"""
One-shot data integrity cleanup for source_roots / folders / photos.

Earlier versions of the scanner stored paths verbatim, so trailing slashes
and redundant separators produced duplicate SourceRoot and Folder rows for
the same physical directory. The watcher also auto-created source roots
when fired with a parent dir. This module merges the duplicates and
re-points photos to the canonical folder so the data lines up with the
post-fix scanner.

Idempotent: safe to run on every backend startup.
"""
import os
import logging
from datetime import datetime
from sqlalchemy import select, update, func
from sqlalchemy.ext.asyncio import AsyncSession

from app.database import AsyncSessionLocal
from app.models import Photo, Folder, SourceRoot

logger = logging.getLogger(__name__)


def _normalize_path(path: str) -> str:
    return os.path.normpath(path)


async def _dedupe_source_roots(session: AsyncSession) -> int:
    """Group source roots by normalized path and merge duplicates. Returns
    the number of rows deleted."""
    result = await session.execute(select(SourceRoot))
    rows = result.scalars().all()

    groups: dict[str, list[SourceRoot]] = {}
    for sr in rows:
        norm = _normalize_path(sr.path)
        groups.setdefault(norm, []).append(sr)

    deleted = 0
    for norm, srs in groups.items():
        if len(srs) == 1:
            # Make sure the canonical row's path is normalized too.
            if srs[0].path != norm:
                srs[0].path = norm
            continue
        # Pick the canonical row: prefer one with a non-empty name and the
        # earliest added_at (most likely the original).
        canonical = sorted(
            srs,
            key=lambda s: (not bool(s.name), s.added_at or datetime.max),
        )[0]
        canonical.path = norm
        for sr in srs:
            if sr.id == canonical.id:
                continue
            # Re-point folders that referenced the duplicate root.
            await session.execute(
                update(Folder)
                .where(Folder.source_root_id == sr.id)
                .values(source_root_id=canonical.id)
            )
            await session.delete(sr)
            deleted += 1

    return deleted


async def _dedupe_folders(session: AsyncSession) -> int:
    """Group folders by normalized path and merge duplicates. Returns the
    number of rows deleted."""
    result = await session.execute(select(Folder))
    rows = result.scalars().all()

    groups: dict[str, list[Folder]] = {}
    for f in rows:
        norm = _normalize_path(f.path)
        groups.setdefault(norm, []).append(f)

    deleted = 0
    for norm, folders in groups.items():
        if len(folders) == 1:
            if folders[0].path != norm:
                folders[0].path = norm
            continue
        # Canonical = the one with the most photos already attached, then
        # the lowest-id (deterministic tiebreaker).
        canonical = sorted(
            folders,
            key=lambda f: (-(f.photo_count or 0), f.id),
        )[0]
        canonical.path = norm
        for f in folders:
            if f.id == canonical.id:
                continue
            # Re-point photos to the canonical folder.
            await session.execute(
                update(Photo)
                .where(Photo.folder_id == f.id)
                .values(folder_id=canonical.id)
            )
            await session.delete(f)
            deleted += 1

    return deleted


async def _recompute_folder_counts(session: AsyncSession) -> None:
    """Set folder.photo_count to the actual non-discarded photo count."""
    result = await session.execute(select(Folder))
    folders = result.scalars().all()
    for f in folders:
        count_result = await session.execute(
            select(func.count(Photo.id)).where(
                Photo.folder_id == f.id,
                Photo.is_discarded == False,  # noqa: E712
            )
        )
        f.photo_count = int(count_result.scalar() or 0)


async def _warn_stale_source_roots(session: AsyncSession) -> int:
    """Log a warning for any active source root whose path no longer exists
    on disk. Doesn't delete — a missing path could be a temporarily
    unmounted drive, and silently dropping user data is worse than
    surfacing a noisy log line.
    """
    result = await session.execute(select(SourceRoot))
    rows = result.scalars().all()
    stale = 0
    for sr in rows:
        if not os.path.isdir(sr.path):
            stale += 1
            logger.warning(
                f"Source root '{sr.name}' path is missing on disk: {sr.path} "
                f"— is the docker mount still in place? "
                f"(Edit docker-compose.yml or PHOTO_DIRS in .env to fix.)"
            )
    return stale


async def find_missing(
    session: AsyncSession,
) -> tuple[list[str], list[str], list[str]]:
    """Walk every non-discarded photo + every folder and check whether
    they still resolve on disk. Returns
    (deletable_photo_ids, deletable_folder_ids, skipped_photo_ids).

    Skipped rows are photos/folders whose owning source_root path itself
    doesn't resolve — that's almost always an unmounted drive, and
    silently deleting those rows would be data loss. The caller can
    surface the skip count separately so the user knows the cleanup
    wasn't a no-op by accident.
    """
    sr_rows = (await session.execute(select(SourceRoot))).scalars().all()
    sr_mounted: dict[str, bool] = {sr.id: os.path.isdir(sr.path) for sr in sr_rows}

    photos = (await session.execute(
        select(Photo.id, Photo.filepath, Photo.folder_id)
        .where(Photo.is_discarded.is_(False))
    )).all()

    folders = (await session.execute(
        select(Folder.id, Folder.path, Folder.source_root_id)
    )).all()
    folder_to_sr = {fid: srid for fid, _path, srid in folders}

    deletable_photos: list[str] = []
    skipped: list[str] = []
    for pid, fp, folder_id in photos:
        sr_id = folder_to_sr.get(folder_id)
        if sr_id is None or not sr_mounted.get(sr_id, False):
            skipped.append(pid)
            continue
        if not os.path.exists(fp):
            deletable_photos.append(pid)

    deletable_folders: list[str] = []
    for fid, fpath, sr_id in folders:
        if sr_id is None or not sr_mounted.get(sr_id, False):
            continue
        if not os.path.isdir(fpath):
            deletable_folders.append(fid)

    return deletable_photos, deletable_folders, skipped


async def prune_missing_photos(dry_run: bool = True) -> dict:
    """Delete photo + folder rows whose paths are no longer on disk *and*
    whose source root is currently mounted. Common cause: PHOTO_DIRS in
    .env was repointed at a different library, leaving every old row
    orphaned.

    Set dry_run=False to actually delete. The default is intentionally
    safe so the matching count can be surfaced in the UI before the
    user commits to it.

    Function name kept for backwards compatibility — it now also prunes
    folders, not just photos.
    """
    from sqlalchemy import delete
    async with AsyncSessionLocal() as session:
        try:
            deletable_photos, deletable_folders, skipped = await find_missing(session)
            if not dry_run:
                CHUNK = 500
                # Photos first (folders may FK from them via folder_id).
                for i in range(0, len(deletable_photos), CHUNK):
                    await session.execute(
                        delete(Photo).where(
                            Photo.id.in_(deletable_photos[i:i + CHUNK])
                        )
                    )
                # Then drop folders that ALSO no longer have any photos
                # pointing at them. We re-check after the photo delete so
                # we don't strand a folder that legitimately exists on
                # disk but happened to match the orphan list.
                if deletable_folders:
                    for i in range(0, len(deletable_folders), CHUNK):
                        chunk = deletable_folders[i:i + CHUNK]
                        # Only delete folders that now have zero photos
                        # left attached (defensive — should always be 0
                        # if the path is gone, but a concurrent scan
                        # could re-create rows).
                        still_used = (await session.execute(
                            select(Photo.folder_id)
                            .where(Photo.folder_id.in_(chunk))
                            .distinct()
                        )).scalars().all()
                        safe = [f for f in chunk if f not in set(still_used)]
                        if safe:
                            await session.execute(
                                delete(Folder).where(Folder.id.in_(safe))
                            )
                await session.commit()
                logger.info(
                    f"Pruned {len(deletable_photos)} photo rows + "
                    f"{len(deletable_folders)} folder rows"
                )
            key_p = "would_delete" if dry_run else "deleted"
            key_f = "would_delete_folders" if dry_run else "deleted_folders"
            return {
                key_p: len(deletable_photos),
                key_f: len(deletable_folders),
                "skipped_unmounted": len(skipped),
                "dry_run": dry_run,
            }
        except Exception as e:
            logger.error(f"prune_missing_photos failed: {e}")
            await session.rollback()
            raise


async def cleanup_data_integrity() -> dict:
    """Top-level entry point. Runs the dedupe + count refresh in a single
    transaction. Returns a small summary dict for logging."""
    async with AsyncSessionLocal() as session:
        try:
            sr_deleted = await _dedupe_source_roots(session)
            f_deleted = await _dedupe_folders(session)
            await _recompute_folder_counts(session)
            stale = await _warn_stale_source_roots(session)
            await session.commit()
            summary = {
                "source_roots_merged": sr_deleted,
                "folders_merged": f_deleted,
                "source_roots_stale": stale,
            }
            if sr_deleted or f_deleted:
                logger.info(f"Cleanup merged duplicates: {summary}")
            return summary
        except Exception as e:
            logger.error(f"Cleanup failed: {e}")
            await session.rollback()
            raise