feat(backend): stats service and routes

packages/backend/src/routes/stats.ts

@@ -0,0 +1,23 @@
+import { Router } from 'express';
+import type { Db } from '../db/client.js';
+import { getCardStats, getHeatmap, getLessonStats, getOverview } from '../services/stats.js';
+
+export function statsRouter(db: Db): Router {
+  const r = Router();
+  r.get('/overview', async (_req, res, next) => {
+    try { res.json(await getOverview(db)); } catch (e) { next(e); }
+  });
+  r.get('/lessons/:id', async (req, res, next) => {
+    try { res.json(await getLessonStats(db, Number(req.params.id))); } catch (e) { next(e); }
+  });
+  r.get('/cards/:id', async (req, res, next) => {
+    try { res.json(await getCardStats(db, Number(req.params.id))); } catch (e) { next(e); }
+  });
+  r.get('/heatmap', async (req, res, next) => {
+    try {
+      const weeks = Math.min(52, Math.max(1, Number(req.query.weeks ?? 12)));
+      res.json(await getHeatmap(db, weeks));
+    } catch (e) { next(e); }
+  });
+  return r;
+}