Add support for the jukebox endpoint

This supports most of jukeboxControl.view as far as i can tell. Things
seem to be playing ok without freaking out

I've also only tested it a little bit with ultrasonic but it does
appear to be working pretty well

jukebox/jukebox.go

@@ -0,0 +1,192 @@
+package jukebox
+
+import (
+	"os"
+	"path"
+	"sync"
+	"time"
+
+	"github.com/faiface/beep"
+	"github.com/faiface/beep/flac"
+	"github.com/faiface/beep/mp3"
+	"github.com/faiface/beep/speaker"
+	"go.senan.xyz/gonic/db"
+	"go.senan.xyz/gonic/server/ctrlsubsonic/spec"
+)
+
+type strmInfo struct {
+	ctrlStrmr beep.Ctrl
+	strm      beep.StreamSeekCloser
+	format    beep.Format
+}
+
+type Jukebox struct {
+	playlist []*db.Track
+	index    int
+	playing  bool
+	// used to notify the player to re read the members
+	updates chan struct{}
+	done    chan bool
+	info    *strmInfo
+	sync.Mutex
+}
+
+func (j *Jukebox) Init(musicPath string) error {
+	j.updates = make(chan struct{})
+	sr := beep.SampleRate(48000)
+	err := speaker.Init(sr, sr.N(time.Second/2))
+	if err != nil {
+		return err
+	}
+	j.done = make(chan bool)
+	go func() {
+		for range j.updates {
+			var streamer beep.Streamer
+			var format beep.Format
+			f, err := os.Open(path.Join(musicPath, j.playlist[j.index].RelPath()))
+			if err != nil {
+				j.index++
+				continue
+			}
+			switch j.playlist[j.index].Ext() {
+			case "mp3":
+				streamer, format, err = mp3.Decode(f)
+			case "flac":
+				streamer, format, err = flac.Decode(f)
+			default:
+				j.index++
+				continue
+			}
+			if err != nil {
+				j.index++
+				continue
+			}
+			if j.playing {
+				j.Lock()
+				{
+					j.info = &strmInfo{}
+					j.info.strm = streamer.(beep.StreamSeekCloser)
+					j.info.ctrlStrmr.Streamer = beep.Resample(4, format.SampleRate, sr, j.info.strm)
+					j.info.format = format
+				}
+				j.Unlock()
+				speaker.Play(beep.Seq(&j.info.ctrlStrmr, beep.Callback(func() {
+					j.done <- false
+				})))
+				if v := <-j.done; !v {
+					j.index++
+					j.Lock()
+					if j.index > len(j.playlist) {
+						j.index = 0
+						j.playing = false
+					}
+					j.Unlock()
+					// in a go routine as otherwise this hangs as the
+					go func() {
+						j.updates <- struct{}{}
+					}()
+				} else {
+					continue
+				}
+			}
+		}
+	}()
+	return nil
+}
+
+func (j *Jukebox) SetTracks(tracks []*db.Track) {
+	j.Lock()
+	j.index = 0
+	j.playing = true
+	if len(j.playlist) > 0 {
+		j.done <- true
+		j.playlist = []*db.Track{}
+		speaker.Clear()
+	}
+	j.playlist = tracks
+	j.Unlock()
+	j.updates <- struct{}{}
+}
+
+func (j *Jukebox) AddTracks(tracks []*db.Track) {
+	j.Lock()
+	j.playlist = append(j.playlist, tracks...)
+	j.Unlock()
+}
+
+func (j *Jukebox) ClearTracks() {
+	j.Lock()
+	j.index = 0
+	j.playing = false
+	j.playlist = []*db.Track{}
+	j.Unlock()
+}
+
+func (j *Jukebox) RemoveTrack(i int) {
+	j.Lock()
+	defer j.Unlock()
+	if i < 0 || i > len(j.playlist) {
+		return
+	}
+	j.playlist = append(j.playlist[:i], j.playlist[i+1:]...)
+}
+
+func (j *Jukebox) Status() *spec.JukeboxStatus {
+	position := 0
+	if j.info != nil {
+		length := j.info.format.SampleRate.D(j.info.strm.Position())
+		position = int(length.Round(time.Millisecond).Seconds())
+	}
+	return &spec.JukeboxStatus{
+		CurrentIndex: j.index,
+		Playing:      j.playing,
+		Gain:         0.9,
+		Position:     position,
+	}
+}
+
+func (j *Jukebox) GetTracks() *spec.JukeboxPlaylist {
+	j.Lock()
+	defer j.Unlock()
+	jb := &spec.JukeboxPlaylist{}
+	jb.List = make([]*spec.TrackChild, len(j.playlist))
+	for i, track := range j.playlist {
+		jb.List[i] = spec.NewTrackByTags(track, track.Album)
+	}
+	jb.CurrentIndex = j.index
+	jb.Playing = j.playing
+	jb.Gain = 0.9
+	jb.Position = 0
+	if j.info != nil {
+		length := j.info.format.SampleRate.D(j.info.strm.Position())
+		jb.Position = int(length.Round(time.Millisecond).Seconds())
+	}
+	return jb
+}
+
+func (j *Jukebox) Stop() {
+	j.Lock()
+	j.playing = false
+	j.info.ctrlStrmr.Paused = true
+	j.Unlock()
+}
+
+func (j *Jukebox) Start() {
+	j.Lock()
+	j.playing = false
+	j.info.ctrlStrmr.Paused = false
+	j.Unlock()
+}
+
+func (j *Jukebox) Skip(i int, skipCurrent bool) {
+	j.Lock()
+	if skipCurrent {
+		j.index++
+	} else {
+		j.index = i
+	}
+	speaker.Clear()
+	j.done <- true
+	j.updates <- struct{}{}
+	j.Unlock()
+}