feat(classroom): remote classroom backend — lifecycle, presence, help queue, dashboard

- classroom.js: create/start/end/cancel (DB-level partial unique index guarantees at most one live classroom per cohort; app layer catches 23505 and returns a clean ALREADY_LIVE), join/ leave/heartbeat, derivePresence (pure, derived from last_seen_at at read time — no stored status to go stale), help-request create/acknowledge/resolve, announcements, current-activity (guidance only, never redirects a browser or marks work complete), append-only event log. - admin-classroom-routes.js: instructor-facing classroom API, RBAC via rbac.js's requireClassroomAccess/requireClassroomWriteAccess/requireHelpRequestWriteAccess (resolves through to the classroom's cohort, same owner/admin/instructor/viewer rules as everywhere else cohort-scoped). The dashboard route (GET /api/admin/classroom-sessions/:id) combines real Provisioner Lab state and real academic records with classroom.js's own data — no second Lab-state or academic-state system. - classroom-routes.js: student-facing API (live classroom, join/leave/heartbeat, help-request, announcements), requireEnrolledClassroom middleware. - prepare-labs.js: shared prepareLabsForCohort, extracted so the existing cohort-level and new classroom-level Prepare Labs routes share one implementation; maps Phase 4.1 admission control's CAPACITY_EXCEEDED into a capacity_waiting per-student result.
2026-08-25 01:19:33 -05:00
parent d34ddae458
commit ee8ccb2ab6
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+// Classroom session lifecycle — Phase 5A §11-§20. A classroom session is a live teaching event,
+// distinct from a cohort (standing roster), an assessment session (one exam attempt), a Lab
+// environment (disposable infra), or a login session. This module owns the pure
+// classroom_sessions/classroom_participants/classroom_events/classroom_announcements/
+// help_requests CRUD and lifecycle rules; route files (admin-classroom-routes.js,
+// classroom-routes.js) own RBAC/session/HTTP shape and the dashboard aggregation that pulls in
+// Provisioner Lab state and Phase 3B academic records (this module doesn't know about either).
+
+const PRESENCE_ONLINE_MS = 45 * 1000;          // ~1.5x the 20-30s heartbeat interval the frontend uses
+const PRESENCE_RECENTLY_ACTIVE_MS = 5 * 60 * 1000;
+const HEARTBEAT_WRITE_THROTTLE_MS = 15 * 1000; // §15 "avoid excessive database writes" — coalesce heartbeats closer together than this into a no-op
+
+async function emitEvent(pool, classroomSessionId, actorType, actorId, eventType, metadata) {
+  await pool.query(
+    `INSERT INTO classroom_events (classroom_session_id, actor_type, actor_id, event_type, metadata)
+     VALUES ($1, $2, $3, $4, $5)`,
+    [classroomSessionId, actorType, actorId ? String(actorId) : null, eventType, metadata ? JSON.stringify(metadata) : null]
+  );
+}
+
+async function createClassroom(pool, { cohortId, title, description, scheduledStart, scheduledEnd, meetingUrl, createdBy }) {
+  const { rows } = await pool.query(
+    `INSERT INTO classroom_sessions (cohort_id, title, description, scheduled_start, scheduled_end, meeting_url, created_by)
+     VALUES ($1, $2, $3, $4, $5, $6, $7) RETURNING *`,
+    [cohortId, title, description || null, scheduledStart || null, scheduledEnd || null, meetingUrl || null, createdBy]
+  );
+  const classroom = rows[0];
+  await emitEvent(pool, classroom.classroom_session_id, 'instructor', createdBy, 'created', { title });
+  return classroom;
+}
+
+async function getClassroom(pool, classroomSessionId) {
+  const { rows } = await pool.query(`SELECT * FROM classroom_sessions WHERE classroom_session_id = $1`, [classroomSessionId]);
+  return rows[0] || null;
+}
+
+async function listClassroomsForCohort(pool, cohortId) {
+  const { rows } = await pool.query(
+    `SELECT * FROM classroom_sessions WHERE cohort_id = $1 ORDER BY COALESCE(scheduled_start, created_at) DESC`,
+    [cohortId]
+  );
+  return rows;
+}
+
+// §13 lifecycle: scheduled -> live -> ended, or -> cancelled from scheduled/live. The DB's
+// partial unique index (idx_classroom_sessions_one_live_per_cohort) is the actual enforcement
+// for "at most one live classroom per cohort" — this pre-check just gives a clean error
+// instead of a raw constraint-violation message.
+async function startClassroom(pool, classroomSessionId, instructorId) {
+  const classroom = await getClassroom(pool, classroomSessionId);
+  if (!classroom) throw Object.assign(new Error('classroom not found'), { code: 'NOT_FOUND' });
+  if (classroom.status !== 'scheduled') throw Object.assign(new Error(`cannot start a classroom in status '${classroom.status}'`), { code: 'INVALID_STATE' });
+  try {
+    const { rows } = await pool.query(
+      `UPDATE classroom_sessions SET status = 'live', started_at = now(), updated_at = now() WHERE classroom_session_id = $1 RETURNING *`,
+      [classroomSessionId]
+    );
+    await emitEvent(pool, classroomSessionId, 'instructor', instructorId, 'started', {});
+    return rows[0];
+  } catch (e) {
+    if (e.code === '23505') throw Object.assign(new Error('this cohort already has a live classroom'), { code: 'ALREADY_LIVE' });
+    throw e;
+  }
+}
+
+// Ending a classroom is purely a status change — never touches Labs, progress, attempts, or
+// any academic data (§13/§26). Labs are only ever destroyed by an explicit, separate action
+// (the existing cohort Destroy Labs / Prepare Labs machinery), never implicitly by this.
+async function endClassroom(pool, classroomSessionId, instructorId) {
+  const { rows } = await pool.query(
+    `UPDATE classroom_sessions SET status = 'ended', ended_at = now(), updated_at = now()
+     WHERE classroom_session_id = $1 AND status = 'live' RETURNING *`,
+    [classroomSessionId]
+  );
+  if (!rows.length) throw Object.assign(new Error('classroom not found or not live'), { code: 'INVALID_STATE' });
+  await emitEvent(pool, classroomSessionId, 'instructor', instructorId, 'ended', {});
+  return rows[0];
+}
+
+async function cancelClassroom(pool, classroomSessionId, instructorId) {
+  const { rows } = await pool.query(
+    `UPDATE classroom_sessions SET status = 'cancelled', updated_at = now()
+     WHERE classroom_session_id = $1 AND status IN ('scheduled', 'live') RETURNING *`,
+    [classroomSessionId]
+  );
+  if (!rows.length) throw Object.assign(new Error('classroom not found or already ended/cancelled'), { code: 'INVALID_STATE' });
+  await emitEvent(pool, classroomSessionId, 'instructor', instructorId, 'cancelled', {});
+  return rows[0];
+}
+
+// §20 — guidance only. Never redirects a browser, never marks anything complete; students just
+// see this value and choose to open that scenario themselves (see classroom-routes.js).
+async function setCurrentActivity(pool, classroomSessionId, scenarioId, instructorId) {
+  const { rows } = await pool.query(
+    `UPDATE classroom_sessions SET current_scenario_id = $1, updated_at = now() WHERE classroom_session_id = $2 RETURNING *`,
+    [scenarioId || null, classroomSessionId]
+  );
+  if (!rows.length) throw Object.assign(new Error('classroom not found'), { code: 'NOT_FOUND' });
+  await emitEvent(pool, classroomSessionId, 'instructor', instructorId, 'activity_changed', { scenario_id: scenarioId });
+  return rows[0];
+}
+
+async function postAnnouncement(pool, classroomSessionId, instructorId, message) {
+  const { rows } = await pool.query(
+    `INSERT INTO classroom_announcements (classroom_session_id, instructor_id, message) VALUES ($1, $2, $3) RETURNING *`,
+    [classroomSessionId, instructorId, message]
+  );
+  await emitEvent(pool, classroomSessionId, 'instructor', instructorId, 'announcement_posted', { announcement_id: rows[0].announcement_id });
+  return rows[0];
+}
+
+async function listAnnouncements(pool, classroomSessionId) {
+  const { rows } = await pool.query(
+    `SELECT announcement_id, message, created_at FROM classroom_announcements
+     WHERE classroom_session_id = $1 ORDER BY created_at DESC LIMIT 50`,
+    [classroomSessionId]
+  );
+  return rows;
+}
+
+// §11/§22 — join is idempotent: re-joining an already-joined classroom just clears left_at and
+// bumps last_seen_at, it doesn't create a second row or duplicate joined_at (PRIMARY KEY is
+// (classroom_session_id, student_id) — there can only ever be one participation row per
+// student per classroom, matching how a student can leave and rejoin the same live session).
+async function joinClassroom(pool, classroomSessionId, studentId) {
+  const { rows } = await pool.query(
+    `INSERT INTO classroom_participants (classroom_session_id, student_id, last_seen_at)
+     VALUES ($1, $2, now())
+     ON CONFLICT (classroom_session_id, student_id)
+       DO UPDATE SET last_seen_at = now(), left_at = NULL
+     RETURNING *`,
+    [classroomSessionId, studentId]
+  );
+  await emitEvent(pool, classroomSessionId, 'student', studentId, 'joined', {});
+  return rows[0];
+}
+
+async function leaveClassroom(pool, classroomSessionId, studentId) {
+  await pool.query(
+    `UPDATE classroom_participants SET left_at = now() WHERE classroom_session_id = $1 AND student_id = $2`,
+    [classroomSessionId, studentId]
+  );
+  await emitEvent(pool, classroomSessionId, 'student', studentId, 'left', {});
+}
+
+// §15 presence — throttled: a heartbeat within HEARTBEAT_WRITE_THROTTLE_MS of the last recorded
+// one is a silent no-op (still returns success to the client, just skips the write) rather than
+// hammering Postgres every 20s per online student. Deliberately NOT a full audit-logged event
+// (§25 "do not turn presence heartbeats into audit spam") — no classroom_events row per beat.
+async function heartbeat(pool, classroomSessionId, studentId) {
+  await pool.query(
+    `UPDATE classroom_participants SET last_seen_at = now()
+     WHERE classroom_session_id = $1 AND student_id = $2
+       AND (last_seen_at IS NULL OR last_seen_at < now() - ($3 || ' milliseconds')::interval)`,
+    [classroomSessionId, studentId, HEARTBEAT_WRITE_THROTTLE_MS]
+  );
+}
+
+function derivePresence(lastSeenAt, leftAt) {
+  if (leftAt) return 'offline';
+  if (!lastSeenAt) return 'offline';
+  const age = Date.now() - new Date(lastSeenAt).getTime();
+  if (age <= PRESENCE_ONLINE_MS) return 'online';
+  if (age <= PRESENCE_RECENTLY_ACTIVE_MS) return 'recently_active';
+  return 'offline';
+}
+
+async function listParticipants(pool, classroomSessionId) {
+  const { rows } = await pool.query(
+    `SELECT cp.student_id, s.display_name, cp.joined_at, cp.last_seen_at, cp.left_at
+     FROM classroom_participants cp JOIN students s ON s.student_id = cp.student_id
+     WHERE cp.classroom_session_id = $1 ORDER BY s.display_name`,
+    [classroomSessionId]
+  );
+  return rows.map((r) => ({ ...r, presence: derivePresence(r.last_seen_at, r.left_at) }));
+}
+
+// §27 — a student may be enrolled in more than one cohort eventually (self-paced compatible);
+// this returns the FIRST live classroom across any cohort they're enrolled in, not "their one
+// cohort's classroom" — matches "My Courses, not My Cohort" (§27) as the eventual shape.
+async function getLiveClassroomForStudent(pool, studentId) {
+  const { rows } = await pool.query(
+    `SELECT cs.* FROM classroom_sessions cs
+     JOIN cohort_enrollments e ON e.cohort_id = cs.cohort_id
+     WHERE e.student_id = $1 AND e.enrollment_status = 'enrolled' AND cs.status = 'live'
+     ORDER BY cs.started_at DESC LIMIT 1`,
+    [studentId]
+  );
+  return rows[0] || null;
+}
+
+// §18 help requests
+async function createHelpRequest(pool, classroomSessionId, studentId, category, message) {
+  const { rows } = await pool.query(
+    `INSERT INTO help_requests (classroom_session_id, student_id, category, message) VALUES ($1, $2, $3, $4) RETURNING *`,
+    [classroomSessionId, studentId, category || null, message || null]
+  );
+  await emitEvent(pool, classroomSessionId, 'student', studentId, 'help_requested', { help_request_id: rows[0].help_request_id, category });
+  return rows[0];
+}
+
+async function listHelpRequests(pool, classroomSessionId, statusFilter) {
+  const { rows } = await pool.query(
+    `SELECT hr.*, s.display_name FROM help_requests hr JOIN students s ON s.student_id = hr.student_id
+     WHERE hr.classroom_session_id = $1 AND ($2::text IS NULL OR hr.status = $2)
+     ORDER BY hr.created_at ASC`,
+    [classroomSessionId, statusFilter || null]
+  );
+  return rows;
+}
+
+async function acknowledgeHelpRequest(pool, helpRequestId, instructorId) {
+  const { rows } = await pool.query(
+    `UPDATE help_requests SET status = 'acknowledged', acknowledged_at = now(), acknowledged_by = $1
+     WHERE help_request_id = $2 AND status = 'open' RETURNING *`,
+    [instructorId, helpRequestId]
+  );
+  if (!rows.length) throw Object.assign(new Error('help request not found or not open'), { code: 'INVALID_STATE' });
+  await emitEvent(pool, rows[0].classroom_session_id, 'instructor', instructorId, 'help_acknowledged', { help_request_id: helpRequestId });
+  return rows[0];
+}
+
+async function resolveHelpRequest(pool, helpRequestId, instructorId, note) {
+  const { rows } = await pool.query(
+    `UPDATE help_requests SET status = 'resolved', resolved_at = now(), instructor_note = COALESCE($1, instructor_note)
+     WHERE help_request_id = $2 AND status IN ('open', 'acknowledged') RETURNING *`,
+    [note || null, helpRequestId]
+  );
+  if (!rows.length) throw Object.assign(new Error('help request not found or already resolved'), { code: 'INVALID_STATE' });
+  await emitEvent(pool, rows[0].classroom_session_id, 'instructor', instructorId, 'help_resolved', { help_request_id: helpRequestId });
+  return rows[0];
+}
+
+module.exports = {
+  createClassroom, getClassroom, listClassroomsForCohort,
+  startClassroom, endClassroom, cancelClassroom, setCurrentActivity,
+  postAnnouncement, listAnnouncements,
+  joinClassroom, leaveClassroom, heartbeat, derivePresence, listParticipants,
+  getLiveClassroomForStudent,
+  createHelpRequest, listHelpRequests, acknowledgeHelpRequest, resolveHelpRequest,
+  emitEvent,
+};