Add global exploration data module (#163 #354 #449 #501)

frontend/src/global/exploration-data.ts

@@ -0,0 +1,88 @@
+import { get, constant } from 'lodash';
+
+import Model from '../core/model';
+import { source, item } from '../common-rdf/ns';
+import ldChannel from '../common-rdf/radio';
+import userChannel from '../common-user/user-radio';
+import ItemGraph from '../common-adapters/item-graph';
+import SparqlSelectCollection from '../common-adapters/sparql-select-collection';
+import {
+    countNodesQuery,
+    nodesByUserQuery,
+    randomNodesQuery,
+} from '../sparql/compile-query';
+
+// Items and sources that the user may want to explore shortly after landing,
+// either because they are her own or because she may not know them yet.
+// These collections are initially empty, but we will take care of this in the
+// `lazyTrigger` function.
+const userItems = new ItemGraph();
+const randomItems = new ItemGraph();
+const userSources = new ItemGraph(source());
+const randomSources = new ItemGraph(source());
+
+// Helper collections that we use to determine the total numbers of items and
+// sources in the backend triple store. Eventually, they will contain just a
+// single model with just a single attribute, 'tally'.
+const itemTally = new SparqlSelectCollection('item');
+const sourceTally = new SparqlSelectCollection('source');
+
+// The model containing the statistics that we want to show on the landing page.
+// It will be updated when the above collections are fetched.
+const statistics = new Model({
+    totalItems: 0,
+    totalSources: 0,
+    userItems: 0,
+    userSources: 0,
+});
+
+// Common pattern for registering an event handler in order to update one of the
+// statistics fields above.
+function trackStatistic(collection, event, sourceKey, targetKey) {
+    collection.once(event, (payload) =>
+        statistics.set(targetKey, get(payload, sourceKey))
+    );
+}
+
+// Inside the single model in the tally collections, this is where we find the
+// number we're interested in.
+const tallyPath = ['attributes', 'tally', 'value'];
+
+// Let's track those statistics!
+trackStatistic(itemTally, 'add', tallyPath, 'totalItems');
+trackStatistic(sourceTally, 'add', tallyPath, 'totalSources');
+trackStatistic(userItems, 'update', 'length', 'userItems');
+trackStatistic(userSources, 'update', 'length', 'userSources');
+
+// Function factory that ensures a query to the backend is issued when one of
+// our collections is first requested.
+function lazyTrigger(collection, queryGen, onItems) {
+    let trigger = () => collection.sparqlQuery(queryGen(onItems));
+    return function() {
+        if (trigger) {
+            if (queryGen === nodesByUserQuery) {
+                userChannel.request('promise').then(trigger);
+            } else {
+                trigger();
+            }
+            trigger = null;
+        }
+        return collection;
+    }
+}
+
+// Issue one of the requests below in order to obtain one of the above
+// collections, or the `statistics` model. Each of the collections has a
+// `promise` property that you can await if you need it to be complete already,
+// though it's probably best to just use a `CollectionView` in order to stay
+// up-to-date. The `statistics` model will update 2 or 4 times; for the most
+// accurate presentation, simply re-render whenever it changes.
+ldChannel.reply({
+    'items:tally': lazyTrigger(itemTally, countNodesQuery, true),
+    'items:user': lazyTrigger(userItems, nodesByUserQuery, true),
+    'items:sample': lazyTrigger(randomItems, randomNodesQuery, true),
+    'sources:tally': lazyTrigger(sourceTally, countNodesQuery, false),
+    'sources:user': lazyTrigger(userSources, nodesByUserQuery, false),
+    'sources:sample': lazyTrigger(randomSources, randomNodesQuery, false),
+    'statistics': constant(statistics),
+});