AOrobator

  @Test
  fun `When unscanned song clicked, song is scanned into library`() {
    val presenter = FolderBrowsingPresenter(queue, MockSongRepository())
    val target: FolderBrowsingPresenter.Target = mock()

    presenter.attach(target)
    presenter.onUnscannedSongClicked(
        DirectoryItemSong(
            name = "01 Get You.m4a",
            lastModifiedTime = 1234L,

AOrobator

  fun onUnscannedSongClicked(song: DirectoryItemSong) {
    val songFile = File(song.path)
    if (songFile.extension in supportedFormats) {
      target?.showLoading()
      songRepo
          .addSongToLibrary(song.path)
          .subscribe {
            target?.hideLoading()
            target?.playSong(it)
          }

AOrobator

class RealmSongRepository: SongRepository {
  
  override fun getSongById(songId: SongId) : Song? = when (songId) {
    is ValidSongId -> getSongFromRealm(songId.id) // smart cast to ValidSongId
    InvalidSongId -> null
    // No else statement required because the compiler knows we’ve covered all cases
  }
  
}

AOrobator

sealed class SongId
data class ValidSongId(id: Long) : SongId()
object InvalidSongId : SongId()

val Song.typedId: SongId = if (this.id == -1L) InvalidSongId else SongId(this.id)

AOrobator

val song: Song = ...
val playlist: Playlist = ...

playlistRepository.addSongToPlaylist(song.typedId, playlist.typedId)

AOrobator

data class SongId(id: Long)
val Song.typedId: SongId = SongId(this.id)

data class PlaylistId(id: Long)
val Playlist.typedId: PlaylistId = PlaylistId(this.id)

AOrobator

// Compiler doesn’t like this. Red squigglies everywhere.
playlistRepository.addSongToPlaylist(songId = PlaylistId(420L), playlistId = SongId(9001L))

AOrobator

interface PlaylistRepository: Repository {
  fun addSongToPlaylist(songId: SongId, playlistId: PlaylistId)
}

AOrobator

data class SongId(id: Long)
data class PlaylistId(id: Long)

AOrobator

val playlist: Playlist = ...
val song: Song = ...

// This is a bug, but the compiler allows it!
playlistRepository.addSongToPlaylist(songId = playlist.id, playlistId = song.id)