data: TrackSection.{start,continue}CountingFrom, Track.trackNumber

2 files changed, 51 insertions, 0 deletions

diff --git a/src/data/composite/things/track/index.js b/src/data/composite/things/track/index.js
index beb8c6ab..bab97882 100644
--- a/src/data/composite/things/track/index.js
+++ b/src/data/composite/things/track/index.js
@@ -14,3 +14,4 @@ export {default as withPropertyFromAlbum} from './withPropertyFromAlbum.js';
 export {default as withPropertyFromMainRelease} from './withPropertyFromMainRelease.js';
 export {default as withSuffixDirectoryFromAlbum} from './withSuffixDirectoryFromAlbum.js';
 export {default as withTrackArtDate} from './withTrackArtDate.js';
+export {default as withTrackNumber} from './withTrackNumber.js';
diff --git a/src/data/composite/things/track/withTrackNumber.js b/src/data/composite/things/track/withTrackNumber.js
new file mode 100644
index 00000000..61428e8c
--- /dev/null
+++ b/src/data/composite/things/track/withTrackNumber.js
@@ -0,0 +1,50 @@
+import {input, templateCompositeFrom} from '#composite';
+
+import {raiseOutputWithoutDependency} from '#composite/control-flow';
+import {withIndexInList, withPropertiesFromObject} from '#composite/data';
+
+import withContainingTrackSection from './withContainingTrackSection.js';
+
+export default templateCompositeFrom({
+  annotation: `withTrackNumber`,
+
+  outputs: ['#trackNumber'],
+
+  steps: () => [
+    withContainingTrackSection(),
+
+    // Zero is the fallback, not one, but in most albums the first track
+    // (and its intended output by this composition) will be one.
+    raiseOutputWithoutDependency({
+      dependency: '#trackSection',
+      output: input.value({'#trackNumber': 0}),
+    }),
+
+    withPropertiesFromObject({
+      object: '#trackSection',
+      properties: input.value(['tracks', 'startCountingFrom']),
+    }),
+
+    withIndexInList({
+      list: '#trackSection.tracks',
+      item: input.myself(),
+    }),
+
+    raiseOutputWithoutDependency({
+      dependency: '#index',
+      output: input.value({'#trackNumber': 0}),
+    }),
+
+    {
+      dependencies: ['#trackSection.startCountingFrom', '#index'],
+      compute: (continuation, {
+        ['#trackSection.startCountingFrom']: startCountingFrom,
+        ['#index']: index,
+      }) => continuation({
+        ['#trackNumber']:
+          startCountingFrom +
+          index,
+      }),
+    },
+  ],
+});