data: TrackSection thing objects

Sorry this commit is kind of monolithic! It's difficult to
separate out any of the changes since they're all related to
track sections' basic functionality.

8 files changed, 182 insertions, 215 deletions

diff --git a/package.json b/package.json
index 983c6796..88f351bc 100644
--- a/package.json
+++ b/package.json
@@ -24,6 +24,7 @@
         "#composite/things/flash": "./src/data/composite/things/flash/index.js",
         "#composite/things/flash-act": "./src/data/composite/things/flash-act/index.js",
         "#composite/things/track": "./src/data/composite/things/track/index.js",
+        "#composite/things/track-section": "./src/data/composite/things/track-section/index.js",
         "#content-dependencies": "./src/content/dependencies/index.js",
         "#content-function": "./src/content-function.js",
         "#cli": "./src/util/cli.js",
diff --git a/src/data/composite/things/album/index.js b/src/data/composite/things/album/index.js
index 8139f10e..8b5098f0 100644
--- a/src/data/composite/things/album/index.js
+++ b/src/data/composite/things/album/index.js
@@ -1,2 +1 @@
 export {default as withTracks} from './withTracks.js';
-export {default as withTrackSections} from './withTrackSections.js';
diff --git a/src/data/composite/things/album/withTrackSections.js b/src/data/composite/things/album/withTrackSections.js
deleted file mode 100644
index 0a1ebebc..00000000
--- a/src/data/composite/things/album/withTrackSections.js
+++ /dev/null
@@ -1,127 +0,0 @@
-import {input, templateCompositeFrom} from '#composite';
-import find from '#find';
-import {empty, filterMultipleArrays, stitchArrays} from '#sugar';
-import {isTrackSectionList} from '#validators';
-
-import {exitWithoutDependency, exitWithoutUpdateValue}
-  from '#composite/control-flow';
-import {withResolvedReferenceList} from '#composite/wiki-data';
-
-import {
-  fillMissingListItems,
-  withFlattenedList,
-  withPropertiesFromList,
-  withUnflattenedList,
-} from '#composite/data';
-
-export default templateCompositeFrom({
-  annotation: `withTrackSections`,
-
-  outputs: ['#trackSections'],
-
-  steps: () => [
-    exitWithoutDependency({
-      dependency: 'ownTrackData',
-      value: input.value([]),
-    }),
-
-    exitWithoutUpdateValue({
-      mode: input.value('empty'),
-      value: input.value([]),
-    }),
-
-    // TODO: input.updateValue description down here is a kludge.
-    withPropertiesFromList({
-      list: input.updateValue({
-        validate: isTrackSectionList,
-      }),
-      prefix: input.value('#sections'),
-      properties: input.value([
-        'tracks',
-        'dateOriginallyReleased',
-        'isDefaultTrackSection',
-        'name',
-        'color',
-      ]),
-    }),
-
-    fillMissingListItems({
-      list: '#sections.tracks',
-      fill: input.value([]),
-    }),
-
-    fillMissingListItems({
-      list: '#sections.isDefaultTrackSection',
-      fill: input.value(false),
-    }),
-
-    fillMissingListItems({
-      list: '#sections.name',
-      fill: input.value('Unnamed Track Section'),
-    }),
-
-    fillMissingListItems({
-      list: '#sections.color',
-      fill: input.dependency('color'),
-    }),
-
-    withFlattenedList({
-      list: '#sections.tracks',
-    }).outputs({
-      ['#flattenedList']: '#trackRefs',
-      ['#flattenedIndices']: '#sections.startIndex',
-    }),
-
-    withResolvedReferenceList({
-      list: '#trackRefs',
-      data: 'ownTrackData',
-      notFoundMode: input.value('null'),
-      find: input.value(find.track),
-    }).outputs({
-      ['#resolvedReferenceList']: '#tracks',
-    }),
-
-    withUnflattenedList({
-      list: '#tracks',
-      indices: '#sections.startIndex',
-    }).outputs({
-      ['#unflattenedList']: '#sections.tracks',
-    }),
-
-    {
-      dependencies: [
-        '#sections.tracks',
-        '#sections.name',
-        '#sections.color',
-        '#sections.dateOriginallyReleased',
-        '#sections.isDefaultTrackSection',
-        '#sections.startIndex',
-      ],
-
-      compute: (continuation, {
-        '#sections.tracks': tracks,
-        '#sections.name': name,
-        '#sections.color': color,
-        '#sections.dateOriginallyReleased': dateOriginallyReleased,
-        '#sections.isDefaultTrackSection': isDefaultTrackSection,
-        '#sections.startIndex': startIndex,
-      }) => {
-        filterMultipleArrays(
-          tracks, name, color, dateOriginallyReleased, isDefaultTrackSection, startIndex,
-          tracks => !empty(tracks));
-
-        return continuation({
-          ['#trackSections']:
-            stitchArrays({
-              tracks,
-              name,
-              color,
-              dateOriginallyReleased,
-              isDefaultTrackSection,
-              startIndex,
-            }),
-        });
-      },
-    },
-  ],
-});
diff --git a/src/data/composite/things/album/withTracks.js b/src/data/composite/things/album/withTracks.js
index fff3d5ae..05f5b24d 100644
--- a/src/data/composite/things/album/withTracks.js
+++ b/src/data/composite/things/album/withTracks.js
@@ -1,9 +1,8 @@
 import {input, templateCompositeFrom} from '#composite';
-import find from '#find';
 
 import {exitWithoutDependency, raiseOutputWithoutDependency}
   from '#composite/control-flow';
-import {withResolvedReferenceList} from '#composite/wiki-data';
+import {withFlattenedList, withPropertyFromList} from '#composite/data';
 
 export default templateCompositeFrom({
   annotation: `withTracks`,
@@ -11,41 +10,22 @@ export default templateCompositeFrom({
   outputs: ['#tracks'],
 
   steps: () => [
-    exitWithoutDependency({
-      dependency: 'ownTrackData',
-      value: input.value([]),
-    }),
-
     raiseOutputWithoutDependency({
       dependency: 'trackSections',
-      mode: input.value('empty'),
       output: input.value({
-        ['#tracks']: [],
+        '#tracks': [],
       }),
     }),
 
-    {
-      dependencies: ['trackSections'],
-      compute: (continuation, {trackSections}) =>
-        continuation({
-          '#trackRefs': trackSections
-            .flatMap(section => section.tracks ?? []),
-        }),
-    },
-
-    withResolvedReferenceList({
-      list: '#trackRefs',
-      data: 'ownTrackData',
-      find: input.value(find.track),
+    withPropertyFromList({
+      list: 'trackSections',
+      property: input.value('tracks'),
     }),
 
-    {
-      dependencies: ['#resolvedReferenceList'],
-      compute: (continuation, {
-        ['#resolvedReferenceList']: resolvedReferenceList,
-      }) => continuation({
-        ['#tracks']: resolvedReferenceList,
-      })
-    },
+    withFlattenedList({
+      list: '#trackSections.tracks',
+    }).outputs({
+      ['#flattenedList']: '#tracks',
+    }),
   ],
 });
diff --git a/src/data/composite/things/track-section/index.js b/src/data/composite/things/track-section/index.js
new file mode 100644
index 00000000..3202ed49
--- /dev/null
+++ b/src/data/composite/things/track-section/index.js
@@ -0,0 +1 @@
+export {default as withAlbum} from './withAlbum.js';
diff --git a/src/data/composite/things/track-section/withAlbum.js b/src/data/composite/things/track-section/withAlbum.js
new file mode 100644
index 00000000..608cc0cd
--- /dev/null
+++ b/src/data/composite/things/track-section/withAlbum.js
@@ -0,0 +1,22 @@
+// Gets the track section's album. This will early exit if ownAlbumData is
+// missing. If there's no album whose list of track sections includes this one,
+// the output dependency will be null.
+
+import {input, templateCompositeFrom} from '#composite';
+
+import {withUniqueReferencingThing} from '#composite/wiki-data';
+
+export default templateCompositeFrom({
+  annotation: `withAlbum`,
+
+  outputs: ['#album'],
+
+  steps: () => [
+    withUniqueReferencingThing({
+      data: 'ownAlbumData',
+      list: input.value('trackSections'),
+    }).outputs({
+      ['#uniqueReferencingThing']: '#album',
+    }),
+  ],
+});
diff --git a/src/data/things/album.js b/src/data/things/album.js
index f8354962..78ecb294 100644
--- a/src/data/things/album.js
+++ b/src/data/things/album.js
@@ -6,15 +6,17 @@ import {input} from '#composite';
 import find from '#find';
 import {traverse} from '#node-utils';
 import {sortAlbumsTracksChronologically, sortChronologically} from '#sort';
-import {empty} from '#sugar';
+import {accumulateSum, empty} from '#sugar';
 import Thing from '#thing';
-import {isDate} from '#validators';
+import {isColor, isDate, validateWikiData} from '#validators';
 import {parseAdditionalFiles, parseContributors, parseDate, parseDimensions}
   from '#yaml';
 
-import {exposeDependency, exposeUpdateValueOrContinue}
+import {exitWithoutDependency, exposeDependency, exposeUpdateValueOrContinue}
   from '#composite/control-flow';
-import {exitWithoutContribs} from '#composite/wiki-data';
+import {withPropertyFromObject} from '#composite/data';
+import {exitWithoutContribs, withDirectory, withResolvedReference}
+  from '#composite/wiki-data';
 
 import {
   additionalFiles,
@@ -31,16 +33,24 @@ import {
   referenceList,
   simpleDate,
   simpleString,
+  singleReference,
   urls,
   wikiData,
 } from '#composite/wiki-properties';
 
-import {withTracks, withTrackSections} from '#composite/things/album';
+import {withTracks} from '#composite/things/album';
+import {withAlbum} from '#composite/things/track-section';
 
 export class Album extends Thing {
   static [Thing.referenceType] = 'album';
 
-  static [Thing.getPropertyDescriptors] = ({ArtTag, Artist, Group, Track}) => ({
+  static [Thing.getPropertyDescriptors] = ({
+    ArtTag,
+    Artist,
+    Group,
+    Track,
+    TrackSection,
+  }) => ({
     // Update & expose
 
     name: name('Unnamed Album'),
@@ -111,10 +121,17 @@ export class Album extends Thing {
     commentary: commentary(),
     additionalFiles: additionalFiles(),
 
-    trackSections: [
-      withTrackSections(),
-      exposeDependency({dependency: '#trackSections'}),
-    ],
+    trackSections: {
+      flags: {update: true, expose: true},
+
+      update: {
+        validate:
+          validateWikiData({
+            referenceType:
+              TrackSection[Thing.referenceType],
+          }),
+      },
+    },
 
     artistContribs: contributionList(),
     coverArtistContribs: contributionList(),
@@ -155,13 +172,6 @@ export class Album extends Thing {
       class: input.value(Group),
     }),
 
-    // Only the tracks which belong to this album.
-    // Necessary for computing the track list, so provide this statically
-    // or keep it updated.
-    ownTrackData: wikiData({
-      class: input.value(Track),
-    }),
-
     // Expose only
 
     commentatorArtists: commentatorArtists(),
@@ -345,7 +355,7 @@ export class Album extends Thing {
     headerDocumentThing: Album,
     entryDocumentThing: document =>
       ('Section' in document
-        ? TrackSectionHelper
+        ? TrackSection
         : Track),
 
     save(results) {
@@ -353,49 +363,49 @@ export class Album extends Thing {
       const trackData = [];
 
       for (const {header: album, entries} of results) {
-        // We can't mutate an array once it's set as a property value,
-        // so prepare the track sections that will show up in a track list
-        // all the way before actually applying them. (It's okay to mutate
-        // an individual section before applying it, since those are just
-        // generic objects; they aren't Things in and of themselves.)
         const trackSections = [];
-        const ownTrackData = [];
 
-        let currentTrackSection = {
+        let currentTrackSection = new TrackSection();
+        let currentTrackSectionTracks = [];
+
+        Object.assign(currentTrackSection, {
           name: `Default Track Section`,
           isDefaultTrackSection: true,
-          tracks: [],
-        };
+        });
 
         const albumRef = Thing.getReference(album);
 
         const closeCurrentTrackSection = () => {
-          if (!empty(currentTrackSection.tracks)) {
-            trackSections.push(currentTrackSection);
+          if (empty(currentTrackSectionTracks)) {
+            return;
           }
+
+          currentTrackSection.tracks =
+            currentTrackSectionTracks
+              .map(track => Thing.getReference(track));
+
+          currentTrackSection.ownTrackData =
+            currentTrackSectionTracks;
+
+          currentTrackSection.ownAlbumData =
+            [album];
+
+          trackSections.push(currentTrackSection);
         };
 
         for (const entry of entries) {
-          if (entry instanceof TrackSectionHelper) {
+          if (entry instanceof TrackSection) {
             closeCurrentTrackSection();
-
-            currentTrackSection = {
-              name: entry.name,
-              color: entry.color,
-              dateOriginallyReleased: entry.dateOriginallyReleased,
-              isDefaultTrackSection: false,
-              tracks: [],
-            };
-
+            currentTrackSection = entry;
+            currentTrackSectionTracks = [];
             continue;
           }
 
+          currentTrackSectionTracks.push(entry);
+
           trackData.push(entry);
 
           entry.dataSourceAlbum = albumRef;
-
-          ownTrackData.push(entry);
-          currentTrackSection.tracks.push(Thing.getReference(entry));
         }
 
         closeCurrentTrackSection();
@@ -403,7 +413,6 @@ export class Album extends Thing {
         albumData.push(album);
 
         album.trackSections = trackSections;
-        album.ownTrackData = ownTrackData;
       }
 
       return {albumData, trackData};
@@ -416,15 +425,97 @@ export class Album extends Thing {
   });
 }
 
-export class TrackSectionHelper extends Thing {
+export class TrackSection extends Thing {
   static [Thing.friendlyName] = `Track Section`;
+  static [Thing.referenceType] = `track-section`;
+
+  static [Thing.getPropertyDescriptors] = ({Album, Track}) => ({
+    // Update & expose
 
-  static [Thing.getPropertyDescriptors] = () => ({
     name: name('Unnamed Track Section'),
-    color: color(),
+
+    unqualifiedDirectory: directory(),
+
+    color: [
+      exposeUpdateValueOrContinue({
+        validate: input.value(isColor),
+      }),
+
+      withAlbum(),
+
+      withPropertyFromObject({
+        object: '#album',
+        property: input.value('color'),
+      }),
+
+      exposeDependency({dependency: '#album.color'}),
+    ],
+
     dateOriginallyReleased: simpleDate(),
-    isDefaultTrackGroup: flag(false),
-  })
+
+    isDefaultTrackSection: flag(false),
+
+    album: [
+      withAlbum(),
+      exposeDependency({dependency: '#album'}),
+    ],
+
+    tracks: referenceList({
+      class: input.value(Track),
+      data: 'ownTrackData',
+      find: input.value(find.track),
+    }),
+
+    // Update only
+
+    ownAlbumData: wikiData({
+      class: input.value(Album),
+    }),
+
+    ownTrackData: wikiData({
+      class: input.value(Track),
+    }),
+
+    // Expose only
+
+    startIndex: [
+      withAlbum(),
+
+      withPropertyFromObject({
+        object: '#album',
+        property: input.value('trackSections'),
+      }),
+
+      {
+        dependencies: ['#album.trackSections', input.myself()],
+        compute: (continuation, {
+          ['#album.trackSections']: trackSections,
+          [input.myself()]: myself,
+        }) => continuation({
+          ['#index']:
+            trackSections.indexOf(myself),
+        }),
+      },
+
+      exitWithoutDependency({
+        dependency: '#index',
+        mode: input.value('index'),
+        value: input.value(0),
+      }),
+
+      {
+        dependencies: ['#album.trackSections', '#index'],
+        compute: ({
+          ['#album.trackSections']: trackSections,
+          ['#index']: index,
+        }) =>
+          accumulateSum(
+            trackSections
+              .slice(0, index)
+              .map(section => section.tracks.length)),
+      },
+    ],
+  });
 
   static [Thing.yamlDocumentSpec] = {
     fields: {
diff --git a/test/lib/wiki-data.js b/test/lib/wiki-data.js
index d2d860ce..75b1170a 100644
--- a/test/lib/wiki-data.js
+++ b/test/lib/wiki-data.js
@@ -13,20 +13,20 @@ export function linkAndBindWikiData(wikiData, {
             .map(([key, value]) => [key, value.slice()]))
         : wikiData));
 
-    // If albumData is present, automatically set albums' ownTrackData values
-    // by resolving track sections' references against the full array. This is
-    // just a nicety for working with albums throughout tests.
+    // If albumData is present, automatically set their sections' ownTrackData
+    // by resolving references against the full array. This is just a nicety
+    // for working with albums throughout tests.
     if (inferAlbumsOwnTrackData && wikiData.albumData && wikiData.trackData) {
       for (const album of wikiData.albumData) {
         const trackSections =
           CacheableObject.getUpdateValue(album, 'trackSections');
 
-        const trackRefs =
-          trackSections.flatMap(section => section.tracks);
-
-        album.ownTrackData =
-          trackRefs.map(ref =>
-            find.track(ref, wikiData.trackData, {mode: 'error'}));
+        for (const trackSection of trackSections) {
+          trackSection.ownTrackData =
+            CacheableObject.getUpdateValue(trackSection, 'tracks')
+              .map(ref =>
+                find.track(ref, wikiData.trackData, {mode: 'error'}));
+        }
       }
     }
   }