detail: default to "no disc" instead of "disc 1"

Default tracks without a disc to a group called "No disc" instead of
disc 1.

This should reduce confusion on the user end, as it will make improper
taggings more apparent instead of simply degrading to a werid sort
ordering.

Resolves #405.

app/src/main/java/org/oxycblt/auxio/detail/DetailViewModel.kt

@@ -30,6 +30,7 @@ import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.yield
 import org.oxycblt.auxio.R
+import org.oxycblt.auxio.detail.list.DiscHeader
 import org.oxycblt.auxio.detail.list.EditHeader
 import org.oxycblt.auxio.detail.list.SortHeader
 import org.oxycblt.auxio.list.BasicHeader
@@ -46,7 +47,6 @@ import org.oxycblt.auxio.music.MusicRepository
 import org.oxycblt.auxio.music.MusicSettings
 import org.oxycblt.auxio.music.Playlist
 import org.oxycblt.auxio.music.Song
-import org.oxycblt.auxio.music.info.Disc
 import org.oxycblt.auxio.music.info.ReleaseType
 import org.oxycblt.auxio.music.metadata.AudioProperties
 import org.oxycblt.auxio.playback.PlaybackSettings
@@ -409,12 +409,11 @@ constructor(
         // To create a good user experience regarding disc numbers, we group the album's
         // songs up by disc and then delimit the groups by a disc header.
         val songs = albumSongSort.songs(album.songs)
-        // Songs without disc tags become part of Disc 1.
+        val byDisc = songs.groupBy { it.disc }
-        val byDisc = songs.groupBy { it.disc ?: Disc(1, null) }
         if (byDisc.size > 1) {
             logD("Album has more than one disc, interspersing headers")
             for (entry in byDisc.entries) {
-                list.add(entry.key)
+                list.add(DiscHeader(entry.key))
                 list.addAll(entry.value)
             }
         } else {

app/src/main/java/org/oxycblt/auxio/detail/list/AlbumDetailListAdapter.kt

@@ -49,14 +49,14 @@ class AlbumDetailListAdapter(private val listener: Listener<Song>) :
     override fun getItemViewType(position: Int) =
         when (getItem(position)) {
             // Support sub-headers for each disc, and special album songs.
-            is Disc -> DiscViewHolder.VIEW_TYPE
+            is DiscHeader -> DiscHeaderViewHolder.VIEW_TYPE
             is Song -> AlbumSongViewHolder.VIEW_TYPE
             else -> super.getItemViewType(position)
         }
 
     override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) =
         when (viewType) {
-            DiscViewHolder.VIEW_TYPE -> DiscViewHolder.from(parent)
+            DiscHeaderViewHolder.VIEW_TYPE -> DiscHeaderViewHolder.from(parent)
             AlbumSongViewHolder.VIEW_TYPE -> AlbumSongViewHolder.from(parent)
             else -> super.onCreateViewHolder(parent, viewType)
         }
@@ -64,7 +64,7 @@ class AlbumDetailListAdapter(private val listener: Listener<Song>) :
     override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
         super.onBindViewHolder(holder, position)
         when (val item = getItem(position)) {
-            is Disc -> (holder as DiscViewHolder).bind(item)
+            is DiscHeader -> (holder as DiscHeaderViewHolder).bind(item)
             is Song -> (holder as AlbumSongViewHolder).bind(item, listener)
         }
     }
@@ -76,7 +76,7 @@ class AlbumDetailListAdapter(private val listener: Listener<Song>) :
                 override fun areContentsTheSame(oldItem: Item, newItem: Item) =
                     when {
                         oldItem is Disc && newItem is Disc ->
-                            DiscViewHolder.DIFF_CALLBACK.areContentsTheSame(oldItem, newItem)
+                            DiscHeaderViewHolder.DIFF_CALLBACK.areContentsTheSame(oldItem, newItem)
                         oldItem is Song && newItem is Song ->
                             AlbumSongViewHolder.DIFF_CALLBACK.areContentsTheSame(oldItem, newItem)
 
@@ -88,23 +88,35 @@ class AlbumDetailListAdapter(private val listener: Listener<Song>) :
 }
 
 /**
- * A [RecyclerView.ViewHolder] that displays a [Disc] to delimit different disc groups. Use [from]
+ * A wrapper around [Disc] signifying that a header should be shown for a disc group.
- * to create an instance.
+ * @author Alexander Capehart (OxygenCobalt)
+ */
+data class DiscHeader(val inner: Disc?) : Item
+
+/**
+ * A [RecyclerView.ViewHolder] that displays a [DiscHeader] to delimit different disc groups. Use
+ * [from] to create an instance.
  *
  * @author Alexander Capehart (OxygenCobalt)
  */
-private class DiscViewHolder(private val binding: ItemDiscHeaderBinding) :
+private class DiscHeaderViewHolder(private val binding: ItemDiscHeaderBinding) :
     RecyclerView.ViewHolder(binding.root) {
     /**
      * Bind new data to this instance.
      *
-     * @param disc The new [disc] to bind.
+     * @param discHeader The new [DiscHeader] to bind.
      */
-    fun bind(disc: Disc) {
+    fun bind(discHeader: DiscHeader) {
+        val disc = discHeader.inner
+        if (disc != null) {
             binding.discNumber.text = binding.context.getString(R.string.fmt_disc_no, disc.number)
             binding.discName.apply {
                 text = disc.name
-            isGone = disc.name == null
+                isGone = text == null
+            }
+        } else {
+            binding.discNumber.text = binding.context.getString(R.string.def_disc)
+            binding.discName.isGone = true
         }
     }
 
@@ -119,7 +131,7 @@ private class DiscViewHolder(private val binding: ItemDiscHeaderBinding) :
          * @return A new instance.
          */
         fun from(parent: View) =
-            DiscViewHolder(ItemDiscHeaderBinding.inflate(parent.context.inflater))
+            DiscHeaderViewHolder(ItemDiscHeaderBinding.inflate(parent.context.inflater))
 
         /** A comparator that can be used with DiffUtil. */
         val DIFF_CALLBACK =

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

@@ -332,6 +332,7 @@
     <string name="def_artist">Unknown artist</string>
     <string name="def_genre">Unknown genre</string>
     <string name="def_date">No date</string>
+    <string name="def_disc">No disc</string>
     <string name="def_track">No track</string>
     <string name="def_song_count">No songs</string>
     <string name="def_playback">No music playing</string>