dwelling-radio/internal/radio/song.go

package radio

import (
	"encoding/json"
	"sync"
	"time"
)

// Song_ stores artist and title of a song, a timestamp of when it started, and
// a maximum number of listeners.
type Song_ struct {
	Artist       string
	Title        string
	Duration     time.Duration
	MaxListeners int
	StartAt      time.Time
}

func (s *Song_) ArtistTitle() string {
	return s.Artist + " - " + s.Title
}

func (s *Song_) MarshalJSON() ([]byte, error) {
	return json.Marshal(&struct {
		Artist       string `json:"artist"`
		Title        string `json:"title"`
		Duration     int64  `json:"duration_milliseconds"`
		MaxListeners int    `json:"listeners"`
		StartAt      string `json:"start_at"`
	}{
		Artist:       s.Artist,
		Title:        s.Title,
		Duration:     s.Duration.Milliseconds(),
		MaxListeners: s.MaxListeners,
		StartAt:      s.StartAt.UTC().Format(time.RFC3339)})
}

type SongList struct {
	mut        sync.Mutex
	current    Song_
	lastSongs  []Song_
	listMaxLen int
}

func NewSongList(length int) *SongList {
	return &SongList{listMaxLen: length, lastSongs: make([]Song_, 0, length)}
}

// Add a new song that is currently playing and update a list.
func (sl *SongList) Add(newSong Song_) {
	sl.mut.Lock()
	defer sl.mut.Unlock()

	if sl.current.StartAt.Year() == 1 {
		sl.current = newSong
		return
	}

	if len(sl.lastSongs) == sl.listMaxLen {
		sl.lastSongs = append(sl.lastSongs[1:], sl.current)
	} else {
		sl.lastSongs = append(sl.lastSongs, sl.current)
	}

	sl.current = newSong
}

// Current returns a current playing song.
func (sl *SongList) Current() *Song_ {
	sl.mut.Lock()
	defer sl.mut.Unlock()
	if sl.current.StartAt.Year() == 1 {
		return nil
	}
	return &sl.current
}

// List returns a list of lastly played songs.
func (sl *SongList) List() []Song_ {
	sl.mut.Lock()
	defer sl.mut.Unlock()
	return sl.lastSongs
}