settings: add the replay gain controls

Final slice: the screen that drives the mode and preamp preferences the
playback side already reads. Until now `setReplayGainMode` and
`setReplayGainPreampDb` had no production caller, so Off and the preamp
were unreachable.

- `SettingsViewModel` exposes both preferences and writes them back.
- The Playback section gains a "Replay gain" row opening an Off / Track /
  Album choice, and a "Preamp" row opening a slider across the +-15 dB
  range in 0.5 dB steps.
- `ReplayGainMode` is ordered Off, Track, Album so the choice list reads
  that way; the stored value is the name, so the order is not persisted
  and the default is still Track.
- The labels live in their own file so the signed decibel formatting can
  be tested, as `formatTrackTime` does.

app/src/main/kotlin/com/subtracks/data/prefs/UserPreferences.kt

@@ -57,7 +57,7 @@ const val MAX_REPLAY_GAIN_PREAMP_DB = 15f
 
 enum class SyncMode { Off, WifiOnly, Always }
 
-enum class ReplayGainMode { Track, Album, Off }
+enum class ReplayGainMode { Off, Track, Album }
 
 data class ArtworkSeedValue(
     val cacheKey: String,

app/src/main/kotlin/com/subtracks/ui/settings/ReplayGainLabels.kt

@@ -0,0 +1,23 @@
+package com.subtracks.ui.settings
+
+import android.content.res.Resources
+import com.subtracks.R
+import com.subtracks.data.prefs.ReplayGainMode
+
+internal fun replayGainModeLabel(
+    resources: Resources,
+    mode: ReplayGainMode,
+): String =
+    when (mode) {
+        ReplayGainMode.Off -> resources.getString(R.string.settings_replay_gain_mode_off)
+        ReplayGainMode.Track -> resources.getString(R.string.settings_replay_gain_mode_track)
+        ReplayGainMode.Album -> resources.getString(R.string.settings_replay_gain_mode_album)
+    }
+
+internal fun replayGainPreampLabel(
+    resources: Resources,
+    decibels: Float,
+): String {
+    val sign = if (decibels > 0f) "+" else ""
+    return resources.getString(R.string.settings_replay_gain_preamp_value, "$sign$decibels")
+}

app/src/main/kotlin/com/subtracks/ui/settings/SettingsScreen.kt

@@ -39,6 +39,7 @@ import androidx.compose.material3.ListItemDefaults
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.RadioButton
 import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Slider
 import androidx.compose.material3.Switch
 import androidx.compose.material3.SwitchDefaults
 import androidx.compose.material3.Text
@@ -46,6 +47,7 @@ import androidx.compose.material3.TextButton
 import androidx.compose.material3.TopAppBar
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableFloatStateOf
 import androidx.compose.runtime.mutableIntStateOf
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
@@ -66,6 +68,9 @@ import com.subtracks.BuildConfig
 import com.subtracks.R
 import com.subtracks.data.model.Source
 import com.subtracks.data.prefs.DEFAULT_SYNC_INTERVAL_MINUTES
+import com.subtracks.data.prefs.MAX_REPLAY_GAIN_PREAMP_DB
+import com.subtracks.data.prefs.MIN_REPLAY_GAIN_PREAMP_DB
+import com.subtracks.data.prefs.ReplayGainMode
 import com.subtracks.data.prefs.StreamQuality
 import com.subtracks.data.prefs.SyncMode
 import com.subtracks.log.Log
@@ -84,7 +89,16 @@ private val streamFormats = listOf(null, "mp3", "opus", "ogg", "webm", "aac", "f
 private const val PROJECT_HOMEPAGE = "https://github.com/austinried/subtracks"
 private const val SUPPORT_URL = "https://ko-fi.com/austinried"
 
-private enum class SettingsDialog { WifiQuality, MobileQuality, DownloadQuality, SyncConcurrency, SyncInterval, SyncMode }
+private enum class SettingsDialog {
+    WifiQuality,
+    MobileQuality,
+    DownloadQuality,
+    SyncConcurrency,
+    SyncInterval,
+    SyncMode,
+    ReplayGain,
+    ReplayGainPreamp,
+}
 
 @Composable
 fun SettingsRoute(
@@ -108,6 +122,8 @@ fun SettingsRoute(
     val scrobbling by viewModel.scrobbling.collectAsStateWithLifecycle()
     val offline by viewModel.offline.collectAsStateWithLifecycle()
     val verboseLogging by viewModel.verboseLogging.collectAsStateWithLifecycle()
+    val replayGainMode by viewModel.replayGainMode.collectAsStateWithLifecycle()
+    val replayGainPreamp by viewModel.replayGainPreamp.collectAsStateWithLifecycle()
     val context = LocalContext.current
     val scope = rememberCoroutineScope()
     SettingsScreen(
@@ -121,6 +137,8 @@ fun SettingsRoute(
         downloadQuality = downloadQuality,
         downloadOverMetered = downloadOverMetered,
         scrobbling = scrobbling,
+        replayGainMode = replayGainMode,
+        replayGainPreamp = replayGainPreamp,
         offline = offline,
         verboseLogging = verboseLogging,
         onSelectSource = viewModel::selectSource,
@@ -133,6 +151,8 @@ fun SettingsRoute(
         onDownloadQualityChange = viewModel::setDownloadQuality,
         onDownloadOverMeteredChange = viewModel::setDownloadOverMetered,
         onScrobblingChange = viewModel::setScrobbling,
+        onReplayGainModeChange = viewModel::setReplayGainMode,
+        onReplayGainPreampChange = viewModel::setReplayGainPreamp,
         onOfflineChange = viewModel::setOfflineMode,
         onVerboseLoggingChange = viewModel::setVerboseLogging,
         onAddServer = onAddServer,
@@ -176,6 +196,8 @@ fun SettingsScreen(
     verboseLogging: Boolean = false,
     syncMode: SyncMode = SyncMode.WifiOnly,
     syncInterval: Int = DEFAULT_SYNC_INTERVAL_MINUTES,
+    replayGainMode: ReplayGainMode = ReplayGainMode.Track,
+    replayGainPreamp: Float = 0f,
     onSelectSource: (Long) -> Unit,
     onEditServer: (Long) -> Unit,
     onWifiQualityChange: (StreamQuality) -> Unit,
@@ -186,6 +208,8 @@ fun SettingsScreen(
     onDownloadQualityChange: (StreamQuality) -> Unit,
     onDownloadOverMeteredChange: (Boolean) -> Unit,
     onScrobblingChange: (Boolean) -> Unit,
+    onReplayGainModeChange: (ReplayGainMode) -> Unit = {},
+    onReplayGainPreampChange: (Float) -> Unit = {},
     onOfflineChange: (Boolean) -> Unit = {},
     onVerboseLoggingChange: (Boolean) -> Unit = {},
     onAddServer: () -> Unit,
@@ -337,6 +361,23 @@ fun SettingsScreen(
                     colors = ListItemDefaults.colors(containerColor = Color.Transparent),
                 )
             }
+            item { SectionHeader(stringResource(R.string.settings_music_name)) }
+            item {
+                ListItem(
+                    headlineContent = { Text(stringResource(R.string.settings_replay_gain_title)) },
+                    supportingContent = { Text(replayGainModeLabel(LocalResources.current, replayGainMode)) },
+                    modifier = Modifier.clickable { dialog = SettingsDialog.ReplayGain },
+                    colors = ListItemDefaults.colors(containerColor = Color.Transparent),
+                )
+            }
+            item {
+                ListItem(
+                    headlineContent = { Text(stringResource(R.string.settings_replay_gain_preamp_title)) },
+                    supportingContent = { Text(replayGainPreampLabel(LocalResources.current, replayGainPreamp)) },
+                    modifier = Modifier.clickable { dialog = SettingsDialog.ReplayGainPreamp },
+                    colors = ListItemDefaults.colors(containerColor = Color.Transparent),
+                )
+            }
             item { SectionHeader(stringResource(R.string.downloads_title)) }
             item {
                 ListItem(
@@ -519,6 +560,22 @@ fun SettingsScreen(
             )
         }
 
+        SettingsDialog.ReplayGain -> {
+            ReplayGainModeDialog(
+                selected = replayGainMode,
+                onSelect = onReplayGainModeChange,
+                onDismiss = { dialog = null },
+            )
+        }
+
+        SettingsDialog.ReplayGainPreamp -> {
+            ReplayGainPreampDialog(
+                selected = replayGainPreamp,
+                onSelect = onReplayGainPreampChange,
+                onDismiss = { dialog = null },
+            )
+        }
+
         null -> {
             Unit
         }
@@ -672,6 +729,82 @@ private fun SyncModeDialog(
     )
 }
 
+private const val REPLAY_GAIN_PREAMP_STEPS = 59
+
+@Composable
+private fun ReplayGainModeDialog(
+    selected: ReplayGainMode,
+    onSelect: (ReplayGainMode) -> Unit,
+    onDismiss: () -> Unit,
+) {
+    val resources = LocalResources.current
+    var draft by remember(selected) { mutableStateOf(selected) }
+    AlertDialog(
+        onDismissRequest = onDismiss,
+        title = { Text(stringResource(R.string.settings_replay_gain_title)) },
+        text = {
+            ChoiceGroup(
+                header = stringResource(R.string.settings_replay_gain_prompt),
+                options = ReplayGainMode.entries.map { it to replayGainModeLabel(resources, it) },
+                selected = draft,
+                onSelect = { draft = it },
+            )
+        },
+        confirmButton = {
+            TextButton(
+                onClick = {
+                    onSelect(draft)
+                    onDismiss()
+                },
+            ) { Text(stringResource(R.string.action_done)) }
+        },
+        dismissButton = {
+            TextButton(onClick = onDismiss) { Text(stringResource(R.string.actions_cancel)) }
+        },
+    )
+}
+
+@Composable
+private fun ReplayGainPreampDialog(
+    selected: Float,
+    onSelect: (Float) -> Unit,
+    onDismiss: () -> Unit,
+) {
+    val resources = LocalResources.current
+    var draft by remember(selected) { mutableFloatStateOf(selected) }
+    AlertDialog(
+        onDismissRequest = onDismiss,
+        title = { Text(stringResource(R.string.settings_replay_gain_preamp_title)) },
+        text = {
+            Column {
+                Text(
+                    stringResource(R.string.settings_replay_gain_preamp_prompt),
+                    style = MaterialTheme.typography.titleSmall,
+                    color = MaterialTheme.colorScheme.primary,
+                )
+                Slider(
+                    value = draft,
+                    onValueChange = { draft = it },
+                    valueRange = MIN_REPLAY_GAIN_PREAMP_DB..MAX_REPLAY_GAIN_PREAMP_DB,
+                    steps = REPLAY_GAIN_PREAMP_STEPS,
+                )
+                Text(replayGainPreampLabel(resources, draft))
+            }
+        },
+        confirmButton = {
+            TextButton(
+                onClick = {
+                    onSelect(draft)
+                    onDismiss()
+                },
+            ) { Text(stringResource(R.string.action_done)) }
+        },
+        dismissButton = {
+            TextButton(onClick = onDismiss) { Text(stringResource(R.string.actions_cancel)) }
+        },
+    )
+}
+
 @Composable
 private fun QualityDialog(
     title: String,

app/src/main/kotlin/com/subtracks/ui/settings/SettingsViewModel.kt

@@ -5,6 +5,7 @@ import androidx.lifecycle.viewModelScope
 import com.subtracks.data.model.Source
 import com.subtracks.data.net.NetworkMode
 import com.subtracks.data.prefs.DEFAULT_SYNC_INTERVAL_MINUTES
+import com.subtracks.data.prefs.ReplayGainMode
 import com.subtracks.data.prefs.StreamQuality
 import com.subtracks.data.prefs.SyncMode
 import com.subtracks.data.prefs.UserPreferences
@@ -65,6 +66,16 @@ class SettingsViewModel(
             .scrobbling()
             .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), true)
 
+    val replayGainMode: StateFlow<ReplayGainMode> =
+        userPreferences
+            .replayGainMode()
+            .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), ReplayGainMode.Track)
+
+    val replayGainPreamp: StateFlow<Float> =
+        userPreferences
+            .replayGainPreampDb()
+            .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), 0f)
+
     val offline: StateFlow<Boolean> = sourceRepository.offline
 
     val verboseLogging: StateFlow<Boolean> =
@@ -115,4 +126,12 @@ class SettingsViewModel(
     fun setScrobbling(enabled: Boolean) {
         viewModelScope.launch { userPreferences.setScrobbling(enabled) }
     }
+
+    fun setReplayGainMode(mode: ReplayGainMode) {
+        viewModelScope.launch { userPreferences.setReplayGainMode(mode) }
+    }
+
+    fun setReplayGainPreamp(value: Float) {
+        viewModelScope.launch { userPreferences.setReplayGainPreampDb(value) }
+    }
 }

app/src/main/res/values/strings.xml

@@ -74,6 +74,14 @@
     <string name="settings_music_name">Playback</string>
     <string name="settings_music_options_scrobble_description_on">Send now playing and play counts</string>
     <string name="settings_music_options_scrobble_title">Scrobble to server</string>
+    <string name="settings_replay_gain_mode_album">Album gain</string>
+    <string name="settings_replay_gain_mode_off">Off</string>
+    <string name="settings_replay_gain_mode_track">Track gain</string>
+    <string name="settings_replay_gain_preamp_prompt">Adjust level on top of the replay gain</string>
+    <string name="settings_replay_gain_preamp_title">Preamp</string>
+    <string name="settings_replay_gain_preamp_value">%1$s dB</string>
+    <string name="settings_replay_gain_prompt">Normalise loudness using the gain from the server</string>
+    <string name="settings_replay_gain_title">Replay gain</string>
     <string name="settings_network_name">Network</string>
     <string name="settings_network_options_max_bitrate_mobile_title">Stream quality: Mobile</string>
     <string name="settings_network_options_max_bitrate_wifi_title">Stream quality: Wi-Fi</string>

app/src/test/kotlin/com/subtracks/ui/settings/ReplayGainLabelsTest.kt

@@ -0,0 +1,28 @@
+package com.subtracks.ui.settings
+
+import android.content.Context
+import androidx.test.core.app.ApplicationProvider
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.subtracks.data.prefs.ReplayGainMode
+import org.junit.Assert.assertEquals
+import org.junit.Test
+import org.junit.runner.RunWith
+
+@RunWith(AndroidJUnit4::class)
+class ReplayGainLabelsTest {
+    private val resources = ApplicationProvider.getApplicationContext<Context>().resources
+
+    @Test
+    fun modeLabelsNameTheGainEachOneUses() {
+        assertEquals("Off", replayGainModeLabel(resources, ReplayGainMode.Off))
+        assertEquals("Track gain", replayGainModeLabel(resources, ReplayGainMode.Track))
+        assertEquals("Album gain", replayGainModeLabel(resources, ReplayGainMode.Album))
+    }
+
+    @Test
+    fun preampLabelsCarryTheSignAndTheUnit() {
+        assertEquals("+3.0 dB", replayGainPreampLabel(resources, 3f))
+        assertEquals("-2.5 dB", replayGainPreampLabel(resources, -2.5f))
+        assertEquals("0.0 dB", replayGainPreampLabel(resources, 0f))
+    }
+}