webmail-client/backend/app/outbox/draft_sync.py

"""Mirror local drafts to the account's IMAP Drafts folder (SPEC §6.5 extension).

Drafts are stored server-side as ``\\Draft`` messages so they can be continued on
any standard mail client. IMAP messages are immutable, so each edit APPENDs a new
copy and expunges the previous one (tracked by ``drafts.imap_uid``). Runs in the
worker (credential decryption is worker-only, §10.2).
"""

from __future__ import annotations

import contextlib
import logging
import uuid
from typing import Any

from sqlalchemy import select

from app.db import session_scope
from app.models import Account, Draft, Mailbox, Message
from app.outbox.attachments import load_attachments
from app.outbox.mime_build import build_mime
from app.sync.provider_factory import build_provider

logger = logging.getLogger(__name__)

_DRAFT_FLAGS = frozenset({"\\Draft", "\\Seen"})


async def _ensure_drafts_folder(provider: Any, account: Account, user_id: uuid.UUID) -> str:
    """Return the account's Drafts folder path, creating one if it is missing."""
    path = "Drafts"
    await provider.create_mailbox(path)
    remote = await provider.list_mailboxes()
    uidvalidity = next((r.uidvalidity for r in remote if r.path == path), 0)
    async with session_scope() as session:
        existing = await session.scalar(
            select(Mailbox).where(
                Mailbox.account_id == account.id, Mailbox.special_use == "drafts"
            )
        )
        if existing is not None:
            return existing.path
        session.add(
            Mailbox(
                account_id=account.id,
                user_id=user_id,
                path=path,
                special_use="drafts",
                uidvalidity=uidvalidity,
            )
        )
    return path


async def push_draft_to_imap_job(ctx: dict[str, Any], draft_id: str) -> None:
    """APPEND the draft to the Drafts folder and expunge the previous copy."""
    did = uuid.UUID(draft_id)
    async with session_scope() as session:
        draft = await session.get(Draft, did)
        if draft is None:
            return
        account = await session.get(Account, draft.account_id)
        if account is None:
            return
        user_id = draft.user_id
        old_uid = draft.imap_uid
        reply_to = (
            await session.get(Message, draft.reply_to_message_id)
            if draft.reply_to_message_id
            else None
        )
        attachments = await load_attachments(session, user_id, draft)
        _, sent_raw, _, _ = build_mime(account, draft, reply_to, attachments)
        drafts_mb = await session.scalar(
            select(Mailbox).where(
                Mailbox.account_id == account.id, Mailbox.special_use == "drafts"
            )
        )
        drafts_path = drafts_mb.path if drafts_mb else None
        account_obj = account

    provider = build_provider(account_obj)
    new_uid = 0
    try:
        if drafts_path is None:
            drafts_path = await _ensure_drafts_folder(provider, account_obj, user_id)
        new_uid = await provider.append(drafts_path, sent_raw, _DRAFT_FLAGS)
        if old_uid:
            with contextlib.suppress(Exception):
                await provider.delete_messages(drafts_path, [old_uid])
    finally:
        await provider.close()

    if new_uid:
        async with session_scope() as session:
            draft = await session.get(Draft, did)
            if draft is not None:
                draft.imap_uid = new_uid


async def remove_imap_draft_job(ctx: dict[str, Any], account_id: str, uid: int) -> None:
    """Expunge a draft copy from the account's Drafts folder (on discard)."""
    aid = uuid.UUID(account_id)
    async with session_scope() as session:
        account = await session.get(Account, aid)
        if account is None:
            return
        drafts_mb = await session.scalar(
            select(Mailbox).where(Mailbox.account_id == aid, Mailbox.special_use == "drafts")
        )
        drafts_path = drafts_mb.path if drafts_mb else None
        account_obj = account
    if drafts_path is None:
        return
    provider = build_provider(account_obj)
    try:
        with contextlib.suppress(Exception):
            await provider.delete_messages(drafts_path, [int(uid)])
    finally:
        await provider.close()