artists: show a credited track artist's name and type on their page

A track artist without an artists row had no name on the artist page, so
the header and the placeholder letter were blank. Derive the name from the
songs that credit them, and label the page 'Album artist' when they lead an
album or 'Artist' when they are only credited on tracks. The hero art keeps
the letter placeholder when there is no artist image.

app/src/main/kotlin/com/subtracks/data/db/LibraryDao.kt

@@ -942,6 +942,16 @@ interface LibraryDao {
         artistId: String,
     ): Flow<Artist?>
 
+    // A credited track artist may not have an artists row; its name only lives on the songs.
+    @Query(
+        "SELECT artist FROM songs WHERE sourceId = :sourceId AND artistId = :artistId " +
+            "AND artist IS NOT NULL AND artist != '' ORDER BY id LIMIT 1",
+    )
+    fun artistName(
+        sourceId: Long,
+        artistId: String,
+    ): Flow<String?>
+
     @Query("SELECT * FROM songs WHERE sourceId = :sourceId AND id = :songId")
     fun song(
         sourceId: Long,

app/src/main/kotlin/com/subtracks/data/repo/LibraryRepository.kt

@@ -348,6 +348,11 @@ class LibraryRepository(
         artistId: String,
     ): Flow<Artist?> = db.libraryDao().artist(sourceId, artistId)
 
+    fun artistName(
+        sourceId: Long,
+        artistId: String,
+    ): Flow<String?> = db.libraryDao().artistName(sourceId, artistId)
+
     fun song(
         sourceId: Long,
         songId: String,

app/src/main/kotlin/com/subtracks/ui/library/ArtistDetailScreen.kt

@@ -152,6 +152,7 @@ fun ArtistDetailRoute(
     playbackController: PlaybackController = koinInject(),
 ) {
     val artist by viewModel.artist.collectAsStateWithLifecycle(initialValue = null)
+    val artistName by viewModel.artistName.collectAsStateWithLifecycle(initialValue = null)
     val albums by viewModel.albums.collectAsStateWithLifecycle(initialValue = emptyList())
     val art by viewModel.art.collectAsStateWithLifecycle()
     val artThumbnail by viewModel.artThumbnail.collectAsStateWithLifecycle()
@@ -184,10 +185,12 @@ fun ArtistDetailRoute(
         )
     ArtistDetailScreen(
         artist = artist,
+        artistName = artistName.orEmpty(),
+        isAlbumArtist = albums.any { it.artistId == artistId },
         albums = albums,
         art = art,
         artThumbnail = artThumbnail,
-        artwork = rememberArtworkColors(shortcutArt ?: artThumbnail ?: art, THEME_TRANSITION_MS, fallbackName = artist?.name),
+        artwork = rememberArtworkColors(shortcutArt ?: artThumbnail ?: art, THEME_TRANSITION_MS, fallbackName = artistName),
         coverArt = viewModel::coverArt,
         onBack = onBack,
         onAlbumClick = onAlbumClick,
@@ -213,6 +216,8 @@ fun ArtistDetailRoute(
 @Composable
 fun ArtistDetailScreen(
     artist: Artist?,
+    artistName: String = "",
+    isAlbumArtist: Boolean = false,
     albums: List<Album>,
     art: CoverArtRef?,
     artThumbnail: CoverArtRef? = null,
@@ -240,6 +245,8 @@ fun ArtistDetailScreen(
     val navBarBottom = with(density) { WindowInsets.navigationBars.getBottom(this).toDp() }
     val barHeight = statusBarTop + TopAppBarDefaults.TopAppBarExpandedHeight
     val albumCount = albums.size.toLong()
+    val displayName = artistName.ifBlank { artist?.name.orEmpty() }
+    val artistType = stringResource(if (isAlbumArtist) R.string.artist_type_album_artist else R.string.artist_type_artist)
     val imageTitleTop = ART_HEIGHT - TITLE_INSET - lineHeight
     val fadeStartPx = with(density) { (imageTitleTop - barHeight - FADE_LEAD).toPx() }
     val fadeEndPx = with(density) { (imageTitleTop + lineHeight / 2 - barHeight).toPx() }
@@ -309,7 +316,7 @@ fun ArtistDetailScreen(
                             Box(Modifier.fillMaxWidth()) {
                                 CoverArt(
                                     ref = art,
-                                    name = artist?.name.orEmpty(),
+                                    name = displayName,
                                     thumbnailRef = artThumbnail,
                                     showPlaceholder = art == null,
                                     modifier = Modifier.fillMaxWidth().height(ART_HEIGHT),
@@ -331,7 +338,7 @@ fun ArtistDetailScreen(
                                 }
                                 Box(Modifier.align(Alignment.BottomStart).fillMaxWidth()) {
                                     ArtistTitle(
-                                        text = artist?.name.orEmpty(),
+                                        text = displayName,
                                         style = imageNameStyle,
                                         color = Color.White,
                                         endReserve = SHUFFLE_RESERVE,
@@ -360,12 +367,18 @@ fun ArtistDetailScreen(
                                 modifier = Modifier.fillMaxWidth().padding(start = 16.dp, end = 8.dp, top = 34.dp, bottom = 0.dp),
                                 verticalAlignment = Alignment.CenterVertically,
                             ) {
+                                Column(Modifier.weight(1f)) {
+                                    Text(
+                                        text = artistType,
+                                        style = MaterialTheme.typography.labelLarge,
+                                        color = MaterialTheme.colorScheme.onSurfaceVariant,
+                                    )
                                     Text(
                                         text = pluralStringResource(R.plurals.resources_album_count, albumCount.toInt(), albumCount),
                                         style = MaterialTheme.typography.bodyLarge,
                                         color = MaterialTheme.colorScheme.onSurfaceVariant,
-                                    modifier = Modifier.weight(1f),
                                     )
+                                }
                                 IconButton(
                                     onClick = { onToggleStar?.invoke() },
                                     enabled = onToggleStar != null,
@@ -452,7 +465,7 @@ fun ArtistDetailScreen(
                 TopAppBar(
                     title = {
                         Text(
-                            text = artist?.name.orEmpty(),
+                            text = displayName,
                             maxLines = 1,
                             overflow = TextOverflow.Ellipsis,
                             modifier = Modifier.graphicsLayer { alpha = barFraction },

app/src/main/kotlin/com/subtracks/ui/library/ArtistDetailViewModel.kt

@@ -38,6 +38,14 @@ class ArtistDetailViewModel(
 
     val artist: Flow<Artist?> = sourceId.flatMapLatest { libraryRepository.artist(it, artistId) }
 
+    val artistName: Flow<String?> =
+        sourceId.flatMapLatest { id ->
+            combine(
+                libraryRepository.artist(id, artistId),
+                libraryRepository.artistName(id, artistId),
+            ) { loaded, fromSongs -> loaded?.name?.takeIf { it.isNotBlank() } ?: fromSongs }
+        }
+
     val offline: StateFlow<Boolean> = sourceRepository.offline
 
     val albums: Flow<List<Album>> =

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

@@ -29,6 +29,8 @@
     <string name="resources_playlist_name">Playlists</string>
     <string name="resources_filter_album">Album</string>
     <string name="resources_filter_artist">Artist</string>
+    <string name="artist_type_artist">Artist</string>
+    <string name="artist_type_album_artist">Album artist</string>
     <string name="resources_filter_genre">Genre</string>
     <string name="resources_filter_starred">Starred</string>
     <string name="resources_song_list_delete_all_content">%1$s\n\nDeleting will free %2$s</string>

app/src/test/kotlin/com/subtracks/data/db/LibraryDaoTest.kt

@@ -558,6 +558,20 @@ class LibraryDaoTest {
             )
         }
 
+    @Test
+    fun aCreditedTrackArtistsNameComesFromItsSongs() =
+        runTest {
+            val sourceId = source()
+            val dao = db.libraryDao()
+            dao.upsertSongs(
+                listOf(
+                    song(sourceId, "s1", "One", starred = null).copy(artistId = "ar-guest", artist = "Guest"),
+                ),
+            )
+
+            assertEquals("Guest", dao.artistName(sourceId, "ar-guest").first())
+        }
+
     @Test
     fun downloadedFilterReportsTheDownloadedAlbumCount() =
         runTest {

app/src/test/kotlin/com/subtracks/ui/library/ArtistDetailScreenTest.kt

@@ -0,0 +1,60 @@
+package com.subtracks.ui.library
+
+import androidx.activity.ComponentActivity
+import androidx.compose.ui.test.junit4.v2.createAndroidComposeRule
+import androidx.compose.ui.test.onAllNodesWithText
+import androidx.compose.ui.test.onNodeWithText
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.subtracks.data.model.Artist
+import com.subtracks.ui.theme.SubtracksTheme
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.annotation.GraphicsMode
+
+@RunWith(AndroidJUnit4::class)
+@GraphicsMode(GraphicsMode.Mode.NATIVE)
+class ArtistDetailScreenTest {
+    @get:Rule
+    val composeRule = createAndroidComposeRule<ComponentActivity>()
+
+    private fun render(
+        artist: Artist?,
+        artistName: String,
+        isAlbumArtist: Boolean,
+    ) {
+        composeRule.setContent {
+            SubtracksTheme {
+                ArtistDetailScreen(
+                    artist = artist,
+                    artistName = artistName,
+                    isAlbumArtist = isAlbumArtist,
+                    albums = emptyList(),
+                    art = null,
+                    coverArt = { _, _ -> null },
+                    onBack = {},
+                    onAlbumClick = {},
+                )
+            }
+        }
+    }
+
+    @Test
+    fun aCreditedTrackArtistShowsItsDerivedNameAndIsLabelledArtist() {
+        render(artist = null, artistName = "Guest", isAlbumArtist = false)
+
+        composeRule.onAllNodesWithText("Guest")[0].assertExists()
+        composeRule.onNodeWithText("Artist").assertExists()
+    }
+
+    @Test
+    fun anAlbumArtistIsLabelledAlbumArtist() {
+        render(
+            artist = Artist(sourceId = 1, id = "ar-1", name = "Radiohead", albumCount = 1, starred = null),
+            artistName = "Radiohead",
+            isAlbumArtist = true,
+        )
+
+        composeRule.onNodeWithText("Album artist").assertExists()
+    }
+}