"""Periodic maintenance: recover stuck import tasks, garbage-collect old finished tasks."""

import logging
import subprocess
from datetime import UTC, datetime, timedelta
from pathlib import Path

from PIL import Image
from sqlalchemy import delete, select, update

from ..celery_app import celery
from ..models import DownloadEvent, ImageRecord, ImportSettings, ImportTask, TaskRun
from ..utils.phash import compute_phash
from ._sync_engine import sync_session_factory as _sync_session_factory

log = logging.getLogger(__name__)

STUCK_THRESHOLD_MINUTES = 5
OLD_TASK_DAYS = 7
PHASH_PAGE = 500
VERIFY_PAGE = 200
FFPROBE_TIMEOUT_SECONDS = 10
TASK_RUN_KEEP_OK_SECONDS = 24 * 3600       # 24 h
TASK_RUN_KEEP_FAILURE_SECONDS = 7 * 24 * 3600  # 7 days


@celery.task(name="backend.app.tasks.maintenance.recover_interrupted_tasks")
def recover_interrupted_tasks() -> int:
    """Find ImportTask rows stuck in 'processing' for >5 min and re-queue them.

    Why 5 min: import_media_file is sub-second for the vast majority of
    files; even a large-video transcode caps at the per-task soft_time_limit
    (5 min) defined on the task itself. Anything still 'processing' after
    that window is a confirmed crash (worker died, DB disconnect mid-flush,
    OOM) and must be recycled. Was 30 min historically; tightened
    2026-05-24 after operator hit a 2224-row zombie pile during the IR
    migration scan.
    """
    SessionLocal = _sync_session_factory()
    cutoff = datetime.now(UTC) - timedelta(minutes=STUCK_THRESHOLD_MINUTES)
    with SessionLocal() as session:
        stuck_ids = session.execute(
            select(ImportTask.id)
            .where(ImportTask.status == "processing")
            .where(ImportTask.started_at < cutoff)
        ).scalars().all()

        if not stuck_ids:
            return 0

        session.execute(
            update(ImportTask)
            .where(ImportTask.id.in_(stuck_ids))
            .values(status="queued", started_at=None, error="recovered from stuck state")
        )
        session.commit()

        from .import_file import import_media_file
        for tid in stuck_ids:
            import_media_file.delay(tid)

        return len(stuck_ids)


@celery.task(name="backend.app.tasks.maintenance.cleanup_old_tasks")
def cleanup_old_tasks() -> int:
    """Delete completed/skipped/failed ImportTask rows older than 7 days.

    Why 7 days: long enough to debug an issue an operator only notices days
    later; short enough that the task table stays a useful operational view
    rather than an archive. Matches IR's default.
    """
    SessionLocal = _sync_session_factory()
    cutoff = datetime.now(UTC) - timedelta(days=OLD_TASK_DAYS)
    with SessionLocal() as session:
        result = session.execute(
            delete(ImportTask)
            .where(ImportTask.status.in_(["complete", "skipped", "failed"]))
            .where(ImportTask.finished_at < cutoff)
        )
        session.commit()
        return result.rowcount or 0


@celery.task(name="backend.app.tasks.maintenance.recover_stalled_task_runs")
def recover_stalled_task_runs() -> int:
    """Flip task_run rows stuck in 'running' for >STUCK_THRESHOLD_MINUTES
    to 'error'. FC-3i.

    A row gets stuck when the worker dies without emitting
    task_postrun / task_failure (e.g. OOM, container restart between
    signals, signal handler raised+logged). Shares the 5-min threshold
    with recover_interrupted_tasks for consistency.
    """
    SessionLocal = _sync_session_factory()
    cutoff = datetime.now(UTC) - timedelta(minutes=STUCK_THRESHOLD_MINUTES)
    with SessionLocal() as session:
        result = session.execute(
            update(TaskRun)
            .where(TaskRun.status == "running")
            .where(TaskRun.started_at < cutoff)
            .values(
                status="error",
                error_type="RecoverySweep",
                error_message=(
                    f"no completion signal received within "
                    f"{STUCK_THRESHOLD_MINUTES} min"
                ),
                finished_at=datetime.now(UTC),
            )
        )
        session.commit()
        return result.rowcount or 0


@celery.task(name="backend.app.tasks.maintenance.prune_task_runs")
def prune_task_runs() -> dict:
    """Daily retention for task_run rows. FC-3i.

    - 'ok' rows: deleted after TASK_RUN_KEEP_OK_SECONDS (24h default).
      Success is high-volume, not interesting after a day.
    - 'error' / 'timeout' rows: deleted after TASK_RUN_KEEP_FAILURE_SECONDS
      (7 days default). Failures are operationally interesting longer.
    - 'running' rows: NEVER deleted by this task. The recovery sweep
      (recover_stalled_task_runs) is the mechanism that flips them to
      terminal state; prune doesn't touch in-flight state.
    - 'retry' rows: treated as failures (>7d).

    Returns dict of how many rows were deleted in each bucket.
    """
    SessionLocal = _sync_session_factory()
    now = datetime.now(UTC)
    ok_cutoff = now - timedelta(seconds=TASK_RUN_KEEP_OK_SECONDS)
    fail_cutoff = now - timedelta(seconds=TASK_RUN_KEEP_FAILURE_SECONDS)
    with SessionLocal() as session:
        ok_deleted = session.execute(
            delete(TaskRun)
            .where(TaskRun.status == "ok")
            .where(TaskRun.finished_at < ok_cutoff)
        ).rowcount or 0
        fail_deleted = session.execute(
            delete(TaskRun)
            .where(TaskRun.status.in_(["error", "timeout", "retry"]))
            .where(TaskRun.finished_at < fail_cutoff)
        ).rowcount or 0
        session.commit()
        return {"ok_deleted": ok_deleted, "failures_deleted": fail_deleted}


@celery.task(name="backend.app.tasks.maintenance.backfill_phash")
def backfill_phash() -> int:
    """Recompute phash for stored images that have none (imported before
    FC-2d-i+ii). Keyset-paginated by id (restart-safe), NULL-only fill,
    idempotent. Videos legitimately keep phash NULL. A missing/unreadable
    file is logged and left NULL — never fails the task."""
    SessionLocal = _sync_session_factory()
    updated = 0
    last_id = 0
    with SessionLocal() as session:
        while True:
            rows = session.execute(
                select(ImageRecord)
                .where(ImageRecord.id > last_id)
                .where(ImageRecord.phash.is_(None))
                .where(ImageRecord.mime.like("image/%"))
                .order_by(ImageRecord.id.asc())
                .limit(PHASH_PAGE)
            ).scalars().all()
            if not rows:
                break
            for rec in rows:
                try:
                    with Image.open(rec.path) as im:
                        ph = compute_phash(im)
                except Exception as exc:
                    log.warning(
                        "backfill_phash: unreadable %s: %s", rec.path, exc
                    )
                    ph = None
                if ph is not None and rec.phash is None:
                    rec.phash = ph
                    updated += 1
            session.commit()
            last_id = rows[-1].id
    return updated


def _verify_one(path: Path, expected_sha: str, mime: str, sha_fn) -> str:
    """Compute the integrity verdict for one file. Status precedence:
    failed_verification (can't run) > corrupt (sha mismatch / decode
    fails) > ok (passes both). Never raises."""
    try:
        if not path.is_file():
            return "failed_verification"
        try:
            actual_sha = sha_fn(path)
        except (OSError, PermissionError):
            return "failed_verification"
        if actual_sha != expected_sha:
            return "corrupt"
        if mime and mime.startswith("image/"):
            try:
                with Image.open(path) as im:
                    im.verify()
            except Exception:
                return "corrupt"
            return "ok"
        if mime and mime.startswith("video/"):
            try:
                proc = subprocess.run(
                    ["ffprobe", "-v", "error", "-i", str(path)],
                    capture_output=True,
                    timeout=FFPROBE_TIMEOUT_SECONDS,
                )
            except FileNotFoundError:
                # ffprobe binary missing — environment problem, not file.
                return "failed_verification"
            except subprocess.TimeoutExpired:
                return "corrupt"
            return "ok" if proc.returncode == 0 else "corrupt"
        # Unknown mime — sha matched already; trust that.
        return "ok"
    except Exception as exc:
        log.warning("verify_integrity unexpected error for %s: %s", path, exc)
        return "failed_verification"


@celery.task(name="backend.app.tasks.maintenance.verify_integrity")
def verify_integrity() -> int:
    """Verify every ImageRecord file: sha256 recompute + decode/probe
    (PIL for images; ffprobe for videos). Writes integrity_status
    (always — the column reflects the most recent verdict).
    Keyset-paginated, fail-soft per row, idempotent. Returns the total
    count verified."""
    from ..services.importer import _sha256_of  # reuse the importer's helper

    SessionLocal = _sync_session_factory()
    total = 0
    counts = {"ok": 0, "corrupt": 0, "failed_verification": 0}
    last_id = 0
    with SessionLocal() as session:
        while True:
            rows = session.execute(
                select(ImageRecord)
                .where(ImageRecord.id > last_id)
                .order_by(ImageRecord.id.asc())
                .limit(VERIFY_PAGE)
            ).scalars().all()
            if not rows:
                break
            for rec in rows:
                rec.integrity_status = _verify_one(
                    Path(rec.path), rec.sha256, rec.mime, _sha256_of
                )
                counts[rec.integrity_status] = (
                    counts.get(rec.integrity_status, 0) + 1
                )
                total += 1
            session.commit()
            last_id = rows[-1].id
    log.info("verify_integrity verdicts: %s (total %d)", counts, total)
    return total


@celery.task(name="backend.app.tasks.maintenance.cleanup_old_download_events")
def cleanup_old_download_events() -> int:
    """FC-3d: delete terminal DownloadEvent rows older than the configured
    retention window. Never touches pending/running rows.

    Why terminal-only: pending/running rows represent in-flight work whose
    owning task may still be alive; deleting them would orphan the task.
    Retention days comes from ImportSettings.download_event_retention_days
    so the operator can tune without a code change.
    """
    SessionLocal = _sync_session_factory()
    with SessionLocal() as session:
        settings = session.execute(
            select(ImportSettings).where(ImportSettings.id == 1)
        ).scalar_one()
        retention_days = settings.download_event_retention_days
        cutoff = datetime.now(UTC) - timedelta(days=retention_days)
        result = session.execute(
            delete(DownloadEvent)
            .where(DownloadEvent.status.in_(["ok", "error", "skipped"]))
            .where(DownloadEvent.started_at < cutoff)
        )
        session.commit()
        return result.rowcount or 0