Implemented lastPlayedSong() function that retrieves one song from a playlist.log file that doesn't run external commands for it.

And now we start with an empty list.

internal/radio/icecast.go

@@ -1,11 +1,12 @@
 package radio
 
 import (
+	"bytes"
 	"dwelling-radio/pkg/watcher"
 	"encoding/json"
-	"fmt"
+	"io"
 	"net/http"
-	"os/exec"
+	"os"
 	"strings"
 	"sync"
 	"syscall"
@@ -17,6 +18,8 @@ import (
 const (
 	IcecastPlaylistDateFormat = "02/Jan/2006:15:04:05 -0700"
 	SongTimeFormat            = "2006 15:04-0700"
+
+	bufferSize = 8192
 )
 
 type IcecastStatusDTO struct {
@@ -85,7 +88,7 @@ func IcecastLastPlayedSongs(lastNSongs int, playlistPath string) ([]Song, error)
 		}
 	}
 
-	return lastPlayedSongs(lastNSongs, playlistPath)
+	return make([]Song, 0), nil
 }
 
 func IcecastLastSong(playlistPath string) (Song, error) {
@@ -97,45 +100,65 @@ func IcecastLastSong(playlistPath string) (Song, error) {
 		}
 	}
 
-	songs, err := lastPlayedSongs(1, playlistPath)
-	if len(songs) == 0 {
-		return Song{}, nil
-	}
-
-	return songs[0], err
-}
-
-func lastPlayedSongs(lastNSongs int, playlistPath string) ([]Song, error) {
-	songs := make([]Song, 0)
-
-	cmd := fmt.Sprintf("tail -n%d %s | head -n-1 | cut -d'|' -f1,3,4", lastNSongs+1, playlistPath)
-	out, err := exec.Command("bash", "-c", cmd).CombinedOutput()
+	song, err := lastPlayedSong(playlistPath)
 	if err != nil {
-		return songs, err
+		return Song{}, err
 	}
 
-	if len(out) == 0 {
-		return songs, nil
+	return *song, nil
 }
 
-	for _, song := range strings.Split(string(out), "\n") {
-		ts := strings.Split(song, "|")
-		if len(ts) <= 1 {
-			continue
+func lastPlayedSong(playlistPath string) (*Song, error) {
+	buf := make([]byte, bufferSize)
+	var last_song_line string
+
+	playlist, err := os.Open(playlistPath)
+	if err != nil {
+		return nil, err
 	}
-		tim, _ := time.Parse(IcecastPlaylistDateFormat, ts[0])
-		songs = append(songs, Song{
+
+	playlist_stat, _ := playlist.Stat()
+
+	if playlist_stat.Size() == 0 {
+		return nil, nil
+	}
+
+	playlist.Seek(-bufferSize, os.SEEK_END)
+
+	_, err = playlist.Read(buf)
+	if err != nil && err != io.EOF {
+		return nil, err
+	}
+
+	newline_end_pos := bytes.LastIndexByte(buf, '\n')
+
+	if newline_end_pos == -1 && !bytes.ContainsRune(buf, '|') {
+		return nil, nil
+	} else if newline_end_pos == -1 {
+		newline_end_pos = len(buf)
+	}
+
+	newline_start_pos := bytes.LastIndexByte(buf[:newline_end_pos-1], '\n')
+
+	last_song_line = string(buf[newline_start_pos+1 : newline_end_pos-1])
+
+	if strings.Count(last_song_line, "|") != 3 {
+		return nil, nil
+	}
+
+	fields := strings.Split(last_song_line, "|")
+
+	tim, _ := time.Parse(IcecastPlaylistDateFormat, fields[0])
+
+	return &Song{
 		Time:      tim.Format(SongTimeFormat),
-			Listeners: ts[1],
-			Song:      ts[2]})
-	}
-
-	return songs, nil
+		Listeners: fields[2],
+		Song:      fields[3]}, nil
 }
 
 var playlistWatcher watcher.InotifyWatcher
 var playlistFired chan uint32 = make(chan uint32)
-var lastPlayedCache []Song
+var lastPlayedCache []Song = make([]Song, 10)
 var lastPlayedCacheMutex sync.Mutex
 
 func IcecastWatchPlaylist(playlistPath string, lastNSongs int) error {
@@ -157,9 +180,11 @@ func IcecastWatchPlaylist(playlistPath string, lastNSongs int) error {
 			case mask := <-playlistFired:
 				if mask&syscall.IN_MODIFY > 0 {
 					lastPlayedCacheMutex.Lock()
-					songs, err := lastPlayedSongs(lastNSongs, playlistPath)
-					if err == nil && len(songs) > 0 {
-						lastPlayedCache = songs
+					if song, err := lastPlayedSong(playlistPath); err == nil {
+						lastPlayedCache = append(lastPlayedCache, *song)
+						if len(lastPlayedCache) > lastNSongs {
+							lastPlayedCache = lastPlayedCache[1:]
+						}
 					}
 					lastPlayedCacheMutex.Unlock()
 				} else if mask&syscall.IN_IGNORED > 0 {
@@ -171,13 +196,6 @@ func IcecastWatchPlaylist(playlistPath string, lastNSongs int) error {
 		}
 	}()
 
-	lastPlayedCacheMutex.Lock()
-	songs, err := lastPlayedSongs(lastNSongs, playlistPath)
-	if err == nil && len(songs) > 0 {
-		lastPlayedCache = songs
-	}
-	lastPlayedCacheMutex.Unlock()
-
 	return nil
 }