Trends: fill in empty tag histories

Fixes https://gitlab.com/soapbox-pub/ditto/-/issues/29

src/controllers/api/trends.ts

@@ -29,7 +29,7 @@ const trendingTagsController: AppController = (c) => {
         accounts: String(accounts),
         uses: String(uses),
       },
-      ...trends.getTagHistory({
+      ...getTagHistoryWithGapsFilled({
         tag: name,
         since: lastWeek,
         until: now,
@@ -44,4 +44,28 @@ const trendingTagsController: AppController = (c) => {
   })));
 };
 
+function generateDateRange(since: Date, until: Date): Date[] {
+  const dates = [];
+
+  const sinceDate = new Date(Date.UTC(since.getUTCFullYear(), since.getUTCMonth(), since.getUTCDate() + 1));
+  const untilDate = new Date(Date.UTC(until.getUTCFullYear(), until.getUTCMonth(), until.getUTCDate()));
+
+  while (sinceDate < untilDate) {
+    dates.push(new Date(sinceDate));
+    sinceDate.setUTCDate(sinceDate.getUTCDate() + 1);
+  }
+
+  return dates.reverse();
+}
+
+function getTagHistoryWithGapsFilled(params: Parameters<typeof trends.getTagHistory>[0]) {
+  const history = trends.getTagHistory(params);
+  const dateRange = generateDateRange(params.since, params.until);
+
+  return dateRange.map((day) => {
+    const data = history.find((item) => item.day.getTime() === day.getTime());
+    return data || { day, accounts: 0, uses: 0 };
+  });
+}
+
 export { trendingTagsController };