package backend

import (
	"context"
	"errors"
	"math/rand/v2"
	"os"
	"path/filepath"
	"slices"
	"strings"
	"sync"

	"music-server/internal/db/repository"
	"music-server/internal/logging"
	"music-server/internal/metrics"

	"github.com/google/uuid"
	"github.com/jackc/pgx/v5"
	"go.uber.org/zap"
)

// maxPickAttempts bounds how many broken songs are skipped before giving up.
const maxPickAttempts = 100

// PickMode is how a random song was picked. It is stored with queued songs and used as
// the mode label of the song metrics.
type PickMode string

const (
	PickRandom  PickMode = "random"
	PickLow     PickMode = "low"
	PickClassic PickMode = "classic"
)

func init() {
	// Start every mode at 0, so the series exist before the first song.
	for _, mode := range []PickMode{PickRandom, PickLow, PickClassic} {
		metrics.SongsRequested.WithLabelValues(string(mode))
		metrics.SongsPlayed.WithLabelValues(string(mode))
	}
}

type SongInfo struct {
	SoundtrackUuid   uuid.UUID `json:"SoundtrackUuid"`
	Soundtrack       string    `json:"Soundtrack"`
	SoundtrackPlayed int32     `json:"SoundtrackPlayed"`
	SongUuid         uuid.UUID `json:"SongUuid"`
	Song             string    `json:"Song"`
	SongPlayed       int32     `json:"SongPlayed"`
	CurrentlyPlaying bool      `json:"CurrentlyPlaying"`
	SongNo           int       `json:"SongNo"`
}

// MusicService picks songs and keeps track of the play queues. Every client has its own queue,
// stored in the database and identified by its UUID.
type MusicService struct {
	q              repository.Querier
	soundCheckPath string

	cacheMu     sync.Mutex
	soundtracks []repository.Soundtrack
}

// NewMusicService creates a MusicService. soundCheckPath is the directory holding sound check songs.
func NewMusicService(q repository.Querier, soundCheckPath string) *MusicService {
	return &MusicService{q: q, soundCheckPath: soundCheckPath}
}

func (m *MusicService) allSoundtracks(ctx context.Context) ([]repository.Soundtrack, error) {
	m.cacheMu.Lock()
	defer m.cacheMu.Unlock()
	if len(m.soundtracks) == 0 {
		soundtracks, err := m.q.FindAllSoundtracks(ctx)
		if err != nil {
			return nil, err
		}
		m.soundtracks = soundtracks
	}
	return m.soundtracks, nil
}

// ReloadSoundtracks reloads the soundtrack list.
func (m *MusicService) ReloadSoundtracks(ctx context.Context) error {
	m.cacheMu.Lock()
	m.soundtracks = nil
	m.cacheMu.Unlock()
	_, err := m.allSoundtracks(ctx)
	return err
}

// ResolveQueue returns the queue with the given ID if it is a running queue.
// Otherwise, for example when id is empty or the queue has ended, it starts a new queue.
func (m *MusicService) ResolveQueue(ctx context.Context, id string) (uuid.UUID, error) {
	if queueID, err := uuid.Parse(id); err == nil {
		queue, err := m.q.GetQueue(ctx, queueID)
		if err == nil && !queue.EndedAt.Valid {
			return queue.Uuid, nil
		}
		if err != nil && !errors.Is(err, pgx.ErrNoRows) {
			return uuid.Nil, err
		}
	}
	queue, err := m.q.CreateQueue(ctx)
	return queue.Uuid, err
}

// NewQueue ends the given queue and starts a new one.
func (m *MusicService) NewQueue(ctx context.Context, queueID uuid.UUID) (uuid.UUID, error) {
	if err := m.q.EndQueue(ctx, queueID); err != nil {
		return uuid.Nil, err
	}
	queue, err := m.q.CreateQueue(ctx)
	return queue.Uuid, err
}

// EndAllQueues ends every running queue. Clients get a new queue on their next request.
func (m *MusicService) EndAllQueues(ctx context.Context) error {
	return m.q.EndActiveQueues(ctx)
}

// SoundCheckSong returns the path of a random sound check song.
func (m *MusicService) SoundCheckSong() (string, error) {
	files, err := os.ReadDir(m.soundCheckPath)
	if err != nil {
		return "", err
	}
	files = slices.DeleteFunc(files, func(f os.DirEntry) bool { return f.IsDir() })
	if len(files) == 0 {
		return "", ErrNoSongs
	}
	return filepath.Join(m.soundCheckPath, files[rand.IntN(len(files))].Name()), nil
}

// AddLatestToQueue appends the last fetched random song to the queue and makes it the current song.
func (m *MusicService) AddLatestToQueue(ctx context.Context, queueID uuid.UUID) error {
	return m.q.AddLastFetchedToQueue(ctx, queueID)
}

// AddLatestPlayed increments the play counters of the current song.
func (m *MusicService) AddLatestPlayed(ctx context.Context, queueID uuid.UUID) error {
	queue, songs, err := m.loadQueue(ctx, queueID)
	if err != nil {
		return err
	}
	return m.markPlayed(ctx, songs, int(queue.CurrentSong))
}

// SetPlayed increments the play counters of the song at the given queue position.
func (m *MusicService) SetPlayed(ctx context.Context, queueID uuid.UUID, songNumber int) error {
	_, songs, err := m.loadQueue(ctx, queueID)
	if err != nil {
		return err
	}
	return m.markPlayed(ctx, songs, songNumber)
}

// markPlayed increments the play counters of songs[songNumber]. Positions outside the queue
// and songs that have been removed from the library are ignored.
func (m *MusicService) markPlayed(ctx context.Context, songs []repository.ListQueueSongsRow, songNumber int) error {
	if songNumber < 0 || songNumber >= len(songs) || songs[songNumber].Path == nil {
		return nil
	}
	song := songs[songNumber]
	if err := m.q.AddSoundtrackPlayedByUUID(ctx, song.SoundtrackUuid); err != nil {
		return err
	}
	if err := m.q.AddSongPlayedByUUID(ctx, song.SongUuid); err != nil {
		return err
	}
	metrics.SongsPlayed.WithLabelValues(song.Mode).Inc()
	return nil
}

func (m *MusicService) loadQueue(ctx context.Context, queueID uuid.UUID) (repository.Queue, []repository.ListQueueSongsRow, error) {
	queue, err := m.q.GetQueue(ctx, queueID)
	if err != nil {
		return repository.Queue{}, nil, err
	}
	songs, err := m.q.ListQueueSongs(ctx, queueID)
	return queue, songs, err
}

// RandomSong picks a random song from a random soundtrack.
func (m *MusicService) RandomSong(ctx context.Context, queueID uuid.UUID) (string, error) {
	soundtracks, err := m.allSoundtracks(ctx)
	if err != nil {
		return "", err
	}
	candidates := make([]weightedSoundtrack, len(soundtracks))
	for i, s := range soundtracks {
		candidates[i] = weightedSoundtrack{soundtrack: s, weight: 1}
	}
	return m.pickAndRemember(ctx, queueID, candidates, PickRandom)
}

// RandomSongLowChance picks a random song, favouring soundtracks played less than average.
func (m *MusicService) RandomSongLowChance(ctx context.Context, queueID uuid.UUID) (string, error) {
	soundtracks, err := m.allSoundtracks(ctx)
	if err != nil {
		return "", err
	}
	return m.pickAndRemember(ctx, queueID, lowChanceWeights(soundtracks), PickLow)
}

func (m *MusicService) pickAndRemember(
	ctx context.Context, queueID uuid.UUID, candidates []weightedSoundtrack, mode PickMode,
) (string, error) {
	song, err := m.pickSong(ctx, candidates)
	if err != nil {
		return "", err
	}
	return m.remember(ctx, queueID, song, mode)
}

// remember stores the song and how it was picked as the queue's last fetched song,
// for AddLatestToQueue.
func (m *MusicService) remember(ctx context.Context, queueID uuid.UUID, song repository.Song, mode PickMode) (string, error) {
	modeName := string(mode)
	err := m.q.SetQueueLastFetched(ctx, repository.SetQueueLastFetchedParams{
		Uuid: queueID, LastFetchedSongUuid: song.Uuid, LastFetchedMode: &modeName,
	})
	if err != nil {
		return "", err
	}
	metrics.SongsRequested.WithLabelValues(modeName).Inc()
	return song.Path, nil
}

// RandomSongClassic picks a random song where every song has the same chance.
func (m *MusicService) RandomSongClassic(ctx context.Context, queueID uuid.UUID) (string, error) {
	for range maxPickAttempts {
		row, err := m.q.GetRandomActiveSong(ctx)
		if errors.Is(err, pgx.ErrNoRows) {
			return "", ErrNoSongs
		}
		if err != nil {
			return "", err
		}
		if !songIsPlayable(row.Song, row.SoundtrackPath) {
			if err := m.removeBrokenSong(ctx, row.Song); err != nil {
				return "", err
			}
			continue
		}
		return m.remember(ctx, queueID, row.Song, PickClassic)
	}
	return "", ErrNoSongs
}

// SongInfo returns information about the current song in the queue.
func (m *MusicService) SongInfo(ctx context.Context, queueID uuid.UUID) (SongInfo, error) {
	queue, songs, err := m.loadQueue(ctx, queueID)
	if err != nil {
		return SongInfo{}, err
	}
	current := int(queue.CurrentSong)
	if current < 0 || current >= len(songs) {
		return SongInfo{}, nil
	}
	return m.songInfo(ctx, songs[current], true), nil
}

// PlayedSongs returns all songs in the queue.
func (m *MusicService) PlayedSongs(ctx context.Context, queueID uuid.UUID) ([]SongInfo, error) {
	queue, songs, err := m.loadQueue(ctx, queueID)
	if err != nil {
		return nil, err
	}
	songList := []SongInfo{}
	for _, song := range songs {
		songList = append(songList, m.songInfo(ctx, song, song.SongNo == queue.CurrentSong))
	}
	return songList, nil
}

// songInfo describes a queued song. Songs removed from the library keep their stored names.
func (m *MusicService) songInfo(ctx context.Context, song repository.ListQueueSongsRow, current bool) SongInfo {
	info := SongInfo{
		SoundtrackUuid:   song.SoundtrackUuid,
		Soundtrack:       song.SoundtrackName,
		SongUuid:         song.SongUuid,
		Song:             song.SongName,
		CurrentlyPlaying: current,
		SongNo:           int(song.SongNo),
	}
	if song.TimesPlayed != nil {
		info.SongPlayed = *song.TimesPlayed
	}
	if soundtrack, ok := m.soundtrackFor(ctx, song.SoundtrackUuid); ok {
		info.Soundtrack = soundtrack.SoundtrackName
		info.SoundtrackPlayed = soundtrack.TimesPlayed
	}
	return info
}

// Song jumps to the given queue position (clamped to the queue) and returns its path.
func (m *MusicService) Song(ctx context.Context, queueID uuid.UUID, songNumber int) (string, error) {
	_, songs, err := m.loadQueue(ctx, queueID)
	if err != nil {
		return "", err
	}
	return m.jump(ctx, queueID, songs, songNumber)
}

// NextSong moves to the next song in the queue, staying on the last one at the end.
func (m *MusicService) NextSong(ctx context.Context, queueID uuid.UUID) (string, error) {
	queue, songs, err := m.loadQueue(ctx, queueID)
	if err != nil {
		return "", err
	}
	return m.jump(ctx, queueID, songs, int(queue.CurrentSong)+1)
}

// PreviousSong moves to the previous song in the queue, staying on the first one at the start.
func (m *MusicService) PreviousSong(ctx context.Context, queueID uuid.UUID) (string, error) {
	queue, songs, err := m.loadQueue(ctx, queueID)
	if err != nil {
		return "", err
	}
	return m.jump(ctx, queueID, songs, int(queue.CurrentSong)-1)
}

func (m *MusicService) jump(ctx context.Context, queueID uuid.UUID, songs []repository.ListQueueSongsRow, songNumber int) (string, error) {
	if len(songs) == 0 {
		return "", ErrQueueEmpty
	}
	songNumber = max(0, min(songNumber, len(songs)-1))
	err := m.q.SetQueueCurrentSong(ctx, repository.SetQueueCurrentSongParams{Uuid: queueID, CurrentSong: int32(songNumber)})
	if err != nil {
		return "", err
	}
	if songs[songNumber].Path == nil {
		return "", ErrNotFound
	}
	return *songs[songNumber].Path, nil
}

// SoundtrackNames returns all soundtrack names in alphabetical order.
func (m *MusicService) SoundtrackNames(ctx context.Context) ([]string, error) {
	soundtracks, err := m.allSoundtracks(ctx)
	if err != nil {
		return nil, err
	}
	names := make([]string, len(soundtracks))
	for i, s := range soundtracks {
		names[i] = s.SoundtrackName
	}
	return names, nil
}

// SoundtrackNamesRandom returns all soundtrack names in random order.
func (m *MusicService) SoundtrackNamesRandom(ctx context.Context) ([]string, error) {
	names, err := m.SoundtrackNames(ctx)
	rand.Shuffle(len(names), func(i, j int) { names[i], names[j] = names[j], names[i] })
	return names, err
}

type weightedSoundtrack struct {
	soundtrack repository.Soundtrack
	weight     int
}

// lowChanceWeights gives each soundtrack a weight of how far it is below the average play count (at least 1).
func lowChanceWeights(soundtracks []repository.Soundtrack) []weightedSoundtrack {
	average := averagePlayed(soundtracks)
	weighted := make([]weightedSoundtrack, len(soundtracks))
	for i, s := range soundtracks {
		weighted[i] = weightedSoundtrack{soundtrack: s, weight: max(1, int(average-s.TimesPlayed))}
	}
	return weighted
}

func averagePlayed(soundtracks []repository.Soundtrack) int32 {
	if len(soundtracks) == 0 {
		return 0
	}
	var sum int64
	for _, s := range soundtracks {
		sum += int64(s.TimesPlayed)
	}
	return int32(sum / int64(len(soundtracks)))
}

func pickWeighted(candidates []weightedSoundtrack) int {
	total := 0
	for _, c := range candidates {
		total += c.weight
	}
	n := rand.IntN(total)
	for i, c := range candidates {
		if n < c.weight {
			return i
		}
		n -= c.weight
	}
	return len(candidates) - 1
}

// pickSong picks a random playable song. Soundtracks without songs are dropped from the candidates
// and broken songs are removed from the database.
func (m *MusicService) pickSong(ctx context.Context, candidates []weightedSoundtrack) (repository.Song, error) {
	candidates = slices.Clone(candidates)
	for range maxPickAttempts {
		if len(candidates) == 0 {
			return repository.Song{}, ErrNoSongs
		}
		i := pickWeighted(candidates)
		soundtrack := candidates[i].soundtrack

		songs, err := m.q.FindSongsFromSoundtrack(ctx, soundtrack.ID)
		if err != nil {
			return repository.Song{}, err
		}
		if len(songs) == 0 {
			candidates = slices.Delete(candidates, i, i+1)
			continue
		}

		song := songs[rand.IntN(len(songs))]
		logging.GetLogger().Debug("Selected song", zap.String("song", song.SongName), zap.String("path", song.Path))
		if !songIsPlayable(song, soundtrack.Path) {
			if err := m.removeBrokenSong(ctx, song); err != nil {
				return repository.Song{}, err
			}
			continue
		}
		return song, nil
	}
	return repository.Song{}, ErrNoSongs
}

func (m *MusicService) removeBrokenSong(ctx context.Context, song repository.Song) error {
	logging.GetLogger().Warn("Song not found, removing from database",
		zap.String("song", song.SongName),
		zap.String("path", song.Path))
	return m.q.RemoveBrokenSongs(ctx, []uuid.UUID{song.Uuid})
}

// songIsPlayable reports whether the song file exists and its stored path is consistent.
func songIsPlayable(song repository.Song, soundtrackPath string) bool {
	if song.FileName != nil {
		if soundtrackPath+*song.FileName != song.Path || strings.HasSuffix(strings.ToLower(*song.FileName), ".wav") {
			return false
		}
	}
	info, err := os.Stat(song.Path)
	return err == nil && !info.IsDir()
}

func (m *MusicService) soundtrackFor(ctx context.Context, soundtrackUUID uuid.UUID) (repository.Soundtrack, bool) {
	soundtracks, err := m.allSoundtracks(ctx)
	if err != nil {
		logging.GetLogger().Error("Failed to load soundtracks", zap.Error(err))
		return repository.Soundtrack{}, false
	}
	for _, soundtrack := range soundtracks {
		if soundtrack.Uuid == soundtrackUUID {
			return soundtrack, true
		}
	}
	return repository.Soundtrack{}, false
}