4 files changed, 55 insertions, 1 deletions
diff --git a/src/data/composite/things/art-tag/index.js b/src/data/composite/things/art-tag/index.js
index 0c365ce2..bbd38293 100644
--- a/src/data/composite/things/art-tag/index.js
+++ b/src/data/composite/things/art-tag/index.js
@@ -1 +1,2 @@
 export {default as withAllDescendantArtTags} from './withAllDescendantArtTags.js';
+export {default as withAncestorArtTagBaobabTree} from './withAncestorArtTagBaobabTree.js';
diff --git a/src/data/composite/things/art-tag/withAncestorArtTagBaobabTree.js b/src/data/composite/things/art-tag/withAncestorArtTagBaobabTree.js
new file mode 100644
index 00000000..e084a42b
--- /dev/null
+++ b/src/data/composite/things/art-tag/withAncestorArtTagBaobabTree.js
@@ -0,0 +1,46 @@
+// Gets all the art tags which are ancestors of this one as a "baobab tree" -
+// what you'd typically think of as roots are all up in the air! Since this
+// really is backwards from the way that the art tag tree is written in data,
+// chances are pretty good that there will be many of the exact same "leaf"
+// nodes - art tags which don't themselves have any ancestors. In the actual
+// data structure, each node is a Map, with keys for each ancestor and values
+// for each ancestor's own baobab (thus a branching structure, just like normal
+// trees in this regard).
+
+import {input, templateCompositeFrom} from '#composite';
+
+import {raiseOutputWithoutDependency} from '#composite/control-flow';
+import {withReverseReferenceList} from '#composite/wiki-data';
+import {soupyReverse} from '#composite/wiki-properties';
+
+export default templateCompositeFrom({
+  annotation: `withAncestorArtTagBaobabTree`,
+
+  outputs: ['#ancestorArtTagBaobabTree'],
+
+  steps: () => [
+    withReverseReferenceList({
+      reverse: soupyReverse.input('artTagsWhichDirectlyAncestor'),
+    }).outputs({
+      ['#reverseReferenceList']: '#directAncestorArtTags',
+    }),
+
+    raiseOutputWithoutDependency({
+      dependency: '#directAncestorArtTags',
+      mode: input.value('empty'),
+      output: input.value({'#ancestorArtTagBaobabTree': new Map()}),
+    }),
+
+    {
+      dependencies: ['#directAncestorArtTags'],
+      compute: (continuation, {
+        ['#directAncestorArtTags']: directAncestorArtTags,
+      }) => continuation({
+        ['#ancestorArtTagBaobabTree']:
+          new Map(
+            directAncestorArtTags
+              .map(artTag => [artTag, artTag.ancestorArtTagBaobabTree])),
+      }),
+    },
+  ],
+});
diff --git a/src/data/things/art-tag.js b/src/data/things/art-tag.js
index 60a4340d..f023eb76 100644
--- a/src/data/things/art-tag.js
+++ b/src/data/things/art-tag.js
@@ -24,7 +24,8 @@ import {
   wikiData,
 } from '#composite/wiki-properties';
 
-import {withAllDescendantArtTags} from '#composite/things/art-tag';
+import {withAllDescendantArtTags, withAncestorArtTagBaobabTree}
+  from '#composite/things/art-tag';
 
 export class ArtTag extends Thing {
   static [Thing.referenceType] = 'tag';
@@ -113,6 +114,11 @@ export class ArtTag extends Thing {
     directAncestorArtTags: reverseReferenceList({
       reverse: soupyReverse.input('artTagsWhichDirectlyAncestor'),
     }),
+
+    ancestorArtTagBaobabTree: [
+      withAncestorArtTagBaobabTree(),
+      exposeDependency({dependency: '#ancestorArtTagBaobabTree'}),
+    ],
   });
 
   static [Thing.findSpecs] = {
diff --git a/src/data/things/language.js b/src/data/things/language.js
index 800c4471..98ce12c6 100644
--- a/src/data/things/language.js
+++ b/src/data/things/language.js
@@ -896,6 +896,7 @@ const countHelper = (stringKey, optionName = stringKey) =>
 Object.assign(Language.prototype, {
   countAdditionalFiles: countHelper('additionalFiles', 'files'),
   countAlbums: countHelper('albums'),
+  countArtTags: countHelper('artTags', 'tags'),
   countArtworks: countHelper('artworks'),
   countCommentaryEntries: countHelper('commentaryEntries', 'entries'),
   countContributions: countHelper('contributions'),