CREATE TABLE courses (
    id       INTEGER PRIMARY KEY,
    name     TEXT NOT NULL,
    semester TEXT NOT NULL
);

CREATE TABLE tutors (
    id            INTEGER PRIMARY KEY,
    name          TEXT NOT NULL,
    email         TEXT UNIQUE NOT NULL,
    password_hash TEXT NOT NULL
);

CREATE TABLE tutor_courses (
    tutor_id  INTEGER NOT NULL REFERENCES tutors(id),
    course_id INTEGER NOT NULL REFERENCES courses(id),
    PRIMARY KEY (tutor_id, course_id)
);

CREATE TABLE students (
    id        INTEGER PRIMARY KEY,
    course_id INTEGER NOT NULL REFERENCES courses(id),
    name      TEXT NOT NULL
);

CREATE TABLE rooms (
    id          INTEGER PRIMARY KEY,
    name        TEXT NOT NULL,
    layout_json TEXT NOT NULL
);

CREATE TABLE sessions (
    id        INTEGER PRIMARY KEY,
    course_id INTEGER NOT NULL REFERENCES courses(id),
    week_nr   INTEGER NOT NULL,
    date      TEXT NOT NULL CHECK (date GLOB '????-??-??'),
    UNIQUE(course_id, week_nr)
);

CREATE TABLE slots (
    id         INTEGER PRIMARY KEY,
    session_id INTEGER NOT NULL REFERENCES sessions(id),
    room_id    INTEGER REFERENCES rooms(id),
    tutor_id   INTEGER NOT NULL REFERENCES tutors(id),
    start_time TEXT NOT NULL CHECK (start_time GLOB '??:??'),
    end_time   TEXT NOT NULL CHECK (end_time   GLOB '??:??'),
    status     TEXT NOT NULL DEFAULT 'closed' CHECK (status IN ('closed','open','locked')),
    code       TEXT UNIQUE
);

CREATE TABLE attendances (
    id            INTEGER PRIMARY KEY,
    slot_id       INTEGER NOT NULL REFERENCES slots(id),
    student_id    INTEGER NOT NULL REFERENCES students(id),
    seat_id       TEXT,
    checked_in_at TEXT NOT NULL CHECK (checked_in_at GLOB '????-??-??T??:??:??*'),
    UNIQUE(slot_id, student_id),
    UNIQUE(slot_id, seat_id)
);

CREATE TABLE notes (
    id         INTEGER PRIMARY KEY,
    slot_id    INTEGER NOT NULL REFERENCES slots(id),
    student_id INTEGER NOT NULL REFERENCES students(id),
    tutor_id   INTEGER NOT NULL REFERENCES tutors(id),
    content    TEXT NOT NULL DEFAULT '',
    updated_at TEXT NOT NULL CHECK (updated_at GLOB '????-??-??T??:??:??*'),
    UNIQUE(slot_id, student_id, tutor_id)
);

-- Indexes on high-frequency FK columns (SQLite does not auto-index FKs)
CREATE INDEX idx_students_course     ON students(course_id);
CREATE INDEX idx_sessions_course     ON sessions(course_id);
CREATE INDEX idx_slots_session       ON slots(session_id);
CREATE INDEX idx_slots_tutor         ON slots(tutor_id);
CREATE INDEX idx_attendances_slot    ON attendances(slot_id);
CREATE INDEX idx_attendances_student ON attendances(student_id);
CREATE INDEX idx_notes_slot          ON notes(slot_id);
CREATE INDEX idx_notes_student       ON notes(student_id);