beginning of reworking playback to use a command queue

backend/playbackcommands.go

@@ -0,0 +1,102 @@
+package backend
+
+import (
+	"slices"
+	"sync"
+)
+
+type PlaybackCommandType int
+
+const (
+	CmdStop PlaybackCommandType = iota
+	CmdContinue
+	CmdPause
+	CmdPlayTrackAt
+	CmdSeekSeconds
+	CmdSeekFwdBackN
+	CmdVolume
+	CmdLoopMode
+)
+
+type PlaybackCommand struct {
+	Type PlaybackCommandType
+	Arg  any
+}
+
+type CommandQueue struct {
+	mutex        sync.Mutex
+	queue        []PlaybackCommand
+	cmdAvailable *sync.Cond
+	nextChan     chan (PlaybackCommand)
+}
+
+func NewCommandQueue() *CommandQueue {
+	c := &CommandQueue{}
+	c.cmdAvailable = sync.NewCond(&c.mutex)
+	go c.chanWriter()
+	return c
+}
+
+func (c *CommandQueue) C() <-chan PlaybackCommand {
+	return c.nextChan
+}
+
+func (c *CommandQueue) Stop() {
+	c.filterCommandsAndAdd([]PlaybackCommandType{CmdContinue, CmdPause, CmdStop},
+		PlaybackCommand{Type: CmdStop})
+}
+
+func (c *CommandQueue) Continue() {
+	c.filterCommandsAndAdd([]PlaybackCommandType{CmdContinue, CmdPause, CmdStop},
+		PlaybackCommand{Type: CmdContinue})
+}
+
+func (c *CommandQueue) Pause() {
+	c.filterCommandsAndAdd([]PlaybackCommandType{CmdContinue, CmdPause, CmdStop},
+		PlaybackCommand{Type: CmdPause})
+}
+
+func (c *CommandQueue) Volume(vol int) {
+	c.filterCommandsAndAdd([]PlaybackCommandType{CmdVolume},
+		PlaybackCommand{Type: CmdVolume, Arg: vol})
+}
+
+func (c *CommandQueue) LoopMode(mode LoopMode) {
+	c.filterCommandsAndAdd([]PlaybackCommandType{CmdLoopMode},
+		PlaybackCommand{Type: CmdLoopMode, Arg: mode})
+}
+
+func (c *CommandQueue) SeekSeconds(s float64) {
+	c.filterCommandsAndAdd([]PlaybackCommandType{CmdVolume},
+		PlaybackCommand{Type: CmdSeekSeconds, Arg: s})
+}
+
+func (c *CommandQueue) filterCommandsAndAdd(excludeTypes []PlaybackCommandType, command PlaybackCommand) {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+
+	j := 0
+	for _, cmd := range c.queue {
+		if slices.Contains(excludeTypes, cmd.Type) {
+			continue
+		}
+		c.queue[j] = cmd
+		j++
+	}
+	c.queue = c.queue[:j]
+	c.queue = append(c.queue, command)
+}
+
+func (c *CommandQueue) chanWriter() {
+	for {
+		c.mutex.Lock()
+		for len(c.queue) == 0 {
+			c.cmdAvailable.Wait()
+		}
+		cmd := c.queue[0]
+		copy(c.queue, c.queue[1:])
+		c.queue = c.queue[:len(c.queue)-1]
+		c.mutex.Unlock()
+		c.nextChan <- cmd
+	}
+}