music: implement genre linking

app/src/main/java/org/oxycblt/auxio/music/stack/interpret/linker/Contribution.kt

@@ -0,0 +1,18 @@
+package org.oxycblt.auxio.music.stack.interpret.linker
+
+class Contribution<T> {
+    private val map = mutableMapOf<T, Int>()
+
+    val candidates: Collection<T> get() = map.keys
+
+    fun contribute(key: T) {
+        map[key] = map.getOrDefault(key, 0) + 1
+    }
+
+    fun contribute(keys: Collection<T>) {
+        keys.forEach { contribute(it) }
+    }
+
+    fun resolve() = map.maxByOrNull { it.value }?.key ?: error("Nothing was contributed")
+
+}

app/src/main/java/org/oxycblt/auxio/music/stack/interpret/linker/GenreLinker.kt

@@ -2,16 +2,60 @@ package org.oxycblt.auxio.music.stack.interpret.linker
 
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.emptyFlow
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.transform
 import org.oxycblt.auxio.music.stack.interpret.model.GenreImpl
 import org.oxycblt.auxio.music.stack.interpret.model.SongImpl
+import org.oxycblt.auxio.music.stack.interpret.prepare.PreGenre
 import org.oxycblt.auxio.music.stack.interpret.prepare.PreSong
 
-class GenreLinker {
-    fun register(preSong: Flow<PreSong>): Flow<LinkedSong> = emptyFlow()
-    fun resolve(): Collection<GenreImpl> = setOf()
+class GenreTree {
+    private val tree = mutableMapOf<String?, GenreLink>()
+
+    fun register(preSong: Flow<PreSong>): Flow<LinkedSong> = preSong.map {
+        val genreLinks = it.preGenres.map { genre ->
+            val nameKey = genre.rawName?.lowercase()
+            val link = tree.getOrPut(nameKey) { GenreLink(GenreNode(Contribution())) }
+            link.node.contributors.contribute(genre)
+            link
+        }
+        LinkedSong(it, MultiGenreLink(genreLinks))
+    }
+
+    fun resolve() =
+        tree.values.map { it.node.resolve() }
 
     data class LinkedSong(
         val preSong: PreSong,
         val genres: Linked<List<GenreImpl>, SongImpl>
     )
+
+    private class MultiGenreLink(
+        val links: List<Linked<GenreImpl, SongImpl>>
+    ) : Linked<List<GenreImpl>, SongImpl> {
+        override fun resolve(child: SongImpl): List<GenreImpl> {
+            return links.map { it.resolve(child) }.distinct()
+        }
+    }
+
+    private data class GenreLink(
+        var node: GenreNode
+    ) : Linked<GenreImpl, SongImpl> {
+        override fun resolve(child: SongImpl): GenreImpl {
+            return requireNotNull(node.genreImpl) { "Link" }
+        }
+    }
+
+    private class GenreNode(
+        val contributors: Contribution<PreGenre>
+    ) {
+        var genreImpl: GenreImpl? = null
+            private set
+
+        fun resolve(): GenreImpl {
+            val impl = GenreImpl(contributors.resolve())
+            genreImpl = impl
+            return impl
+        }
+    }
 }

app/src/main/java/org/oxycblt/auxio/music/stack/interpret/prepare/PreMusic.kt

@@ -16,7 +16,7 @@ import java.util.UUID
 data class PreSong(
     val musicBrainzId: UUID?,
     val name: Name,
-    val rawName: String?,
+    val rawName: String,
     val track: Int?,
     val disc: Disc?,
     val date: Date?,