"""FC-3k: first-class admin destructive operations.

Projections are pure SELECTs used by both dry-run preview endpoints
and Tier-B count prompts. Mutations (Task 2) are called from sync
HTTP handlers (small ops) and from Celery tasks in
backend.app.tasks.admin (long ops).

This module is the PERMANENT home of artist-cascade + image-unlink
logic. The legacy copy at backend/app/services/migrators/cleanup.py
stays in place until FC-3j; FC-3j will replace its body with thin
re-exports from this module and then delete the wrapper.
"""
from __future__ import annotations

from sqlalchemy import func, select
from sqlalchemy.orm import Session

from ..models import Artist, ImageRecord, Tag
from ..models.series_page import SeriesPage
from ..models.tag import image_tag


def project_artist_cascade(session: Session, *, slug: str) -> dict:
    """Read-only projection of what delete_artist_cascade would touch.

    Returns:
        {
          "artist": {"id": int, "name": str, "slug": str},
          "projected": {
            "images": int,
            "sources": int,
            "thumbs": int,        # images with a thumbnail_path set
            "import_tasks": int,  # ImportTask rows referencing the artist's images
            "bytes_on_disk": int, # SUM(image_record.size_bytes) — column is NOT NULL
          },
        }
    Raises LookupError if slug not found. No mutations.
    """
    from ..models.import_task import ImportTask
    from ..models.source import Source

    artist = session.execute(
        select(Artist).where(Artist.slug == slug)
    ).scalar_one_or_none()
    if artist is None:
        raise LookupError(f"artist slug not found: {slug!r}")

    images_count = session.execute(
        select(func.count(ImageRecord.id))
        .where(ImageRecord.artist_id == artist.id)
    ).scalar_one()
    sources_count = session.execute(
        select(func.count(Source.id))
        .where(Source.artist_id == artist.id)
    ).scalar_one()
    thumbs_count = session.execute(
        select(func.count(ImageRecord.id))
        .where(ImageRecord.artist_id == artist.id)
        .where(ImageRecord.thumbnail_path.is_not(None))
    ).scalar_one()
    import_tasks_count = session.execute(
        select(func.count(ImportTask.id))
        .where(
            ImportTask.result_image_id.in_(
                select(ImageRecord.id).where(ImageRecord.artist_id == artist.id)
            )
        )
    ).scalar_one()
    bytes_on_disk = session.execute(
        select(func.coalesce(func.sum(ImageRecord.size_bytes), 0))
        .where(ImageRecord.artist_id == artist.id)
    ).scalar_one()

    return {
        "artist": {"id": artist.id, "name": artist.name, "slug": artist.slug},
        "projected": {
            "images": images_count,
            "sources": sources_count,
            "thumbs": thumbs_count,
            "import_tasks": import_tasks_count,
            "bytes_on_disk": int(bytes_on_disk),
        },
    }


def project_bulk_image_delete(
    session: Session, *, image_ids: list[int],
) -> dict:
    """Read-only projection of what delete_images would touch.

    Returns:
        {
          "images_found": int,
          "thumbs_to_unlink": int,
          "bytes_on_disk": int,
          "missing_ids": list[int],   # ids passed in that don't exist
        }
    No mutations.
    """
    if not image_ids:
        return {
            "images_found": 0,
            "thumbs_to_unlink": 0,
            "bytes_on_disk": 0,
            "missing_ids": [],
        }

    rows = session.execute(
        select(
            ImageRecord.id,
            ImageRecord.thumbnail_path,
            ImageRecord.size_bytes,
        ).where(ImageRecord.id.in_(image_ids))
    ).all()
    found_ids = {r.id for r in rows}
    missing = sorted(set(image_ids) - found_ids)
    return {
        "images_found": len(rows),
        "thumbs_to_unlink": sum(1 for r in rows if r.thumbnail_path),
        "bytes_on_disk": sum(r.size_bytes for r in rows),
        "missing_ids": missing,
    }


def count_tag_associations(session: Session, *, tag_id: int) -> int:
    """COUNT(*) FROM image_tag WHERE tag_id=?. For Tier-B prompt."""
    return session.execute(
        select(func.count())
        .select_from(image_tag)
        .where(image_tag.c.tag_id == tag_id)
    ).scalar_one()


def find_unused_tags(
    session: Session, *, limit: int | None = None,
) -> list[Tag]:
    """Tags with no image_tag rows AND no series_page rows.

    Sorted by name. Used by both dry-run preview and the live prune.
    A tag is "unused" iff it has zero rows in image_tag AND zero rows
    in series_page (so we don't accidentally prune a series tag that
    happens to have no images yet).
    """
    used_via_image_tag = select(image_tag.c.tag_id).distinct()
    used_via_series = select(SeriesPage.series_tag_id).where(
        SeriesPage.series_tag_id.is_not(None)
    ).distinct()
    stmt = (
        select(Tag)
        .where(Tag.id.not_in(used_via_image_tag))
        .where(Tag.id.not_in(used_via_series))
        .order_by(Tag.name)
    )
    if limit is not None:
        stmt = stmt.limit(limit)
    return list(session.execute(stmt).scalars().all())