party_for_export(event.organizer))
     for attendee in event.attendees or []:
-        properties.append(party_to_property("ATTENDEE", attendee))
+        component.add("attendee", party_for_export(attendee))
+    for record in getattr(event, "rdate", None) or []:
+        add_raw_property(component, "RDATE", record)
+    for record in getattr(event, "exdate", None) or []:
+        add_raw_property(component, "EXDATE", record)
+    for record in getattr(event, "attachments", None) or []:
+        add_raw_property(component, "ATTACH", record)
+    for record in getattr(event, "related_to", None) or []:
+        add_raw_property(component, "RELATED-TO", record)
 
-    lines = ["BEGIN:VCALENDAR", "VERSION:2.0", "PRODID:-//GovOPlaN//Calendar//EN", "CALSCALE:GREGORIAN", "BEGIN:VEVENT"]
-    lines.extend(fold_ical_line(serialize_content_line(name, params, value)) for name, params, value in properties if value is not None)
-    lines.extend(["END:VEVENT", "END:VCALENDAR", ""])
-    return "\r\n".join(lines)
+    add_preserved_properties(component, getattr(event, "icalendar", None) or {})
+    for alarm in alarms_for_export(event):
+        component.add_component(alarm)
+    return component
 
 
-def unfold_ical_lines(ics: str) -> list[str]:
-    raw_lines = ics.replace("\r\n", "\n").replace("\r", "\n").split("\n")
-    lines: list[str] = []
-    for line in raw_lines:
-        if not line:
-            continue
-        if line[:1] in {" ", "\t"} and lines:
-            lines[-1] += line[1:]
-        else:
-            lines.append(line)
-    return lines
+def expand_event_occurrences(event: Any, range_start: datetime, range_end: datetime, *, limit: int = 1000) -> list[dict[str, Any]]:
+    """Expand an event's recurrence primitives within a range.
+
+    This is a backend primitive for later API/UI recurrence handling. It expands
+    RRULE/RDATE/EXDATE data stored by this module and returns occurrence starts
+    with the event's original duration.
+    """
+
+    start_at = normalize_datetime(event.start_at)
+    end_at = normalize_datetime(event.end_at) if event.end_at is not None else None
+    range_start = normalize_datetime(range_start)
+    range_end = normalize_datetime(range_end)
+    duration = occurrence_duration(event, start_at=start_at, end_at=end_at)
+
+    if not event.rrule and not event.rdate:
+        return [occurrence_payload(start_at, duration, event)] if occurrence_overlaps(start_at, duration, range_start, range_end) else []
+
+    rules = rruleset()
+    if event.rrule:
+        rules.rrule(rrulestr(serialize_key_value_property(event.rrule), dtstart=start_at))
+    for rdate in temporal_values_from_records(event.rdate or []):
+        rules.rdate(rdate)
+    for exdate in temporal_values_from_records(event.exdate or []):
+        rules.exdate(exdate)
+
+    starts = rules.between(range_start - duration, range_end, inc=True)
+    occurrences: list[dict[str, Any]] = []
+    for occurrence_start in starts:
+        occurrence_start = normalize_datetime(occurrence_start)
+        if occurrence_overlaps(occurrence_start, duration, range_start, range_end):
+            occurrences.append(occurrence_payload(occurrence_start, duration, event))
+            if len(occurrences) >= limit:
+                break
+    return occurrences
 
 
-def component_lines(lines: list[str], component: str) -> list[str]:
-    begin = f"BEGIN:{component.upper()}"
-    end = f"END:{component.upper()}"
-    depth = 0
-    collected: list[str] = []
-    for line in lines:
-        upper = line.upper()
-        if upper == begin:
-            depth += 1
-            if depth == 1:
-                collected = []
-            continue
-        if upper == end and depth:
-            depth -= 1
-            if depth == 0:
-                return collected
-            continue
-        if depth:
-            collected.append(line)
+def first_vevent(calendar: Calendar) -> Event:
+    for component in calendar.walk("VEVENT"):
+        if component.name == "VEVENT":
+            return component
+    raise ICalendarError("No VEVENT component found")
+
+
+def first_property_value(component: Any, name: str) -> Any | None:
+    values = property_values(component, name)
+    return values[0] if values else None
+
+
+def property_values(component: Any, name: str) -> list[Any]:
+    value = component.get(name.upper())
+    if value is None:
         return []
+    return value if isinstance(value, list) else [value]
 
 
-def parse_content_line(line: str) -> ICalendarProperty:
-    head, sep, value = line.partition(":")
-    if not sep:
-        raise ICalendarError(f"Invalid iCalendar content line: {line}")
-    parts = head.split(";")
-    name = parts[0].upper()
-    params: dict[str, list[str]] = {}
-    for raw_param in parts[1:]:
-        key, param_sep, raw_value = raw_param.partition("=")
-        if not param_sep:
-            params[key.upper()] = [""]
-        else:
-            params[key.upper()] = [unescape_text(item.strip('"')) for item in raw_value.split(",")]
-    return ICalendarProperty(name=name, params=params, value=unescape_text(value))
-
-
-def group_properties(properties: list[ICalendarProperty]) -> dict[str, list[ICalendarProperty]]:
-    grouped: dict[str, list[ICalendarProperty]] = {}
-    for prop in properties:
-        grouped.setdefault(prop.name, []).append(prop)
-    return grouped
-
-
-def first_property(grouped: dict[str, list[ICalendarProperty]], name: str) -> ICalendarProperty | None:
-    items = grouped.get(name.upper()) or []
-    return items[0] if items else None
-
-
-def first_value(grouped: dict[str, list[ICalendarProperty]], name: str) -> str | None:
-    prop = first_property(grouped, name)
-    return prop.value if prop else None
-
-
-def parse_temporal_property(prop: ICalendarProperty) -> tuple[datetime, bool, str | None]:
-    value_type = (prop.params.get("VALUE") or [""])[0].upper()
-    tzid = (prop.params.get("TZID") or [None])[0]
-    if value_type == "DATE" or (len(prop.value) == 8 and "T" not in prop.value):
-        parsed_date = datetime.strptime(prop.value, "%Y%m%d").date()
-        return datetime.combine(parsed_date, time.min, tzinfo=timezone.utc), True, tzid
-    return parse_ical_datetime(prop.value), False, tzid
-
-
-def parse_ical_datetime(value: str) -> datetime:
-    if value.endswith("Z"):
-        return datetime.strptime(value, "%Y%m%dT%H%M%SZ").replace(tzinfo=timezone.utc)
-    parsed = datetime.strptime(value, "%Y%m%dT%H%M%S")
-    return parsed.replace(tzinfo=timezone.utc)
-
-
-def format_ical_temporal(value: datetime, *, all_day: bool) -> str:
-    if all_day:
-        return value.date().strftime("%Y%m%d")
-    return format_ical_datetime(value)
-
-
-def format_ical_datetime(value: datetime) -> str:
-    if value.tzinfo is None:
-        value = value.replace(tzinfo=timezone.utc)
-    return value.astimezone(timezone.utc).strftime("%Y%m%dT%H%M%SZ")
-
-
-def date_params(event: Any) -> dict[str, list[str]]:
-    if event.all_day:
-        return {"VALUE": ["DATE"]}
-    if event.timezone:
-        return {"TZID": [event.timezone]}
-    return {}
-
-
-def property_party(prop: ICalendarProperty | None) -> dict[str, Any] | None:
-    if prop is None:
+def decoded_property(component: Any, name: str) -> Any | None:
+    try:
+        return component.decoded(name.upper())
+    except KeyError:
         return None
-    return {"value": prop.value, "params": prop.params}
 
 
-def party_to_property(name: str, party: dict[str, Any]) -> tuple[str, dict[str, list[str]], str]:
-    params = party.get("params") if isinstance(party.get("params"), dict) else {}
+def temporal_property(value: Any) -> tuple[datetime, bool, str | None]:
+    decoded = decoded_temporal_value(value)
+    params = params_to_json(getattr(value, "params", {}))
+    tzid = first_param(params, "TZID")
+    if isinstance(decoded, datetime):
+        return normalize_datetime(decoded), False, tzid
+    if isinstance(decoded, date):
+        return datetime.combine(decoded, time.min, tzinfo=timezone.utc), True, tzid
+    raise ICalendarError(f"Unsupported temporal value: {value}")
+
+
+def decoded_temporal_value(value: Any) -> Any:
+    decoded = getattr(value, "dt", None)
+    return decoded if decoded is not None else value
+
+
+def recurrence_id_value(value: Any | None) -> str | None:
+    if value is None:
+        return None
+    raw_value = ical_value(value)
+    params = params_to_json(getattr(value, "params", {}))
+    tzid = first_param(params, "TZID")
+    return f"TZID={tzid}:{raw_value}" if tzid else raw_value
+
+
+def recurrence_rule(value: Any | None) -> dict[str, Any] | None:
+    if value is None:
+        return None
+    if hasattr(value, "items"):
+        result: dict[str, Any] = {}
+        for key, raw_items in value.items():
+            items = raw_items if isinstance(raw_items, list) else [raw_items]
+            normalized = [rrule_item(item) for item in items]
+            result[str(key).upper()] = normalized if len(normalized) > 1 else normalized[0]
+        return result
+    return parse_key_value_property(ical_value(value))
+
+
+def rrule_item(value: Any) -> str:
+    if isinstance(value, datetime):
+        return format_ical_datetime(value)
+    if isinstance(value, date):
+        return value.strftime("%Y%m%d")
+    return str(value).upper() if isinstance(value, str) else str(value)
+
+
+def category_values(component: Any) -> list[str]:
+    decoded = decoded_property(component, "CATEGORIES")
+    if decoded is None:
+        return []
+    groups = decoded if isinstance(decoded, list) else [decoded]
+    categories: list[str] = []
+    for group in groups:
+        values = group if isinstance(group, list) else [group]
+        categories.extend(str(value) for value in values if str(value))
+    return categories
+
+
+def component_property_records(component: Any) -> list[dict[str, Any]]:
+    records: list[dict[str, Any]] = []
+    for name, value in component.items():
+        for item in value if isinstance(value, list) else [value]:
+            records.append(property_record(name, item))
+    return records
+
+
+def property_record(name: str, value: Any) -> dict[str, Any]:
+    record: dict[str, Any] = {
+        "name": str(name).upper(),
+        "value": ical_value(value),
+        "params": params_to_json(getattr(value, "params", {})),
+    }
+    decoded = decoded_temporal_value(value)
+    json_decoded = json_value(decoded)
+    if json_decoded is not None and json_decoded != record["value"]:
+        record["decoded"] = json_decoded
+    return record
+
+
+def component_alarm_record(alarm: Any) -> dict[str, Any]:
+    return {
+        "component": "VALARM",
+        "properties": component_property_records(alarm),
+    }
+
+
+def alarm_to_reminder(alarm: dict[str, Any]) -> dict[str, Any]:
+    properties = alarm.get("properties") or []
+    trigger = first_record(properties, "TRIGGER")
+    return {
+        "action": record_value(properties, "ACTION") or "DISPLAY",
+        "trigger": trigger,
+        "description": record_value(properties, "DESCRIPTION"),
+        "summary": record_value(properties, "SUMMARY"),
+        "attendees": records_for_name(properties, "ATTENDEE"),
+        "duration": first_record(properties, "DURATION"),
+        "repeat": record_value(properties, "REPEAT"),
+        "attachments": records_for_name(properties, "ATTACH"),
+        "properties": properties,
+    }
+
+
+def standard_property_index(properties: list[dict[str, Any]]) -> dict[str, Any]:
+    names = (
+        "DTSTAMP",
+        "CREATED",
+        "LAST-MODIFIED",
+        "PRIORITY",
+        "URL",
+        "GEO",
+        "COMMENT",
+        "CONTACT",
+        "REQUEST-STATUS",
+        "RESOURCES",
+    )
+    result: dict[str, Any] = {}
+    for name in names:
+        matching = records_for_name(properties, name)
+        if not matching:
+            continue
+        result[name.lower().replace("-", "_")] = matching if len(matching) > 1 else matching[0]
+    return result
+
+
+def records_for_name(records: list[dict[str, Any]], name: str) -> list[dict[str, Any]]:
+    return [record for record in records if record.get("name") == name.upper()]
+
+
+def first_record(records: list[dict[str, Any]], name: str) -> dict[str, Any] | None:
+    matching = records_for_name(records, name)
+    return matching[0] if matching else None
+
+
+def record_value(records: list[dict[str, Any]], name: str) -> str | None:
+    record = first_record(records, name)
+    if not record:
+        return None
+    return str(record.get("value") or "")
+
+
+def party_record(value: Any | None) -> dict[str, Any] | None:
+    if value is None:
+        return None
+    return {"value": text_value(value) or "", "params": params_to_json(getattr(value, "params", {}))}
+
+
+def party_for_export(party: dict[str, Any]) -> Any:
     value = str(party.get("value") or party.get("email") or "")
-    normalized_params = {str(key).upper(): [str(item) for item in value] for key, value in params.items() if isinstance(value, list)}
-    return name, normalized_params, value
+    cal_address = vCalAddress(value)
+    for key, item in flattened_params(party.get("params") if isinstance(party.get("params"), dict) else {}).items():
+        cal_address.params[key] = item
+    return cal_address
+
+
+def text_value(value: Any | None) -> str | None:
+    if value is None:
+        return None
+    raw = value.decode("utf-8") if isinstance(value, bytes) else str(value)
+    return raw if raw != "" else None
+
+
+def ical_value(value: Any) -> str:
+    if hasattr(value, "to_ical"):
+        raw = value.to_ical()
+        return raw.decode("utf-8") if isinstance(raw, bytes) else str(raw)
+    if isinstance(value, bytes):
+        return value.decode("utf-8")
+    return str(value)
+
+
+def params_to_json(params: Any) -> dict[str, list[str]]:
+    result: dict[str, list[str]] = {}
+    for key, value in dict(params or {}).items():
+        values = value if isinstance(value, list) else [value]
+        result[str(key).upper()] = [str(item) for item in values]
+    return result
+
+
+def flattened_params(params: dict[str, Any]) -> dict[str, str]:
+    result: dict[str, str] = {}
+    for key, value in (params or {}).items():
+        values = value if isinstance(value, list) else [value]
+        if values:
+            result[str(key).upper()] = ",".join(str(item) for item in values)
+    return result
+
+
+def first_param(params: dict[str, list[str]], name: str) -> str | None:
+    values = params.get(name.upper()) or []
+    return values[0] if values else None
+
+
+def json_value(value: Any) -> Any:
+    if isinstance(value, datetime):
+        return normalize_datetime(value).isoformat()
+    if isinstance(value, date):
+        return value.isoformat()
+    if isinstance(value, timedelta):
+        return int(value.total_seconds())
+    if isinstance(value, (str, int, float, bool)) or value is None:
+        return value
+    return None
+
+
+def calendar_timezones(calendar: Calendar) -> list[str]:
+    timezones: list[str] = []
+    for component in calendar.walk("VTIMEZONE"):
+        tzid = text_value(first_property_value(component, "TZID"))
+        if tzid and tzid not in timezones:
+            timezones.append(tzid)
+    return timezones
+
+
+def metadata_value(event: Any, key: str) -> str | None:
+    raw_metadata = getattr(event, "icalendar", None)
+    metadata = raw_metadata if isinstance(raw_metadata, dict) else {}
+    value = metadata.get(key)
+    return str(value) if value else None
+
+
+def event_temporal_value(value: datetime, *, all_day: bool, timezone_id: str | None) -> date | datetime:
+    value = normalize_datetime(value)
+    if all_day:
+        return value.date()
+    if timezone_id:
+        try:
+            return value.astimezone(ZoneInfo(timezone_id))
+        except ZoneInfoNotFoundError:
+            return value
+    return value
+
+
+def add_raw_property(component: Event | Alarm, default_name: str, record: dict[str, Any]) -> None:
+    name = str(record.get("name") or default_name).upper()
+    value = record.get("value")
+    if not name or value is None:
+        return
+    raw_value = RawICalendarValue(str(value), flattened_params(record.get("params") or {}))
+    component.add(name, raw_value, encode=False)
+
+
+def add_recurrence_id(component: Event, value: str) -> None:
+    params: dict[str, list[str]] = {}
+    raw_value = value
+    if value.startswith("TZID=") and ":" in value:
+        tzid, raw_value = value.removeprefix("TZID=").split(":", 1)
+        params["TZID"] = [tzid]
+    add_raw_property(component, "RECURRENCE-ID", {"name": "RECURRENCE-ID", "value": raw_value, "params": params})
+
+
+def add_preserved_properties(component: Event, metadata: dict[str, Any]) -> None:
+    for record in metadata.get("properties") or []:
+        if not isinstance(record, dict):
+            continue
+        name = str(record.get("name") or "").upper()
+        if not name or name in GENERATED_EVENT_PROPERTIES:
+            continue
+        add_raw_property(component, name, record)
+
+
+def alarms_for_export(event: Any) -> list[Alarm]:
+    reminders = getattr(event, "reminders", None) or []
+    raw_metadata = getattr(event, "icalendar", None)
+    if not reminders and isinstance(raw_metadata, dict):
+        reminders = raw_metadata.get("alarms") or []
+    alarms: list[Alarm] = []
+    for reminder in reminders:
+        if not isinstance(reminder, dict):
+            continue
+        alarm = Alarm()
+        properties = reminder.get("properties")
+        if isinstance(properties, list):
+            for record in properties:
+                if isinstance(record, dict):
+                    add_raw_property(alarm, str(record.get("name") or ""), record)
+        else:
+            alarm.add("action", reminder.get("action") or "DISPLAY")
+            trigger = reminder.get("trigger")
+            if isinstance(trigger, dict):
+                add_raw_property(alarm, "TRIGGER", trigger)
+            if reminder.get("description"):
+                alarm.add("description", reminder["description"])
+            if reminder.get("summary"):
+                alarm.add("summary", reminder["summary"])
+        if alarm:
+            alarms.append(alarm)
+    return alarms
+
+
+def normalized_rrule_for_export(value: dict[str, Any]) -> dict[str, list[Any]]:
+    result: dict[str, list[Any]] = {}
+    for key, item in value.items():
+        result[str(key).lower()] = item if isinstance(item, list) else [item]
+    return result
 
 
 def parse_key_value_property(value: str | None) -> dict[str, Any] | None:
@@ -243,7 +557,8 @@ def parse_key_value_property(value: str | None) -> dict[str, Any] | None:
     for item in value.split(";"):
         key, sep, raw = item.partition("=")
         if sep:
-            result[key.upper()] = raw.split(",") if "," in raw else raw
+            values = raw.split(",") if "," in raw else [raw]
+            result[key.upper()] = values if len(values) > 1 else values[0]
     return result or {"raw": value}
 
 
@@ -257,8 +572,59 @@ def serialize_key_value_property(value: dict[str, Any]) -> str:
     return ";".join(parts)
 
 
-def split_csv(value: str) -> list[str]:
-    return [item.strip() for item in value.split(",") if item.strip()]
+def temporal_values_from_records(records: list[dict[str, Any]]) -> list[datetime]:
+    values: list[datetime] = []
+    for record in records:
+        params = record.get("params") if isinstance(record.get("params"), dict) else {}
+        for raw_value in str(record.get("value") or "").split(","):
+            parsed = parse_ical_temporal(raw_value, params)
+            if parsed is not None:
+                values.append(parsed)
+    return values
+
+
+def parse_ical_temporal(value: str, params: dict[str, Any]) -> datetime | None:
+    if not value:
+        return None
+    value_type = first_param(params_to_json(params), "VALUE")
+    if value_type == "DATE" or (len(value) == 8 and "T" not in value):
+        return datetime.combine(datetime.strptime(value, "%Y%m%d").date(), time.min, tzinfo=timezone.utc)
+    try:
+        if value.endswith("Z"):
+            return datetime.strptime(value, "%Y%m%dT%H%M%SZ").replace(tzinfo=timezone.utc)
+        parsed = datetime.strptime(value, "%Y%m%dT%H%M%S")
+    except ValueError:
+        return None
+    tzid = first_param(params_to_json(params), "TZID")
+    if tzid:
+        try:
+            return parsed.replace(tzinfo=ZoneInfo(tzid)).astimezone(timezone.utc)
+        except ZoneInfoNotFoundError:
+            return parsed.replace(tzinfo=timezone.utc)
+    return parsed.replace(tzinfo=timezone.utc)
+
+
+def occurrence_duration(event: Any, *, start_at: datetime, end_at: datetime | None) -> timedelta:
+    if end_at is not None:
+        return end_at - start_at
+    if event.duration_seconds is not None:
+        return timedelta(seconds=int(event.duration_seconds))
+    return timedelta(days=1) if event.all_day else timedelta(0)
+
+
+def occurrence_overlaps(start_at: datetime, duration: timedelta, range_start: datetime, range_end: datetime) -> bool:
+    end_at = start_at + duration
+    return end_at >= range_start and start_at <= range_end
+
+
+def occurrence_payload(start_at: datetime, duration: timedelta, event: Any) -> dict[str, Any]:
+    return {
+        "uid": event.uid,
+        "recurrence_id": format_ical_datetime(start_at),
+        "start_at": start_at,
+        "end_at": start_at + duration if duration else None,
+        "all_day": event.all_day,
+    }
 
 
 def int_or_zero(value: str | None) -> int:
@@ -268,42 +634,20 @@ def int_or_zero(value: str | None) -> int:
         return 0
 
 
+def normalize_datetime(value: datetime) -> datetime:
+    if value.tzinfo is None:
+        return value.replace(tzinfo=timezone.utc)
+    return value.astimezone(timezone.utc)
+
+
 def normalize_ics(ics: str) -> str:
     stripped = ics.strip().replace("\r\n", "\n").replace("\r", "\n")
     return "\r\n".join(stripped.split("\n")) + "\r\n"
 
 
-def serialize_content_line(name: str, params: dict[str, list[str]], value: str) -> str:
-    param_text = "".join(f";{key}={','.join(escape_param(item) for item in items)}" for key, items in params.items() if items)
-    return f"{name}{param_text}:{escape_text(value)}"
-
-
-def fold_ical_line(line: str, limit: int = 75) -> str:
-    if len(line) <= limit:
-        return line
-    parts = [line[:limit]]
-    line = line[limit:]
-    while line:
-        parts.append(" " + line[: limit - 1])
-        line = line[limit - 1 :]
-    return "\r\n".join(parts)
-
-
-def escape_text(value: str) -> str:
-    return value.replace("\\", "\\\\").replace("\n", "\\n").replace(";", "\\;").replace(",", "\\,")
-
-
-def unescape_text(value: str) -> str:
-    return value.replace("\\n", "\n").replace("\\N", "\n").replace("\\;", ";").replace("\\,", ",").replace("\\\\", "\\")
-
-
-def escape_param(value: str) -> str:
-    if any(char in value for char in [":", ";", ","]):
-        return '"' + value.replace('"', "'") + '"'
-    return value
+def format_ical_datetime(value: datetime) -> str:
+    return normalize_datetime(value).strftime("%Y%m%dT%H%M%SZ")
 
 
 def http_last_modified(value: datetime) -> str:
-    if value.tzinfo is None:
-        value = value.replace(tzinfo=timezone.utc)
-    return format_datetime(value.astimezone(timezone.utc), usegmt=True)
+    return format_datetime(normalize_datetime(value), usegmt=True)

src/govoplan_calendar/backend/manifest.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 from pathlib import Path
 
 from govoplan_calendar.backend.db import models as calendar_models  # noqa: F401 - populate Calendar ORM metadata
+from govoplan_core.core.module_guards import drop_table_retirement_provider, persistent_table_uninstall_guard
 from govoplan_core.core.modules import FrontendModule, MigrationSpec, ModuleContext, ModuleManifest, NavItem, PermissionDefinition, RoleTemplate
 from govoplan_core.db.base import Base
 
@@ -64,11 +65,13 @@ ROLE_TEMPLATES = (
 
 
 def _tenant_summary(session, tenant_id: str) -> dict[str, int]:
-    from govoplan_calendar.backend.db.models import CalendarCollection, CalendarEvent
+    from govoplan_calendar.backend.db.models import CalendarCollection, CalendarEvent, CalendarSyncCredential, CalendarSyncSource
 
     return {
         "calendars": session.query(CalendarCollection).filter(CalendarCollection.tenant_id == tenant_id, CalendarCollection.deleted_at.is_(None)).count(),
         "calendar_events": session.query(CalendarEvent).filter(CalendarEvent.tenant_id == tenant_id, CalendarEvent.deleted_at.is_(None)).count(),
+        "calendar_sync_sources": session.query(CalendarSyncSource).filter(CalendarSyncSource.tenant_id == tenant_id, CalendarSyncSource.deleted_at.is_(None)).count(),
+        "calendar_sync_credentials": session.query(CalendarSyncCredential).filter(CalendarSyncCredential.tenant_id == tenant_id, CalendarSyncCredential.deleted_at.is_(None)).count(),
     }
 
 
@@ -84,7 +87,7 @@ def _calendar_router(context: ModuleContext):
 manifest = ModuleManifest(
     id="calendar",
     name="Calendar",
-    version="0.1.4",
+    version="0.1.5",
     dependencies=("access",),
     optional_dependencies=("mail", "tasks", "scheduling", "appointments", "workflow", "notifications", "dms", "connectors"),
     permissions=PERMISSIONS,
@@ -101,6 +104,24 @@ manifest = ModuleManifest(
         module_id="calendar",
         metadata=Base.metadata,
         script_location=str(Path(__file__).with_name("migrations") / "versions"),
+        retirement_supported=True,
+        retirement_provider=drop_table_retirement_provider(
+            calendar_models.CalendarCollection,
+            calendar_models.CalendarEvent,
+            calendar_models.CalendarSyncCredential,
+            calendar_models.CalendarSyncSource,
+            label="Calendar",
+        ),
+        retirement_notes="Destructive retirement drops calendar-owned database tables after the installer captures a database snapshot.",
+    ),
+    uninstall_guard_providers=(
+        persistent_table_uninstall_guard(
+            calendar_models.CalendarCollection,
+            calendar_models.CalendarEvent,
+            calendar_models.CalendarSyncCredential,
+            calendar_models.CalendarSyncSource,
+            label="Calendar",
+        ),
     ),
 )
 

src/govoplan_calendar/backend/migrations/versions/8d9e0f1a2b3c_caldav_sync_sources.py

@@ -0,0 +1,75 @@
+"""CalDAV sync sources
+
+Revision ID: 8d9e0f1a2b3c
+Revises: 7c8d9e0f1a2b
+Create Date: 2026-07-07 00:00:00.000000
+"""
+from __future__ import annotations
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = "8d9e0f1a2b3c"
+down_revision = "7c8d9e0f1a2b"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    inspector = sa.inspect(op.get_bind())
+    tables = set(inspector.get_table_names())
+    if "calendar_sync_sources" in tables:
+        return
+    op.create_table(
+        "calendar_sync_sources",
+        sa.Column("id", sa.String(length=36), nullable=False),
+        sa.Column("tenant_id", sa.String(length=36), nullable=False),
+        sa.Column("calendar_id", sa.String(length=36), nullable=False),
+        sa.Column("source_kind", sa.String(length=30), nullable=False),
+        sa.Column("collection_url", sa.String(length=1000), nullable=False),
+        sa.Column("display_name", sa.String(length=255), nullable=True),
+        sa.Column("auth_type", sa.String(length=30), nullable=False),
+        sa.Column("username", sa.String(length=255), nullable=True),
+        sa.Column("credential_ref", sa.String(length=255), nullable=True),
+        sa.Column("sync_token", sa.Text(), nullable=True),
+        sa.Column("ctag", sa.String(length=255), nullable=True),
+        sa.Column("last_synced_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("last_status", sa.String(length=30), nullable=True),
+        sa.Column("last_error", sa.Text(), nullable=True),
+        sa.Column("deleted_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("metadata", sa.JSON(), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False),
+        sa.ForeignKeyConstraint(["calendar_id"], ["calendar_collections.id"], name=op.f("fk_calendar_sync_sources_calendar_id_calendar_collections"), ondelete="CASCADE"),
+        sa.ForeignKeyConstraint(["tenant_id"], ["tenants.id"], name=op.f("fk_calendar_sync_sources_tenant_id_tenants"), ondelete="CASCADE"),
+        sa.PrimaryKeyConstraint("id", name=op.f("pk_calendar_sync_sources")),
+    )
+    for column in ("tenant_id", "calendar_id", "source_kind", "deleted_at"):
+        op.create_index(op.f(f"ix_calendar_sync_sources_{column}"), "calendar_sync_sources", [column], unique=False)
+    op.create_index("ix_calendar_sync_sources_calendar", "calendar_sync_sources", ["tenant_id", "calendar_id", "source_kind"], unique=False)
+    op.create_index(
+        "uq_calendar_sync_sources_active_url",
+        "calendar_sync_sources",
+        ["tenant_id", "source_kind", "collection_url"],
+        unique=True,
+        sqlite_where=sa.text("deleted_at IS NULL"),
+        postgresql_where=sa.text("deleted_at IS NULL"),
+    )
+
+
+def downgrade() -> None:
+    inspector = sa.inspect(op.get_bind())
+    tables = set(inspector.get_table_names())
+    if "calendar_sync_sources" not in tables:
+        return
+    for name in (
+        "uq_calendar_sync_sources_active_url",
+        "ix_calendar_sync_sources_calendar",
+        op.f("ix_calendar_sync_sources_deleted_at"),
+        op.f("ix_calendar_sync_sources_source_kind"),
+        op.f("ix_calendar_sync_sources_calendar_id"),
+        op.f("ix_calendar_sync_sources_tenant_id"),
+    ):
+        op.drop_index(name, table_name="calendar_sync_sources")
+    op.drop_table("calendar_sync_sources")

src/govoplan_calendar/backend/migrations/versions/9e0f1a2b3c4d_caldav_credentials_outbound_sync.py

@@ -0,0 +1,88 @@
+"""CalDAV credentials and outbound sync metadata
+
+Revision ID: 9e0f1a2b3c4d
+Revises: 8d9e0f1a2b3c
+Create Date: 2026-07-07 00:00:00.000000
+"""
+from __future__ import annotations
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = "9e0f1a2b3c4d"
+down_revision = "8d9e0f1a2b3c"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    bind = op.get_bind()
+    inspector = sa.inspect(bind)
+    tables = set(inspector.get_table_names())
+    if "calendar_sync_sources" in tables:
+        columns = {column["name"] for column in inspector.get_columns("calendar_sync_sources")}
+        add_column_if_missing(columns, "sync_enabled", sa.Column("sync_enabled", sa.Boolean(), server_default=sa.true(), nullable=False))
+        add_column_if_missing(columns, "sync_interval_seconds", sa.Column("sync_interval_seconds", sa.Integer(), server_default="900", nullable=False))
+        add_column_if_missing(columns, "sync_direction", sa.Column("sync_direction", sa.String(length=30), server_default="two_way", nullable=False))
+        add_column_if_missing(columns, "conflict_policy", sa.Column("conflict_policy", sa.String(length=30), server_default="etag", nullable=False))
+        add_column_if_missing(columns, "last_attempt_at", sa.Column("last_attempt_at", sa.DateTime(timezone=True), nullable=True))
+        add_column_if_missing(columns, "next_sync_at", sa.Column("next_sync_at", sa.DateTime(timezone=True), nullable=True))
+        indexes = {index["name"] for index in inspector.get_indexes("calendar_sync_sources")}
+        if "ix_calendar_sync_sources_sync_enabled" not in indexes:
+            op.create_index(op.f("ix_calendar_sync_sources_sync_enabled"), "calendar_sync_sources", ["sync_enabled"], unique=False)
+        if "ix_calendar_sync_sources_next_sync_at" not in indexes:
+            op.create_index(op.f("ix_calendar_sync_sources_next_sync_at"), "calendar_sync_sources", ["next_sync_at"], unique=False)
+
+    if "calendar_sync_credentials" not in tables:
+        op.create_table(
+            "calendar_sync_credentials",
+            sa.Column("id", sa.String(length=36), nullable=False),
+            sa.Column("tenant_id", sa.String(length=36), nullable=False),
+            sa.Column("credential_kind", sa.String(length=30), nullable=False),
+            sa.Column("label", sa.String(length=255), nullable=True),
+            sa.Column("secret_encrypted", sa.Text(), nullable=True),
+            sa.Column("created_by_user_id", sa.String(length=36), nullable=True),
+            sa.Column("deleted_at", sa.DateTime(timezone=True), nullable=True),
+            sa.Column("metadata", sa.JSON(), nullable=True),
+            sa.Column("created_at", sa.DateTime(timezone=True), nullable=False),
+            sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False),
+            sa.ForeignKeyConstraint(["created_by_user_id"], ["users.id"], name=op.f("fk_calendar_sync_credentials_created_by_user_id_users"), ondelete="SET NULL"),
+            sa.ForeignKeyConstraint(["tenant_id"], ["tenants.id"], name=op.f("fk_calendar_sync_credentials_tenant_id_tenants"), ondelete="CASCADE"),
+            sa.PrimaryKeyConstraint("id", name=op.f("pk_calendar_sync_credentials")),
+        )
+        for column in ("tenant_id", "credential_kind", "created_by_user_id", "deleted_at"):
+            op.create_index(op.f(f"ix_calendar_sync_credentials_{column}"), "calendar_sync_credentials", [column], unique=False)
+        op.create_index("ix_calendar_sync_credentials_tenant_kind", "calendar_sync_credentials", ["tenant_id", "credential_kind"], unique=False)
+
+
+def downgrade() -> None:
+    inspector = sa.inspect(op.get_bind())
+    tables = set(inspector.get_table_names())
+    if "calendar_sync_credentials" in tables:
+        for name in (
+            "ix_calendar_sync_credentials_tenant_kind",
+            op.f("ix_calendar_sync_credentials_deleted_at"),
+            op.f("ix_calendar_sync_credentials_created_by_user_id"),
+            op.f("ix_calendar_sync_credentials_credential_kind"),
+            op.f("ix_calendar_sync_credentials_tenant_id"),
+        ):
+            op.drop_index(name, table_name="calendar_sync_credentials")
+        op.drop_table("calendar_sync_credentials")
+    if "calendar_sync_sources" in tables:
+        indexes = {index["name"] for index in inspector.get_indexes("calendar_sync_sources")}
+        if "ix_calendar_sync_sources_next_sync_at" in indexes:
+            op.drop_index(op.f("ix_calendar_sync_sources_next_sync_at"), table_name="calendar_sync_sources")
+        if "ix_calendar_sync_sources_sync_enabled" in indexes:
+            op.drop_index(op.f("ix_calendar_sync_sources_sync_enabled"), table_name="calendar_sync_sources")
+        columns = {column["name"] for column in inspector.get_columns("calendar_sync_sources")}
+        for column in ("next_sync_at", "last_attempt_at", "conflict_policy", "sync_direction", "sync_interval_seconds", "sync_enabled"):
+            if column in columns:
+                op.drop_column("calendar_sync_sources", column)
+
+
+def add_column_if_missing(existing: set[str], name: str, column: sa.Column) -> None:
+    if name in existing:
+        return
+    op.add_column("calendar_sync_sources", column)
+    existing.add(name)

src/govoplan_calendar/backend/router.py

@@ -2,13 +2,23 @@ from __future__ import annotations
 
 from datetime import datetime
 
-from fastapi import APIRouter, Depends, HTTPException, Query, Response, status
+from fastapi import APIRouter, Body, Depends, HTTPException, Query, Response, status
 from sqlalchemy.orm import Session
 
 from govoplan_access.backend.auth.dependencies import ApiPrincipal, get_api_principal, has_scope
 from govoplan_calendar.backend.ical import ICalendarError, event_to_ics, http_last_modified
+from govoplan_calendar.backend.caldav import CalDAVError
 from govoplan_calendar.backend.schemas import (
+    CalendarCalDavDueSyncItemResponse,
+    CalendarCalDavDueSyncResponse,
+    CalendarCalDavSourceCreateRequest,
+    CalendarCalDavSourceListResponse,
+    CalendarCalDavSourceResponse,
+    CalendarCalDavSourceUpdateRequest,
+    CalendarCalDavSyncRequest,
+    CalendarCalDavSyncResponse,
     CalendarCollectionCreateRequest,
+    CalendarCollectionDeleteRequest,
     CalendarCollectionListResponse,
     CalendarCollectionResponse,
     CalendarCollectionUpdateRequest,
@@ -16,21 +26,33 @@ from govoplan_calendar.backend.schemas import (
     CalendarEventListResponse,
     CalendarEventResponse,
     CalendarEventUpdateRequest,
+    CalendarFreeBusyRequest,
+    CalendarFreeBusyResponse,
     CalendarIcsImportRequest,
 )
 from govoplan_calendar.backend.service import (
     CalendarError,
+    caldav_source_response,
+    caldav_sync_response,
     calendar_response,
     create_calendar,
+    create_caldav_source,
     create_event,
     delete_calendar,
+    delete_caldav_source,
     delete_event,
     event_response,
+    get_caldav_source,
     get_event,
     import_ics_event,
+    list_freebusy,
+    list_caldav_sources,
     list_calendars,
     list_events,
+    sync_due_caldav_sources,
+    sync_caldav_source,
     update_calendar,
+    update_caldav_source,
     update_event,
 )
 from govoplan_core.db.session import get_session
@@ -56,6 +78,10 @@ def _event_response(event) -> CalendarEventResponse:
     return CalendarEventResponse.model_validate(event_response(event))
 
 
+def _caldav_source_response(source) -> CalendarCalDavSourceResponse:
+    return CalendarCalDavSourceResponse.model_validate(caldav_source_response(source))
+
+
 @router.get("/calendars", response_model=CalendarCollectionListResponse)
 def api_list_calendars(
     principal: ApiPrincipal = Depends(get_api_principal),
@@ -105,12 +131,13 @@ def api_update_calendar(
 @router.delete("/calendars/{calendar_id}", status_code=status.HTTP_204_NO_CONTENT)
 def api_delete_calendar(
     calendar_id: str,
+    payload: CalendarCollectionDeleteRequest | None = Body(default=None),
     principal: ApiPrincipal = Depends(get_api_principal),
     session: Session = Depends(get_session),
 ):
     _require_scope(principal, "calendar:calendar:admin")
     try:
-        delete_calendar(session, tenant_id=principal.tenant_id, calendar_id=calendar_id)
+        delete_calendar(session, tenant_id=principal.tenant_id, calendar_id=calendar_id, payload=payload)
         session.commit()
         return Response(status_code=status.HTTP_204_NO_CONTENT)
     except CalendarError as exc:
@@ -118,6 +145,122 @@ def api_delete_calendar(
         raise HTTPException(status_code=status.HTTP_422_UNPROCESSABLE_ENTITY, detail=str(exc)) from exc
 
 
+@router.get("/caldav/sources", response_model=CalendarCalDavSourceListResponse)
+def api_list_caldav_sources(
+    calendar_id: str | None = None,
+    principal: ApiPrincipal = Depends(get_api_principal),
+    session: Session = Depends(get_session),
+):
+    _require_scope(principal, "calendar:calendar:read")
+    sources = list_caldav_sources(session, tenant_id=principal.tenant_id, calendar_id=calendar_id)
+    return CalendarCalDavSourceListResponse(sources=[_caldav_source_response(source) for source in sources])
+
+
+@router.post("/caldav/sources", response_model=CalendarCalDavSourceResponse, status_code=status.HTTP_201_CREATED)
+def api_create_caldav_source(
+    payload: CalendarCalDavSourceCreateRequest,
+    principal: ApiPrincipal = Depends(get_api_principal),
+    session: Session = Depends(get_session),
+):
+    _require_scope(principal, "calendar:calendar:admin")
+    try:
+        source = create_caldav_source(session, tenant_id=principal.tenant_id, user_id=principal.user.id, payload=payload)
+        session.commit()
+        session.refresh(source)
+        return _caldav_source_response(source)
+    except CalendarError as exc:
+        session.rollback()
+        raise HTTPException(status_code=status.HTTP_422_UNPROCESSABLE_ENTITY, detail=str(exc)) from exc
+
+
+@router.patch("/caldav/sources/{source_id}", response_model=CalendarCalDavSourceResponse)
+def api_update_caldav_source(
+    source_id: str,
+    payload: CalendarCalDavSourceUpdateRequest,
+    principal: ApiPrincipal = Depends(get_api_principal),
+    session: Session = Depends(get_session),
+):
+    _require_scope(principal, "calendar:calendar:admin")
+    try:
+        source = update_caldav_source(session, tenant_id=principal.tenant_id, source_id=source_id, payload=payload)
+        session.commit()
+        session.refresh(source)
+        return _caldav_source_response(source)
+    except CalendarError as exc:
+        session.rollback()
+        raise HTTPException(status_code=status.HTTP_422_UNPROCESSABLE_ENTITY, detail=str(exc)) from exc
+
+
+@router.delete("/caldav/sources/{source_id}", status_code=status.HTTP_204_NO_CONTENT)
+def api_delete_caldav_source(
+    source_id: str,
+    principal: ApiPrincipal = Depends(get_api_principal),
+    session: Session = Depends(get_session),
+):
+    _require_scope(principal, "calendar:calendar:admin")
+    try:
+        delete_caldav_source(session, tenant_id=principal.tenant_id, source_id=source_id)
+        session.commit()
+        return Response(status_code=status.HTTP_204_NO_CONTENT)
+    except CalendarError as exc:
+        session.rollback()
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail=str(exc)) from exc
+
+
+@router.post("/caldav/sources/{source_id}/sync", response_model=CalendarCalDavSyncResponse)
+def api_sync_caldav_source(
+    source_id: str,
+    payload: CalendarCalDavSyncRequest | None = None,
+    principal: ApiPrincipal = Depends(get_api_principal),
+    session: Session = Depends(get_session),
+):
+    _require_scope(principal, "calendar:event:import")
+    payload = payload or CalendarCalDavSyncRequest()
+    try:
+        source, stats = sync_caldav_source(
+            session,
+            tenant_id=principal.tenant_id,
+            user_id=principal.user.id,
+            source_id=source_id,
+            password=payload.password,
+            bearer_token=payload.bearer_token,
+            force_full=payload.force_full,
+        )
+        session.commit()
+        session.refresh(source)
+        return CalendarCalDavSyncResponse.model_validate(caldav_sync_response(source, stats))
+    except (CalendarError, CalDAVError, ICalendarError) as exc:
+        session.rollback()
+        raise HTTPException(status_code=status.HTTP_422_UNPROCESSABLE_ENTITY, detail=str(exc)) from exc
+
+
+@router.post("/caldav/sync-due", response_model=CalendarCalDavDueSyncResponse)
+def api_sync_due_caldav_sources(
+    limit: int = Query(default=50, ge=1, le=200),
+    principal: ApiPrincipal = Depends(get_api_principal),
+    session: Session = Depends(get_session),
+):
+    _require_scope(principal, "calendar:event:import")
+    results = sync_due_caldav_sources(session, tenant_id=principal.tenant_id, user_id=principal.user.id, limit=limit)
+    session.commit()
+    return CalendarCalDavDueSyncResponse(
+        results=[
+            CalendarCalDavDueSyncItemResponse(
+                source_id=item.source_id,
+                calendar_id=item.calendar_id,
+                status=item.status,
+                error=item.error,
+                created=item.stats.created if item.stats else 0,
+                updated=item.stats.updated if item.stats else 0,
+                deleted=item.stats.deleted if item.stats else 0,
+                unchanged=item.stats.unchanged if item.stats else 0,
+                fetched=item.stats.fetched if item.stats else 0,
+            )
+            for item in results
+        ]
+    )
+
+
 @router.get("/events", response_model=CalendarEventListResponse)
 def api_list_events(
     calendar_id: str | None = None,
@@ -242,3 +385,23 @@ def api_export_ics_event(
             "Last-Modified": http_last_modified(event.updated_at),
         },
     )
+
+
+@router.post("/availability/freebusy", response_model=CalendarFreeBusyResponse)
+def api_freebusy(
+    payload: CalendarFreeBusyRequest,
+    principal: ApiPrincipal = Depends(get_api_principal),
+    session: Session = Depends(get_session),
+):
+    _require_scope(principal, "calendar:availability:read")
+    try:
+        busy = list_freebusy(
+            session,
+            tenant_id=principal.tenant_id,
+            start_at=payload.start_at,
+            end_at=payload.end_at,
+            calendar_ids=payload.calendar_ids,
+        )
+        return CalendarFreeBusyResponse(start_at=payload.start_at, end_at=payload.end_at, busy=busy)
+    except CalendarError as exc:
+        raise HTTPException(status_code=status.HTTP_422_UNPROCESSABLE_ENTITY, detail=str(exc)) from exc

src/govoplan_calendar/backend/schemas.py

@@ -3,11 +3,15 @@ from __future__ import annotations
 from datetime import datetime
 from typing import Any, Literal
 
-from pydantic import BaseModel, ConfigDict, Field
+from pydantic import BaseModel, ConfigDict, Field, SecretStr
 
 
 CalendarOwnerType = Literal["tenant", "user", "group", "resource"]
 CalendarVisibility = Literal["private", "tenant", "shared", "public"]
+CalendarDeleteEventAction = Literal["delete", "move"]
+CalendarSyncAuthType = Literal["none", "basic", "bearer"]
+CalendarSyncDirection = Literal["inbound", "two_way"]
+CalendarCalDavConflictPolicy = Literal["etag", "overwrite"]
 
 
 class CalendarCollectionCreateRequest(BaseModel):
@@ -37,6 +41,14 @@ class CalendarCollectionUpdateRequest(BaseModel):
     metadata: dict[str, Any] | None = None
 
 
+class CalendarCollectionDeleteRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+
+    event_action: CalendarDeleteEventAction = "delete"
+    target_calendar_id: str | None = None
+    make_target_default: bool = False
+
+
 class CalendarCollectionResponse(BaseModel):
     id: str
     tenant_id: str
@@ -58,6 +70,113 @@ class CalendarCollectionListResponse(BaseModel):
     calendars: list[CalendarCollectionResponse] = Field(default_factory=list)
 
 
+class CalendarCalDavSourceCreateRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+
+    calendar_id: str
+    collection_url: str = Field(min_length=1, max_length=1000)
+    display_name: str | None = Field(default=None, max_length=255)
+    auth_type: CalendarSyncAuthType = "none"
+    username: str | None = Field(default=None, max_length=255)
+    credential_ref: str | None = Field(default=None, max_length=255)
+    password: SecretStr | None = None
+    bearer_token: SecretStr | None = None
+    sync_enabled: bool = True
+    sync_interval_seconds: int = Field(default=900, ge=60)
+    sync_direction: CalendarSyncDirection = "two_way"
+    conflict_policy: CalendarCalDavConflictPolicy = "etag"
+    metadata: dict[str, Any] = Field(default_factory=dict)
+
+
+class CalendarCalDavSourceUpdateRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+
+    calendar_id: str | None = None
+    collection_url: str | None = Field(default=None, min_length=1, max_length=1000)
+    display_name: str | None = Field(default=None, max_length=255)
+    auth_type: CalendarSyncAuthType | None = None
+    username: str | None = Field(default=None, max_length=255)
+    credential_ref: str | None = Field(default=None, max_length=255)
+    password: SecretStr | None = None
+    bearer_token: SecretStr | None = None
+    sync_enabled: bool | None = None
+    sync_interval_seconds: int | None = Field(default=None, ge=60)
+    sync_direction: CalendarSyncDirection | None = None
+    conflict_policy: CalendarCalDavConflictPolicy | None = None
+    sync_token: str | None = None
+    ctag: str | None = Field(default=None, max_length=255)
+    metadata: dict[str, Any] | None = None
+
+
+class CalendarCalDavSourceResponse(BaseModel):
+    id: str
+    tenant_id: str
+    calendar_id: str
+    source_kind: str
+    collection_url: str
+    display_name: str | None = None
+    auth_type: str
+    username: str | None = None
+    credential_ref: str | None = None
+    has_credential: bool = False
+    sync_enabled: bool
+    sync_interval_seconds: int
+    sync_direction: str
+    conflict_policy: str
+    sync_token: str | None = None
+    ctag: str | None = None
+    last_attempt_at: datetime | None = None
+    last_synced_at: datetime | None = None
+    next_sync_at: datetime | None = None
+    last_status: str | None = None
+    last_error: str | None = None
+    created_at: datetime
+    updated_at: datetime
+    metadata: dict[str, Any] = Field(default_factory=dict)
+
+
+class CalendarCalDavSourceListResponse(BaseModel):
+    sources: list[CalendarCalDavSourceResponse] = Field(default_factory=list)
+
+
+class CalendarCalDavSyncRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+
+    password: str | None = None
+    bearer_token: str | None = None
+    force_full: bool = False
+
+
+class CalendarCalDavSyncResponse(BaseModel):
+    source: CalendarCalDavSourceResponse
+    created: int = 0
+    updated: int = 0
+    deleted: int = 0
+    unchanged: int = 0
+    fetched: int = 0
+    full_sync: bool = False
+    used_sync_token: bool = False
+    sync_token: str | None = None
+    ctag: str | None = None
+    errors: list[str] = Field(default_factory=list)
+
+
+class CalendarCalDavDueSyncItemResponse(BaseModel):
+    source_id: str
+    calendar_id: str
+    status: str
+    error: str | None = None
+    created: int = 0
+    updated: int = 0
+    deleted: int = 0
+    unchanged: int = 0
+    fetched: int = 0
+
+
+class CalendarCalDavDueSyncResponse(BaseModel):
+    results: list[CalendarCalDavDueSyncItemResponse] = Field(default_factory=list)
+
+
 class CalendarEventCreateRequest(BaseModel):
     model_config = ConfigDict(extra="forbid")
 
@@ -164,6 +283,32 @@ class CalendarEventListResponse(BaseModel):
     events: list[CalendarEventResponse] = Field(default_factory=list)
 
 
+class CalendarFreeBusyRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+
+    start_at: datetime
+    end_at: datetime
+    calendar_ids: list[str] | None = None
+
+
+class CalendarBusyBlockResponse(BaseModel):
+    calendar_id: str
+    event_id: str
+    uid: str
+    recurrence_id: str | None = None
+    start_at: datetime
+    end_at: datetime | None = None
+    all_day: bool = False
+    transparency: str
+    status: str
+
+
+class CalendarFreeBusyResponse(BaseModel):
+    start_at: datetime
+    end_at: datetime
+    busy: list[CalendarBusyBlockResponse] = Field(default_factory=list)
+
+
 class CalendarIcsImportRequest(BaseModel):
     model_config = ConfigDict(extra="forbid")
 

src/govoplan_calendar/backend/tasks.py

@@ -0,0 +1,27 @@
+from __future__ import annotations
+
+from celery import shared_task
+
+
+@shared_task(name="govoplan_calendar.sync_due_caldav_sources")
+def sync_due_caldav_sources_task(tenant_id: str | None = None, limit: int = 50) -> list[dict[str, object]]:
+    from govoplan_calendar.backend.service import sync_due_caldav_sources
+    from govoplan_core.db.session import get_database
+
+    with get_database().SessionLocal() as session:
+        results = sync_due_caldav_sources(session, tenant_id=tenant_id, limit=limit)
+        session.commit()
+        return [
+            {
+                "source_id": item.source_id,
+                "calendar_id": item.calendar_id,
+                "status": item.status,
+                "error": item.error,
+                "created": item.stats.created if item.stats else 0,
+                "updated": item.stats.updated if item.stats else 0,
+                "deleted": item.stats.deleted if item.stats else 0,
+                "unchanged": item.stats.unchanged if item.stats else 0,
+                "fetched": item.stats.fetched if item.stats else 0,
+            }
+            for item in results
+        ]

tests/test_caldav.py

@@ -0,0 +1,435 @@
+from __future__ import annotations
+
+import unittest
+from datetime import datetime, timezone
+from types import SimpleNamespace
+from unittest.mock import patch
+
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+
+from govoplan_access.backend.db import models as access_models  # noqa: F401 - populate users/accounts tables
+from govoplan_calendar.backend.caldav import CalDAVObject, CalDAVPreconditionFailed, CalDAVReportResult, CalDAVWriteResult, parse_multistatus
+from govoplan_calendar.backend.db.models import CalendarEvent, CalendarSyncCredential, CalendarSyncSource
+from govoplan_calendar.backend.schemas import CalendarCalDavSourceCreateRequest, CalendarCollectionCreateRequest, CalendarEventCreateRequest, CalendarEventUpdateRequest
+from govoplan_calendar.backend.service import (
+    CALDAV_INTERNAL_CREDENTIAL_PREFIX,
+    CalendarError,
+    caldav_client_for_source,
+    create_calendar,
+    create_caldav_source,
+    create_event,
+    delete_event,
+    list_freebusy,
+    sync_caldav_source,
+    sync_due_caldav_sources,
+    update_event,
+)
+from govoplan_core.db.base import Base
+from govoplan_tenancy.backend.db.models import Tenant
+
+
+class FakeCalDAVClient:
+    def __init__(
+        self,
+        *,
+        list_result: CalDAVReportResult | None = None,
+        sync_result: CalDAVReportResult | None = None,
+        objects: dict[str, str] | None = None,
+        put_etags: list[str | None] | None = None,
+        fail_precondition: bool = False,
+    ) -> None:
+        self.list_result = list_result or CalDAVReportResult()
+        self.sync_result = sync_result
+        self.objects = objects or {}
+        self.put_etags = put_etags or ['"etag-written"']
+        self.fail_precondition = fail_precondition
+        self.fetched: list[str] = []
+        self.puts: list[dict[str, object]] = []
+        self.deletes: list[dict[str, object]] = []
+
+    def propfind_collection(self) -> CalDAVReportResult:
+        return CalDAVReportResult(sync_token="prop-token", ctag="ctag-1")
+
+    def list_objects(self) -> CalDAVReportResult:
+        return self.list_result
+
+    def sync_collection(self, sync_token: str) -> CalDAVReportResult:
+        if self.sync_result is None:
+            raise AssertionError(f"Unexpected sync_collection call with {sync_token}")
+        return self.sync_result
+
+    def fetch_object(self, href: str) -> str:
+        self.fetched.append(href)
+        return self.objects[href]
+
+    def put_object(self, href: str, ics: str, *, etag: str | None = None, create: bool = False, overwrite: bool = False) -> CalDAVWriteResult:
+        if self.fail_precondition:
+            raise CalDAVPreconditionFailed("changed")
+        self.puts.append({"href": href, "ics": ics, "etag": etag, "create": create, "overwrite": overwrite})
+        result_etag = self.put_etags.pop(0) if self.put_etags else None
+        return CalDAVWriteResult(href=href, etag=result_etag, status=201 if create else 204)
+
+    def delete_object(self, href: str, *, etag: str | None = None, overwrite: bool = False) -> CalDAVWriteResult:
+        if self.fail_precondition:
+            raise CalDAVPreconditionFailed("changed")
+        self.deletes.append({"href": href, "etag": etag, "overwrite": overwrite})
+        return CalDAVWriteResult(href=href, status=204)
+
+
+class CalDAVParsingTests(unittest.TestCase):
+    def test_parse_multistatus_extracts_objects_sync_token_and_deletions(self) -> None:
+        result = parse_multistatus(
+            b"""<?xml version="1.0" encoding="utf-8"?>
+<D:multistatus xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav">
+  <D:sync-token>token-2</D:sync-token>
+  <D:response>
+    <D:href>/cal/event-1.ics</D:href>
+    <D:propstat>
+      <D:prop>
+        <D:getetag>"etag-1"</D:getetag>
+        <C:calendar-data>BEGIN:VCALENDAR
+BEGIN:VEVENT
+UID:event-1@example.test
+DTSTART:20260708T090000Z
+SUMMARY:One
+END:VEVENT
+END:VCALENDAR</C:calendar-data>
+      </D:prop>
+      <D:status>HTTP/1.1 200 OK</D:status>
+    </D:propstat>
+  </D:response>
+  <D:response>
+    <D:href>/cal/event-2.ics</D:href>
+    <D:propstat>
+      <D:prop><D:getetag/></D:prop>
+      <D:status>HTTP/1.1 404 Not Found</D:status>
+    </D:propstat>
+  </D:response>
+</D:multistatus>
+"""
+        )
+
+        self.assertEqual(result.sync_token, "token-2")
+        self.assertEqual(result.objects[0].href, "/cal/event-1.ics")
+        self.assertEqual(result.objects[0].etag, '"etag-1"')
+        self.assertIn("BEGIN:VEVENT", result.objects[0].calendar_data or "")
+        self.assertTrue(result.objects[1].deleted)
+
+
+class CalDAVSyncTests(unittest.TestCase):
+    def setUp(self) -> None:
+        self.engine = create_engine("sqlite:///:memory:")
+        Base.metadata.create_all(bind=self.engine)
+        self.Session = sessionmaker(bind=self.engine)
+
+    def tearDown(self) -> None:
+        Base.metadata.drop_all(bind=self.engine)
+
+    def test_source_creation_encrypts_credential_and_resolves_client_secret(self) -> None:
+        session = self.Session()
+        session.add(Tenant(id="tenant-1", slug="tenant-1", name="Tenant"))
+        calendar = create_calendar(session, tenant_id="tenant-1", user_id=None, payload=CalendarCollectionCreateRequest(name="Remote"))
+
+        source = create_caldav_source(
+            session,
+            tenant_id="tenant-1",
+            user_id=None,
+            payload=CalendarCalDavSourceCreateRequest(
+                calendar_id=calendar.id,
+                collection_url="https://dav.example.test/cal",
+                auth_type="basic",
+                username="ada",
+                password="secret",
+            ),
+        )
+        session.commit()
+
+        credential = session.query(CalendarSyncCredential).one()
+        client = caldav_client_for_source(session, source)
+
+        self.assertTrue(source.credential_ref.startswith(CALDAV_INTERNAL_CREDENTIAL_PREFIX))
+        self.assertNotEqual(credential.secret_encrypted, "secret")
+        self.assertEqual(client.username, "ada")
+        self.assertEqual(client.password, "secret")
+
+    def test_due_sync_runs_due_sources_and_reschedules(self) -> None:
+        session = self.Session()
+        session.add(Tenant(id="tenant-1", slug="tenant-1", name="Tenant"))
+        calendar = create_calendar(session, tenant_id="tenant-1", user_id=None, payload=CalendarCollectionCreateRequest(name="Remote"))
+        source = create_caldav_source(
+            session,
+            tenant_id="tenant-1",
+            user_id=None,
+            payload=CalendarCalDavSourceCreateRequest(calendar_id=calendar.id, collection_url="https://dav.example.test/cal"),
+        )
+        source.next_sync_at = datetime(2026, 7, 7, 8, 0, tzinfo=timezone.utc)
+        session.commit()
+
+        fake = FakeCalDAVClient(list_result=CalDAVReportResult(sync_token="token-1"))
+        results = sync_due_caldav_sources(
+            session,
+            tenant_id="tenant-1",
+            now=datetime(2026, 7, 7, 8, 1, tzinfo=timezone.utc),
+            client_factory=lambda _source: fake,
+        )
+        session.commit()
+
+        self.assertEqual(results[0].status, "ok")
+        self.assertEqual(source.sync_token, "token-1")
+        next_sync_at = source.next_sync_at if source.next_sync_at.tzinfo else source.next_sync_at.replace(tzinfo=timezone.utc)
+        self.assertGreater(next_sync_at, datetime(2026, 7, 7, 8, 1, tzinfo=timezone.utc))
+
+    def test_create_and_update_event_puts_caldav_resource_with_etag(self) -> None:
+        session = self.Session()
+        session.add(Tenant(id="tenant-1", slug="tenant-1", name="Tenant"))
+        calendar = create_calendar(session, tenant_id="tenant-1", user_id=None, payload=CalendarCollectionCreateRequest(name="Remote"))
+        create_caldav_source(session, tenant_id="tenant-1", user_id=None, payload=CalendarCalDavSourceCreateRequest(calendar_id=calendar.id, collection_url="https://dav.example.test/cal"))
+        session.commit()
+
+        fake = FakeCalDAVClient(put_etags=['"etag-1"', '"etag-2"'])
+        with patch("govoplan_calendar.backend.service.caldav_client_for_source", return_value=fake):
+            event = create_event(
+                session,
+                tenant_id="tenant-1",
+                user_id=None,
+                payload=CalendarEventCreateRequest(
+                    calendar_id=calendar.id,
+                    uid="event-1@example.test",
+                    summary="Planning",
+                    start_at=datetime(2026, 7, 8, 9, 0, tzinfo=timezone.utc),
+                    end_at=datetime(2026, 7, 8, 10, 0, tzinfo=timezone.utc),
+                ),
+            )
+            update_event(session, tenant_id="tenant-1", user_id=None, event_id=event.id, payload=CalendarEventUpdateRequest(summary="Updated"))
+        session.commit()
+
+        self.assertEqual(len(fake.puts), 2)
+        self.assertTrue(fake.puts[0]["create"])
+        self.assertEqual(fake.puts[1]["etag"], '"etag-1"')
+        self.assertFalse(fake.puts[1]["create"])
+        self.assertEqual(event.source_kind, "caldav")
+        self.assertEqual(event.etag, '"etag-2"')
+        self.assertIn("SUMMARY:Updated", event.raw_ics or "")
+
+    def test_update_event_reports_remote_etag_conflict(self) -> None:
+        session = self.Session()
+        session.add(Tenant(id="tenant-1", slug="tenant-1", name="Tenant"))
+        calendar = create_calendar(session, tenant_id="tenant-1", user_id=None, payload=CalendarCollectionCreateRequest(name="Remote"))
+        create_caldav_source(session, tenant_id="tenant-1", user_id=None, payload=CalendarCalDavSourceCreateRequest(calendar_id=calendar.id, collection_url="https://dav.example.test/cal"))
+        event = caldav_event(calendar.id, summary="Remote", href="https://dav.example.test/cal/event-1.ics", etag='"etag-1"')
+        session.add(event)
+        session.commit()
+
+        fake = FakeCalDAVClient(fail_precondition=True)
+        with patch("govoplan_calendar.backend.service.caldav_client_for_source", return_value=fake):
+            with self.assertRaisesRegex(CalendarError, "changed remotely"):
+                update_event(session, tenant_id="tenant-1", user_id=None, event_id=event.id, payload=CalendarEventUpdateRequest(summary="Updated"))
+
+    def test_delete_one_component_puts_remaining_resource_instead_of_deleting_object(self) -> None:
+        session = self.Session()
+        session.add(Tenant(id="tenant-1", slug="tenant-1", name="Tenant"))
+        calendar = create_calendar(session, tenant_id="tenant-1", user_id=None, payload=CalendarCollectionCreateRequest(name="Remote"))
+        create_caldav_source(session, tenant_id="tenant-1", user_id=None, payload=CalendarCalDavSourceCreateRequest(calendar_id=calendar.id, collection_url="https://dav.example.test/cal"))
+        href = "https://dav.example.test/cal/series.ics"
+        master = caldav_event(calendar.id, summary="Master", href=href, etag='"etag-1"')
+        override = caldav_event(calendar.id, summary="Override", href=href, etag='"etag-1"', recurrence_id="20260715T090000Z")
+        session.add_all([master, override])
+        session.commit()
+
+        fake = FakeCalDAVClient(put_etags=['"etag-2"'])
+        with patch("govoplan_calendar.backend.service.caldav_client_for_source", return_value=fake):
+            delete_event(session, tenant_id="tenant-1", event_id=override.id)
+        session.commit()
+
+        self.assertEqual(len(fake.puts), 1)
+        self.assertEqual(fake.deletes, [])
+        self.assertIn("SUMMARY:Master", fake.puts[0]["ics"])
+        self.assertNotIn("SUMMARY:Override", fake.puts[0]["ics"])
+        self.assertEqual(master.etag, '"etag-2"')
+        self.assertIsNotNone(override.deleted_at)
+
+    def test_freebusy_expands_recurring_events_and_skips_transparent_items(self) -> None:
+        session = self.Session()
+        session.add(Tenant(id="tenant-1", slug="tenant-1", name="Tenant"))
+        calendar = create_calendar(session, tenant_id="tenant-1", user_id=None, payload=CalendarCollectionCreateRequest(name="Local"))
+        create_event(
+            session,
+            tenant_id="tenant-1",
+            user_id=None,
+            payload=CalendarEventCreateRequest(
+                calendar_id=calendar.id,
+                uid="busy@example.test",
+                summary="Busy",
+                start_at=datetime(2026, 7, 8, 9, 0, tzinfo=timezone.utc),
+                end_at=datetime(2026, 7, 8, 10, 0, tzinfo=timezone.utc),
+                rrule={"FREQ": "WEEKLY", "COUNT": "2"},
+            ),
+        )
+        create_event(
+            session,
+            tenant_id="tenant-1",
+            user_id=None,
+            payload=CalendarEventCreateRequest(
+                calendar_id=calendar.id,
+                uid="free@example.test",
+                summary="Free",
+                transparency="TRANSPARENT",
+                start_at=datetime(2026, 7, 8, 11, 0, tzinfo=timezone.utc),
+                end_at=datetime(2026, 7, 8, 12, 0, tzinfo=timezone.utc),
+            ),
+        )
+        session.commit()
+
+        busy = list_freebusy(
+            session,
+            tenant_id="tenant-1",
+            start_at=datetime(2026, 7, 1, tzinfo=timezone.utc),
+            end_at=datetime(2026, 7, 31, tzinfo=timezone.utc),
+        )
+
+        self.assertEqual([item["uid"] for item in busy], ["busy@example.test", "busy@example.test"])
+        self.assertEqual(busy[0]["start_at"], datetime(2026, 7, 8, 9, 0, tzinfo=timezone.utc))
+
+    def test_full_sync_imports_multi_vevent_resource_and_fetches_missing_calendar_data(self) -> None:
+        session = self.Session()
+        tenant = Tenant(id="tenant-1", slug="tenant-1", name="Tenant")
+        session.add(tenant)
+        calendar = create_calendar(
+            session,
+            tenant_id="tenant-1",
+            user_id=None,
+            payload=CalendarCollectionCreateRequest(name="Remote", metadata={}),
+        )
+        source = create_caldav_source(
+            session,
+            tenant_id="tenant-1",
+            user_id=None,
+            payload=CalendarCalDavSourceCreateRequest(calendar_id=calendar.id, collection_url="https://dav.example.test/cal"),
+        )
+        session.commit()
+
+        href = "/cal/series.ics"
+        client = FakeCalDAVClient(
+            list_result=CalDAVReportResult(
+                objects=[CalDAVObject(href=href, etag='"etag-1"', calendar_data=None)],
+                sync_token="token-1",
+                ctag="ctag-2",
+            ),
+            objects={href: recurring_resource()},
+        )
+        source, stats = sync_caldav_source(session, tenant_id="tenant-1", user_id=None, source_id=source.id, client=client)
+        session.commit()
+
+        events = session.query(CalendarEvent).filter(CalendarEvent.calendar_id == calendar.id, CalendarEvent.deleted_at.is_(None)).order_by(CalendarEvent.recurrence_id.asc()).all()
+        self.assertEqual(stats.created, 2)
+        self.assertEqual(stats.fetched, 1)
+        self.assertTrue(stats.full_sync)
+        self.assertEqual(source.sync_token, "token-1")
+        self.assertEqual(source.ctag, "ctag-2")
+        self.assertEqual(client.fetched, [href])
+        self.assertEqual({event.summary for event in events}, {"Series", "Moved instance"})
+        self.assertEqual({event.source_href for event in events}, {"https://dav.example.test/cal/series.ics"})
+        self.assertEqual(calendar.metadata_["source_kind"], "caldav")
+
+    def test_sync_token_deletion_soft_deletes_remote_resource_events(self) -> None:
+        session = self.Session()
+        tenant = Tenant(id="tenant-1", slug="tenant-1", name="Tenant")
+        session.add(tenant)
+        calendar = create_calendar(session, tenant_id="tenant-1", user_id=None, payload=CalendarCollectionCreateRequest(name="Remote"))
+        source = create_caldav_source(
+            session,
+            tenant_id="tenant-1",
+            user_id=None,
+            payload=CalendarCalDavSourceCreateRequest(calendar_id=calendar.id, collection_url="https://dav.example.test/cal"),
+        )
+        source.sync_token = "token-1"
+        session.add(
+            CalendarEvent(
+                tenant_id="tenant-1",
+                calendar_id=calendar.id,
+                uid="event-1@example.test",
+                recurrence_id=None,
+                summary="Remote",
+                status="CONFIRMED",
+                transparency="OPAQUE",
+                classification="PUBLIC",
+                start_at=datetime(2026, 7, 8, 9, 0, tzinfo=timezone.utc),
+                all_day=False,
+                attendees=[],
+                categories=[],
+                rdate=[],
+                exdate=[],
+                reminders=[],
+                attachments=[],
+                related_to=[],
+                source_kind="caldav",
+                source_href="https://dav.example.test/cal/event-1.ics",
+                icalendar={},
+                metadata_={"caldav": {"source_id": source.id}},
+            )
+        )
+        session.commit()
+
+        client = FakeCalDAVClient(sync_result=CalDAVReportResult(objects=[CalDAVObject(href="/cal/event-1.ics", deleted=True)], sync_token="token-2"))
+        source, stats = sync_caldav_source(session, tenant_id="tenant-1", user_id=None, source_id=source.id, client=client)
+        session.commit()
+
+        event = session.query(CalendarEvent).filter(CalendarEvent.uid == "event-1@example.test").one()
+        self.assertTrue(stats.used_sync_token)
+        self.assertEqual(stats.deleted, 1)
+        self.assertEqual(source.sync_token, "token-2")
+        self.assertIsNotNone(event.deleted_at)
+
+
+def recurring_resource() -> str:
+    return """BEGIN:VCALENDAR
+VERSION:2.0
+BEGIN:VEVENT
+UID:series@example.test
+DTSTART;TZID=Europe/Berlin:20260708T090000
+DTEND;TZID=Europe/Berlin:20260708T100000
+RRULE:FREQ=WEEKLY;COUNT=2
+SUMMARY:Series
+END:VEVENT
+BEGIN:VEVENT
+UID:series@example.test
+RECURRENCE-ID;TZID=Europe/Berlin:20260715T090000
+DTSTART;TZID=Europe/Berlin:20260715T110000
+DTEND;TZID=Europe/Berlin:20260715T120000
+SUMMARY:Moved instance
+END:VEVENT
+END:VCALENDAR
+"""
+
+
+def caldav_event(calendar_id: str, *, summary: str, href: str, etag: str, recurrence_id: str | None = None) -> CalendarEvent:
+    return CalendarEvent(
+        tenant_id="tenant-1",
+        calendar_id=calendar_id,
+        uid="series@example.test" if recurrence_id else "event-1@example.test",
+        recurrence_id=recurrence_id,
+        summary=summary,
+        status="CONFIRMED",
+        transparency="OPAQUE",
+        classification="PUBLIC",
+        start_at=datetime(2026, 7, 8, 9, 0, tzinfo=timezone.utc),
+        end_at=datetime(2026, 7, 8, 10, 0, tzinfo=timezone.utc),
+        all_day=False,
+        attendees=[],
+        categories=[],
+        rdate=[],
+        exdate=[],
+        reminders=[],
+        attachments=[],
+        related_to=[],
+        source_kind="caldav",
+        source_href=href,
+        etag=etag,
+        icalendar={},
+        metadata_={},
+    )
+
+
+if __name__ == "__main__":
+    unittest.main()

tests/test_ical.py

@@ -1,8 +1,10 @@
 from __future__ import annotations
 
 import unittest
+from datetime import datetime, timezone
+from types import SimpleNamespace
 
-from govoplan_calendar.backend.ical import event_to_ics, parse_vevent
+from govoplan_calendar.backend.ical import expand_event_occurrences, event_to_ics, parse_vevent
 
 
 class ICalendarParsingTests(unittest.TestCase):
@@ -48,6 +50,154 @@ END:VCALENDAR
         self.assertTrue(event["all_day"])
         self.assertEqual(event["start_at"].hour, 0)
 
+    def test_parse_advanced_vevent_fields_and_valarm(self) -> None:
+        event = parse_vevent(
+            """BEGIN:VCALENDAR
+VERSION:2.0
+METHOD:REQUEST
+BEGIN:VEVENT
+UID:event-advanced@example.test
+DTSTAMP:20260707T080000Z
+CREATED:20260707T070000Z
+LAST-MODIFIED:20260707T073000Z
+DTSTART;TZID=Europe/Berlin:20260708T090000
+DURATION:PT1H30M
+SUMMARY:Planning
+DESCRIPTION:Line one\\nLine two
+LOCATION:Room\\; 1
+PRIORITY:5
+URL:https://example.test/events/event-advanced
+GEO:52.5200;13.4050
+COMMENT:First comment
+RESOURCES:Projector,Room
+REQUEST-STATUS:2.0;Success
+ORGANIZER;CN=Orga:mailto:orga@example.test
+ATTENDEE;CN=Ada;ROLE=REQ-PARTICIPANT;PARTSTAT=ACCEPTED:mailto:ada@example.test
+RRULE:FREQ=WEEKLY;COUNT=2
+EXDATE;TZID=Europe/Berlin:20260715T090000
+RDATE;TZID=Europe/Berlin:20260722T090000
+ATTACH;FMTTYPE=application/pdf:https://example.test/a.pdf
+RELATED-TO;RELTYPE=PARENT:parent@example.test
+X-GOVOPLAN-CUSTOM:kept
+BEGIN:VALARM
+ACTION:DISPLAY
+DESCRIPTION:Reminder
+TRIGGER:-PT15M
+END:VALARM
+END:VEVENT
+END:VCALENDAR
+"""
+        )
+
+        self.assertEqual(event["start_at"], datetime(2026, 7, 8, 7, 0, tzinfo=timezone.utc))
+        self.assertEqual(event["end_at"], datetime(2026, 7, 8, 8, 30, tzinfo=timezone.utc))
+        self.assertEqual(event["duration_seconds"], 5400)
+        self.assertEqual(event["description"], "Line one\nLine two")
+        self.assertEqual(event["location"], "Room; 1")
+        self.assertEqual(event["timezone"], "Europe/Berlin")
+        self.assertEqual(event["organizer"]["params"]["CN"], ["Orga"])
+        self.assertEqual(event["attendees"][0]["params"]["PARTSTAT"], ["ACCEPTED"])
+        self.assertEqual(event["icalendar"]["method"], "REQUEST")
+        self.assertEqual(event["icalendar"]["standard"]["priority"]["value"], "5")
+        self.assertEqual(event["icalendar"]["standard"]["url"]["value"], "https://example.test/events/event-advanced")
+        self.assertEqual(event["reminders"][0]["trigger"]["value"], "-PT15M")
+        self.assertEqual(event["reminders"][0]["trigger"]["decoded"], -900)
+        property_names = [item["name"] for item in event["icalendar"]["properties"]]
+        self.assertIn("REQUEST-STATUS", property_names)
+        self.assertIn("X-GOVOPLAN-CUSTOM", property_names)
+
+    def test_generated_ics_preserves_unmapped_properties_and_alarms(self) -> None:
+        event = SimpleNamespace(
+            uid="event-export@example.test",
+            start_at=datetime(2026, 7, 8, 7, 0, tzinfo=timezone.utc),
+            end_at=datetime(2026, 7, 8, 8, 0, tzinfo=timezone.utc),
+            duration_seconds=None,
+            all_day=False,
+            timezone="Europe/Berlin",
+            summary="Generated",
+            sequence=4,
+            status="CONFIRMED",
+            transparency="OPAQUE",
+            classification="PUBLIC",
+            description=None,
+            location=None,
+            categories=["GovOPlaN"],
+            rrule={"FREQ": "WEEKLY", "COUNT": "2"},
+            organizer={"value": "mailto:orga@example.test", "params": {"CN": ["Orga"]}},
+            attendees=[{"value": "mailto:ada@example.test", "params": {"CN": ["Ada"], "ROLE": ["REQ-PARTICIPANT"]}}],
+            rdate=[],
+            exdate=[],
+            reminders=[],
+            attachments=[{"name": "ATTACH", "value": "https://example.test/a.pdf", "params": {"FMTTYPE": ["application/pdf"]}}],
+            related_to=[{"name": "RELATED-TO", "value": "parent@example.test", "params": {"RELTYPE": ["PARENT"]}}],
+            icalendar={
+                "method": "PUBLISH",
+                "properties": [
+                    {"name": "URL", "value": "https://example.test/events/event-export", "params": {}},
+                    {"name": "X-GOVOPLAN-CUSTOM", "value": "kept", "params": {}},
+                    {"name": "SUMMARY", "value": "Stale summary", "params": {}},
+                ],
+                "alarms": [
+                    {
+                        "component": "VALARM",
+                        "properties": [
+                            {"name": "ACTION", "value": "DISPLAY", "params": {}},
+                            {"name": "DESCRIPTION", "value": "Reminder", "params": {}},
+                            {"name": "TRIGGER", "value": "-PT15M", "params": {}},
+                        ],
+                    }
+                ],
+            },
+        )
+
+        ics = event_to_ics(event)
+
+        self.assertIn("METHOD:PUBLISH", ics)
+        self.assertIn("DTSTART;TZID=Europe/Berlin:20260708T090000", ics)
+        self.assertIn("SUMMARY:Generated", ics)
+        self.assertNotIn("SUMMARY:Stale summary", ics)
+        self.assertIn("RRULE:FREQ=WEEKLY;COUNT=2", ics)
+        self.assertIn("ATTACH;FMTTYPE=application/pdf:https://example.test/a.pdf", ics)
+        self.assertIn("RELATED-TO;RELTYPE=PARENT:parent@example.test", ics)
+        self.assertIn("URL:https://example.test/events/event-export", ics)
+        self.assertIn("X-GOVOPLAN-CUSTOM:kept", ics)
+        self.assertIn("BEGIN:VALARM", ics)
+        self.assertIn("TRIGGER:-PT15M", ics)
+
+    def test_expand_event_occurrences_applies_rrule_rdate_and_exdate(self) -> None:
+        parsed = parse_vevent(
+            """BEGIN:VCALENDAR
+VERSION:2.0
+BEGIN:VEVENT
+UID:event-recur@example.test
+DTSTART;TZID=Europe/Berlin:20260708T090000
+DTEND;TZID=Europe/Berlin:20260708T100000
+SUMMARY:Recurring
+RRULE:FREQ=WEEKLY;COUNT=3
+EXDATE;TZID=Europe/Berlin:20260715T090000
+RDATE;TZID=Europe/Berlin:20260729T090000
+END:VEVENT
+END:VCALENDAR
+"""
+        )
+        event = SimpleNamespace(**parsed)
+
+        occurrences = expand_event_occurrences(
+            event,
+            datetime(2026, 7, 1, tzinfo=timezone.utc),
+            datetime(2026, 7, 31, 23, 59, tzinfo=timezone.utc),
+        )
+
+        self.assertEqual(
+            [item["start_at"] for item in occurrences],
+            [
+                datetime(2026, 7, 8, 7, 0, tzinfo=timezone.utc),
+                datetime(2026, 7, 22, 7, 0, tzinfo=timezone.utc),
+                datetime(2026, 7, 29, 7, 0, tzinfo=timezone.utc),
+            ],
+        )
+        self.assertEqual(occurrences[0]["end_at"], datetime(2026, 7, 8, 8, 0, tzinfo=timezone.utc))
+
     def test_generated_ics_contains_required_vevent_fields(self) -> None:
         class Event:
             uid = "event-3@example.test"

tests/test_service.py

@@ -0,0 +1,115 @@
+from __future__ import annotations
+
+import unittest
+from datetime import datetime, timedelta, timezone
+from types import SimpleNamespace
+from unittest.mock import patch
+
+from govoplan_calendar.backend.schemas import CalendarCollectionDeleteRequest, CalendarEventResponse
+from govoplan_calendar.backend.service import delete_calendar, event_response
+
+
+class FakeSession:
+    def __init__(self) -> None:
+        self.flushed = False
+
+    def flush(self) -> None:
+        self.flushed = True
+
+
+class CalendarServiceResponseTests(unittest.TestCase):
+    def test_event_response_marks_naive_database_datetimes_as_utc(self) -> None:
+        event = SimpleNamespace(
+            id="event-1",
+            tenant_id="tenant-1",
+            calendar_id="calendar-1",
+            uid="event-1@example.test",
+            recurrence_id=None,
+            sequence=0,
+            summary="Planning",
+            description=None,
+            location=None,
+            status="CONFIRMED",
+            transparency="OPAQUE",
+            classification="PUBLIC",
+            start_at=datetime(2026, 7, 7, 18, 0),
+            end_at=datetime(2026, 7, 7, 19, 0),
+            duration_seconds=None,
+            all_day=False,
+            timezone=None,
+            organizer=None,
+            attendees=[],
+            categories=[],
+            rrule=None,
+            rdate=[],
+            exdate=[],
+            reminders=[],
+            attachments=[],
+            related_to=[],
+            source_kind="local",
+            source_href=None,
+            etag=None,
+            icalendar={},
+            created_at=datetime(2026, 7, 7, 17, 55),
+            updated_at=datetime(2026, 7, 7, 17, 55),
+            metadata_={},
+        )
+
+        payload = event_response(event)
+        response = CalendarEventResponse.model_validate(payload)
+
+        self.assertEqual(response.start_at.utcoffset(), timedelta(0))
+        self.assertEqual(response.end_at.utcoffset(), timedelta(0))
+        self.assertEqual(response.created_at.utcoffset(), timedelta(0))
+        self.assertEqual(response.updated_at.utcoffset(), timedelta(0))
+        self.assertEqual(response.start_at.tzinfo, timezone.utc)
+
+
+class CalendarServiceDeleteTests(unittest.TestCase):
+    def test_delete_default_calendar_soft_deletes_calendar_and_events(self) -> None:
+        session = FakeSession()
+        event = SimpleNamespace(calendar_id="calendar-1", deleted_at=None)
+        calendar = SimpleNamespace(id="calendar-1", is_default=True, deleted_at=None, events=[event])
+
+        with patch("govoplan_calendar.backend.service.get_calendar", return_value=calendar):
+            delete_calendar(
+                session,
+                tenant_id="tenant-1",
+                calendar_id="calendar-1",
+                payload=CalendarCollectionDeleteRequest(event_action="delete"),
+            )
+
+        self.assertTrue(session.flushed)
+        self.assertFalse(calendar.is_default)
+        self.assertIsNotNone(calendar.deleted_at)
+        self.assertEqual(event.deleted_at, calendar.deleted_at)
+        self.assertEqual(event.calendar_id, "calendar-1")
+
+    def test_delete_calendar_can_move_events_to_another_calendar_and_make_it_default(self) -> None:
+        session = FakeSession()
+        event = SimpleNamespace(calendar_id="calendar-1", deleted_at=None)
+        calendar = SimpleNamespace(id="calendar-1", is_default=True, deleted_at=None, events=[event])
+        target = SimpleNamespace(id="calendar-2", is_default=False, deleted_at=None, events=[])
+
+        with (
+            patch("govoplan_calendar.backend.service.get_calendar", side_effect=[calendar, target]),
+            patch("govoplan_calendar.backend.service.clear_default_calendar") as clear_default_calendar,
+        ):
+            delete_calendar(
+                session,
+                tenant_id="tenant-1",
+                calendar_id="calendar-1",
+                payload=CalendarCollectionDeleteRequest(event_action="move", target_calendar_id="calendar-2", make_target_default=True),
+            )
+
+        self.assertTrue(session.flushed)
+        clear_default_calendar.assert_called_once_with(session, tenant_id="tenant-1")
+        self.assertFalse(calendar.is_default)
+        self.assertTrue(target.is_default)
+        self.assertIsNotNone(calendar.deleted_at)
+        self.assertIsNone(event.deleted_at)
+        self.assertEqual(event.calendar_id, "calendar-2")
+
+
+if __name__ == "__main__":
+    unittest.main()

webui/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@govoplan/calendar-webui",
-  "version": "0.1.4",
+  "version": "0.1.5",
   "private": true,
   "type": "module",
   "main": "src/index.ts",
@@ -14,7 +14,7 @@
     "./styles/calendar.css": "./src/styles/calendar.css"
   },
   "peerDependencies": {
-    "@govoplan/core-webui": "^0.1.4",
+    "@govoplan/core-webui": "^0.1.5",
     "lucide-react": "^0.555.0",
     "react": "^19.0.0",
     "react-dom": "^19.0.0",

webui/src/api/calendar.ts

@@ -56,6 +56,27 @@ export type CalendarEvent = {
 export type CalendarCollectionListResponse = { calendars: CalendarCollection[] };
 export type CalendarEventListResponse = { events: CalendarEvent[] };
 
+export type CalendarCollectionCreatePayload = {
+  name: string;
+  slug?: string | null;
+  description?: string | null;
+  timezone?: string;
+  color?: string | null;
+  owner_type?: "tenant" | "user" | "group" | "resource";
+  owner_id?: string | null;
+  visibility?: "private" | "tenant" | "shared" | "public";
+  is_default?: boolean;
+  metadata?: Record<string, unknown>;
+};
+
+export type CalendarCollectionUpdatePayload = Partial<CalendarCollectionCreatePayload>;
+export type CalendarDeleteEventAction = "delete" | "move";
+export type CalendarCollectionDeletePayload = {
+  event_action?: CalendarDeleteEventAction;
+  target_calendar_id?: string | null;
+  make_target_default?: boolean;
+};
+
 export type CalendarEventCreatePayload = {
   calendar_id?: string | null;
   summary: string;
@@ -71,10 +92,24 @@ export type CalendarEventCreatePayload = {
   categories?: string[];
 };
 
+export type CalendarEventUpdatePayload = Partial<CalendarEventCreatePayload>;
+
 export function listCalendars(settings: ApiSettings): Promise<CalendarCollectionListResponse> {
   return apiFetch<CalendarCollectionListResponse>(settings, "/api/v1/calendar/calendars");
 }
 
+export function createCalendar(settings: ApiSettings, payload: CalendarCollectionCreatePayload): Promise<CalendarCollection> {
+  return apiFetch<CalendarCollection>(settings, "/api/v1/calendar/calendars", { method: "POST", body: JSON.stringify(payload) });
+}
+
+export function updateCalendar(settings: ApiSettings, calendarId: string, payload: CalendarCollectionUpdatePayload): Promise<CalendarCollection> {
+  return apiFetch<CalendarCollection>(settings, `/api/v1/calendar/calendars/${calendarId}`, { method: "PATCH", body: JSON.stringify(payload) });
+}
+
+export function deleteCalendar(settings: ApiSettings, calendarId: string, payload: CalendarCollectionDeletePayload = { event_action: "delete" }): Promise<void> {
+  return apiFetch<void>(settings, `/api/v1/calendar/calendars/${calendarId}`, { method: "DELETE", body: JSON.stringify(payload) });
+}
+
 export function listCalendarEvents(
   settings: ApiSettings,
   params: { calendar_id?: string; start_at?: string; end_at?: string } = {}
@@ -90,3 +125,11 @@ export function listCalendarEvents(
 export function createCalendarEvent(settings: ApiSettings, payload: CalendarEventCreatePayload): Promise<CalendarEvent> {
   return apiFetch<CalendarEvent>(settings, "/api/v1/calendar/events", { method: "POST", body: JSON.stringify(payload) });
 }
+
+export function updateCalendarEvent(settings: ApiSettings, eventId: string, payload: CalendarEventUpdatePayload): Promise<CalendarEvent> {
+  return apiFetch<CalendarEvent>(settings, `/api/v1/calendar/events/${eventId}`, { method: "PATCH", body: JSON.stringify(payload) });
+}
+
+export function deleteCalendarEvent(settings: ApiSettings, eventId: string): Promise<void> {
+  return apiFetch<void>(settings, `/api/v1/calendar/events/${eventId}`, { method: "DELETE" });
+}