govoplan-calendar/docs/CALENDAR_INTEGRATION_CONCEPT.md

# GovOPlaN Calendar Integration Concept

## Module Boundary

`govoplan-calendar` owns calendar primitives:

- calendar collections
- VEVENT storage and iCalendar import/export
- event recurrence data, recurrence expansion, and recurrence exceptions
- availability and free/busy semantics
- resources such as rooms, shared equipment, and service desks
- groupware calendar adapter boundaries, including CalDAV and Open-Xchange

Calendar does not own meeting-poll decisions, bookable service appointments, task lifecycle, mail transport, or document lifecycle. Those modules should reference calendar events through stable IDs, iCalendar UIDs, capabilities, or API contracts.

## First Implementation

The first standalone module provides:

- `CalendarCollection` records for tenant calendars
- `CalendarEvent` records for VEVENT data
- 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
- bounded occurrence expansion with RRULE, RDATE, EXDATE, detached overrides,
  instance/series editing, and free/busy reconciliation
- durable per-user calendar view preferences exposed through the platform
  Settings surface
- 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
- a Calendar-owned durable desired-state outbox for two-way CalDAV writes. Event
  state and the exact external resource snapshot commit atomically; workers use
  deterministic hrefs, conditional requests, expiring leases, bounded
  exponential retry, and semantic GET reconciliation after ambiguous outcomes
- WebUI views: month, week, workweek, day, and continuous week-row scrolling
- an Open-Xchange profile over the CalDAV transport, with explicit connector,
  IDM/group-mapping, and resource-calendar references

The implementation is not yet a full CalDAV network server. It is the internal
calendar storage, recurrence, sync, availability, and UI foundation on which
scheduling inbox/outbox behavior and CalDAV server endpoints can be built.

## Open-Xchange profile

Open-Xchange is an explicit external profile backed by Calendar's CalDAV
engine. A profile therefore receives the same bounded discovery, VEVENT
round-trip, RRULE/RDATE/EXDATE and detached-exception handling, sync-token/ctag
tracking, per-resource ETag conflict detection, and durable two-way outbox as a
generic CalDAV source. Calendar's availability capability reads the resulting
projection, so free/busy and collision checks use the same recurrence-aware
event set. Availability is current as of the source's visible last successful
sync; GovOPlaN does not claim live Open-Xchange state while a source is stale.

The source metadata retains three optional, non-secret bindings:

- `connector_profile_ref` links the endpoint to a Connectors-owned inventory or
  deployment profile.
- `identity_mapping_ref` links attendee/group identifiers to an IDM- or
  Access-governed mapping without importing either module.
- `resource_calendar_ref` identifies an Open-Xchange room/equipment calendar;
  the corresponding Calendar collection is owned as a `resource`.

The `calendar.externalProfiles` capability lets an optional connector configure
the same profile through a Core contract. Direct Calendar setup remains
available when Connectors is absent. The connector never supplies a Calendar
event model and the references never contain credentials. Open-Xchange
credentials remain a reusable credential-envelope reference or a
Calendar-owned encrypted credential. The WebUI exposes Open-Xchange as a source
type and reuses CalDAV discovery; deployments must enter a DAV endpoint that
resolves to the intended collection.

## Outbound delivery operations

No event API or cross-module capability performs CalDAV network I/O inside the
caller's transaction. A local mutation instead creates a
`calendar_outbox_operations` row containing the exact desired ICS resource,
target href, expected ETag, conflict-policy snapshot, and idempotency key.

The registered `govoplan.calendar.dispatch_outbox` worker commits an expiring
lease before doing network I/O and commits each outcome independently. If a
worker loses the database connection after a successful remote write, the next
attempt reads the remote object and compares semantic ICS fingerprints. A
matching PUT or an already absent DELETE completes successfully without a blind
duplicate write. Pending updates for one href supersede older never-attempted
rows; attempted predecessors are reconciled first, and updates queued behind an
in-flight write inherit the ETag produced by that write. Delivery and inbound
REPORT application take the same source-row lock,
and only one operation per source is leased at a time. This deliberately trades
per-source throughput for a simple ordering guarantee: a stale inbound report
cannot land after a newer outbound result, and queued leases do not expire while
waiting behind another network request for the same source.

Operators open **Outbound changes** from a synchronized calendar's settings to
inspect a bounded queue and use only the retry, reconcile, or discard actions
that are valid for the latest resource generation. Dispatch and due-source
routes are worker-only and reject interactive sessions even when the account is
an administrator. Terminal ETag
conflicts and exhausted retries remain the current local desired state and
shield that resource from inbound overwrite until explicitly resolved.
Discarding is the administrator's accept-remote transition: it is allowed only
for the latest generation, atomically cancels its unresolved predecessor chain,
marks the event projection as discarded, clears the sync token, and schedules a
full inbound reconciliation so an unchanged remote object is not missed.
The UI requires a separate destructive confirmation and explains that accepting
remote may lose the unresolved local desired state. Disabled and inbound-only
sources still permit discard when the retained source belongs to the tenant,
but they cannot be retried or reconciled until made writable again. Missing
sources, active worker leases, stale generations, and already-resolved rows
expose diagnostics instead of unsafe action buttons.

Disabling outbound delivery or switching to inbound-only is rejected while
unresolved desired state exists; retirement is the explicit exception and
cancels unresolved work. Endpoint/calendar changes also require no active event
bindings or unresolved delivery. Credential rotation does not discard committed
desired state. Public event mutation cannot set sync-owned source hrefs, kinds,
or ETags. Deleting a synchronized collection or retiring its source is a local
unlink: it never deletes the remote collection or its remaining remote events.
The unlink immediately scrubs Calendar-owned credential ciphertext and external
provider references and audits the deletion. External provider failure blocks
retirement before queued work is changed; a later retry tolerates a provider
secret already removed by an earlier attempt whose database transaction rolled
back. Provider errors and audit details never contain credential values or
secret references.

### Runtime provider state

Calendar registers tenant-aware runtime state for
`calendar.caldav_sync`. Each active CalDAV source is projected by a stable
`calendar:sync-source:<id>` reference with its effective source-authority mode,
enabled state, health, freshness, unresolved-conflict state, recovery readiness,
last successful synchronization, and bounded outbox counts. Collection URLs,
usernames, credential references, remote resource paths, and error text are not
included.

Docs uses the projection to explain configured availability, Ops aggregates it
for operator inspection, and configuration-package preflight can require one
exact source binding. A source with dead or conflicting desired-state work
requires recovery attention; a never-synchronized source remains unknown rather
than being reported healthy.
The current singular ownership model permits one active sync source per
calendar; multi-source fan-in will require per-event source routing. Celery beat
triggers recovery every minute, while root-transaction after-commit dispatch
provides the normal low-latency path.

### Collection retirement and bulk event moves

Collection deletion accepts two explicit, non-destructive external actions for
`event_action="move"`:

- `detach_keep_remote` applies only when the source collection is synchronized
  and the target is local. It moves the local event projections, clears their
  sync-owned source kind, href, ETag, and CalDAV projection metadata, retires
  the source locally, and cancels undelivered outbox state. An active delivery
  lease blocks the transaction. The action never enqueues a remote DELETE, so
  the remote collection and remote events remain unchanged.
- `copy_to_remote` applies only when the source is local and the target has an
  active, enabled, two-way CalDAV source. It moves the local events and commits
  destination PUT desired states in the durable outbox in the same database
  transaction. Remote failures therefore remain visible and retryable without
  rolling back or hiding the local move.

Local-to-local moves retain their existing behavior and do not accept an
`external_action`. Implicit or mismatched actions, inbound-only destinations,
and synchronized-to-synchronized moves are rejected. `remote_move` is a known
but deliberately unsupported action: implementing it requires a separately
approved saga for destination reconciliation, conditional source deletion,
collision handling, and concurrent-edit policy. The WebUI does not offer that
destructive mode.

Resolved terminal rows (`succeeded`, `superseded`, and `cancelled`) are removed
in bounded batches after `CALENDAR_OUTBOX_TERMINAL_RETENTION_DAYS` (90 days by
default; `0` disables cleanup). `conflict` and `dead` rows are never removed by
this cleanup because they still carry unresolved local desired state. Each
periodic or after-commit dispatch also performs one bounded cleanup batch for
the same tenant scope.

## Integration Points

### Scheduling

`govoplan-scheduling` should use calendar for:

- organizer availability lookup
- candidate slot conflict checks
- final event creation after a poll decision
- participant invitation state as VEVENT attendees when a meeting becomes real

Scheduling remains owner of polls, candidate ranking, external participation links, and decision audit.

### Appointments

`govoplan-appointments` should use calendar for:

- confirmed appointment placement
- staff/resource conflict checks
- room and desk calendars
- cancellation or rescheduling events

Appointments remains owner of public booking flows, service definitions, capacity rules, queues, and no-show handling.

### Tasks And Workflow

`govoplan-tasks` and `govoplan-workflow` should use calendar for:

- due-date and reminder calendar overlays
- workflow deadlines
- escalation dates
- optional event creation for hearings, reviews, inspections, and internal meetings

Tasks/workflow remain owners of assignment, status, SLA logic, and completion semantics.

### Mail And Notifications

`govoplan-mail` and `govoplan-notifications` should use calendar for:

- outbound iCalendar invites and updates
- inbound invite parsing from messages
- RSVP state changes
- reminders and digest notifications

Mail remains owner of SMTP/IMAP profiles and mailbox transport. Notifications remains owner of delivery channels and delivery policy.

### Documents And DMS

`govoplan-dms` can link documents to events for:

- agendas
- minutes
- attachments
- legal deadlines
- retention and audit context

DMS remains owner of versions, locks, approvals, collaboration, legal hold, and document retention.

### Cases, Campaigns, Forms, And Portal

Domain modules may attach calendar references to domain objects:

- cases: hearings, inspections, review meetings
- campaigns: send windows and review deadlines
- forms: submission windows and office-hour sessions
- portal: citizen-facing event or appointment visibility

Calendar should expose reusable event and availability APIs instead of importing those modules.

### Connectors And Public-Sector Groupware

`govoplan-connectors` should own generic connector catalogue behavior, connection setup patterns, and external-system inventory. Calendar owns the actual calendar semantics for:

- CalDAV
- Open-Xchange calendar
- OpenDesk calendar stack integration
- resource-calendar mapping
- free/busy sync
- recurrence and exception mapping
- conflict handling

The connector boundary should hand calendar a configured profile and credentials reference, not a domain-specific event model.

## Follow-Up Work

- 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.
- Calendar ACLs beyond tenant-wide permissions.