got bulk of player api

backend/player/volume.go

@@ -0,0 +1,30 @@
+package player
+
+type UserVolume int
+type PlayerVolume float64
+
+const MinUserVol UserVolume = 0
+const MaxUserVol UserVolume = 100
+
+const MinPlayerVol PlayerVolume = -10
+const MaxPlayerVol PlayerVolume = 10
+
+func (oldVol UserVolume) ToPlayerVolume() PlayerVolume {
+	var newVol PlayerVolume
+
+	if oldVol >= MinUserVol && oldVol <= MaxUserVol {
+		ratio := PlayerVolume(oldVol-MinUserVol) / PlayerVolume(MaxUserVol-MinUserVol)
+		newVol = ratio*(MaxPlayerVol-MinPlayerVol) + MinPlayerVol
+	}
+	return newVol
+}
+
+func (oldVolFloat PlayerVolume) ToUserVolume() UserVolume {
+	var newVol UserVolume
+
+	if oldVolFloat >= MinPlayerVol && oldVolFloat <= MaxPlayerVol {
+		ratio := (oldVolFloat - MinPlayerVol) / (MaxPlayerVol - MinPlayerVol)
+		newVol = UserVolume(ratio*PlayerVolume(MaxUserVol-MinUserVol)) + MinUserVol
+	}
+	return newVol
+}