Do not alter Song struct listeners with its methods, use a ListenerCounter to populate Listeners and MaxListeners. Eliminates the need for a mutex and SetFrom(), UpdateMaxListeners() and IncListeners() methods.

internal/radio/song.go

@@ -2,50 +2,20 @@ package radio
 
 import (
 	"encoding/json"
-	"sync"
 	"time"
 )
 
 type Song struct {
-	mutex        sync.Mutex
 	Artist       string
 	Title        string
+	StartAt      time.Time
 	Duration     time.Duration
 	Listeners    int64
 	MaxListeners int64
-	StartAt      time.Time
-}
-
-func (s *Song) SetFrom(os *Song) {
-	s.mutex.Lock()
-	s.Artist = os.Artist
-	s.Title = os.Title
-	s.Duration = os.Duration
-	s.Listeners = os.Listeners
-	s.MaxListeners = os.MaxListeners
-	s.StartAt = os.StartAt
-	s.mutex.Unlock()
-}
-
-func (s *Song) UpdateMaxListeners(listeners int64) {
-	s.mutex.Lock()
-	if listeners > s.MaxListeners {
-		s.MaxListeners = listeners
-	}
-	s.mutex.Unlock()
-}
-
-// IncListeners increments by one an overall amount of listeners of this song.
-func (s *Song) IncListeners() {
-	s.mutex.Lock()
-	s.Listeners++
-	s.mutex.Unlock()
 }
 
 // DurationString returns song's duration as a string formatted as [H:]M:SS.
 func (s *Song) DurationString() string {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
 	if s.Duration.Hours() >= 1 {
 		return time.UnixMilli(s.Duration.Milliseconds()).Format("3:4:05")
 	}
@@ -53,8 +23,6 @@ func (s *Song) DurationString() string {
 }
 
 func (s *Song) MarshalJSON() ([]byte, error) {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
 	return json.Marshal(&struct {
 		Artist       string `json:"artist"`
 		Title        string `json:"title"`