govoplan-mail/src/govoplan_mail/backend/postbox_bridge.py

from __future__ import annotations

import hashlib
from email import policy
from email.message import Message
from email.parser import BytesParser
from email.utils import getaddresses

from sqlalchemy.orm import Session

from govoplan_core.core.mail import (
    MailPostboxBridgeProvider,
    MailPostboxBridgeRequest,
    MailPostboxBridgeResult,
)
from govoplan_core.core.modules import ModuleContext
from govoplan_core.core.postbox import (
    PostboxAttachmentRef,
    PostboxDeliveryRequest,
    PostboxParticipantRef,
    PostboxTargetRef,
    postbox_delivery_provider,
)
from govoplan_mail.backend.db.models import MailServerProfile
from govoplan_mail.backend.runtime import configure_runtime, get_registry


MAX_BRIDGE_MESSAGE_BYTES = 50 * 1024 * 1024
MAX_POSTBOX_BODY_CHARS = 500_000


class MailPostboxBridgeError(RuntimeError):
    pass


class MailPostboxBridge(MailPostboxBridgeProvider):
    """Translate immutable IMAP observations into native Postbox delivery."""

    def bridge_message(
        self,
        session: object,
        request: MailPostboxBridgeRequest,
    ) -> MailPostboxBridgeResult:
        if not isinstance(session, Session):
            raise TypeError("Mail Postbox bridging requires a SQLAlchemy session.")
        if not isinstance(request.target, PostboxTargetRef):
            raise MailPostboxBridgeError("A typed Postbox target is required.")
        if len(request.raw_message) > MAX_BRIDGE_MESSAGE_BYTES:
            raise MailPostboxBridgeError("Mail message exceeds the Postbox bridge limit.")
        profile = session.get(MailServerProfile, request.profile_id)
        if profile is None or profile.tenant_id != request.tenant_id:
            raise MailPostboxBridgeError("Mail profile not found.")
        folder = request.folder.strip()
        uid = request.uid.strip()
        uidvalidity = request.uidvalidity.strip()
        if not folder or not uid or not uidvalidity:
            raise MailPostboxBridgeError(
                "Mail folder, UIDVALIDITY, and immutable UID are required."
            )
        try:
            message = BytesParser(policy=policy.default).parsebytes(request.raw_message)
        except Exception as exc:
            raise MailPostboxBridgeError("Mail message could not be parsed.") from exc

        provider = postbox_delivery_provider(get_registry())
        if provider is None:
            raise MailPostboxBridgeError("Postbox delivery is not available.")
        source_digest = hashlib.sha256(request.raw_message).hexdigest()
        source_key = hashlib.sha256(
            f"{request.tenant_id}\0{request.profile_id}\0{folder}\0{uidvalidity}\0{uid}".encode("utf-8")
        ).hexdigest()
        result = provider.deliver(
            session,
            PostboxDeliveryRequest(
                tenant_id=request.tenant_id,
                target=request.target,
                producer_module="mail",
                producer_resource_type="imap_message",
                producer_resource_id=source_key,
                idempotency_key=f"mail-postbox:{source_key}:{source_digest}",
                subject=_header(message, "Subject") or "(No subject)",
                body_text=_plain_text_body(message),
                sender_label=_header(message, "From"),
                classification=request.classification,
                participants=_participants(message),
                attachments=_attachments(
                    message,
                    profile_id=request.profile_id,
                    folder=folder,
                    uidvalidity=uidvalidity,
                    uid=uid,
                ),
                metadata={
                    **dict(request.metadata),
                    "transport": "mail-imap",
                    "mail_profile_id": request.profile_id,
                    "mailbox_folder": folder,
                    "mailbox_uidvalidity": uidvalidity,
                    "mailbox_uid": uid,
                    "rfc_message_id": _header(message, "Message-ID"),
                    "raw_sha256": source_digest,
                },
            ),
        )
        return MailPostboxBridgeResult(
            postbox_id=result.postbox_id,
            message_id=result.message_id,
            delivery_id=result.delivery_id,
            duplicate=result.duplicate,
            source_digest=source_digest,
        )


def _header(message: Message, name: str) -> str | None:
    value = " ".join(str(message.get(name) or "").split())
    return value[:1000] or None


def _plain_text_body(message: Message) -> str | None:
    candidates = message.walk() if message.is_multipart() else (message,)
    for part in candidates:
        if part.get_content_type() != "text/plain":
            continue
        if part.get_content_disposition() == "attachment":
            continue
        try:
            value = part.get_content()
        except Exception:
            payload = part.get_payload(decode=True) or b""
            value = payload.decode(part.get_content_charset() or "utf-8", errors="replace")
        if isinstance(value, bytes):
            value = value.decode(part.get_content_charset() or "utf-8", errors="replace")
        normalized = str(value).strip()
        if normalized:
            return normalized[:MAX_POSTBOX_BODY_CHARS]
    return None


def _participants(message: Message) -> tuple[PostboxParticipantRef, ...]:
    result: list[PostboxParticipantRef] = []
    for kind, headers in (
        ("sender", ("From",)),
        ("to", ("To",)),
        ("cc", ("Cc",)),
        ("bcc", ("Bcc",)),
    ):
        for name, address in getaddresses(
            [str(value) for header in headers for value in message.get_all(header, [])]
        ):
            clean_address = address.strip()[:500]
            if not clean_address:
                continue
            result.append(
                PostboxParticipantRef(
                    kind=kind,
                    reference_type="external_email",
                    label=name.strip()[:500] or None,
                    address=clean_address,
                )
            )
    return tuple(result)


def _attachments(
    message: Message,
    *,
    profile_id: str,
    folder: str,
    uidvalidity: str,
    uid: str,
) -> tuple[PostboxAttachmentRef, ...]:
    result: list[PostboxAttachmentRef] = []
    for index, part in enumerate(message.walk()):
        filename = part.get_filename()
        if part.get_content_disposition() != "attachment" and not filename:
            continue
        payload = part.get_payload(decode=True) or b""
        digest = hashlib.sha256(payload).hexdigest()
        reference_id = hashlib.sha256(
            f"{profile_id}\0{folder}\0{uidvalidity}\0{uid}\0{index}\0{digest}".encode("utf-8")
        ).hexdigest()
        result.append(
            PostboxAttachmentRef(
                reference_type="mail_attachment",
                reference_id=reference_id,
                name=str(filename or f"attachment-{index + 1}")[:1000],
                media_type=part.get_content_type(),
                size_bytes=len(payload),
                digest=digest,
                metadata={
                    "mail_profile_id": profile_id,
                    "mailbox_folder": folder,
                    "mailbox_uidvalidity": uidvalidity,
                    "mailbox_uid": uid,
                    "mime_part_index": index,
                },
            )
        )
    return tuple(result)


def create_postbox_bridge(context: ModuleContext) -> MailPostboxBridge:
    configure_runtime(registry=context.registry, settings=context.settings)
    return MailPostboxBridge()


__all__ = [
    "MailPostboxBridge",
    "MailPostboxBridgeError",
    "create_postbox_bridge",
]