Changes again

frontend/src/hooks/useTelemetry.ts

@@ -0,0 +1,58 @@
+import { useEffect, useRef } from 'react';
+import { apiUrl } from '../lib/api';
+
+/**
+ * Sends a telemetry beacon every 30 seconds with session duration
+ * and the number of active filters (parsed from the URL `f` param).
+ * On the first beacon, also sends the entry path and referrer domain.
+ */
+export function useTelemetry() {
+  const startTime = useRef(Date.now());
+  const entryPath = useRef(window.location.pathname);
+  const referrer = useRef(extractReferrerDomain());
+  const sentEntry = useRef(false);
+
+  useEffect(() => {
+    const send = () => {
+      const sessionSeconds = Math.round((Date.now() - startTime.current) / 1000);
+
+      // Count active filters from URL (filters are encoded as `f=name:min:max;;name:val`)
+      const params = new URLSearchParams(window.location.search);
+      const filterStr = params.get('f') || '';
+      const filterCount = filterStr ? filterStr.split(';;').length : 0;
+
+      const payload: Record<string, unknown> = {
+        session_seconds: sessionSeconds,
+        filter_count: filterCount,
+      };
+
+      // Include entrypoint info on first beacon only
+      if (!sentEntry.current) {
+        payload.entry_path = entryPath.current;
+        payload.referrer = referrer.current;
+        sentEntry.current = true;
+      }
+
+      navigator.sendBeacon(
+        apiUrl('telemetry'),
+        new Blob([JSON.stringify(payload)], { type: 'application/json' })
+      );
+    };
+
+    const interval = setInterval(send, 30_000);
+    return () => clearInterval(interval);
+  }, []);
+}
+
+/** Extract the referrer domain, or "direct" if none / same-origin. */
+function extractReferrerDomain(): string {
+  if (!document.referrer) return 'direct';
+  try {
+    const url = new URL(document.referrer);
+    // Same-origin navigation isn't a real external referrer
+    if (url.origin === window.location.origin) return 'direct';
+    return url.hostname;
+  } catch {
+    return 'direct';
+  }
+}