fix(ui): show effective dB of track when playing (#3293)

* show effective db of track when playing

* tests

ui/src/utils/calculateReplayGain.js

@@ -0,0 +1,31 @@
+const calculateReplayGain = (preAmp, gain, peak) => {
+  if (gain === undefined || peak === undefined) {
+    return 1
+  }
+
+  // https://wiki.hydrogenaud.io/index.php?title=ReplayGain_1.0_specification&section=19
+  // Normalized to max gain
+  return Math.min(10 ** ((gain + preAmp) / 20), 1 / peak)
+}
+
+export const calculateGain = (gainInfo, song) => {
+  switch (gainInfo.gainMode) {
+    case 'album': {
+      return calculateReplayGain(
+        gainInfo.preAmp,
+        song.rgAlbumGain,
+        song.rgAlbumPeak,
+      )
+    }
+    case 'track': {
+      return calculateReplayGain(
+        gainInfo.preAmp,
+        song.rgTrackGain,
+        song.rgTrackPeak,
+      )
+    }
+    default: {
+      return 1
+    }
+  }
+}