events: add events table and prepared statements

src/db.js

@@ -56,6 +56,22 @@ db.exec(`
 
   CREATE INDEX IF NOT EXISTS idx_bifrost_joins_email      ON bifrost_joins(email);
   CREATE INDEX IF NOT EXISTS idx_bifrost_joins_clicked_at ON bifrost_joins(clicked_at);
+
+  CREATE TABLE IF NOT EXISTS events (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    event_type  TEXT    NOT NULL,
+    email       TEXT    NOT NULL,
+    occurred_at INTEGER NOT NULL,
+    session_id  TEXT,
+    device_type TEXT,
+    os          TEXT,
+    browser     TEXT,
+    user_agent  TEXT,
+    meta        TEXT
+  );
+
+  CREATE INDEX IF NOT EXISTS idx_events_email     ON events(email);
+  CREATE INDEX IF NOT EXISTS idx_events_type_time ON events(event_type, occurred_at);
 `);
 
 // ─── Migrations ──────────────────────────────────────────────
@@ -173,6 +189,49 @@ export const q = {
   countJoins:        db.prepare(`SELECT COUNT(*)           AS n FROM bifrost_joins`),
   countUniqueJoiners: db.prepare(`SELECT COUNT(DISTINCT email) AS n FROM bifrost_joins`),
 
+  // events — engagement tracking. One row per landmark event
+  // (login, timeline_view) with device fields parsed from the UA.
+  // Read-only from the app side; written once per event, never updated.
+  recordEvent: db.prepare(
+    `INSERT INTO events
+       (event_type, email, occurred_at, session_id, device_type, os, browser, user_agent, meta)
+     VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)`
+  ),
+  listEvents: db.prepare(
+    `SELECT id, event_type, email, occurred_at, session_id, device_type, os, browser, user_agent, meta
+     FROM events ORDER BY occurred_at DESC LIMIT ?`
+  ),
+  listEventsByType: db.prepare(
+    `SELECT id, event_type, email, occurred_at, session_id, device_type, os, browser, user_agent, meta
+     FROM events WHERE event_type = ? ORDER BY occurred_at DESC LIMIT ?`
+  ),
+  listEventsForEmail: db.prepare(
+    `SELECT id, event_type, occurred_at, session_id, device_type, os, browser, meta
+     FROM events WHERE email = ? ORDER BY occurred_at DESC`
+  ),
+  // Per-user summary: pivot login + timeline_view counts onto one row.
+  summariseEvents: db.prepare(
+    `SELECT email,
+            SUM(CASE WHEN event_type = 'login'         THEN 1 ELSE 0 END) AS logins,
+            SUM(CASE WHEN event_type = 'timeline_view' THEN 1 ELSE 0 END) AS timeline_views,
+            MAX(occurred_at) AS last_seen
+     FROM events
+     GROUP BY email
+     ORDER BY last_seen DESC`
+  ),
+  countEventsByType: db.prepare(
+    `SELECT event_type,
+            COUNT(*)              AS total,
+            COUNT(DISTINCT email) AS unique_users
+     FROM events GROUP BY event_type ORDER BY event_type`
+  ),
+  deviceBreakdown: db.prepare(
+    `SELECT device_type, COUNT(*) AS n
+     FROM events
+     WHERE device_type IS NOT NULL
+     GROUP BY device_type ORDER BY n DESC`
+  ),
+
   // cleanup
   cleanup: {
     sessions: db.prepare('DELETE FROM sessions     WHERE expires_at < ?'),