"""Series = a series-kind Tag + ordered series_page membership.

All mutations are Core/set-based and run in the request transaction.
"""

from sqlalchemy import and_, func, select, update
from sqlalchemy.dialects.postgresql import insert as pg_insert
from sqlalchemy.ext.asyncio import AsyncSession

from ..models import ImageRecord, Tag, TagKind
from ..models.series_page import SeriesPage
from .gallery_service import thumbnail_url


class SeriesError(ValueError):
    """Series validation failure. The API maps 'not a series'/'not found'
    to 404 and everything else to 400."""


class SeriesService:
    def __init__(self, session: AsyncSession):
        self.session = session

    async def _require_series(self, series_tag_id: int) -> Tag:
        tag = await self.session.get(Tag, series_tag_id)
        if tag is None:
            raise SeriesError(f"Tag {series_tag_id} not found")
        if tag.kind != TagKind.series:
            raise SeriesError(f"Tag {series_tag_id} is not a series")
        return tag

    @staticmethod
    def _clean_ids(ids: list[int]) -> list[int]:
        if not ids:
            raise SeriesError("image_ids must be a non-empty list")
        if len(ids) > 500:
            raise SeriesError("selection too large (max 500)")
        seen: set[int] = set()
        out: list[int] = []
        for x in ids:
            if x not in seen:
                seen.add(x)
                out.append(int(x))
        return out

    async def _member_order(self, series_tag_id: int) -> list[int]:
        rows = (
            await self.session.execute(
                select(SeriesPage.image_id)
                .where(SeriesPage.series_tag_id == series_tag_id)
                .order_by(SeriesPage.page_number.asc())
            )
        ).scalars().all()
        return list(rows)

    async def list_pages(self, series_tag_id: int) -> dict:
        tag = await self._require_series(series_tag_id)
        rows = (
            await self.session.execute(
                select(
                    SeriesPage.image_id,
                    SeriesPage.page_number,
                    ImageRecord.sha256,
                    ImageRecord.mime,
                    ImageRecord.path,
                    ImageRecord.thumbnail_path,
                )
                .join(ImageRecord, ImageRecord.id == SeriesPage.image_id)
                .where(SeriesPage.series_tag_id == series_tag_id)
                .order_by(SeriesPage.page_number.asc())
            )
        ).all()
        return {
            "series": {"id": tag.id, "name": tag.name},
            "pages": [
                {
                    "image_id": r.image_id,
                    "page_number": r.page_number,
                    "thumbnail_url": thumbnail_url(r.thumbnail_path, r.sha256, r.mime),
                    "image_url": f"/images/{r.path.split('/images/', 1)[-1]}",
                }
                for r in rows
            ],
        }

    async def add_images(
        self, series_tag_id: int, image_ids: list[int]
    ) -> int:
        await self._require_series(series_tag_id)
        ids = self._clean_ids(image_ids)
        existing = dict(
            (
                await self.session.execute(
                    select(SeriesPage.image_id, SeriesPage.series_tag_id)
                    .where(SeriesPage.image_id.in_(ids))
                )
            ).all()
        )
        # Already in THIS series → leave untouched (no churn).
        to_add = [i for i in ids if existing.get(i) != series_tag_id]
        if not to_add:
            return 0
        # Remove any prior membership for the to_add images (the "move").
        await self.session.execute(
            SeriesPage.__table__.delete().where(
                SeriesPage.image_id.in_(to_add)
            )
        )
        max_pn = (
            await self.session.scalar(
                select(func.coalesce(func.max(SeriesPage.page_number), 0))
                .where(SeriesPage.series_tag_id == series_tag_id)
            )
        ) or 0
        await self.session.execute(
            pg_insert(SeriesPage).values(
                [
                    {
                        "series_tag_id": series_tag_id,
                        "image_id": iid,
                        "page_number": max_pn + offset,
                    }
                    for offset, iid in enumerate(to_add, start=1)
                ]
            )
        )
        return len(to_add)

    async def remove_images(
        self, series_tag_id: int, image_ids: list[int]
    ) -> int:
        await self._require_series(series_tag_id)
        ids = self._clean_ids(image_ids)
        res = await self.session.execute(
            SeriesPage.__table__.delete().where(
                and_(
                    SeriesPage.series_tag_id == series_tag_id,
                    SeriesPage.image_id.in_(ids),
                )
            )
        )
        return res.rowcount or 0

    async def reorder(
        self, series_tag_id: int, ordered_image_ids: list[int]
    ) -> None:
        await self._require_series(series_tag_id)
        ordered = self._clean_ids(ordered_image_ids)
        current = set(await self._member_order(series_tag_id))
        if set(ordered) != current or len(ordered) != len(current):
            raise SeriesError(
                "ordered image_ids must exactly match series membership"
            )
        for idx, iid in enumerate(ordered, start=1):
            await self.session.execute(
                update(SeriesPage)
                .where(
                    and_(
                        SeriesPage.series_tag_id == series_tag_id,
                        SeriesPage.image_id == iid,
                    )
                )
                .values(page_number=idx)
            )

    async def set_cover(self, series_tag_id: int, image_id: int) -> None:
        await self._require_series(series_tag_id)
        order = await self._member_order(series_tag_id)
        if image_id not in order:
            raise SeriesError(f"image {image_id} is not in this series")
        new_order = [image_id] + [i for i in order if i != image_id]
        await self.reorder(series_tag_id, new_order)