"""Reader's reads: a user's labels, saved views, watch state and playlists, for the HTTP layer and
for the other units that ask about them.

Every read of a user's row goes through `userscope`, so "someone else's row" is the same answer as
a missing one. Reader reads Catalog's videos along its declared edge (a playlist's cover and
length, whether a video exists); another unit asks the questions at the end of this module rather
than joining Reader's tables itself.
"""

from sqlalchemy import ColumnElement, and_, func, or_, select
from sqlalchemy.orm import InstrumentedAttribute, Session, aliased

from app.feedquery import feed_columns
from app.models import User
from app.catalog.models import Channel, Video
from app.reader.models import ChannelTag, Playlist, PlaylistItem, SavedView, Tag, VideoState
from app.userscope import owned_by, owned_row

# --- catalog, read along the edge ------------------------------------------------------------


def video(db: Session, video_id: str) -> Video | None:
    return db.get(Video, video_id)


# --- tags ------------------------------------------------------------------------------------


def tags_with_counts(db: Session, user: User) -> list[tuple[Tag, int]]:
    """The tags this user sees (the shared system ones and their own), each with how many channel
    links it has, by category then name."""
    return [
        (tag, count)
        for tag, count in db.execute(
            select(Tag, func.count(ChannelTag.id))
            .outerjoin(ChannelTag, ChannelTag.tag_id == Tag.id)
            .where(or_(Tag.user_id.is_(None), owned_by(Tag.user_id, user)))
            .group_by(Tag.id)
            .order_by(Tag.category, Tag.name)
        ).tuples()
    ]


def own_tag(db: Session, user: User, tag_id: int) -> Tag | None:
    """One of the user's own tags. A system tag (no owner) is nobody's to edit, so it reads as
    missing too."""
    return owned_row(db, Tag, tag_id, user)


# --- saved views -----------------------------------------------------------------------------


def views(db: Session, user: User, source: str) -> list[SavedView]:
    return list(
        db.execute(
            select(SavedView)
            .where(owned_by(SavedView.user_id, user), SavedView.source == source)
            .order_by(SavedView.position, SavedView.id)
        ).scalars()
    )


def all_views(db: Session, user: User) -> list[SavedView]:
    return list(db.execute(select(SavedView).where(owned_by(SavedView.user_id, user))).scalars())


def own_view(db: Session, user: User, view_id: int) -> SavedView | None:
    return owned_row(db, SavedView, view_id, user)


# --- watch state -----------------------------------------------------------------------------


def video_state(db: Session, user: User, video_id: str) -> VideoState | None:
    return db.execute(
        select(VideoState).where(
            owned_by(VideoState.user_id, user), VideoState.video_id == video_id
        )
    ).scalar_one_or_none()


# --- playlists -------------------------------------------------------------------------------


def own_playlist(
    db: Session, user: User, playlist_id: int, *, lock: bool = False
) -> Playlist | None:
    return owned_row(db, Playlist, playlist_id, user, lock=lock)


def playlists_for(db: Session, user: User) -> list[Playlist]:
    """The user's playlists in their rail order."""
    return list(
        db.execute(
            select(Playlist)
            .where(owned_by(Playlist.user_id, user))
            .order_by(Playlist.position, Playlist.created_at)
        ).scalars()
    )


def watch_later(db: Session, user: User) -> Playlist | None:
    return db.scalar(
        select(Playlist).where(owned_by(Playlist.user_id, user), Playlist.kind == "watch_later")
    )


def item_counts(db: Session, ids: list[int]) -> dict[int, int]:
    return dict(
        db.execute(
            select(PlaylistItem.playlist_id, func.count())
            .where(PlaylistItem.playlist_id.in_(ids))
            .group_by(PlaylistItem.playlist_id)
        )
        .tuples()
        .all()
    )


def durations(db: Session, ids: list[int]) -> dict[int, int]:
    """Each playlist's running time: the sum of its videos' lengths."""
    return {
        pid: int(total or 0)
        for pid, total in db.execute(
            select(PlaylistItem.playlist_id, func.coalesce(func.sum(Video.duration_seconds), 0))
            .join(Video, Video.id == PlaylistItem.video_id)
            .where(PlaylistItem.playlist_id.in_(ids))
            .group_by(PlaylistItem.playlist_id)
        ).tuples()
    }


def containing(db: Session, ids: list[int], video_id: str) -> set[int]:
    """Which of these playlists already hold the video (the add-to-playlist popover's ticks)."""
    return set(
        db.execute(
            select(PlaylistItem.playlist_id).where(
                PlaylistItem.playlist_id.in_(ids), PlaylistItem.video_id == video_id
            )
        ).scalars()
    )


def covers(db: Session, ids: list[int]) -> dict[int, str | None]:
    """Each playlist's cover: its first item's thumbnail, for every list in ONE window query rather
    than a lookup per playlist."""
    rn = (
        func.row_number()
        .over(partition_by=PlaylistItem.playlist_id, order_by=PlaylistItem.position)
        .label("rn")
    )
    first_items = (
        select(PlaylistItem.playlist_id.label("pid"), Video.thumbnail_url.label("thumb"), rn)
        .join(Video, Video.id == PlaylistItem.video_id)
        .where(PlaylistItem.playlist_id.in_(ids))
        .subquery()
    )
    return dict(
        db.execute(select(first_items.c.pid, first_items.c.thumb).where(first_items.c.rn == 1))
        .tuples()
        .all()
    )


def playlist_totals(db: Session, playlist_id: int) -> tuple[int, int, str | None]:
    """One playlist's item count, running time and cover. An outer join, so an empty list still
    answers (0, 0, None)."""
    count, total = db.execute(
        select(func.count(PlaylistItem.id), func.coalesce(func.sum(Video.duration_seconds), 0))
        .select_from(PlaylistItem)
        .outerjoin(Video, Video.id == PlaylistItem.video_id)
        .where(PlaylistItem.playlist_id == playlist_id)
    ).one()
    cover = db.scalar(
        select(Video.thumbnail_url)
        .join(PlaylistItem, PlaylistItem.video_id == Video.id)
        .where(PlaylistItem.playlist_id == playlist_id)
        .order_by(PlaylistItem.position)
        .limit(1)
    )
    return count or 0, total or 0, cover


def playlist_rows(db: Session, user: User, playlist_id: int) -> list:
    """A playlist's videos as feed rows (the same columns the feed serializes), in list order."""
    state = aliased(VideoState)
    return list(
        db.execute(
            select(*feed_columns(user, state))
            .join(PlaylistItem, PlaylistItem.video_id == Video.id)
            .join(Channel, Channel.id == Video.channel_id)
            .outerjoin(state, and_(state.video_id == Video.id, owned_by(state.user_id, user)))
            .where(PlaylistItem.playlist_id == playlist_id)
            # `id` breaks a position tie the same way on every read (the renumbering add does too).
            .order_by(PlaylistItem.position, PlaylistItem.id)
        ).all()
    )


def items(db: Session, playlist_id: int) -> list[PlaylistItem]:
    """A playlist's item rows, in list order."""
    return list(
        db.execute(
            select(PlaylistItem)
            .where(PlaylistItem.playlist_id == playlist_id)
            .order_by(PlaylistItem.position, PlaylistItem.id)
        ).scalars()
    )


def item(db: Session, playlist_id: int, video_id: str) -> PlaylistItem | None:
    return db.scalar(
        select(PlaylistItem).where(
            PlaylistItem.playlist_id == playlist_id, PlaylistItem.video_id == video_id
        )
    )


# --- for the other units ---------------------------------------------------------------------


def kept_by_a_reader(video_id: InstrumentedAttribute[str]) -> ColumnElement[bool]:
    """A video someone holds: watched, in progress or hidden (a `VideoState`), or in one of their
    playlists. The catalog's cleanup jobs keep such a video; as a clause, so their DELETE stays
    one statement."""
    return or_(
        select(VideoState.id).where(VideoState.video_id == video_id).exists(),
        select(PlaylistItem.id).where(PlaylistItem.video_id == video_id).exists(),
    )


def playlisted_by(db: Session, video_ids: list[str]) -> list[tuple[int, str]]:
    """(user id, video id) for every user who has one of these videos in a playlist."""
    return list(
        db.execute(
            select(Playlist.user_id, PlaylistItem.video_id)
            .join(PlaylistItem, PlaylistItem.playlist_id == Playlist.id)
            .where(PlaylistItem.video_id.in_(video_ids))
        ).tuples()
    )


def has_auto_tags(channel_id: InstrumentedAttribute[str]) -> ColumnElement[bool]:
    """A channel the auto-tagger has already labelled, as a clause for its "only the missing" scan."""
    return (
        select(ChannelTag.id)
        .where(
            ChannelTag.channel_id == channel_id,
            ChannelTag.source == "auto",
            ChannelTag.user_id.is_(None),
        )
        .exists()
    )


def view_tag_ids(filters: object) -> list[int]:
    """The tag ids a stored view's filters name; anything else in that slot names none."""
    tags = filters.get("tags") if isinstance(filters, dict) else None
    if not isinstance(tags, list):
        return []
    return [t for t in tags if type(t) is int]  # `type`, not isinstance: True is not a tag id


def tags_in_feed_views(db: Session) -> set[int]:
    """Every tag id any user's saved feed view filters on. Read defensively (`view_tag_ids`): a view
    stored before its route checked the shape must not raise for everyone's job."""
    return {
        t
        for (filters,) in db.execute(select(SavedView.filters).where(SavedView.source == "feed"))
        for t in view_tag_ids(filters)
    }