package library

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"

	"github.com/google/uuid"
	"github.com/jackc/pgx/v5"
)

// Ref — ссылка на исполнителя.
type Ref struct {
	ID   uuid.UUID `json:"id"`
	Name string    `json:"name"`
}

// AlbumRow — альбом для карточек и страниц.
type AlbumRow struct {
	ID          uuid.UUID
	Title       string
	Year        *int
	CoverPath   *string
	CoverColors []string
	Artist      Ref
	TrackCount  int
}

// TrackRow — трек с исполнителями, альбомом и жанрами.
type TrackRow struct {
	ID         uuid.UUID
	Title      string
	DurationMs int
	DiscNo     *int
	TrackNo    *int
	Artists    []Ref
	Album      AlbumRow
	Genres     []string
	Available  bool
}

// ArtistRow — исполнитель со счётчиками.
type ArtistRow struct {
	ID         uuid.UUID
	Name       string
	AlbumCount int
	TrackCount int
}

// trackSelect — общий SELECT треков; доступен трек, у которого есть основной файл
// в подключённом хранилище.
const trackSelect = `
	SELECT t.id, t.title, t.duration_ms, t.disc_no, t.track_no,
		COALESCE((SELECT json_agg(json_build_object('id', a.id, 'name', a.name) ORDER BY ta.role DESC, ta.position)
			FROM track_artists ta JOIN artists a ON a.id = ta.artist_id WHERE ta.track_id = t.id), '[]'),
		al.id, al.title, al.year, al.cover_path, COALESCE(al.cover_colors, '{}'), aa.id, aa.name,
		COALESCE((SELECT array_agg(g.name ORDER BY g.name) FROM track_genres tg JOIN genres g ON g.id = tg.genre_id
			WHERE tg.track_id = t.id), '{}'),
		EXISTS (SELECT 1 FROM media_files f JOIN library_sources s ON s.id = f.source_id
			WHERE f.id = t.primary_file_id AND s.status = 'mounted')
	FROM tracks t
	JOIN albums al ON al.id = t.album_id
	JOIN artists aa ON aa.id = al.album_artist_id`

func scanTrack(row pgx.Row) (TrackRow, error) {
	var (
		t       TrackRow
		artists []byte
	)
	err := row.Scan(&t.ID, &t.Title, &t.DurationMs, &t.DiscNo, &t.TrackNo, &artists,
		&t.Album.ID, &t.Album.Title, &t.Album.Year, &t.Album.CoverPath, &t.Album.CoverColors,
		&t.Album.Artist.ID, &t.Album.Artist.Name, &t.Genres, &t.Available)
	if errors.Is(err, pgx.ErrNoRows) {
		return TrackRow{}, ErrNotFound
	}
	if err != nil {
		return TrackRow{}, fmt.Errorf("library: scan track: %w", err)
	}
	if err := json.Unmarshal(artists, &t.Artists); err != nil {
		return TrackRow{}, fmt.Errorf("library: track artists: %w", err)
	}
	return t, nil
}

func (st *Store) queryTracks(ctx context.Context, where string, args ...any) ([]TrackRow, error) {
	rows, err := st.pool.Query(ctx, trackSelect+" "+where, args...)
	if err != nil {
		return nil, fmt.Errorf("library: tracks: %w", err)
	}
	defer rows.Close()
	var out []TrackRow
	for rows.Next() {
		t, err := scanTrack(rows)
		if err != nil {
			return nil, err
		}
		out = append(out, t)
	}
	return out, rows.Err()
}

// Track — трек по id.
func (st *Store) Track(ctx context.Context, id uuid.UUID) (TrackRow, error) {
	return scanTrack(st.pool.QueryRow(ctx, trackSelect+" WHERE t.id = $1", id))
}

// TracksByIDs — треки в порядке ids (недостающие пропускаются).
func (st *Store) TracksByIDs(ctx context.Context, ids []uuid.UUID) ([]TrackRow, error) {
	rows, err := st.queryTracks(ctx, "WHERE t.id = ANY($1)", ids)
	if err != nil {
		return nil, err
	}
	byID := make(map[uuid.UUID]TrackRow, len(rows))
	for _, t := range rows {
		byID[t.ID] = t
	}
	out := make([]TrackRow, 0, len(ids))
	for _, id := range ids {
		if t, ok := byID[id]; ok {
			out = append(out, t)
		}
	}
	return out, nil
}

// AlbumTracks — треки альбома по дискам и номерам.
func (st *Store) AlbumTracks(ctx context.Context, albumID uuid.UUID) ([]TrackRow, error) {
	return st.queryTracks(ctx, "WHERE t.album_id = $1 ORDER BY t.disc_no NULLS FIRST, t.track_no NULLS LAST, t.title", albumID)
}

const albumSelect = `
	SELECT al.id, al.title, al.year, al.cover_path, COALESCE(al.cover_colors, '{}'), aa.id, aa.name,
		(SELECT count(*) FROM tracks t WHERE t.album_id = al.id)
	FROM albums al JOIN artists aa ON aa.id = al.album_artist_id`

func scanAlbum(row pgx.Row) (AlbumRow, error) {
	var a AlbumRow
	err := row.Scan(&a.ID, &a.Title, &a.Year, &a.CoverPath, &a.CoverColors, &a.Artist.ID, &a.Artist.Name, &a.TrackCount)
	if errors.Is(err, pgx.ErrNoRows) {
		return AlbumRow{}, ErrNotFound
	}
	if err != nil {
		return AlbumRow{}, fmt.Errorf("library: scan album: %w", err)
	}
	return a, nil
}

// Album — альбом по id.
func (st *Store) Album(ctx context.Context, id uuid.UUID) (AlbumRow, error) {
	return scanAlbum(st.pool.QueryRow(ctx, albumSelect+" WHERE al.id = $1", id))
}

// ArtistAlbums — альбомы исполнителя и сборники, где есть его треки; новые сверху.
func (st *Store) ArtistAlbums(ctx context.Context, artistID uuid.UUID) ([]AlbumRow, error) {
	rows, err := st.pool.Query(ctx, albumSelect+`
		WHERE al.album_artist_id = $1 OR EXISTS (
			SELECT 1 FROM tracks t JOIN track_artists ta ON ta.track_id = t.id
			WHERE t.album_id = al.id AND ta.artist_id = $1)
		ORDER BY (al.album_artist_id = $1) DESC, al.year DESC NULLS LAST, al.title`, artistID)
	if err != nil {
		return nil, fmt.Errorf("library: artist albums: %w", err)
	}
	defer rows.Close()
	var out []AlbumRow
	for rows.Next() {
		a, err := scanAlbum(rows)
		if err != nil {
			return nil, err
		}
		out = append(out, a)
	}
	return out, rows.Err()
}

// Artist — исполнитель со счётчиками альбомов и треков.
func (st *Store) Artist(ctx context.Context, id uuid.UUID) (ArtistRow, error) {
	var a ArtistRow
	err := st.pool.QueryRow(ctx, `
		SELECT a.id, a.name,
			(SELECT count(*) FROM albums al WHERE al.album_artist_id = a.id),
			(SELECT count(DISTINCT ta.track_id) FROM track_artists ta WHERE ta.artist_id = a.id)
		FROM artists a WHERE a.id = $1`, id).Scan(&a.ID, &a.Name, &a.AlbumCount, &a.TrackCount)
	if errors.Is(err, pgx.ErrNoRows) {
		return ArtistRow{}, ErrNotFound
	}
	if err != nil {
		return ArtistRow{}, fmt.Errorf("library: artist: %w", err)
	}
	return a, nil
}