feat(telemetry): Phase 3 — policy preview endpoint (count matching clients from recent events)

services/platform-service/src/modules/telemetry/routes.ts

@@ -697,6 +697,62 @@ export async function telemetryRoutes(app: FastifyInstance) {
     return { clusters, total: clusters.length };
   });
 
+  // ── Admin: policy preview (count matching clients) ──────────
+  app.post('/telemetry/policies/preview', async req => {
+    requireAdmin(req);
+    const productId = getRequestProductId(req);
+    const targeting = (req.body as Record<string, unknown>)?.targeting as
+      | Record<string, unknown>
+      | undefined;
+
+    // Fetch recent events (last 7 days, up to 500)
+    const sevenDaysAgo = new Date(Date.now() - 7 * 86400000).toISOString();
+    const { events } = await repo.queryEvents(productId, {
+      from: sevenDaysAgo,
+      limit: 500,
+    });
+
+    // Filter events that match targeting
+    const matchedIds = new Set<string>();
+    for (const evt of events) {
+      if (
+        targeting?.platforms &&
+        Array.isArray(targeting.platforms) &&
+        targeting.platforms.length > 0
+      ) {
+        if (!targeting.platforms.includes(evt.platform)) continue;
+      }
+      if (
+        targeting?.channels &&
+        Array.isArray(targeting.channels) &&
+        targeting.channels.length > 0
+      ) {
+        if (!targeting.channels.includes(evt.channel)) continue;
+      }
+      if (
+        targeting?.osFamilies &&
+        Array.isArray(targeting.osFamilies) &&
+        targeting.osFamilies.length > 0
+      ) {
+        if (!targeting.osFamilies.includes(evt.osFamily)) continue;
+      }
+      if (
+        targeting?.releaseChannels &&
+        Array.isArray(targeting.releaseChannels) &&
+        targeting.releaseChannels.length > 0
+      ) {
+        if (!targeting.releaseChannels.includes(evt.releaseChannel)) continue;
+      }
+      matchedIds.add(evt.anonymousInstallId || evt.userId || evt.id);
+    }
+
+    return {
+      matchedClients: matchedIds.size,
+      totalClients: new Set(events.map(e => e.anonymousInstallId || e.userId || e.id)).size,
+      sampleSize: events.length,
+    };
+  });
+
   // ── Admin: list policies ──────────────────────────────────────
   app.get('/telemetry/policies', async req => {
     requireAdmin(req);