-- Live classroom sessions — Phase 5A §11/§12. A classroom session is a distinct concept from a
-- cohort (a standing roster), an assessment session (one student's exam attempt), a Lab
-- environment (disposable infrastructure), or a login session (one browser's auth) — it
-- represents ONE live teaching event, e.g. "Week 3 — Kubernetes Workloads, Aug 29 6-8pm."
--
-- Deliberately five tables, not one JSONB blob: classroom_sessions (the event itself),
-- classroom_participants (who's in it + presence), classroom_events (append-only audit trail),
-- classroom_announcements and help_requests get their own tables rather than being folded into
-- classroom_events, since both need efficient direct queries ("show me the open help queue",
-- "show me this classroom's announcements in order") that a generic event log would make
-- awkward. classroom_events stays the audit trail (docs/PHASE5A... §25) — it does NOT duplicate
-- announcement/help-request content, just records that the action happened.

CREATE TABLE IF NOT EXISTS classroom_sessions (
  classroom_session_id   UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  cohort_id              TEXT NOT NULL REFERENCES cohorts(cohort_id),
  title                  TEXT NOT NULL,
  description            TEXT,
  status                 TEXT NOT NULL DEFAULT 'scheduled'
                           CHECK (status IN ('scheduled', 'live', 'ended', 'cancelled')),
  scheduled_start        TIMESTAMPTZ,
  scheduled_end          TIMESTAMPTZ,
  started_at             TIMESTAMPTZ,
  ended_at               TIMESTAMPTZ,
  created_by             UUID REFERENCES instructors(instructor_id),
  -- "Current activity" (§20) — a scenario id, not a stage id, matching how students actually
  -- work (one scenario at a time). NULL means the instructor hasn't set one yet. This is
  -- guidance only — never used to redirect a browser or auto-mark work complete (enforced in
  -- application code: nothing reads this to gate access or grade anything).
  current_scenario_id    TEXT,
  -- Optional external video-conferencing link (§23) — a plain URL, RootNode never validates
  -- which provider it points at and never proxies/embeds it.
  meeting_url            TEXT,
  created_at             TIMESTAMPTZ NOT NULL DEFAULT now(),
  updated_at             TIMESTAMPTZ NOT NULL DEFAULT now()
);

CREATE INDEX IF NOT EXISTS idx_classroom_sessions_cohort ON classroom_sessions(cohort_id);
CREATE INDEX IF NOT EXISTS idx_classroom_sessions_status ON classroom_sessions(status);

-- At most one LIVE classroom per cohort at a time — an instructor starting a second live
-- session for the same cohort while one is already live is almost certainly a mistake, not a
-- real use case (see classroom.js's startClassroom for the app-level check this backs).
CREATE UNIQUE INDEX IF NOT EXISTS idx_classroom_sessions_one_live_per_cohort
  ON classroom_sessions(cohort_id) WHERE status = 'live';

CREATE TABLE IF NOT EXISTS classroom_participants (
  classroom_session_id   UUID NOT NULL REFERENCES classroom_sessions(classroom_session_id),
  student_id              TEXT NOT NULL REFERENCES students(student_id),
  joined_at               TIMESTAMPTZ NOT NULL DEFAULT now(),
  -- Presence (§15) — updated by a throttled heartbeat while the student has this classroom
  -- open, never by Lab terminal activity. online/recently-active/offline is DERIVED from this
  -- at read time (see admin-classroom-routes.js), not stored as a separate status column, so
  -- there's nothing to keep in sync or go stale on its own.
  last_seen_at            TIMESTAMPTZ,
  left_at                 TIMESTAMPTZ,
  PRIMARY KEY (classroom_session_id, student_id)
);

CREATE INDEX IF NOT EXISTS idx_classroom_participants_student ON classroom_participants(student_id);

CREATE TABLE IF NOT EXISTS classroom_events (
  event_id                BIGSERIAL PRIMARY KEY,
  classroom_session_id    UUID NOT NULL REFERENCES classroom_sessions(classroom_session_id),
  actor_type               TEXT NOT NULL CHECK (actor_type IN ('instructor', 'student', 'system')),
  actor_id                 TEXT,
  event_type                TEXT NOT NULL,
  metadata                  JSONB,
  created_at                 TIMESTAMPTZ NOT NULL DEFAULT now()
);

CREATE INDEX IF NOT EXISTS idx_classroom_events_session ON classroom_events(classroom_session_id, created_at);

CREATE TABLE IF NOT EXISTS classroom_announcements (
  announcement_id          BIGSERIAL PRIMARY KEY,
  classroom_session_id     UUID NOT NULL REFERENCES classroom_sessions(classroom_session_id),
  instructor_id             UUID REFERENCES instructors(instructor_id),
  message                    TEXT NOT NULL,
  created_at                  TIMESTAMPTZ NOT NULL DEFAULT now()
);

CREATE INDEX IF NOT EXISTS idx_classroom_announcements_session ON classroom_announcements(classroom_session_id, created_at);

CREATE TABLE IF NOT EXISTS help_requests (
  help_request_id           BIGSERIAL PRIMARY KEY,
  classroom_session_id      UUID NOT NULL REFERENCES classroom_sessions(classroom_session_id),
  student_id                 TEXT NOT NULL REFERENCES students(student_id),
  category                    TEXT,   -- free text ('lab_problem' | 'dont_understand' | 'validation_failing' | 'other' from the frontend, not a DB-enforced enum — see §18's example list)
  message                     TEXT,
  status                       TEXT NOT NULL DEFAULT 'open' CHECK (status IN ('open', 'acknowledged', 'resolved')),
  created_at                    TIMESTAMPTZ NOT NULL DEFAULT now(),
  acknowledged_at               TIMESTAMPTZ,
  acknowledged_by               UUID REFERENCES instructors(instructor_id),
  resolved_at                    TIMESTAMPTZ,
  instructor_note                 TEXT
);

CREATE INDEX IF NOT EXISTS idx_help_requests_session_status ON help_requests(classroom_session_id, status);
CREATE INDEX IF NOT EXISTS idx_help_requests_student ON help_requests(student_id);