fix(ui): treat null ReplayGain values as missing

The native API sends absent album gain as null, so the album fallback
never ran for library songs. A missing peak no longer drops the gain,
which keeps R128 files without peak tags normalized.

Signed-off-by: junkerderprovinz <jdp@braethoria.com>

ui/src/utils/calculateReplayGain.js

@@ -1,20 +1,19 @@
 const calculateReplayGain = (preAmp, gain, peak) => {
-  if (gain === undefined || peak === undefined) {
+  if (gain == null) {
     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)
+  const replayGain = 10 ** ((gain + preAmp) / 20)
+  return peak == null ? replayGain : Math.min(replayGain, 1 / peak)
 }
 
 export const calculateGain = (gainInfo, song) => {
   switch (gainInfo.gainMode) {
     case 'album': {
-      // Fall back to track gain when the album gain is missing (singles, or
-      // tracks without album ReplayGain tags), matching common ReplayGain
-      // players instead of applying no adjustment at all.
-      if (song.rgAlbumGain === undefined || song.rgAlbumPeak === undefined) {
+      // Singles and untagged albums have no album gain, so use the track gain.
+      if (song.rgAlbumGain == null) {
         return calculateReplayGain(
           gainInfo.preAmp,
           song.rgTrackGain,

ui/src/utils/calculateReplayGain.test.js

@@ -14,6 +14,12 @@ describe('calculateGain', () => {
     rgTrackGain: -3,
     rgTrackPeak: 1,
   }
+  const nativeTrackOnlySong = {
+    rgAlbumGain: null,
+    rgAlbumPeak: null,
+    rgTrackGain: -3,
+    rgTrackPeak: 1,
+  }
   const noGainSong = {}
 
   it('uses album gain in album mode when it is present', () => {
@@ -23,12 +29,28 @@ describe('calculateGain', () => {
 
   it('falls back to track gain in album mode when the album gain is missing', () => {
     const result = calculateGain({ gainMode: 'album', preAmp }, trackOnlySong)
-    // Without the fallback this returned 1 (no adjustment). It should now use
-    // the track gain instead.
     expect(result).toBeCloseTo(10 ** (-3 / 20))
-    expect(result).not.toBe(1)
   })
 
+  it('falls back to track gain in album mode when the album gain is null', () => {
+    const result = calculateGain(
+      { gainMode: 'album', preAmp },
+      nativeTrackOnlySong,
+    )
+    expect(result).toBeCloseTo(10 ** (-3 / 20))
+  })
+
+  it.each([null, undefined])(
+    'keeps the album gain in album mode when the album peak is %s',
+    (rgAlbumPeak) => {
+      const result = calculateGain(
+        { gainMode: 'album', preAmp },
+        { ...albumSong, rgAlbumPeak },
+      )
+      expect(result).toBeCloseTo(10 ** (-6 / 20))
+    },
+  )
+
   it('returns 1 in album mode when neither album nor track gain is present', () => {
     const result = calculateGain({ gainMode: 'album', preAmp }, noGainSong)
     expect(result).toBe(1)
@@ -39,6 +61,17 @@ describe('calculateGain', () => {
     expect(result).toBeCloseTo(10 ** (-3 / 20))
   })
 
+  it.each([null, undefined])(
+    'keeps the track gain in track mode when the track peak is %s',
+    (rgTrackPeak) => {
+      const result = calculateGain(
+        { gainMode: 'track', preAmp },
+        { ...albumSong, rgTrackPeak },
+      )
+      expect(result).toBeCloseTo(10 ** (-3 / 20))
+    },
+  )
+
   it('returns 1 when gain is disabled', () => {
     const result = calculateGain({ gainMode: 'none', preAmp }, albumSong)
     expect(result).toBe(1)