go-mxl-player/internal/playback/playlist_controller.go

package playback

import (
	"context"
	"errors"
	"sync"
)

type PlaylistController struct {
	playlist Playlist
	retry    RetryPolicy
	sessions chan<- SessionCommand

	mu          sync.RWMutex
	snapshot    PlaylistSnapshot
	hasSnapshot bool
}

type PlaylistSnapshot struct {
	State    PlaylistState
	Entry    PlaylistEntry
	Revision uint64
}

var (
	ErrNilSessionCommandChannel = errors.New("session-command channel is nil")
)

func NewPlaylistController(
	playlist Playlist,
	retry RetryPolicy,
	sessions chan<- SessionCommand,
) (*PlaylistController, error) {
	if err := playlist.Validate(); err != nil {
		return nil, err
	}
	if err := retry.Validate(); err != nil {
		return nil, err
	}
	if sessions == nil {
		return nil, ErrNilSessionCommandChannel
	}
	return &PlaylistController{
		playlist: playlist,
		retry:    retry,
		sessions: sessions,
	}, nil
}

func (c *PlaylistController) Run(
	ctx context.Context,
	commands <-chan PlaylistCommand,
) error {
	state := PlaylistState{}
	revision := uint64(0)
	c.publish(state, revision)

	for {
		select {
		case <-ctx.Done():
			return ctx.Err()

		case command, ok := <-commands:
			if !ok {
				return nil
			}

			next, sessionCommand, apply, err := ApplyPlaylistSelection(
				c.playlist,
				state,
				command,
				c.retry,
			)
			if err != nil {
				continue
			}
			if apply {
				select {
				case <-ctx.Done():
					return ctx.Err()
				case c.sessions <- sessionCommand:
				}
				revision++
			}

			state = next
			c.publish(state, revision)
		}
	}
}

func (c *PlaylistController) Snapshot() (PlaylistSnapshot, bool) {
	c.mu.RLock()
	defer c.mu.RUnlock()
	return c.snapshot, c.hasSnapshot
}

func (c *PlaylistController) publish(state PlaylistState, revision uint64) {
	entry, _ := state.Entry(c.playlist)

	c.mu.Lock()
	c.snapshot = PlaylistSnapshot{
		State:    state,
		Entry:    entry,
		Revision: revision,
	}
	c.hasSnapshot = true
	c.mu.Unlock()
}