package backend

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

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

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

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

type SongInfo struct {
	Soundtrack       string `json:"Soundtrack"`
	SoundtrackPlayed int32  `json:"SoundtrackPlayed"`
	Song             string `json:"Song"`
	SongPlayed       int32  `json:"SongPlayed"`
	CurrentlyPlaying bool   `json:"CurrentlyPlaying"`
	SongNo           int    `json:"SongNo"`
}

// MusicService picks songs and keeps track of the shared play queue.
type MusicService struct {
	q              repository.Querier
	soundCheckPath string

	cacheMu     sync.Mutex
	soundtracks []repository.Soundtrack

	// Queue state is shared by all clients and intentionally not locked.
	queue       []repository.Song
	currentSong int
	lastFetched repository.Song
}

// 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, currentSong: -1}
}

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
}

// Reset clears the play queue and reloads the soundtrack list.
func (m *MusicService) Reset(ctx context.Context) error {
	m.queue = nil
	m.currentSong = -1
	m.cacheMu.Lock()
	m.soundtracks = nil
	m.cacheMu.Unlock()
	_, err := m.allSoundtracks(ctx)
	return err
}

// 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.
func (m *MusicService) AddLatestToQueue() {
	if m.lastFetched.Path != "" {
		m.currentSong = len(m.queue)
		m.queue = append(m.queue, m.lastFetched)
		m.lastFetched = repository.Song{}
	}
}

// AddLatestPlayed increments the play counters of the current song.
func (m *MusicService) AddLatestPlayed(ctx context.Context) error {
	if !m.validIndex(m.currentSong) {
		return nil
	}
	return m.markPlayed(ctx, m.queue[m.currentSong])
}

// SetPlayed increments the play counters of the song at the given queue position.
func (m *MusicService) SetPlayed(ctx context.Context, songNumber int) error {
	if !m.validIndex(songNumber) {
		return nil
	}
	return m.markPlayed(ctx, m.queue[songNumber])
}

func (m *MusicService) markPlayed(ctx context.Context, song repository.Song) error {
	if err := m.q.AddSoundtrackPlayed(ctx, song.SoundtrackID); err != nil {
		return err
	}
	return m.q.AddSongPlayed(ctx, repository.AddSongPlayedParams{SoundtrackID: song.SoundtrackID, SongName: song.SongName})
}

func (m *MusicService) validIndex(i int) bool {
	return i >= 0 && i < len(m.queue)
}

// RandomSong picks a random song from a random soundtrack.
func (m *MusicService) RandomSong(ctx context.Context) (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, candidates)
}

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

func (m *MusicService) pickAndRemember(ctx context.Context, candidates []weightedSoundtrack) (string, error) {
	song, err := m.pickSong(ctx, candidates)
	if err != nil {
		return "", err
	}
	m.lastFetched = song
	return song.Path, nil
}

// RandomSongClassic picks a random song where every song has the same chance.
func (m *MusicService) RandomSongClassic(ctx context.Context) (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
		}
		m.lastFetched = row.Song
		return row.Song.Path, nil
	}
	return "", ErrNoSongs
}

// SongInfo returns information about the current song in the queue.
func (m *MusicService) SongInfo(ctx context.Context) SongInfo {
	if !m.validIndex(m.currentSong) {
		return SongInfo{}
	}
	song := m.queue[m.currentSong]
	soundtrack := m.soundtrackFor(ctx, song)
	return SongInfo{
		Soundtrack:       soundtrack.SoundtrackName,
		SoundtrackPlayed: soundtrack.TimesPlayed,
		Song:             song.SongName,
		SongPlayed:       song.TimesPlayed,
		CurrentlyPlaying: true,
		SongNo:           m.currentSong,
	}
}

// PlayedSongs returns all songs in the queue.
func (m *MusicService) PlayedSongs(ctx context.Context) []SongInfo {
	var songList []SongInfo
	for i, song := range m.queue {
		soundtrack := m.soundtrackFor(ctx, song)
		songList = append(songList, SongInfo{
			Soundtrack:       soundtrack.SoundtrackName,
			SoundtrackPlayed: soundtrack.TimesPlayed,
			Song:             song.SongName,
			SongPlayed:       song.TimesPlayed,
			CurrentlyPlaying: i == m.currentSong,
			SongNo:           i,
		})
	}
	return songList
}

// Song jumps to the given queue position (clamped to the queue) and returns its path.
func (m *MusicService) Song(songNumber int) (string, error) {
	if len(m.queue) == 0 {
		return "", ErrQueueEmpty
	}
	m.currentSong = max(0, min(songNumber, len(m.queue)-1))
	return m.queue[m.currentSong].Path, nil
}

// NextSong moves to the next song in the queue, staying on the last one at the end.
func (m *MusicService) NextSong() (string, error) {
	if len(m.queue) == 0 {
		return "", ErrQueueEmpty
	}
	return m.Song(m.currentSong + 1)
}

// PreviousSong moves to the previous song in the queue, staying on the first one at the start.
func (m *MusicService) PreviousSong() (string, error) {
	if len(m.queue) == 0 {
		return "", ErrQueueEmpty
	}
	return m.Song(m.currentSong - 1)
}

// 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.RemoveBrokenSong(ctx, repository.RemoveBrokenSongParams{SoundtrackID: song.SoundtrackID, Path: song.Path})
}

// 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, song repository.Song) repository.Soundtrack {
	soundtracks, err := m.allSoundtracks(ctx)
	if err != nil {
		logging.GetLogger().Error("Failed to load soundtracks", zap.Error(err))
		return repository.Soundtrack{}
	}
	for _, soundtrack := range soundtracks {
		if soundtrack.ID == song.SoundtrackID {
			return soundtrack
		}
	}
	return repository.Soundtrack{}
}