feat(android): the audio cache keeps a Liked songs budget and a Recently played budget (#6307)

SimpleCache ran one LRU evictor at the rolling cap, so liked audio was
dropped like anything else and the offline Liked pool shrank as other
music played. TwoBucketCacheEvictor replaces it:

- a span counts against Liked when its track is liked, else Recently
  played; a liked track that is also played is charged to Liked only;
- each budget has its own cap (0 = unlimited) and drops its own
  least-recently-used audio first;
- CacheBudgetSync feeds it the signed-in user's liked ids and the Storage
  caps, so a like, an unlike or a cap change applies at once;
- nothing is evicted until the liked set is known, so startup never trims
  liked audio as Recently played.

The decisions live in a Media3-free BucketLedger with unit tests.
CacheConfig and PlayerModule, which only snapshotted the caps at launch,
are gone.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

android/app/src/main/java/com/fabledsword/minstrel/MinstrelApplication.kt

@@ -8,6 +8,7 @@ import coil3.SingletonImageLoader
 import coil3.network.okhttp.OkHttpNetworkFetcherFactory
 import coil3.request.crossfade
 import com.fabledsword.minstrel.cache.CacheIndexer
+import com.fabledsword.minstrel.cache.audiocache.CacheBudgetSync
 import com.fabledsword.minstrel.cache.mutations.MutationReplayer
 import com.fabledsword.minstrel.cache.sync.SyncController
 import com.fabledsword.minstrel.di.ApplicationScope
@@ -120,6 +121,14 @@ class MinstrelApplication :
      */
     @Suppress("unused") @Inject lateinit var cacheIndexer: CacheIndexer
 
+    /**
+     * Same construct-the-singleton trick — CacheBudgetSync's init block
+     * feeds the audio cache's evictor the liked set and the Storage caps.
+     * Without this @Inject the evictor would never arm, and the cache
+     * would grow without a limit.
+     */
+    @Suppress("unused") @Inject lateinit var cacheBudgetSync: CacheBudgetSync
+
     /**
      * Same construct-the-singleton trick — AudioPrefetcher's init
      * block subscribes to PlayerController.uiState +

android/app/src/main/java/com/fabledsword/minstrel/cache/audiocache/BucketLedger.kt

@@ -0,0 +1,122 @@
+package com.fabledsword.minstrel.cache.audiocache
+
+import java.util.TreeSet
+
+/** Which budget a cached track's bytes count against. */
+enum class CacheBucket { LIKED, RECENT }
+
+/**
+ * The bookkeeping behind [TwoBucketCacheEvictor]: which budget each cached
+ * span counts against, how full each budget is, and which span to drop
+ * next. It knows nothing of Media3, so it is tested directly.
+ *
+ * A span belongs to [CacheBucket.LIKED] when its key (the track id) is in
+ * the liked set, and to [CacheBucket.RECENT] otherwise. A track that is
+ * liked and also recently played is therefore charged to Liked only; the
+ * two budgets never count the same bytes. Each bucket drops its own
+ * least-recently-used span first, so filling one never evicts the other.
+ *
+ * Nothing is evicted until [setLiked] has been called once. Before then
+ * every span would read as Recently played, and trimming at the Recently
+ * played cap would throw away liked audio at startup.
+ *
+ * Not thread-safe; the evictor serialises every call.
+ */
+class BucketLedger<S : Any>(
+    private val keyOf: (S) -> String,
+    private val lengthOf: (S) -> Long,
+    lruOrder: Comparator<S>,
+) {
+    private val spans = mapOf(
+        CacheBucket.LIKED to TreeSet(lruOrder),
+        CacheBucket.RECENT to TreeSet(lruOrder),
+    )
+    private val bytes = mutableMapOf(CacheBucket.LIKED to 0L, CacheBucket.RECENT to 0L)
+    private val spansByKey = HashMap<String, MutableSet<S>>()
+    private val bucketByKey = HashMap<String, CacheBucket>()
+    private var liked: Set<String> = emptySet()
+    private var armed = false
+
+    /** Cap on Liked bytes; 0 means unlimited. */
+    var likedCapBytes: Long = 0L
+
+    /** Cap on Recently played bytes; 0 means unlimited. */
+    var recentCapBytes: Long = 0L
+
+    fun bucketOf(key: String): CacheBucket =
+        if (key in liked) CacheBucket.LIKED else CacheBucket.RECENT
+
+    fun bytesIn(bucket: CacheBucket): Long = bytes.getValue(bucket)
+
+    /** Bytes the Liked budget can still take; [Long.MAX_VALUE] when unlimited. */
+    fun likedRoomBytes(): Long = when {
+        likedCapBytes <= 0L -> Long.MAX_VALUE
+        else -> (likedCapBytes - bytesIn(CacheBucket.LIKED)).coerceAtLeast(0L)
+    }
+
+    fun add(span: S) {
+        val key = keyOf(span)
+        val bucket = bucketByKey[key] ?: bucketOf(key).also { bucketByKey[key] = it }
+        if (spans.getValue(bucket).add(span)) {
+            bytes[bucket] = bytesIn(bucket) + lengthOf(span)
+            spansByKey.getOrPut(key) { HashSet() }.add(span)
+        }
+    }
+
+    fun remove(span: S) {
+        val key = keyOf(span)
+        val bucket = bucketByKey[key] ?: return
+        if (spans.getValue(bucket).remove(span)) {
+            bytes[bucket] = bytesIn(bucket) - lengthOf(span)
+        }
+        val forKey = spansByKey[key] ?: return
+        forKey.remove(span)
+        if (forKey.isEmpty()) {
+            spansByKey.remove(key)
+            bucketByKey.remove(key)
+        }
+    }
+
+    /**
+     * Replace the liked set and move every cached track whose bucket
+     * changed: a newly liked track's bytes leave Recently played for Liked,
+     * an unliked track's go the other way. Arms eviction.
+     */
+    fun setLiked(ids: Set<String>) {
+        liked = ids
+        armed = true
+        val moves = bucketByKey.filter { (key, bucket) -> bucketOf(key) != bucket }.keys.toList()
+        for (key in moves) {
+            val from = bucketByKey.getValue(key)
+            val to = bucketOf(key)
+            for (span in spansByKey[key].orEmpty()) {
+                if (spans.getValue(from).remove(span)) {
+                    bytes[from] = bytesIn(from) - lengthOf(span)
+                    spans.getValue(to).add(span)
+                    bytes[to] = bytesIn(to) + lengthOf(span)
+                }
+            }
+            bucketByKey[key] = to
+        }
+    }
+
+    /**
+     * The span to drop next, or null when both budgets fit. [pendingKey] and
+     * [pendingBytes] describe a write about to start, so room is made for it
+     * in its own bucket first. Recently played is trimmed before Liked.
+     */
+    fun nextEviction(pendingKey: String? = null, pendingBytes: Long = 0L): S? {
+        if (!armed) return null
+        val pendingBucket = pendingKey?.let(::bucketOf)
+        return listOf(CacheBucket.RECENT, CacheBucket.LIKED).firstNotNullOfOrNull { bucket ->
+            val incoming = if (bucket == pendingBucket) pendingBytes.coerceAtLeast(0L) else 0L
+            oldestIfOver(bucket, incoming)
+        }
+    }
+
+    private fun oldestIfOver(bucket: CacheBucket, incoming: Long): S? {
+        val cap = if (bucket == CacheBucket.LIKED) likedCapBytes else recentCapBytes
+        val over = cap > 0L && bytesIn(bucket) + incoming > cap
+        return if (over) spans.getValue(bucket).firstOrNull() else null
+    }
+}

android/app/src/main/java/com/fabledsword/minstrel/cache/audiocache/CacheBudgetSync.kt

@@ -0,0 +1,40 @@
+package com.fabledsword.minstrel.cache.audiocache
+
+import com.fabledsword.minstrel.auth.AuthStore
+import com.fabledsword.minstrel.di.ApplicationScope
+import com.fabledsword.minstrel.likes.data.LikesRepository
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.launch
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * Keeps [TwoBucketCacheEvictor] in step with the signed-in user's liked
+ * tracks and the Storage caps. A like moves that track's cached audio into
+ * the Liked budget, an unlike moves it out, and a cap change trims at once.
+ *
+ * The liked set only flows once a user is signed in, and the evictor drops
+ * nothing until it has one, so liked audio is never trimmed as Recently
+ * played while the session is still loading.
+ *
+ * Eager-constructed via the construct-the-singleton trick in
+ * `MinstrelApplication`.
+ */
+@Singleton
+class CacheBudgetSync @Inject constructor(
+    likes: LikesRepository,
+    authStore: AuthStore,
+    evictor: TwoBucketCacheEvictor,
+    @ApplicationScope scope: CoroutineScope,
+) {
+    init {
+        scope.launch(Dispatchers.IO) {
+            combine(likes.observeSignedInLikedTrackIds(), authStore.cacheSettings, ::Pair)
+                .collect { (ids, settings) ->
+                    evictor.update(ids, settings.likedCapBytes, settings.rollingCapBytes)
+                }
+        }
+    }
+}

android/app/src/main/java/com/fabledsword/minstrel/cache/audiocache/CacheConfig.kt

@@ -1,23 +0,0 @@
-package com.fabledsword.minstrel.cache.audiocache
-
-/**
- * Defaults for the audio cache; the user's Storage settings override them.
- *
- *  - `likedCapBytes`: cap meant for a protected bucket of liked tracks'
- *    files. Nothing enforces it yet; SimpleCache evicts by the rolling
- *    cap alone.
- *  - `rollingCapBytes`: cap for incidental / auto-prefetch downloads,
- *    evicted least-recently-used first.
- *
- * The values are generous so first-time installs work well without
- * configuration.
- */
-data class CacheConfig(
-    val likedCapBytes: Long = DEFAULT_LIKED_CAP_BYTES,
-    val rollingCapBytes: Long = DEFAULT_ROLLING_CAP_BYTES,
-) {
-    companion object {
-        const val DEFAULT_LIKED_CAP_BYTES: Long = 200L * 1024 * 1024 // 200 MiB
-        const val DEFAULT_ROLLING_CAP_BYTES: Long = 150L * 1024 * 1024 // 150 MiB
-    }
-}

android/app/src/main/java/com/fabledsword/minstrel/cache/audiocache/CacheSettings.kt

@@ -9,12 +9,12 @@ private const val DEFAULT_PREFETCH_WINDOW = 5
  * User-tunable audio cache settings. Persisted as a JSON
  * blob on the auth_session single-row table via [AuthStore].
  *
- * - [likedCapBytes]: budget for cached files of liked tracks. 0 means
- *   unlimited. Nothing enforces it yet: SimpleCache evicts by
- *   [rollingCapBytes] alone, and the Storage card hides this control.
- * - [rollingCapBytes]: budget for incidental / auto-prefetch downloads.
- *   0 means unlimited. Effective at next app start (SimpleCache is
- *   built once per process).
+ * - [likedCapBytes]: the Liked songs budget, for the cached audio of
+ *   liked tracks. 0 means unlimited.
+ * - [rollingCapBytes]: the Recently played budget, for everything else
+ *   streamed or prefetched. 0 means unlimited.
+ *   A track that is liked and also recently played counts against Liked
+ *   only. Both caps apply as soon as they change ([TwoBucketCacheEvictor]).
  * - [prefetchWindow]: 1..10. Number of next-tracks `AudioPrefetcher`
  *   pre-downloads.
  * - [cacheLikedTracks]: when true, liking a track should also pin its

android/app/src/main/java/com/fabledsword/minstrel/cache/audiocache/TwoBucketCacheEvictor.kt

@@ -0,0 +1,112 @@
+package com.fabledsword.minstrel.cache.audiocache
+
+import androidx.media3.common.C
+import androidx.media3.datasource.cache.Cache
+import androidx.media3.datasource.cache.CacheEvictor
+import androidx.media3.datasource.cache.CacheSpan
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * Bytes held against each audio-cache budget, and how much more the Liked
+ * budget can take ([Long.MAX_VALUE] when it is unlimited).
+ */
+data class CacheUsage(val likedBytes: Long, val recentBytes: Long, val likedRoomBytes: Long)
+
+/**
+ * The audio cache's eviction policy: two budgets, Liked songs and Recently
+ * played, each with its own cap and its own least-recently-used order (see
+ * [BucketLedger]). SimpleCache takes exactly one evictor, so this one
+ * carries both budgets.
+ *
+ * [CacheBudgetSync] feeds it the signed-in user's liked set and the caps
+ * from Storage settings, so a like, an unlike or a cap change applies at
+ * once, without restarting the app.
+ *
+ * Locking: SimpleCache calls every [CacheEvictor] method while holding its
+ * own monitor. Outside calls take the cache's monitor first and the
+ * ledger's second, the same order as those callbacks, so the two never
+ * deadlock.
+ */
+@Singleton
+class TwoBucketCacheEvictor @Inject constructor() : CacheEvictor {
+    private val ledger = BucketLedger<CacheSpan>(
+        keyOf = { it.key },
+        lengthOf = { it.length },
+        lruOrder = compareBy<CacheSpan> { it.lastTouchTimestamp }.then(naturalOrder()),
+    )
+
+    @Volatile private var cache: Cache? = null
+
+    /** Called once the SimpleCache exists, so updates can trim it. */
+    fun attach(cache: Cache) {
+        this.cache = cache
+    }
+
+    /** Apply a new liked set and caps, then trim whatever no longer fits. */
+    fun update(likedIds: Set<String>, likedCapBytes: Long, recentCapBytes: Long) {
+        val c = cache
+        val apply = {
+            ledger.likedCapBytes = likedCapBytes
+            ledger.recentCapBytes = recentCapBytes
+            ledger.setLiked(likedIds)
+        }
+        if (c == null) {
+            synchronized(ledger) { apply() }
+        } else {
+            synchronized(c) {
+                synchronized(ledger) {
+                    apply()
+                    evict(c, pendingKey = null, pendingBytes = 0L)
+                }
+            }
+        }
+    }
+
+    fun usage(): CacheUsage = synchronized(ledger) {
+        CacheUsage(
+            likedBytes = ledger.bytesIn(CacheBucket.LIKED),
+            recentBytes = ledger.bytesIn(CacheBucket.RECENT),
+            likedRoomBytes = ledger.likedRoomBytes(),
+        )
+    }
+
+    override fun requiresCacheSpanTouches(): Boolean = true
+
+    override fun onCacheInitialized() = Unit
+
+    override fun onStartFile(cache: Cache, key: String, position: Long, length: Long) {
+        synchronized(ledger) {
+            evict(cache, key, if (length == C.LENGTH_UNSET.toLong()) 0L else length)
+        }
+    }
+
+    override fun onSpanAdded(cache: Cache, span: CacheSpan) {
+        synchronized(ledger) {
+            ledger.add(span)
+            evict(cache, pendingKey = null, pendingBytes = 0L)
+        }
+    }
+
+    override fun onSpanRemoved(cache: Cache, span: CacheSpan) {
+        synchronized(ledger) { ledger.remove(span) }
+    }
+
+    override fun onSpanTouched(cache: Cache, oldSpan: CacheSpan, newSpan: CacheSpan) {
+        synchronized(ledger) {
+            ledger.remove(oldSpan)
+            ledger.add(newSpan)
+            evict(cache, pendingKey = null, pendingBytes = 0L)
+        }
+    }
+
+    private fun evict(cache: Cache, pendingKey: String?, pendingBytes: Long) {
+        while (true) {
+            val span = ledger.nextEviction(pendingKey, pendingBytes) ?: return
+            cache.removeSpan(span)
+            // removeSpan reports back through onSpanRemoved; removing here as
+            // well guarantees the loop advances even if it did not.
+            ledger.remove(span)
+        }
+    }
+}

android/app/src/main/java/com/fabledsword/minstrel/likes/data/LikesRepository.kt

@@ -14,8 +14,12 @@ import com.fabledsword.minstrel.models.AlbumRef
 import com.fabledsword.minstrel.models.ArtistRef
 import com.fabledsword.minstrel.models.TrackRef
 import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.distinctUntilChanged
+import kotlinx.coroutines.flow.filterNotNull
 import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.launch
 import retrofit2.Retrofit
@@ -117,6 +121,20 @@ class LikesRepository @Inject constructor(
     fun observeLikedTrackIds(): Flow<Set<String>> =
         likeDao.observeLikedIdsOfType(currentUserId(), ENTITY_TRACK).map { it.toSet() }
 
+    /**
+     * The liked track ids of whoever is signed in, following sign-in and
+     * account changes. Emits nothing while signed out, so a long-lived
+     * collector never mistakes the anonymous empty set for "no likes".
+     */
+    @OptIn(ExperimentalCoroutinesApi::class)
+    fun observeSignedInLikedTrackIds(): Flow<Set<String>> =
+        authController.currentUser
+            .map { it?.id }
+            .distinctUntilChanged()
+            .filterNotNull()
+            .flatMapLatest { userId -> likeDao.observeLikedIdsOfType(userId, ENTITY_TRACK) }
+            .map { it.toSet() }
+
     /** One-shot snapshot of the liked track-id set — for the offline pool filter. */
     suspend fun likedTrackIds(): Set<String> =
         likeDao.observeLikedIdsOfType(currentUserId(), ENTITY_TRACK).first().toSet()

android/app/src/main/java/com/fabledsword/minstrel/player/PlayerFactory.kt

@@ -10,7 +10,6 @@ import androidx.media3.database.StandaloneDatabaseProvider
 import androidx.media3.datasource.DataSourceBitmapLoader
 import androidx.media3.datasource.cache.CacheDataSink
 import androidx.media3.datasource.cache.CacheDataSource
-import androidx.media3.datasource.cache.LeastRecentlyUsedCacheEvictor
 import androidx.media3.datasource.cache.SimpleCache
 import androidx.media3.datasource.okhttp.OkHttpDataSource
 import androidx.media3.exoplayer.DefaultRenderersFactory
@@ -20,7 +19,7 @@ import androidx.media3.exoplayer.audio.DefaultAudioSink
 import androidx.media3.exoplayer.source.DefaultMediaSourceFactory
 import androidx.media3.session.CacheBitmapLoader
 import com.fabledsword.minstrel.auth.AuthStore
-import com.fabledsword.minstrel.cache.audiocache.CacheConfig
+import com.fabledsword.minstrel.cache.audiocache.TwoBucketCacheEvictor
 import com.fabledsword.minstrel.player.gain.GainAudioProcessor
 import com.fabledsword.minstrel.player.gain.ReplayGainStore
 import com.fabledsword.minstrel.player.output.ActiveUpnpHolder
@@ -42,8 +41,8 @@ import javax.inject.Singleton
  *
  * `simpleCache` is exposed as a val for what needs the on-disk bytes:
  * the cached-track ids, the offline pools, the prefetcher and the
- * Storage card. The `LeastRecentlyUsedCacheEvictor` bounds it at the
- * rolling cap; there is no separate liked-track bucket yet.
+ * Storage card. [TwoBucketCacheEvictor] bounds it by two budgets, Liked
+ * songs and Recently played.
  *
  * `build()` returns a [MinstrelForwardingPlayer] wrapping the internal
  * ExoPlayer. When the UPnP route drops (the poll loop's consecutive-
@@ -56,7 +55,7 @@ import javax.inject.Singleton
 class PlayerFactory @Inject constructor(
     @ApplicationContext private val context: Context,
     private val okHttpClient: OkHttpClient,
-    private val cacheConfig: CacheConfig,
+    private val cacheEvictor: TwoBucketCacheEvictor,
     private val activeUpnpHolder: ActiveUpnpHolder,
     private val remoteState: RemotePlayerState,
     private val serverHealth: com.fabledsword.minstrel.connectivity.NetworkStatusController,
@@ -68,9 +67,9 @@ class PlayerFactory @Inject constructor(
 
     val simpleCache: SimpleCache = SimpleCache(
         cacheDir,
-        LeastRecentlyUsedCacheEvictor(cacheConfig.rollingCapBytes),
+        cacheEvictor,
         StandaloneDatabaseProvider(context),
-    )
+    ).also(cacheEvictor::attach)
 
     // MutableSharedFlow with extraBufferCapacity=1 + DROP_OLDEST so a burst
     // of drop events (rapid SOAP failures during a single tear-down) surfaces

android/app/src/main/java/com/fabledsword/minstrel/player/PlayerModule.kt

@@ -1,43 +0,0 @@
-package com.fabledsword.minstrel.player
-
-import com.fabledsword.minstrel.auth.AuthStore
-import com.fabledsword.minstrel.cache.audiocache.CacheConfig
-import dagger.Module
-import dagger.Provides
-import dagger.hilt.InstallIn
-import dagger.hilt.components.SingletonComponent
-import javax.inject.Singleton
-
-/**
- * Player + audio-cache wiring. PlayerFactory has @Inject so it doesn't
- * need a @Provides here; this module provides the configuration values
- * (CacheConfig) it depends on, and any player-related singletons that
- * aren't @Inject-constructible.
- *
- * MinstrelPlayerService injects PlayerFactory and calls `build()` from
- * `onCreate`.
- */
-@Module
-@InstallIn(SingletonComponent::class)
-object PlayerModule {
-
-    /**
-     * CacheConfig snapshot from the user's persisted CacheSettings.
-     * SimpleCache is constructed once per process, so changes via the
-     * Settings UI take effect on next app launch (not mid-flight).
-     * AuthStore's StateFlow hydrates async from Room — when the
-     * factory @Provides runs, the value is either the persisted
-     * setting (if Room finished first) or CacheSettings.DEFAULT.
-     * Worst case the user's tuning lands on next-next launch, which
-     * is acceptable for a single-user device pref.
-     */
-    @Provides
-    @Singleton
-    fun provideCacheConfig(authStore: AuthStore): CacheConfig {
-        val s = authStore.cacheSettings.value
-        return CacheConfig(
-            likedCapBytes = s.likedCapBytes,
-            rollingCapBytes = s.rollingCapBytes,
-        )
-    }
-}

android/app/src/test/java/com/fabledsword/minstrel/cache/audiocache/BucketLedgerTest.kt

@@ -0,0 +1,155 @@
+package com.fabledsword.minstrel.cache.audiocache
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+
+/**
+ * The two audio-cache budgets: Liked songs and Recently played. A track
+ * that is liked and also played counts against Liked only, and each budget
+ * drops its own least-recently-used audio first.
+ */
+class BucketLedgerTest {
+    private data class Span(val key: String, val position: Long, val length: Long, val touched: Long)
+
+    private fun ledger(likedCap: Long = 0L, recentCap: Long = 0L) = BucketLedger<Span>(
+        keyOf = { it.key },
+        lengthOf = { it.length },
+        lruOrder = compareBy<Span> { it.touched }.thenBy { it.key }.thenBy { it.position },
+    ).apply {
+        likedCapBytes = likedCap
+        recentCapBytes = recentCap
+    }
+
+    /** Drop spans the way the evictor does, until both budgets fit. */
+    private fun BucketLedger<Span>.drain(): List<Span> {
+        val dropped = mutableListOf<Span>()
+        while (true) {
+            val span = nextEviction() ?: return dropped
+            remove(span)
+            dropped += span
+        }
+    }
+
+    @Test
+    fun `a liked track's bytes count against Liked only`() {
+        val l = ledger()
+        l.setLiked(setOf("liked"))
+        l.add(Span("liked", 0, 300, touched = 1))
+        l.add(Span("other", 0, 200, touched = 2))
+
+        assertEquals(300, l.bytesIn(CacheBucket.LIKED))
+        assertEquals(200, l.bytesIn(CacheBucket.RECENT))
+    }
+
+    @Test
+    fun `filling Recently played drops its oldest audio and never liked audio`() {
+        val l = ledger(likedCap = 1_000, recentCap = 250)
+        l.setLiked(setOf("liked"))
+        val liked = Span("liked", 0, 100, touched = 0)
+        val oldest = Span("a", 0, 100, touched = 1)
+        l.add(liked)
+        l.add(oldest)
+        l.add(Span("b", 0, 100, touched = 2))
+        l.add(Span("c", 0, 100, touched = 3))
+
+        assertEquals(listOf(oldest), l.drain())
+        assertEquals(200, l.bytesIn(CacheBucket.RECENT))
+        assertEquals(100, l.bytesIn(CacheBucket.LIKED))
+    }
+
+    @Test
+    fun `filling Liked drops its least recently played liked audio`() {
+        val l = ledger(likedCap = 150, recentCap = 1_000)
+        l.setLiked(setOf("x", "y"))
+        val older = Span("x", 0, 100, touched = 1)
+        l.add(older)
+        l.add(Span("y", 0, 100, touched = 2))
+        l.add(Span("recent", 0, 500, touched = 0))
+
+        assertEquals(listOf(older), l.drain())
+        assertEquals(500, l.bytesIn(CacheBucket.RECENT))
+    }
+
+    @Test
+    fun `liking a cached track moves its bytes into Liked`() {
+        val l = ledger(likedCap = 1_000, recentCap = 150)
+        l.setLiked(emptySet())
+        l.add(Span("t", 0, 100, touched = 1))
+        l.add(Span("t", 100, 50, touched = 2))
+        l.add(Span("u", 0, 100, touched = 3))
+        assertEquals(250, l.bytesIn(CacheBucket.RECENT))
+
+        l.setLiked(setOf("t"))
+
+        assertEquals(150, l.bytesIn(CacheBucket.LIKED))
+        assertEquals(100, l.bytesIn(CacheBucket.RECENT))
+        assertEquals(emptyList(), l.drain())
+    }
+
+    @Test
+    fun `unliking moves the bytes to Recently played, which then trims`() {
+        val l = ledger(likedCap = 1_000, recentCap = 150)
+        l.setLiked(setOf("t"))
+        val unliked = Span("t", 0, 100, touched = 1)
+        l.add(unliked)
+        l.add(Span("u", 0, 100, touched = 2))
+
+        l.setLiked(emptySet())
+
+        assertEquals(listOf(unliked), l.drain())
+        assertEquals(0, l.bytesIn(CacheBucket.LIKED))
+    }
+
+    @Test
+    fun `shrinking a cap trims at once`() {
+        val l = ledger(recentCap = 1_000)
+        l.setLiked(emptySet())
+        l.add(Span("a", 0, 100, touched = 1))
+        l.add(Span("b", 0, 100, touched = 2))
+        assertEquals(emptyList(), l.drain())
+
+        l.recentCapBytes = 100
+
+        assertEquals(listOf("a"), l.drain().map { it.key })
+    }
+
+    @Test
+    fun `a cap of 0 never evicts`() {
+        val l = ledger(likedCap = 0, recentCap = 0)
+        l.setLiked(setOf("liked"))
+        repeat(50) { l.add(Span("k$it", 0, 1_000_000, touched = it.toLong())) }
+        l.add(Span("liked", 0, 1_000_000, touched = 99))
+
+        assertNull(l.nextEviction())
+    }
+
+    @Test
+    fun `nothing is evicted before the liked set is known`() {
+        val l = ledger(likedCap = 100, recentCap = 100)
+        l.add(Span("maybe-liked", 0, 500, touched = 1))
+
+        assertNull(l.nextEviction())
+    }
+
+    @Test
+    fun `a write about to start makes room in its own bucket`() {
+        val l = ledger(likedCap = 1_000, recentCap = 200)
+        l.setLiked(setOf("liked"))
+        l.add(Span("a", 0, 150, touched = 1))
+
+        assertNull(l.nextEviction(pendingKey = "liked", pendingBytes = 100))
+        assertEquals("a", l.nextEviction(pendingKey = "new", pendingBytes = 100)?.key)
+    }
+
+    @Test
+    fun `Liked room is what the Liked cap has left`() {
+        val l = ledger(likedCap = 500)
+        l.setLiked(setOf("x"))
+        l.add(Span("x", 0, 200, touched = 1))
+
+        assertEquals(300, l.likedRoomBytes())
+        l.likedCapBytes = 0
+        assertEquals(Long.MAX_VALUE, l.likedRoomBytes())
+    }
+}