"""Soft-delete / trash service — single source of truth for recoverable deletes.

A delete stamps `deleted_at` + a shared `deleted_batch_id` on the target row and
its descendants (cascade). Restore clears the batch; purge hard-deletes it; the
retention cron purges rows older than the configured window. Live reads exclude
trashed rows via `alive()`.
"""
from __future__ import annotations

import uuid
from datetime import datetime, timezone

from sqlalchemy import or_, select, update

from fabledassistant.models import async_session
from fabledassistant.models.note import Note
from fabledassistant.models.event import Event
from fabledassistant.models.project import Project
from fabledassistant.models.milestone import Milestone
from fabledassistant.models.rulebook import Rulebook, RulebookTopic, Rule

# entity_type -> Model. Used to resolve which table a trash op targets.
_MODEL_FOR = {
    "note": Note,
    "task": Note,
    "event": Event,
    "project": Project,
    "milestone": Milestone,
    "rulebook": Rulebook,
    "topic": RulebookTopic,
    "rule": Rule,
}


def _owner_clause(model, user_id: int):
    """Boolean expr scoping `model` rows to the ones `user_id` owns.

    EVERY trash query (exists-check, restore, purge, list, retention sweep)
    must carry this — a batch_id is a bearer token, so without an owner
    predicate a leaked/guessed id lets one tenant read, restore, or
    permanently destroy another's content. Topics and rules carry no
    user_id of their own; ownership is derived through the parent rulebook
    (or, for project-scoped rules, the owning project).
    """
    if model is Rulebook:
        return Rulebook.owner_user_id == user_id
    if model is RulebookTopic:
        return RulebookTopic.rulebook_id.in_(
            select(Rulebook.id).where(Rulebook.owner_user_id == user_id)
        )
    if model is Rule:
        return or_(
            Rule.topic_id.in_(
                select(RulebookTopic.id)
                .join(Rulebook, RulebookTopic.rulebook_id == Rulebook.id)
                .where(Rulebook.owner_user_id == user_id)
            ),
            Rule.project_id.in_(
                select(Project.id).where(Project.user_id == user_id)
            ),
        )
    # Note, Event, Project, Milestone all carry user_id directly.
    return model.user_id == user_id


async def _set(session, model, where, batch, now) -> None:
    """Stamp deleted_at + batch on live rows matching `where`."""
    await session.execute(
        update(model)
        .where(*where, model.deleted_at.is_(None))
        .values(deleted_at=now, deleted_batch_id=batch)
    )


async def _exists_alive(session, user_id: int, etype: str, eid: int) -> bool:
    model = _MODEL_FOR[etype]
    where = [model.id == eid, model.deleted_at.is_(None), _owner_clause(model, user_id)]
    return (await session.execute(select(model.id).where(*where))).first() is not None


async def _cascade(session, user_id: int, etype: str, eid: int, batch: str, now) -> None:
    if etype == "project":
        await _set(session, Note, [Note.user_id == user_id, Note.project_id == eid], batch, now)
        await _set(session, Milestone, [Milestone.user_id == user_id, Milestone.project_id == eid], batch, now)
        # Project-scoped rules cascade with the project they're attached to.
        await _set(session, Rule, [Rule.project_id == eid], batch, now)
        # Suppressions are pure associations (no deleted_at) — hard-delete
        # them here so restoring the project doesn't bring stale mutes back.
        # FK CASCADE would handle a full DELETE on the project row, but the
        # soft-delete path keeps the project row alive; this guarantees the
        # rows are gone whether or not the project ever gets purged.
        from sqlalchemy import delete as _sql_delete
        from fabledassistant.models.rulebook import (
            project_rule_suppressions, project_topic_suppressions,
        )
        await session.execute(
            _sql_delete(project_rule_suppressions)
            .where(project_rule_suppressions.c.project_id == eid)
        )
        await session.execute(
            _sql_delete(project_topic_suppressions)
            .where(project_topic_suppressions.c.project_id == eid)
        )
        await _set(session, Project, [Project.user_id == user_id, Project.id == eid], batch, now)
    elif etype == "milestone":
        await _set(session, Note, [Note.user_id == user_id, Note.milestone_id == eid], batch, now)
        await _set(session, Milestone, [Milestone.user_id == user_id, Milestone.id == eid], batch, now)
    elif etype in ("note", "task"):
        # Stamp the entire sub-task subtree (not just direct children) so a
        # deeply nested task and all its descendants trash/restore as one batch.
        ids = [eid]
        frontier = [eid]
        while frontier:
            children = (await session.execute(
                select(Note.id).where(
                    Note.user_id == user_id,
                    Note.parent_id.in_(frontier),
                    Note.deleted_at.is_(None),
                )
            )).scalars().all()
            frontier = [c for c in children if c not in ids]
            ids.extend(frontier)
        await _set(session, Note, [Note.user_id == user_id, Note.id.in_(ids)], batch, now)
    elif etype == "event":
        await _set(session, Event, [Event.user_id == user_id, Event.id == eid], batch, now)
    elif etype == "rulebook":
        topic_ids = (await session.execute(
            select(RulebookTopic.id)
            .join(Rulebook, RulebookTopic.rulebook_id == Rulebook.id)
            .where(Rulebook.id == eid, Rulebook.owner_user_id == user_id)
        )).scalars().all()
        if topic_ids:
            await _set(session, Rule, [Rule.topic_id.in_(topic_ids)], batch, now)
        await _set(session, RulebookTopic, [RulebookTopic.rulebook_id == eid], batch, now)
        await _set(session, Rulebook, [Rulebook.id == eid, Rulebook.owner_user_id == user_id], batch, now)
    elif etype == "topic":
        await _set(session, Rule, [Rule.topic_id == eid], batch, now)
        await _set(session, RulebookTopic, [RulebookTopic.id == eid], batch, now)
    elif etype == "rule":
        await _set(session, Rule, [Rule.id == eid], batch, now)
    else:
        raise ValueError(f"unknown entity_type: {etype!r}")


async def delete(user_id: int, entity_type: str, entity_id: int) -> str | None:
    """Soft-delete an entity + its descendants under one batch_id.

    Returns the batch_id, or None if the entity wasn't found / not owned.
    """
    batch = str(uuid.uuid4())
    now = datetime.now(timezone.utc)
    caldav_event: tuple[str, str] | None = None
    async with async_session() as session:
        if not await _exists_alive(session, user_id, entity_type, entity_id):
            return None
        # Capture CalDAV linkage before soft-deleting so we can propagate the
        # deletion to the external server (the row stays present locally).
        if entity_type == "event":
            row = (await session.execute(
                select(Event.caldav_uid, Event.title).where(
                    Event.id == entity_id, Event.user_id == user_id
                )
            )).first()
            if row and row[0]:
                caldav_event = (row[0], row[1])
        await _cascade(session, user_id, entity_type, entity_id, batch, now)
        await session.commit()
    # Without this the soft-delete only hides the event locally and the remote
    # copy lingers forever (and re-appears on any client syncing that server).
    if caldav_event:
        import asyncio
        from fabledassistant.services.events import _push_delete
        asyncio.create_task(_push_delete(caldav_event[0], caldav_event[1], user_id))
    return batch


# All soft-deletable models, and their trash-listing type label.
_ALL = [Note, Event, Project, Milestone, Rulebook, RulebookTopic, Rule]
_TYPE = {
    Note: "note", Event: "event", Project: "project", Milestone: "milestone",
    Rulebook: "rulebook", RulebookTopic: "topic", Rule: "rule",
}


def alive(stmt, model):
    """Append a 'not trashed' filter to a select. Use in every live read."""
    return stmt.where(model.deleted_at.is_(None))


async def restore(user_id: int, batch_id: str) -> int:
    """Clear deleted_at for every row in the batch. Returns rows restored."""
    n = 0
    async with async_session() as session:
        for model in _ALL:
            res = await session.execute(
                update(model)
                .where(model.deleted_batch_id == batch_id, _owner_clause(model, user_id))
                .values(deleted_at=None, deleted_batch_id=None)
            )
            n += res.rowcount or 0
        await session.commit()
    return n


async def purge(user_id: int, batch_id: str) -> int:
    """Hard-delete every row in the batch. Irreversible."""
    from sqlalchemy import delete as sql_delete
    n = 0
    async with async_session() as session:
        for model in _ALL:
            res = await session.execute(
                sql_delete(model).where(
                    model.deleted_batch_id == batch_id, _owner_clause(model, user_id)
                )
            )
            n += res.rowcount or 0
        await session.commit()
    return n


async def list_trash(user_id: int) -> list[dict]:
    """Trashed rows across all soft-deletable tables, grouped by batch_id."""
    batches: dict[str, dict] = {}
    async with async_session() as session:
        for model in _ALL:
            rows = (await session.execute(
                select(model).where(
                    model.deleted_at.isnot(None), _owner_clause(model, user_id)
                )
            )).scalars().all()
            for r in rows:
                grp = batches.setdefault(
                    r.deleted_batch_id,
                    {"batch_id": r.deleted_batch_id,
                     "deleted_at": r.deleted_at.isoformat() if r.deleted_at else None,
                     "items": []},
                )
                grp["items"].append({
                    "type": _TYPE[model], "id": r.id,
                    "title": getattr(r, "title", "") or "",
                })
    out = list(batches.values())
    for g in out:
        lead = g["items"][0]
        g["summary"] = lead["title"] or f"{lead['type']} {lead['id']}"
        g["count"] = len(g["items"])
    out.sort(key=lambda g: g["deleted_at"] or "", reverse=True)
    return out


async def purge_expired(user_id: int, retention_days: int) -> int:
    """Cron entry: hard-delete THIS user's rows trashed more than retention_days ago.

    Scoped to one owner so the scheduler can apply each user's own
    `trash_retention_days` window — a single global sweep would let one
    user's short window prematurely destroy another's data.
    retention_days <= 0 disables auto-purge (returns 0 without touching anything).
    """
    from datetime import timedelta
    from sqlalchemy import delete as sql_delete
    if retention_days <= 0:
        return 0
    cutoff = datetime.now(timezone.utc) - timedelta(days=retention_days)
    n = 0
    async with async_session() as session:
        for model in _ALL:
            res = await session.execute(
                sql_delete(model).where(
                    model.deleted_at.isnot(None),
                    model.deleted_at < cutoff,
                    _owner_clause(model, user_id),
                )
            )
            n += res.rowcount or 0
        await session.commit()
    return n