yellowjacket/backend/queue/queue.go

// Package queue manages the playback queue and auto-advance logic.
package queue

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"log/slog"
	"math/rand/v2"
	"sync"

	"github.com/wailsapp/wails/v2/pkg/runtime"

	"yellowjacket/backend/database"
	"yellowjacket/backend/database/sql/sqlcgen"
	"yellowjacket/backend/events"
)

// RepeatMode represents the queue repeat behavior.
type RepeatMode string

// Repeat mode values.
const (
	RepeatOff RepeatMode = "off"
	RepeatAll RepeatMode = "all"
	RepeatOne RepeatMode = "one"
)

// PreviousRestartThreshold is the number of seconds into a track before
// "Previous" restarts the current track instead of going to the prior one.
const PreviousRestartThreshold = 3

// TrackLoader is the interface the queue uses to tell the player to load a file.
type TrackLoader interface {
	LoadFile(filePath string) error
	Play() error
	CurrentPositionSeconds() (int, error)
	UnloadTrack()
}

// Track represents a track in the queue with its metadata.
type Track struct {
	ID          int64  `json:"id"`
	AudioFileID int64  `json:"audioFileId"`
	FilePath    string `json:"filePath"`
	Position    int64  `json:"position"`
	Title       string `json:"title"`
	Artist      string `json:"artist"`
}

// State is the full state emitted to the frontend.
type State struct {
	Tracks           []Track    `json:"tracks"`
	CurrentIndex     int        `json:"currentIndex"`
	ShuffleMode      bool       `json:"shuffleMode"`
	RepeatMode       RepeatMode `json:"repeatMode"`
	SourcePlaylistID int64      `json:"sourcePlaylistId"`
}

// Queue manages an ordered list of tracks for playback.
type Queue struct {
	ctx    context.Context
	logger *slog.Logger
	db     *database.DB
	player TrackLoader

	mu               sync.Mutex
	tracks           []Track
	currentIndex     int
	shuffleMode      bool
	repeatMode       RepeatMode
	shuffleOrder     []int
	sourcePlaylistID int64
}

// NewQueue creates a new queue manager.
func NewQueue(logger *slog.Logger, db *database.DB) *Queue {
	return &Queue{
		logger:     logger.WithGroup("queue"),
		db:         db,
		repeatMode: RepeatOff,
	}
}

// SetContext sets the Wails runtime context and registers event handlers.
func (q *Queue) SetContext(ctx context.Context) {
	q.ctx = ctx
	q.registerEventHandlers()
}

// SetPlayer provides the queue with a reference to the player for auto-advance.
func (q *Queue) SetPlayer(player TrackLoader) {
	q.player = player
}

// OnPlaybackFinished is called when a track finishes playing naturally.
// This drives the auto-advance behavior.
func (q *Queue) OnPlaybackFinished() {
	q.mu.Lock()
	defer q.mu.Unlock()

	if len(q.tracks) == 0 {
		return
	}

	// Repeat One: replay the current track.
	if q.repeatMode == RepeatOne {
		q.playCurrentTrack()
		q.emitQueueChanged()

		return
	}

	nextIdx := q.nextIndex()
	if nextIdx == -1 {
		// Queue exhausted — this is the extension point for a future fallback playlist.
		q.onQueueExhausted()

		return
	}

	q.currentIndex = nextIdx
	q.playCurrentTrack()
	q.emitQueueChanged()
}

// registerEventHandlers sets up Wails event listeners for queue commands.
func (q *Queue) registerEventHandlers() {
	if q.ctx == nil {
		q.logger.Error("Context is nil, cannot register event handlers")

		return
	}

	runtime.EventsOn(q.ctx, events.RequestPlay, func(_ ...any) {
		q.logger.Info("Received RequestPlay")
		q.PlayFromStart()
	})

	runtime.EventsOn(q.ctx, events.RequestNext, func(_ ...any) {
		q.logger.Info("Received RequestNext")
		q.Next()
	})

	runtime.EventsOn(q.ctx, events.RequestPrevious, func(_ ...any) {
		q.logger.Info("Received RequestPrevious")
		q.Previous()
	})

	runtime.EventsOn(q.ctx, events.RequestSetQueue, func(data ...any) {
		q.logger.Info("Received RequestSetQueue")
		q.handleSetQueue(data...)
	})

	runtime.EventsOn(q.ctx, events.RequestAddToQueue, func(data ...any) {
		q.logger.Info("Received RequestAddToQueue")
		q.handleAddToQueue(data...)
	})

	runtime.EventsOn(q.ctx, events.RequestPlayNext, func(data ...any) {
		q.logger.Info("Received RequestPlayNext")
		q.handlePlayNext(data...)
	})

	runtime.EventsOn(q.ctx, events.RequestRemoveFromQueue, func(data ...any) {
		q.logger.Info("Received RequestRemoveFromQueue")
		q.handleRemoveFromQueue(data...)
	})

	runtime.EventsOn(q.ctx, events.RequestToggleShuffle, func(_ ...any) {
		q.logger.Info("Received RequestToggleShuffle")
		q.ToggleShuffle()
	})

	runtime.EventsOn(q.ctx, events.RequestCycleRepeat, func(_ ...any) {
		q.logger.Info("Received RequestCycleRepeat")
		q.CycleRepeat()
	})

	runtime.EventsOn(q.ctx, events.RequestAddTracksToQueue, func(data ...any) {
		q.logger.Info("Received RequestAddTracksToQueue")
		q.handleAddTracksToQueue(data...)
	})

	runtime.EventsOn(q.ctx, events.RequestPlayTracksNext, func(data ...any) {
		q.logger.Info("Received RequestPlayTracksNext")
		q.handlePlayTracksNext(data...)
	})

	runtime.EventsOn(q.ctx, events.RequestPlayQueueIndex, func(data ...any) {
		q.logger.Info("Received RequestPlayQueueIndex")
		q.handlePlayQueueIndex(data...)
	})
}

// handleSetQueue processes the RequestSetQueue event payload.
// Expects data[0] = []interface{} of file path strings, data[1] = float64 start index.
func (q *Queue) handleSetQueue(data ...any) {
	if len(data) < 2 {
		q.logger.Error("RequestSetQueue: missing data")

		return
	}

	filePathsRaw, ok := data[0].([]interface{})
	if !ok {
		q.logger.Error("RequestSetQueue: invalid filePaths type")

		return
	}

	filePaths := make([]string, 0, len(filePathsRaw))

	for _, fp := range filePathsRaw {
		if s, ok := fp.(string); ok {
			filePaths = append(filePaths, s)
		}
	}

	startIndex := 0

	if si, ok := data[1].(float64); ok {
		startIndex = int(si)
	}

	q.SetQueue(filePaths, startIndex)
}

// handleAddToQueue processes the RequestAddToQueue event payload.
// Expects data[0] = string file path.
func (q *Queue) handleAddToQueue(data ...any) {
	if len(data) < 1 {
		q.logger.Error("RequestAddToQueue: missing data")

		return
	}

	filePath, ok := data[0].(string)
	if !ok {
		q.logger.Error("RequestAddToQueue: invalid filePath type", "got", data[0])

		return
	}

	q.AddTrack(filePath)
}

// handlePlayNext processes the RequestPlayNext event payload.
// Expects data[0] = string file path.
func (q *Queue) handlePlayNext(data ...any) {
	if len(data) < 1 {
		q.logger.Error("RequestPlayNext: missing data")

		return
	}

	filePath, ok := data[0].(string)
	if !ok {
		q.logger.Error("RequestPlayNext: invalid filePath type", "got", data[0])

		return
	}

	q.InsertNext(filePath)
}

// handleRemoveFromQueue processes the RequestRemoveFromQueue event payload.
// Expects data[0] = float64 position.
func (q *Queue) handleRemoveFromQueue(data ...any) {
	if len(data) < 1 {
		q.logger.Error("RequestRemoveFromQueue: missing data")

		return
	}

	position, ok := data[0].(float64)
	if !ok {
		q.logger.Error("RequestRemoveFromQueue: invalid position type", "got", data[0])

		return
	}

	q.RemoveTrack(int(position))
}

// handleAddTracksToQueue processes the RequestAddTracksToQueue event payload.
// Expects data[0] = []interface{} of file path strings.
func (q *Queue) handleAddTracksToQueue(data ...any) {
	if len(data) < 1 {
		q.logger.Error("RequestAddTracksToQueue: missing data")

		return
	}

	filePathsRaw, ok := data[0].([]interface{})
	if !ok {
		q.logger.Error("RequestAddTracksToQueue: invalid filePaths type", "got", data[0])

		return
	}

	filePaths := make([]string, 0, len(filePathsRaw))

	for _, fp := range filePathsRaw {
		if s, ok := fp.(string); ok {
			filePaths = append(filePaths, s)
		}
	}

	q.AddTracks(filePaths)
}

// handlePlayQueueIndex processes the RequestPlayQueueIndex event payload.
// Expects data[0] = float64 index.
func (q *Queue) handlePlayQueueIndex(data ...any) {
	if len(data) < 1 {
		q.logger.Error("RequestPlayQueueIndex: missing data")

		return
	}

	index, ok := data[0].(float64)
	if !ok {
		q.logger.Error("RequestPlayQueueIndex: invalid index type", "got", data[0])

		return
	}

	q.PlayIndex(int(index))
}

// handlePlayTracksNext processes the RequestPlayTracksNext event payload.
// Expects data[0] = []interface{} of file path strings.
func (q *Queue) handlePlayTracksNext(data ...any) {
	if len(data) < 1 {
		q.logger.Error("RequestPlayTracksNext: missing data")

		return
	}

	filePathsRaw, ok := data[0].([]interface{})
	if !ok {
		q.logger.Error("RequestPlayTracksNext: invalid filePaths type", "got", data[0])

		return
	}

	filePaths := make([]string, 0, len(filePathsRaw))

	for _, fp := range filePathsRaw {
		if s, ok := fp.(string); ok {
			filePaths = append(filePaths, s)
		}
	}

	q.InsertNextTracks(filePaths)
}

// SetQueue replaces the entire queue with new tracks and starts playing.
func (q *Queue) SetQueue(filePaths []string, startIndex int) {
	q.mu.Lock()
	defer q.mu.Unlock()

	// Look up audio file IDs and metadata for all paths.
	tracks := make([]Track, 0, len(filePaths))

	for i, fp := range filePaths {
		af, err := q.db.Queries.GetAudioFileByPath(q.db.Ctx, fp)
		if err != nil {
			q.logger.Warn("Could not find audio file in database", "path", fp, "err", err)

			continue
		}

		track := Track{
			AudioFileID: af.ID,
			FilePath:    fp,
			Position:    int64(i),
		}

		// Try to get metadata.
		meta, metaErr := q.db.Queries.GetTrackMetadataByPath(q.db.Ctx, fp)
		if metaErr == nil {
			track.Title = meta.Title
			track.Artist = meta.Artist
		}

		tracks = append(tracks, track)
	}

	q.tracks = tracks
	q.sourcePlaylistID = 0

	if startIndex >= 0 && startIndex < len(q.tracks) {
		q.currentIndex = startIndex
	} else {
		q.currentIndex = 0
	}

	// Regenerate shuffle order if shuffle is on.
	if q.shuffleMode {
		q.generateShuffleOrder()
	}

	// Persist to DB.
	q.persistTracks()
	q.persistState()

	// Start playing the selected track.
	q.playCurrentTrack()
	q.emitQueueChanged()
}

// AddTrack appends a track to the end of the queue.
// If the queue was empty, it starts playing the added track immediately.
func (q *Queue) AddTrack(filePath string) {
	q.mu.Lock()
	defer q.mu.Unlock()

	af, err := q.db.Queries.GetAudioFileByPath(q.db.Ctx, filePath)
	if err != nil {
		q.logger.Error("Could not find audio file", "path", filePath, "err", err)

		return
	}

	wasEmpty := len(q.tracks) == 0

	track := Track{
		AudioFileID: af.ID,
		FilePath:    filePath,
		Position:    int64(len(q.tracks)),
	}

	// Try to get metadata.
	meta, metaErr := q.db.Queries.GetTrackMetadataByPath(q.db.Ctx, filePath)
	if metaErr == nil {
		track.Title = meta.Title
		track.Artist = meta.Artist
	}

	q.tracks = append(q.tracks, track)

	// Persist.
	_, insertErr := q.db.Queries.InsertQueueTrack(q.db.Ctx, sqlcgen.InsertQueueTrackParams{
		AudioFileID: af.ID,
		Position:    track.Position,
	})
	if insertErr != nil {
		q.logger.Error("Failed to persist queue track", "err", insertErr)
	}

	// Update shuffle order if shuffle is on.
	if q.shuffleMode {
		q.shuffleOrder = append(q.shuffleOrder, len(q.tracks)-1)
	}

	// Auto-play if this is the first track added to an empty queue.
	if wasEmpty {
		q.currentIndex = 0
		q.playCurrentTrack()
	}

	q.emitQueueChanged()
}

// AddTracks appends multiple tracks to the end of the queue.
// If the queue was empty, it starts playing the first added track immediately.
func (q *Queue) AddTracks(filePaths []string) {
	q.mu.Lock()
	defer q.mu.Unlock()

	wasEmpty := len(q.tracks) == 0

	for _, fp := range filePaths {
		af, err := q.db.Queries.GetAudioFileByPath(q.db.Ctx, fp)
		if err != nil {
			q.logger.Warn("Could not find audio file", "path", fp, "err", err)

			continue
		}

		track := Track{
			AudioFileID: af.ID,
			FilePath:    fp,
			Position:    int64(len(q.tracks)),
		}

		meta, metaErr := q.db.Queries.GetTrackMetadataByPath(q.db.Ctx, fp)
		if metaErr == nil {
			track.Title = meta.Title
			track.Artist = meta.Artist
		}

		q.tracks = append(q.tracks, track)
	}

	if q.shuffleMode {
		q.generateShuffleOrder()
	}

	q.persistTracks()
	q.persistState()

	if wasEmpty && len(q.tracks) > 0 {
		q.currentIndex = 0
		q.playCurrentTrack()
	}

	q.emitQueueChanged()
}

// InsertNextTracks inserts multiple tracks as a contiguous block after the current track.
func (q *Queue) InsertNextTracks(filePaths []string) {
	q.mu.Lock()
	defer q.mu.Unlock()

	insertPos := q.currentIndex + 1
	if insertPos > len(q.tracks) {
		insertPos = len(q.tracks)
	}

	wasEmpty := len(q.tracks) == 0

	var newTracks []Track

	for _, fp := range filePaths {
		af, err := q.db.Queries.GetAudioFileByPath(q.db.Ctx, fp)
		if err != nil {
			q.logger.Warn("Could not find audio file", "path", fp, "err", err)

			continue
		}

		track := Track{
			AudioFileID: af.ID,
			FilePath:    fp,
		}

		meta, metaErr := q.db.Queries.GetTrackMetadataByPath(q.db.Ctx, fp)
		if metaErr == nil {
			track.Title = meta.Title
			track.Artist = meta.Artist
		}

		newTracks = append(newTracks, track)
	}

	if len(newTracks) == 0 {
		return
	}

	// Insert the block into the slice at insertPos.
	tail := make([]Track, len(q.tracks[insertPos:]))
	copy(tail, q.tracks[insertPos:])
	q.tracks = append(q.tracks[:insertPos], newTracks...)
	q.tracks = append(q.tracks, tail...)

	q.reindexPositions()

	if q.shuffleMode {
		q.generateShuffleOrder()
	}

	q.persistTracks()
	q.persistState()

	if wasEmpty {
		q.currentIndex = 0
		q.playCurrentTrack()
	}

	q.emitQueueChanged()
}

// InsertNext inserts a track right after the currently playing track.
func (q *Queue) InsertNext(filePath string) {
	q.mu.Lock()
	defer q.mu.Unlock()

	af, err := q.db.Queries.GetAudioFileByPath(q.db.Ctx, filePath)
	if err != nil {
		q.logger.Error("Could not find audio file", "path", filePath, "err", err)

		return
	}

	insertPos := q.currentIndex + 1
	if insertPos > len(q.tracks) {
		insertPos = len(q.tracks)
	}

	track := Track{
		AudioFileID: af.ID,
		FilePath:    filePath,
		Position:    int64(insertPos),
	}

	// Try to get metadata.
	meta, metaErr := q.db.Queries.GetTrackMetadataByPath(q.db.Ctx, filePath)
	if metaErr == nil {
		track.Title = meta.Title
		track.Artist = meta.Artist
	}

	// Insert into slice.
	q.tracks = append(q.tracks, Track{})
	copy(q.tracks[insertPos+1:], q.tracks[insertPos:])
	q.tracks[insertPos] = track

	// Reindex positions.
	q.reindexPositions()

	// Regenerate shuffle order if needed.
	if q.shuffleMode {
		q.generateShuffleOrder()
	}

	q.persistTracks()
	q.emitQueueChanged()
}

// RemoveTrack removes a track at the given position from the queue.
func (q *Queue) RemoveTrack(position int) {
	q.mu.Lock()
	defer q.mu.Unlock()

	if position < 0 || position >= len(q.tracks) {
		q.logger.Warn("RemoveTrack: position out of range", "position", position)

		return
	}

	q.tracks = append(q.tracks[:position], q.tracks[position+1:]...)

	// Adjust current index if needed. A currentIndex of -1 means no track
	// is loaded, so only shift when a valid track is selected.
	if q.currentIndex >= 0 && position < q.currentIndex {
		q.currentIndex--
	} else if position == q.currentIndex && q.currentIndex >= len(q.tracks) && len(q.tracks) > 0 {
		q.currentIndex = len(q.tracks) - 1
	}

	q.reindexPositions()

	if q.shuffleMode {
		q.generateShuffleOrder()
	}

	q.persistTracks()
	q.persistState()
	q.emitQueueChanged()
}

// Next advances to the next track. In RepeatOne mode, the current
// track is replayed instead of advancing.
func (q *Queue) Next() {
	q.mu.Lock()
	defer q.mu.Unlock()

	if len(q.tracks) == 0 {
		return
	}

	// Repeat One: replay the current track.
	if q.repeatMode == RepeatOne {
		q.playCurrentTrack()
		q.emitQueueChanged()

		return
	}

	nextIdx := q.nextIndex()
	if nextIdx == -1 {
		q.onQueueExhausted()

		return
	}

	q.currentIndex = nextIdx
	q.playCurrentTrack()
	q.emitQueueChanged()
}

// Previous goes to the previous track (or restarts current if >3s in).
// In RepeatOne mode, the current track is replayed instead of navigating.
func (q *Queue) Previous() {
	q.mu.Lock()
	defer q.mu.Unlock()

	if len(q.tracks) == 0 || q.currentIndex < 0 {
		return
	}

	// Repeat One: replay the current track.
	if q.repeatMode == RepeatOne {
		q.playCurrentTrack()
		q.emitQueueChanged()

		return
	}

	// If more than 3 seconds into the track, restart it.
	if q.player != nil {
		posSecs, err := q.player.CurrentPositionSeconds()
		if err == nil && posSecs > PreviousRestartThreshold {
			q.playCurrentTrack()
			q.emitQueueChanged()

			return
		}
	}

	prevIdx := q.previousIndex()
	if prevIdx == -1 {
		// At the beginning — just restart the current track.
		q.playCurrentTrack()
		q.emitQueueChanged()

		return
	}

	q.currentIndex = prevIdx
	q.playCurrentTrack()
	q.emitQueueChanged()
}

// PlayFromStart restarts playback from the beginning of the queue.
// If shuffle is enabled, a new shuffle order is generated and playback
// starts from a random track. This is a no-op when a track is already
// active (currentIndex != -1) or the queue is empty.
func (q *Queue) PlayFromStart() {
	q.mu.Lock()
	defer q.mu.Unlock()

	if q.currentIndex != -1 {
		return
	}

	if len(q.tracks) == 0 {
		return
	}

	if q.shuffleMode {
		q.generateShuffleOrder()
		q.currentIndex = q.shuffleOrder[0]
	} else {
		q.currentIndex = 0
	}

	q.playCurrentTrack()
	q.emitQueueChanged()
}

// PlayIndex jumps to and plays the track at the given index.
func (q *Queue) PlayIndex(index int) {
	q.mu.Lock()
	defer q.mu.Unlock()

	if len(q.tracks) == 0 {
		return
	}

	if index < 0 || index >= len(q.tracks) {
		q.logger.Warn("PlayIndex: index out of range", "index", index, "trackCount", len(q.tracks))

		return
	}

	q.currentIndex = index
	q.playCurrentTrack()
	q.emitQueueChanged()
}

// ToggleShuffle toggles shuffle mode on/off.
func (q *Queue) ToggleShuffle() {
	q.mu.Lock()
	defer q.mu.Unlock()

	q.shuffleMode = !q.shuffleMode

	if q.shuffleMode {
		q.generateShuffleOrder()
	} else {
		q.shuffleOrder = nil
	}

	q.persistState()
	q.emitQueueChanged()
}

// CycleRepeat cycles through repeat modes: off → all → one → off.
func (q *Queue) CycleRepeat() {
	q.mu.Lock()
	defer q.mu.Unlock()

	switch q.repeatMode {
	case RepeatOff:
		q.repeatMode = RepeatAll
	case RepeatAll:
		q.repeatMode = RepeatOne
	case RepeatOne:
		q.repeatMode = RepeatOff
	}

	q.persistState()
	q.emitQueueChanged()
}

// GetState returns the current queue state for the frontend.
func (q *Queue) GetState() State {
	q.mu.Lock()
	defer q.mu.Unlock()

	tracks := make([]Track, len(q.tracks))
	copy(tracks, q.tracks)

	return State{
		Tracks:           tracks,
		CurrentIndex:     q.currentIndex,
		ShuffleMode:      q.shuffleMode,
		RepeatMode:       q.repeatMode,
		SourcePlaylistID: q.sourcePlaylistID,
	}
}

// EmitCurrentState emits the current queue state to the frontend.
// This is called after the frontend DOM is ready.
func (q *Queue) EmitCurrentState() {
	q.mu.Lock()
	defer q.mu.Unlock()

	q.emitQueueChanged()
}

// SaveState persists the queue state to the database.
func (q *Queue) SaveState() {
	q.mu.Lock()
	defer q.mu.Unlock()

	q.persistTracks()
	q.persistState()
	q.logger.Info("Queue state saved",
		"trackCount", len(q.tracks),
		"currentIndex", q.currentIndex,
		"shuffleMode", q.shuffleMode,
		"repeatMode", q.repeatMode,
	)
}

// RestoreState loads the queue state from the database.
func (q *Queue) RestoreState() {
	q.mu.Lock()
	defer q.mu.Unlock()

	// Restore queue metadata.
	state, err := q.db.Queries.GetQueueState(q.db.Ctx)
	if err != nil {
		q.logger.Error("Failed to load queue state", "err", err)

		return
	}

	q.currentIndex = int(state.CurrentPosition)
	q.shuffleMode = state.ShuffleMode
	q.repeatMode = RepeatMode(state.RepeatMode)

	if state.SourcePlaylistID.Valid {
		q.sourcePlaylistID = state.SourcePlaylistID.Int64
	}

	// Restore shuffle order.
	if state.ShuffleOrder.Valid && state.ShuffleOrder.String != "" {
		var order []int

		if err := json.Unmarshal([]byte(state.ShuffleOrder.String), &order); err != nil {
			q.logger.Warn("Failed to parse shuffle order", "err", err)
		} else {
			q.shuffleOrder = order
		}
	}

	// Restore queue tracks.
	rows, err := q.db.Queries.GetQueueTracks(q.db.Ctx)
	if err != nil {
		q.logger.Error("Failed to load queue tracks", "err", err)

		return
	}

	q.tracks = make([]Track, 0, len(rows))

	for _, row := range rows {
		q.tracks = append(q.tracks, Track{
			ID:          row.ID,
			AudioFileID: row.AudioFileID,
			FilePath:    row.FilePath,
			Position:    row.Position,
			Title:       row.Title,
			Artist:      row.Artist,
		})
	}

	// Clamp current index. A value of -1 is valid and means "no current
	// track" (e.g. the queue was exhausted before shutdown). Only clamp
	// when the index exceeds the restored track count.
	if q.currentIndex >= len(q.tracks) && len(q.tracks) > 0 {
		q.currentIndex = len(q.tracks) - 1
	}

	q.logger.Info("Queue state restored",
		"trackCount", len(q.tracks),
		"currentIndex", q.currentIndex,
		"shuffleMode", q.shuffleMode,
		"repeatMode", q.repeatMode,
	)
}

// nextIndex returns the next track index respecting shuffle and repeat modes.
// Returns -1 if there is no next track (queue exhausted).
func (q *Queue) nextIndex() int {
	if len(q.tracks) == 0 {
		return -1
	}

	if q.shuffleMode && len(q.shuffleOrder) > 0 {
		return q.nextShuffledIndex()
	}

	next := q.currentIndex + 1
	if next >= len(q.tracks) {
		if q.repeatMode == RepeatAll {
			return 0
		}

		return -1
	}

	return next
}

// previousIndex returns the previous track index respecting shuffle and repeat.
// Returns -1 if there is no previous track.
func (q *Queue) previousIndex() int {
	if len(q.tracks) == 0 {
		return -1
	}

	if q.shuffleMode && len(q.shuffleOrder) > 0 {
		return q.previousShuffledIndex()
	}

	prev := q.currentIndex - 1
	if prev < 0 {
		if q.repeatMode == RepeatAll {
			return len(q.tracks) - 1
		}

		return -1
	}

	return prev
}

// nextShuffledIndex finds the next index in the shuffle order.
func (q *Queue) nextShuffledIndex() int {
	shufflePos := q.currentShufflePosition()
	if shufflePos == -1 {
		// Current track not found in shuffle order — shouldn't happen.
		return -1
	}

	nextShufflePos := shufflePos + 1
	if nextShufflePos >= len(q.shuffleOrder) {
		if q.repeatMode == RepeatAll {
			return q.shuffleOrder[0]
		}

		return -1
	}

	return q.shuffleOrder[nextShufflePos]
}

// previousShuffledIndex finds the previous index in the shuffle order.
func (q *Queue) previousShuffledIndex() int {
	shufflePos := q.currentShufflePosition()
	if shufflePos == -1 {
		return -1
	}

	prevShufflePos := shufflePos - 1
	if prevShufflePos < 0 {
		if q.repeatMode == RepeatAll {
			return q.shuffleOrder[len(q.shuffleOrder)-1]
		}

		return -1
	}

	return q.shuffleOrder[prevShufflePos]
}

// currentShufflePosition finds where the current track index is in the shuffle order.
func (q *Queue) currentShufflePosition() int {
	for i, idx := range q.shuffleOrder {
		if idx == q.currentIndex {
			return i
		}
	}

	return -1
}

// generateShuffleOrder creates a Fisher-Yates shuffled index order,
// placing the current track at position 0 so it doesn't replay immediately.
func (q *Queue) generateShuffleOrder() {
	n := len(q.tracks)
	if n == 0 {
		q.shuffleOrder = nil

		return
	}

	order := make([]int, n)
	for i := range order {
		order[i] = i
	}

	// Fisher-Yates shuffle.
	for i := n - 1; i > 0; i-- {
		j := rand.IntN(i + 1)
		order[i], order[j] = order[j], order[i]
	}

	// Move the current track to position 0 so it doesn't replay immediately.
	for i, idx := range order {
		if idx == q.currentIndex {
			order[0], order[i] = order[i], order[0]

			break
		}
	}

	q.shuffleOrder = order
}

// playCurrentTrack tells the player to load and play the current track.
func (q *Queue) playCurrentTrack() {
	if q.player == nil {
		q.logger.Error("No player set, cannot play track")

		return
	}

	if q.currentIndex < 0 || q.currentIndex >= len(q.tracks) {
		q.logger.Warn(
			"Current index out of range",
			"index", q.currentIndex, "trackCount", len(q.tracks),
		)

		return
	}

	track := q.tracks[q.currentIndex]
	q.logger.Info(
		"Playing track from queue",
		"filePath", track.FilePath, "position", q.currentIndex,
	)

	err := q.player.LoadFile(track.FilePath)
	if err != nil {
		q.logger.Error("Failed to load file from queue", "filePath", track.FilePath, "err", err)

		return
	}

	err = q.player.Play()
	if err != nil {
		q.logger.Error("Failed to play file from queue", "filePath", track.FilePath, "err", err)
	}

	q.persistState()
}

// onQueueExhausted is called when there are no more tracks to play.
// It unloads the current track, resets the index to -1 (no current track),
// and notifies the frontend.
func (q *Queue) onQueueExhausted() {
	q.logger.Info("Queue exhausted, unloading track")

	q.currentIndex = -1

	if q.player != nil {
		q.player.UnloadTrack()
	}

	q.emitQueueChanged()
	q.persistState()
}

// reindexPositions updates the Position field of all tracks to match slice index.
func (q *Queue) reindexPositions() {
	for i := range q.tracks {
		q.tracks[i].Position = int64(i)
	}
}

// persistTracks writes the current queue tracks to the database.
func (q *Queue) persistTracks() {
	err := q.db.Queries.ClearQueueTracks(q.db.Ctx)
	if err != nil {
		q.logger.Error("Failed to clear queue tracks", "err", err)

		return
	}

	for _, track := range q.tracks {
		_, err := q.db.Queries.InsertQueueTrack(q.db.Ctx, sqlcgen.InsertQueueTrackParams{
			AudioFileID: track.AudioFileID,
			Position:    track.Position,
		})
		if err != nil {
			q.logger.Error("Failed to insert queue track", "err", err)
		}
	}
}

// persistState writes the queue metadata to the database.
func (q *Queue) persistState() {
	var shuffleOrderJSON sql.NullString

	if len(q.shuffleOrder) > 0 {
		data, err := json.Marshal(q.shuffleOrder)
		if err != nil {
			q.logger.Error("Failed to marshal shuffle order", "err", err)
		} else {
			shuffleOrderJSON = sql.NullString{String: string(data), Valid: true}
		}
	}

	sourcePlaylistID := sql.NullInt64{}
	if q.sourcePlaylistID > 0 {
		sourcePlaylistID = sql.NullInt64{Int64: q.sourcePlaylistID, Valid: true}
	}

	err := q.db.Queries.UpdateQueueState(q.db.Ctx, sqlcgen.UpdateQueueStateParams{
		SourcePlaylistID: sourcePlaylistID,
		CurrentPosition:  int64(q.currentIndex),
		ShuffleMode:      q.shuffleMode,
		RepeatMode:       string(q.repeatMode),
		ShuffleOrder:     shuffleOrderJSON,
	})
	if err != nil {
		q.logger.Error("Failed to persist queue state", "err", err)
	}
}

// emitQueueChanged emits the full queue state to the frontend.
func (q *Queue) emitQueueChanged() {
	if q.ctx == nil {
		return
	}

	state := State{
		Tracks:           q.tracks,
		CurrentIndex:     q.currentIndex,
		ShuffleMode:      q.shuffleMode,
		RepeatMode:       q.repeatMode,
		SourcePlaylistID: q.sourcePlaylistID,
	}

	// Ensure tracks is never nil in JSON.
	if state.Tracks == nil {
		state.Tracks = []Track{}
	}

	runtime.EventsEmit(q.ctx, events.QueueChanged, state)
}

// Sentinel errors.
var (
	ErrEmptyQueue = errors.New("queue is empty")
	ErrNoPlayer   = errors.New("no player set")
)