segmento/pkg/playlist/playlist.go

package playlist

import (
	"fmt"
	"io"
	"segmento/pkg/media"
	"time"
)

const DefaultMaxSegments = 10

type PlaylistSegment struct {
	media.Segment
	url   string
	seqId int
}

type Playlist interface {
	Len() int
	AddConsumer(c Consumer)
	RemoveConsumer(c Consumer) error
}

type Consumer interface {
	PlaylistUpdated(p Playlist)
	PlaylistSegmentAdded(p Playlist, s *PlaylistSegment)
}

// so we know that we can publish a segment (i.e. make available a URL to access it from elsewhere)
// but what does it mean to publish a Playlist?
// A playlist contains lists of Segments but it wouldn't necessarily be published in the same location
// for example, Segments may be published to S3 but a playlist may be published periodically to a static
// hosting location elsewhere.

type MediaPlaylist struct {
	nextSeqId int
	src       io.Reader              // read a stream of bytes e.g. MP3
	segmenter media.Segmenter        // segment the incoming bytes. For now, up to the caller to provider a matching src and segmenter.
	publisher media.SegmentPublisher // publish the segments somewhere (i.e. make available a URL with them)
	segments  []*PlaylistSegment     // a slice of the last n segments
	consumers map[Consumer]bool
}

func NewMediaPlaylist(src io.Reader, segmenter media.Segmenter, publisher media.SegmentPublisher) *MediaPlaylist {
	p := MediaPlaylist{
		src:       src,
		segmenter: segmenter,
		publisher: publisher,
		segments:  make([]*PlaylistSegment, 0, 10),
		consumers: make(map[Consumer]bool),
	}
	return &p
}

func (p *MediaPlaylist) Len() int {
	return len(p.segments)
}

func (p *MediaPlaylist) AddConsumer(c Consumer) {
	p.consumers[c] = true
}

func (p *MediaPlaylist) RemoveConsumer(c Consumer) error {
	delete(p.consumers, c)
	return nil
}

func (p *MediaPlaylist) Run() error {
	segments, err := p.segmenter.Segment(p.src)
	if err != nil {
		return err
	}

	for s := range segments {
		if err = p.handleSegment(s); err != nil {
			return err
		}
	}

	return nil
}

func (p *MediaPlaylist) handleSegment(s *media.Segment) error {
	// first, publish the segment:
	url, err := p.publisher.Publish(s)
	if err != nil {
		return err
	}

	// initialize a new playlist segment:
	nextSeqId := p.nextSeqId
	p.nextSeqId++
	ps := PlaylistSegment{
		Segment: *s, // TODO make the Segmenter publish values, not pointers
		seqId:   nextSeqId,
		url:     url,
	}

	// append the playlist segment to our slice of segments:
	p.segments = append(p.segments, &ps)

	// trim the start of the playlist if needed:
	if len(p.segments) > DefaultMaxSegments {
		p.segments = p.segments[len(p.segments)-DefaultMaxSegments:]
	}

	for c, _ := range p.consumers {
		c.PlaylistSegmentAdded(p, &ps)
	}

	return nil
}

func (p *MediaPlaylist) Render() string {
	var r string
	r += "#EXTM3U\n"
	r += "#EXT-X-VERSION:3\n"
	r += "#EXT-X-TARGETDURATION:3\n" // TODO
	for _, s := range p.segments {
		r += fmt.Sprintf("#EXTINF:%.05f\n", float32(s.Duration())/float32(time.Second))
		r += "http://www.example.com/x.mp3\n"
	}
	r += "#EXT-X-ENDLIST"
	return r
}