website/app/routes/apiv1/music.php

<?php

// retrieve album info
$app->get('/apiv1/music/album-info/:albumid', function($albumid) use($app) {

  if (!ctype_digit($albumid)) {
    echo 'Don\'t do that';
    return;
  }

  $album = $app->album->where('id', $albumid)->first();

  if ($album) {
    echo json_encode($album);
  } else {
    $app->notFound();
  }

})->name('apiv1.music.album-info');

// retrieve an album's songs
$app->get('/apiv1/music/album-songs/:albumid', function($albumid) use($app) {

  if (!ctype_digit($albumid)) {
    echo 'Don\'t do that';
    return;
  }

  $album = $app->album->where('id', $albumid)->first();

  if ($album) {
    $json = [songs => $album->songs()];
    echo json_encode($json);
  } else {
    $app->notFound();
  }

})->name('apiv1.music.album-songs');