"""Playlist service."""
from datetime import datetime
from typing import List, Optional
from uuid import UUID

from sqlalchemy import select, delete
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.orm import selectinload

from app.models.playlist import Playlist
from app.models.playlist_track import PlaylistTrack
from app.models.track import Track


class PlaylistService:
    """Service for playlist operations."""

    def __init__(self, db: AsyncSession):
        self.db = db

    async def create_playlist(
        self,
        user_id: UUID,
        name: str,
        description: Optional[str] = None,
        image_url: Optional[str] = None,
        is_public: bool = False,
        is_collaborative: bool = False,
    ) -> Playlist:
        """
        Create a new playlist.

        Args:
            user_id: User UUID
            name: Playlist name
            description: Optional description
            image_url: Optional cover image URL
            is_public: Whether playlist is public
            is_collaborative: Whether playlist is collaborative

        Returns:
            Created playlist
        """
        playlist = Playlist(
            user_id=user_id,
            name=name,
            description=description,
            image_url=image_url,
            is_public=is_public,
            is_collaborative=is_collaborative,
            track_count=0,
            total_duration=0,
        )

        self.db.add(playlist)
        await self.db.commit()
        await self.db.refresh(playlist)

        return playlist

    async def get_playlist(
        self,
        playlist_id: UUID,
        include_tracks: bool = False,
    ) -> Optional[Playlist]:
        """
        Get playlist by ID.

        Args:
            playlist_id: Playlist UUID
            include_tracks: Whether to include tracks

        Returns:
            Playlist or None
        """
        stmt = select(Playlist).where(Playlist.id == playlist_id)

        if include_tracks:
            stmt = stmt.options(selectinload(Playlist.playlist_tracks))

        result = await self.db.execute(stmt)
        return result.scalar_one_or_none()

    async def get_user_playlists(
        self,
        user_id: UUID,
        limit: int = 50,
        offset: int = 0,
    ) -> List[Playlist]:
        """
        Get all playlists for a user.

        Args:
            user_id: User UUID
            limit: Maximum results
            offset: Pagination offset

        Returns:
            List of playlists
        """
        stmt = (
            select(Playlist)
            .where(Playlist.user_id == user_id)
            .order_by(Playlist.updated_at.desc())
            .limit(limit)
            .offset(offset)
        )
        result = await self.db.execute(stmt)
        return list(result.scalars().all())

    async def update_playlist(
        self,
        playlist_id: UUID,
        user_id: UUID,
        name: Optional[str] = None,
        description: Optional[str] = None,
        image_url: Optional[str] = None,
        is_public: Optional[bool] = None,
    ) -> Playlist:
        """
        Update playlist.

        Args:
            playlist_id: Playlist UUID
            user_id: User UUID (for ownership check)
            name: New name
            description: New description
            image_url: New image URL
            is_public: New public status

        Returns:
            Updated playlist

        Raises:
            ValueError: If playlist not found or user not owner
        """
        playlist = await self.get_playlist(playlist_id)
        if not playlist:
            raise ValueError("Playlist not found")

        if playlist.user_id != user_id:
            raise ValueError("Not authorized to update this playlist")

        if name is not None:
            playlist.name = name
        if description is not None:
            playlist.description = description
        if image_url is not None:
            playlist.image_url = image_url
        if is_public is not None:
            playlist.is_public = is_public

        playlist.updated_at = datetime.utcnow()
        await self.db.commit()
        await self.db.refresh(playlist)

        return playlist

    async def delete_playlist(
        self,
        playlist_id: UUID,
        user_id: UUID,
    ) -> None:
        """
        Delete a playlist.

        Args:
            playlist_id: Playlist UUID
            user_id: User UUID (for ownership check)

        Raises:
            ValueError: If playlist not found or user not owner
        """
        playlist = await self.get_playlist(playlist_id)
        if not playlist:
            raise ValueError("Playlist not found")

        if playlist.user_id != user_id:
            raise ValueError("Not authorized to delete this playlist")

        await self.db.delete(playlist)
        await self.db.commit()

    async def add_tracks(
        self,
        playlist_id: UUID,
        track_ids: List[UUID],
        user_id: UUID,
        position: Optional[int] = None,
    ) -> Playlist:
        """
        Add tracks to a playlist.

        Args:
            playlist_id: Playlist UUID
            track_ids: List of track UUIDs
            user_id: User UUID adding the tracks
            position: Optional starting position

        Returns:
            Updated playlist

        Raises:
            ValueError: If playlist not found
        """
        playlist = await self.get_playlist(playlist_id)
        if not playlist:
            raise ValueError("Playlist not found")

        # Get current max position
        stmt = (
            select(PlaylistTrack)
            .where(PlaylistTrack.playlist_id == playlist_id)
            .order_by(PlaylistTrack.position.desc())
            .limit(1)
        )
        result = await self.db.execute(stmt)
        last_track = result.scalar_one_or_none()
        max_position = last_track.position if last_track else -1

        # Determine starting position
        if position is None:
            position = max_position + 1

        # Add tracks
        current_position = position
        for track_id in track_ids:
            # Verify track exists
            track_stmt = select(Track).where(Track.id == track_id)
            track_result = await self.db.execute(track_stmt)
            track = track_result.scalar_one_or_none()

            if not track:
                continue

            # Create playlist track
            playlist_track = PlaylistTrack(
                playlist_id=playlist_id,
                track_id=track_id,
                position=current_position,
                added_by=user_id,
            )
            self.db.add(playlist_track)
            current_position += 1

        # Update playlist stats
        playlist.track_count += len(track_ids)
        playlist.total_duration = await self._calculate_playlist_duration(playlist_id)
        playlist.updated_at = datetime.utcnow()

        await self.db.commit()
        await self.db.refresh(playlist)

        return playlist

    async def remove_track(
        self,
        playlist_id: UUID,
        track_id: UUID,
        user_id: UUID,
    ) -> Playlist:
        """
        Remove a track from a playlist.

        Args:
            playlist_id: Playlist UUID
            track_id: Track UUID to remove
            user_id: User UUID (for ownership check)

        Returns:
            Updated playlist

        Raises:
            ValueError: If playlist or track not found
        """
        playlist = await self.get_playlist(playlist_id)
        if not playlist:
            raise ValueError("Playlist not found")

        if playlist.user_id != user_id:
            raise ValueError("Not authorized to modify this playlist")

        # Find and remove the track
        stmt = select(PlaylistTrack).where(
            PlaylistTrack.playlist_id == playlist_id,
            PlaylistTrack.track_id == track_id,
        )
        result = await self.db.execute(stmt)
        playlist_track = result.scalar_one_or_none()

        if not playlist_track:
            raise ValueError("Track not in playlist")

        # Remove track
        await self.db.delete(playlist_track)

        # Reorder remaining tracks
        tracks_stmt = (
            select(PlaylistTrack)
            .where(PlaylistTrack.playlist_id == playlist_id)
            .order_by(PlaylistTrack.position)
        )
        tracks_result = await self.db.execute(tracks_stmt)
        tracks = tracks_result.scalars().all()

        for index, track in enumerate(tracks):
            track.position = index

        # Update playlist stats
        playlist.track_count -= 1
        playlist.total_duration = await self._calculate_playlist_duration(playlist_id)
        playlist.updated_at = datetime.utcnow()

        await self.db.commit()
        await self.db.refresh(playlist)

        return playlist

    async def reorder_track(
        self,
        playlist_id: UUID,
        track_id: UUID,
        new_position: int,
        user_id: UUID,
    ) -> Playlist:
        """
        Reorder a track within a playlist.

        Args:
            playlist_id: Playlist UUID
            track_id: Track UUID to reorder
            new_position: New position (0-indexed)
            user_id: User UUID (for ownership check)

        Returns:
            Updated playlist

        Raises:
            ValueError: If playlist or track not found
        """
        playlist = await self.get_playlist(playlist_id)
        if not playlist:
            raise ValueError("Playlist not found")

        if playlist.user_id != user_id:
            raise ValueError("Not authorized to modify this playlist")

        # Get all tracks in playlist
        stmt = (
            select(PlaylistTrack)
            .where(PlaylistTrack.playlist_id == playlist_id)
            .order_by(PlaylistTrack.position)
        )
        result = await self.db.execute(stmt)
        tracks = list(result.scalars().all())

        # Find the track to move
        track_to_move = None
        for track in tracks:
            if track.track_id == track_id:
                track_to_move = track
                break

        if not track_to_move:
            raise ValueError("Track not in playlist")

        # Reorder
        old_position = track_to_move.position
        if old_position < new_position:
            # Moving down: shift tracks between old+1 and new up by 1
            for track in tracks:
                if old_position < track.position <= new_position:
                    track.position -= 1
        else:
            # Moving up: shift tracks between new and old-1 down by 1
            for track in tracks:
                if new_position <= track.position < old_position:
                    track.position += 1

        # Set new position
        track_to_move.position = new_position

        playlist.updated_at = datetime.utcnow()
        await self.db.commit()
        await self.db.refresh(playlist)

        return playlist

    async def _calculate_playlist_duration(self, playlist_id: UUID) -> int:
        """Calculate total duration of a playlist in seconds."""
        stmt = (
            select(Track)
            .join(PlaylistTrack, Track.id == PlaylistTrack.track_id)
            .where(PlaylistTrack.playlist_id == playlist_id)
        )
        result = await self.db.execute(stmt)
        tracks = result.scalars().all()

        total_duration = sum(
            track.duration for track in tracks if track.duration is not None
        )
        return total_duration