1 files changed, 57 insertions, 0 deletions
diff --git a/src/data/composite/things/track/withAlbum.js b/src/data/composite/things/track/withAlbum.js
new file mode 100644
index 0000000..34845ab
--- /dev/null
+++ b/src/data/composite/things/track/withAlbum.js
@@ -0,0 +1,57 @@
+// Gets the track's album. This will early exit if albumData is missing.
+// By default, if there's no album whose list of tracks includes this track,
+// the output dependency will be null; set {notFoundMode: 'exit'} to early
+// exit instead.
+
+import {input, templateCompositeFrom} from '#composite';
+import {is} from '#validators';
+
+import {raiseOutputWithoutDependency} from '#composite/control-flow';
+
+export default templateCompositeFrom({
+  annotation: `withAlbum`,
+
+  inputs: {
+    notFoundMode: input({
+      validate: is('exit', 'null'),
+      defaultValue: 'null',
+    }),
+  },
+
+  outputs: ['#album'],
+
+  steps: () => [
+    raiseOutputWithoutDependency({
+      dependency: 'albumData',
+      mode: input.value('empty'),
+      output: input.value({
+        ['#album']: null,
+      }),
+    }),
+
+    {
+      dependencies: [input.myself(), 'albumData'],
+      compute: (continuation, {
+        [input.myself()]: track,
+        ['albumData']: albumData,
+      }) =>
+        continuation({
+          ['#album']:
+            albumData.find(album => album.tracks.includes(track)),
+        }),
+    },
+
+    raiseOutputWithoutDependency({
+      dependency: '#album',
+      output: input.value({
+        ['#album']: null,
+      }),
+    }),
+
+    {
+      dependencies: ['#album'],
+      compute: (continuation, {'#album': album}) =>
+        continuation.raiseOutput({'#album': album}),
+    },
+  ],
+});