bambuddy/backend/app/services/library_trash.py

"""Library trash sweeper + purge service (#1008).

Two-stage file deletion for the library:

1. Users / admins soft-delete files — the row stays in ``library_files`` with
   ``deleted_at`` stamped; the bytes stay on disk. This is handled inline in
   ``backend.app.api.routes.library`` and exposed to admins as a bulk "purge
   old files" operation via :meth:`LibraryTrashService.purge_older_than`.

2. A background sweeper in this service hard-deletes rows (and their bytes)
   whose ``deleted_at`` is older than the configured retention window.

External files (``is_external=True``) are never placed in the trash — their
bytes live outside Bambuddy's control, so there's nothing to restore.
"""

from __future__ import annotations

import asyncio
import logging
from datetime import datetime, timedelta, timezone
from pathlib import Path

from sqlalchemy import and_, delete, func, or_, select
from sqlalchemy.ext.asyncio import AsyncSession

from backend.app.core.config import settings as app_settings
from backend.app.core.database import async_session
from backend.app.models.library import LibraryFile
from backend.app.models.print_queue import PrintQueueVariant
from backend.app.models.settings import Settings

logger = logging.getLogger(__name__)

# Settings key used to persist the trash retention window (days). The sweeper
# reads this on every tick so the UI can change it without a restart.
TRASH_RETENTION_KEY = "library_trash_retention_days"
DEFAULT_RETENTION_DAYS = 30
# Clamp retention to a sensible range. 1 day is a reasonable floor (anything
# shorter just makes trash into hard-delete); 365 gives admins plenty of rope
# without letting accidental typos (99999) grow the table unboundedly.
MIN_RETENTION_DAYS = 1
MAX_RETENTION_DAYS = 365

# Auto-purge settings (#1008 follow-up). When enabled, the sweeper loop also
# runs the admin bulk purge once per 24h using the saved age threshold.
# Default-off so existing installs don't surprise users — opt-in via Settings.
AUTO_PURGE_ENABLED_KEY = "library_auto_purge_enabled"
AUTO_PURGE_DAYS_KEY = "library_auto_purge_days"
AUTO_PURGE_INCLUDE_NEVER_PRINTED_KEY = "library_auto_purge_include_never_printed"
AUTO_PURGE_LAST_RUN_KEY = "library_auto_purge_last_run"
DEFAULT_AUTO_PURGE_DAYS = 90
MIN_AUTO_PURGE_DAYS = 7  # anything shorter is begging for accidents
MAX_AUTO_PURGE_DAYS = 3650


def _to_absolute_path(relative_path: str | None) -> Path | None:
    """Mirror of the routes helper so this service has no route-module import.

    Accepts the legacy absolute paths that predate the relative-path migration
    verbatim; new rows always store paths relative to ``base_dir``.
    """
    if not relative_path:
        return None
    path = Path(relative_path)
    if path.is_absolute():
        return path
    return (
        Path(app_settings.base_dir) / path
    )  # SEC-PATH-OK: relative_path is LibraryFile.file_path / LibraryFile.thumbnail_path — DB-stored, internally generated by the upload pipeline


def _age_cutoff(now: datetime, older_than_days: int) -> datetime:
    return now - timedelta(days=older_than_days)


def _purge_filter(cutoff: datetime, include_never_printed: bool):
    """SQLAlchemy clause selecting files eligible for admin purge.

    A file is "old" if either (a) ``last_printed_at`` is set and predates the
    cutoff, or (b) ``last_printed_at`` is NULL *and* the file was uploaded
    before the cutoff — but only when ``include_never_printed`` is True.
    """
    last_printed_old = and_(
        LibraryFile.last_printed_at.isnot(None),
        LibraryFile.last_printed_at < cutoff,
    )
    if include_never_printed:
        never_printed_old = and_(
            LibraryFile.last_printed_at.is_(None),
            LibraryFile.created_at < cutoff,
        )
        age_clause = or_(last_printed_old, never_printed_old)
    else:
        age_clause = last_printed_old
    return and_(
        LibraryFile.deleted_at.is_(None),
        LibraryFile.is_external.is_(False),
        age_clause,
    )


class LibraryTrashService:
    """Manages the trash retention sweeper and admin-triggered bulk purges."""

    def __init__(self):
        self._scheduler_task: asyncio.Task | None = None
        # Tick every 15 minutes — the window is a day, so this is plenty
        # responsive without burning CPU.
        self._check_interval = 900

    async def start_scheduler(self):
        """Start the background sweeper task (idempotent)."""
        if self._scheduler_task is not None:
            return
        logger.info("Starting library trash sweeper")
        self._scheduler_task = asyncio.create_task(self._scheduler_loop())

    def stop_scheduler(self):
        if self._scheduler_task:
            self._scheduler_task.cancel()
            self._scheduler_task = None
            logger.info("Stopped library trash sweeper")

    async def _scheduler_loop(self):
        while True:
            try:
                await asyncio.sleep(self._check_interval)
                async with async_session() as db:
                    await self._sweep(db)
                    await self._maybe_run_auto_purge(db)
            except asyncio.CancelledError:
                break
            except Exception as e:  # pragma: no cover - defensive
                logger.error("Error in library trash sweeper: %s", e)
                await asyncio.sleep(60)

    # ---- Settings -----------------------------------------------------

    async def get_retention_days(self, db: AsyncSession | None = None) -> int:
        if db is None:
            async with async_session() as session:
                return await self._read_retention(session)
        return await self._read_retention(db)

    @staticmethod
    async def _read_retention(db: AsyncSession) -> int:
        result = await db.execute(select(Settings.value).where(Settings.key == TRASH_RETENTION_KEY))
        raw = result.scalar_one_or_none()
        if raw is None:
            return DEFAULT_RETENTION_DAYS
        try:
            days = int(raw)
        except (TypeError, ValueError):
            return DEFAULT_RETENTION_DAYS
        return max(MIN_RETENTION_DAYS, min(MAX_RETENTION_DAYS, days))

    async def set_retention_days(self, db: AsyncSession, days: int) -> int:
        """Persist the retention window. Clamped to [MIN, MAX]."""
        clamped = max(MIN_RETENTION_DAYS, min(MAX_RETENTION_DAYS, int(days)))
        result = await db.execute(select(Settings).where(Settings.key == TRASH_RETENTION_KEY))
        row = result.scalar_one_or_none()
        if row is None:
            db.add(Settings(key=TRASH_RETENTION_KEY, value=str(clamped)))
        else:
            row.value = str(clamped)
        await db.commit()
        return clamped

    @staticmethod
    async def _read_setting(db: AsyncSession, key: str) -> str | None:
        result = await db.execute(select(Settings.value).where(Settings.key == key))
        return result.scalar_one_or_none()

    @staticmethod
    async def _write_setting(db: AsyncSession, key: str, value: str) -> None:
        result = await db.execute(select(Settings).where(Settings.key == key))
        row = result.scalar_one_or_none()
        if row is None:
            db.add(Settings(key=key, value=value))
        else:
            row.value = value

    async def get_auto_purge_settings(self, db: AsyncSession) -> dict:
        """Return the current auto-purge config.

        Returns a dict with ``enabled`` (bool), ``days`` (int, clamped) and
        ``include_never_printed`` (bool). Missing keys default to disabled /
        90 days / include-never-printed-on, matching the manual purge UX.
        """
        enabled_raw = await self._read_setting(db, AUTO_PURGE_ENABLED_KEY)
        days_raw = await self._read_setting(db, AUTO_PURGE_DAYS_KEY)
        incl_raw = await self._read_setting(db, AUTO_PURGE_INCLUDE_NEVER_PRINTED_KEY)

        enabled = (enabled_raw or "false").lower() == "true"
        try:
            days = int(days_raw) if days_raw is not None else DEFAULT_AUTO_PURGE_DAYS
        except (TypeError, ValueError):
            days = DEFAULT_AUTO_PURGE_DAYS
        days = max(MIN_AUTO_PURGE_DAYS, min(MAX_AUTO_PURGE_DAYS, days))
        include_never_printed = (incl_raw or "true").lower() == "true"
        return {
            "enabled": enabled,
            "days": days,
            "include_never_printed": include_never_printed,
        }

    async def set_auto_purge_settings(
        self,
        db: AsyncSession,
        *,
        enabled: bool,
        days: int,
        include_never_printed: bool,
    ) -> dict:
        """Persist auto-purge config; returns the saved (clamped) values."""
        clamped_days = max(MIN_AUTO_PURGE_DAYS, min(MAX_AUTO_PURGE_DAYS, int(days)))
        await self._write_setting(db, AUTO_PURGE_ENABLED_KEY, "true" if enabled else "false")
        await self._write_setting(db, AUTO_PURGE_DAYS_KEY, str(clamped_days))
        await self._write_setting(
            db,
            AUTO_PURGE_INCLUDE_NEVER_PRINTED_KEY,
            "true" if include_never_printed else "false",
        )
        await db.commit()
        return {
            "enabled": enabled,
            "days": clamped_days,
            "include_never_printed": include_never_printed,
        }

    async def _get_last_auto_purge_run(self, db: AsyncSession) -> datetime | None:
        raw = await self._read_setting(db, AUTO_PURGE_LAST_RUN_KEY)
        if not raw:
            return None
        try:
            # Stored as ISO 8601 UTC; tolerate both with and without 'Z' suffix.
            return datetime.fromisoformat(raw.replace("Z", "+00:00"))
        except ValueError:
            return None

    async def _stamp_last_auto_purge_run(self, db: AsyncSession, when: datetime) -> None:
        await self._write_setting(db, AUTO_PURGE_LAST_RUN_KEY, when.isoformat())
        await db.commit()

    async def _maybe_run_auto_purge(self, db: AsyncSession) -> int:
        """If auto-purge is enabled and >=24h has elapsed since the last run, run it.

        Returns the number of files moved to trash (0 if disabled or throttled).
        The 24h throttle means a 15-minute sweeper cadence still only triggers
        one actual purge per day, keeping the DB churn predictable.
        """
        cfg = await self.get_auto_purge_settings(db)
        if not cfg["enabled"]:
            return 0

        now = datetime.now(timezone.utc)
        last = await self._get_last_auto_purge_run(db)
        if last is not None and (now - last) < timedelta(hours=24):
            return 0

        moved = await self.purge_older_than(
            db,
            older_than_days=cfg["days"],
            include_never_printed=cfg["include_never_printed"],
        )
        await self._stamp_last_auto_purge_run(db, now)
        if moved:
            logger.info("Library auto-purge: moved %d file(s) to trash (threshold=%d days)", moved, cfg["days"])
        return moved

    # ---- Preview / purge ---------------------------------------------

    async def preview_purge(
        self,
        db: AsyncSession,
        older_than_days: int,
        include_never_printed: bool = True,
        sample_limit: int = 5,
    ) -> dict:
        """Count + size of files eligible for purge. Reads only; never mutates."""
        if older_than_days < 1:
            return {"count": 0, "total_bytes": 0, "sample_filenames": []}
        now = datetime.now(timezone.utc)
        cutoff = _age_cutoff(now, older_than_days)
        clause = _purge_filter(cutoff, include_never_printed)

        count_result = await db.execute(select(func.count(LibraryFile.id)).where(clause))
        count = int(count_result.scalar() or 0)

        size_result = await db.execute(select(func.coalesce(func.sum(LibraryFile.file_size), 0)).where(clause))
        total_bytes = int(size_result.scalar() or 0)

        sample_result = await db.execute(
            select(LibraryFile.filename).where(clause).order_by(LibraryFile.created_at).limit(sample_limit)
        )
        samples = [row[0] for row in sample_result.all()]

        return {
            "count": count,
            "total_bytes": total_bytes,
            "sample_filenames": samples,
            "older_than_days": older_than_days,
            "include_never_printed": include_never_printed,
        }

    async def purge_older_than(
        self,
        db: AsyncSession,
        older_than_days: int,
        include_never_printed: bool = True,
    ) -> int:
        """Move matching files to trash (stamps ``deleted_at``). Returns count."""
        if older_than_days < 1:
            return 0
        now = datetime.now(timezone.utc)
        cutoff = _age_cutoff(now, older_than_days)
        clause = _purge_filter(cutoff, include_never_printed)

        # We need the IDs so callers can audit or display them if they want.
        # Doing a single UPDATE ... WHERE is safe even under concurrent
        # uploads — the clause already excludes rows with deleted_at set.
        id_result = await db.execute(select(LibraryFile.id).where(clause))
        ids = [row[0] for row in id_result.all()]
        if not ids:
            return 0

        await db.execute(LibraryFile.__table__.update().where(LibraryFile.id.in_(ids)).values(deleted_at=now))
        await db.commit()
        logger.info("Library purge: moved %d file(s) to trash (older_than_days=%d)", len(ids), older_than_days)
        return len(ids)

    # ---- Sweeper ------------------------------------------------------

    async def _sweep(self, db: AsyncSession) -> int:
        """Hard-delete trashed rows whose retention window has elapsed."""
        retention = await self._read_retention(db)
        now = datetime.now(timezone.utc)
        cutoff = now - timedelta(days=retention)

        result = await db.execute(
            select(LibraryFile).where(
                LibraryFile.deleted_at.isnot(None),
                LibraryFile.deleted_at < cutoff,
            )
        )
        rows = result.scalars().all()
        if not rows:
            return 0

        deleted = 0
        for row in rows:
            self._unlink_on_disk(row)
            deleted += 1
        await delete_dependent_variants(db, [r.id for r in rows])
        # Single DELETE is faster than N await db.delete() round-trips; we
        # still need the Python loop above to unlink bytes on disk.
        await db.execute(delete(LibraryFile).where(LibraryFile.id.in_([r.id for r in rows])))
        await db.commit()
        logger.info("Library trash sweeper: hard-deleted %d row(s) past %d-day retention", deleted, retention)
        return deleted

    @staticmethod
    def _unlink_on_disk(row: LibraryFile) -> None:
        """Best-effort cleanup of the file + thumbnail on disk."""
        for rel in (row.file_path, row.thumbnail_path):
            abs_path = _to_absolute_path(rel)
            if abs_path is None:
                continue
            try:
                if abs_path.exists():
                    abs_path.unlink()
            except OSError as e:
                logger.warning("Trash sweep: failed to unlink %s: %s", abs_path, e)

    # ---- User-facing trash ops ----------------------------------------

    async def restore(self, db: AsyncSession, file: LibraryFile) -> LibraryFile:
        """Clear ``deleted_at`` so the file reappears in listings."""
        file.deleted_at = None
        await db.commit()
        await db.refresh(file)
        return file

    async def hard_delete_now(self, db: AsyncSession, file: LibraryFile) -> None:
        """Bypass retention and delete this trashed file + its bytes immediately."""
        self._unlink_on_disk(file)
        await delete_dependent_variants(db, [file.id])
        await db.delete(file)
        await db.commit()


async def delete_dependent_variants(db: AsyncSession, file_ids: list[int]) -> None:
    """Drop cross-model queue candidates that pointed at these files (#671).

    SQLite ships with ``PRAGMA foreign_keys`` off — verified, not assumed — so
    the ON DELETE CASCADE on ``print_queue_variants.library_file_id`` never fires
    on the default deployment and the rows would outlive the file.

    The scheduler already refuses to dispatch a candidate whose file is missing
    or trashed, so nothing prints wrongly without this. It is here so the table
    does not fill with rows referencing files that no longer exist.
    """
    if not file_ids:
        return
    await db.execute(delete(PrintQueueVariant).where(PrintQueueVariant.library_file_id.in_(file_ids)))


library_trash_service = LibraryTrashService()