dwelling-radio/internal/radio/icecast.go

package radio

import (
	"bytes"
	"dwelling-radio/pkg/watcher"
	"encoding/json"
	"io"
	"net/http"
	"os"
	"sync"
	"syscall"
	"time"

	"github.com/pkg/errors"
)

const (
	IcecastPlaylistDateFormat = "02/Jan/2006:15:04:05 -0700"
	SongTimeFormat            = "2006 15:04-0700"

	bufferSize = 16384
)

var (
	lastPlayedCache      []Song
	lastPlayedCacheMutex sync.Mutex
)

type IcecastStatusDTO struct {
	Icestats struct {
		ServerStartISO8601 string `json:"server_start_iso8601"`
		ServerStartDate    string `json:"server_start"`
		Source             struct {
			Artist       string `json:"artist"`
			Title        string `json:"title"`
			ListenerPeak int    `json:"listener_peak"`
			Listeners    int    `json:"listeners"`
		} `json:"source"`
	} `json:"icestats"`
}

func (is *IcecastStatusDTO) SongName() string {
	return is.Icestats.Source.Artist + " - " + is.Icestats.Source.Title
}

type IcecastStatus struct {
	ServerStartISO8601 string `json:"server_start_iso8601"`
	ServerStartDate    string `json:"server_start_date"`
	SongName           string `json:"song"`
	ListenerPeak       int    `json:"listener_peak"`
	Listeners          int    `json:"listeners"`
}

type Song struct {
	Time      string `json:"time"`
	Listeners string `json:"listeners"`
	Song      string `json:"song"`
}

func IcecastGetStatus(icecastURL string) (*IcecastStatus, error) {
	resp, err := http.Get(icecastURL)
	if err != nil {
		return nil, err
	}

	iceStatDTO := &IcecastStatusDTO{}

	if err := json.NewDecoder(resp.Body).Decode(iceStatDTO); err != nil {
		return nil, err
	}

	return &IcecastStatus{
		ServerStartISO8601: iceStatDTO.Icestats.ServerStartISO8601,
		ServerStartDate:    iceStatDTO.Icestats.ServerStartDate,
		SongName:           iceStatDTO.SongName(),
		ListenerPeak:       iceStatDTO.Icestats.Source.ListenerPeak,
		Listeners:          iceStatDTO.Icestats.Source.Listeners,
	}, nil
}

func IcecastLastPlayedSongs(lastNSongs int, playlistPath string) ([]Song, error) {
	{
		lastPlayedCacheMutex.Lock()
		defer lastPlayedCacheMutex.Unlock()
		if lpcLen := len(lastPlayedCache); lpcLen > 0 {
			if lastNSongs > lpcLen {
				lastNSongs = lpcLen
			}
			var ret []Song = make([]Song, lastNSongs)
			copy(ret[:], lastPlayedCache[lpcLen-lastNSongs:])
			return ret, nil
		}
	}

	songs, err := icecastLastPlayedSongs(playlistPath, lastNSongs)
	if err != nil {
		return make([]Song, 0), err
	}

	return songs, nil
}

func IcecastLastSong(playlistPath string) (Song, error) {
	{
		lastPlayedCacheMutex.Lock()
		defer lastPlayedCacheMutex.Unlock()
		if lpcLen := len(lastPlayedCache); lpcLen > 0 {
			return lastPlayedCache[lpcLen-1], nil
		}
	}

	song, err := icecastLastPlayedSongs(playlistPath, 1)
	if err != nil {
		return Song{}, err
	}

	return song[0], nil
}

func icecastLastPlayedSongs(playlistPath string, n int) ([]Song, error) {
	songs := make([]Song, n)
	var buf []byte
	var offset int64 = 0

	playlist, err := os.Open(playlistPath)
	if err != nil {
		return nil, err
	}
	defer playlist.Close()

	playlist_stat, _ := playlist.Stat()

	if playlist_stat.Size() == 0 {
		return nil, nil
	}

	if playlist_stat.Size() < bufferSize {
		buf = make([]byte, playlist_stat.Size())
	} else {
		buf = make([]byte, bufferSize)
		offset = playlist_stat.Size() - bufferSize
	}

	_, err = playlist.ReadAt(buf, offset)
	if err != nil && err != io.EOF {
		return nil, err
	}

	lines := bytes.Split(buf, []byte("\n"))

	if len(lines) < 3 {
		return nil, nil
	}

	lines = lines[:len(lines)-2]

	if len(lines) > n {
		lines = lines[len(lines)-n:]
	}

	for _, line := range lines {
		fields := bytes.Split(line, []byte("|"))

		tim, _ := time.Parse(IcecastPlaylistDateFormat, string(fields[0]))

		songs = append(songs, Song{
			Time:      tim.Format(SongTimeFormat),
			Listeners: string(fields[2]),
			Song:      string(fields[3])})
	}

	return songs, nil
}

type PlaylistLogWatcher struct {
	watcher *watcher.InotifyWatcher
	changed chan uint32
}

func NewPlaylistLogWatcher() *PlaylistLogWatcher {
	return &PlaylistLogWatcher{changed: make(chan uint32)}
}

func (pw *PlaylistLogWatcher) Watch(playlistPath string, n int) (err error) {
	if pw.watcher != nil {
		pw.watcher.Close()
	}

	pw.watcher, err = watcher.NewInotifyWatcher()
	if err != nil {
		return errors.Wrap(err, "cannot instantiate inotify watcher")
	}

	err = pw.watcher.AddWatch(playlistPath, watcher.ModIgnMask)
	if err != nil {
		return errors.Wrap(err, "cannot set a playlist to watch")
	}

	pw.watcher.WatchForMask(pw.changed, watcher.ModIgnMask)

	go func() {
		for {
			select {
			case mask := <-pw.changed:
				if mask&syscall.IN_MODIFY > 0 {
					lastPlayedCacheMutex.Lock()
					if lastPlayedCache == nil {
						lastPlayedCache = make([]Song, n)
					}
					if songs, err := icecastLastPlayedSongs(playlistPath, 1); err == nil && len(songs) > 0 {
						if len(lastPlayedCache) == n {
							lastPlayedCache = append(lastPlayedCache[1:], songs...)
						} else {
							lastPlayedCache = append(lastPlayedCache, songs...)
						}
					}
					lastPlayedCacheMutex.Unlock()
				} else if mask&syscall.IN_IGNORED > 0 {
					pw.Close()
					pw.Watch(playlistPath, n)
					return
				}
			}
		}
	}()

	return nil
}

func (pw *PlaylistLogWatcher) Close() {
	pw.watcher.Close()
}