CREATE TABLE IF NOT EXISTS users (
  id INTEGER PRIMARY KEY,
  name TEXT UNIQUE NOT NULL,
  password_hash TEXT NOT NULL,
  created_at DATETIME DEFAULT CURRENT_TIMESTAMP
);

CREATE TABLE IF NOT EXISTS questions (
  id TEXT PRIMARY KEY,
  text TEXT NOT NULL,
  source TEXT,
  created_at DATETIME DEFAULT CURRENT_TIMESTAMP
);

CREATE TABLE IF NOT EXISTS answers (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  question_id TEXT NOT NULL REFERENCES questions(id) ON DELETE CASCADE,
  text TEXT NOT NULL,
  is_correct BOOLEAN NOT NULL,
  position INTEGER NOT NULL
);

CREATE TABLE IF NOT EXISTS tests (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  user_id INTEGER NOT NULL REFERENCES users(id),
  created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
  completed_at DATETIME,
  n_questions INTEGER NOT NULL,
  question_ids TEXT NOT NULL
);

CREATE TABLE IF NOT EXISTS test_answers (
  test_id INTEGER NOT NULL REFERENCES tests(id) ON DELETE CASCADE,
  question_id TEXT NOT NULL REFERENCES questions(id),
  selected_answer_id INTEGER REFERENCES answers(id),
  is_correct BOOLEAN,
  answered_at DATETIME,
  PRIMARY KEY (test_id, question_id)
);

CREATE TABLE IF NOT EXISTS user_question_stats (
  user_id INTEGER NOT NULL REFERENCES users(id),
  question_id TEXT NOT NULL REFERENCES questions(id) ON DELETE CASCADE,
  times_seen INTEGER NOT NULL DEFAULT 0,
  times_correct INTEGER NOT NULL DEFAULT 0,
  last_seen_at DATETIME,
  PRIMARY KEY (user_id, question_id)
);

CREATE TABLE IF NOT EXISTS sessions (
  token TEXT PRIMARY KEY,
  data BLOB NOT NULL,
  expiry INTEGER NOT NULL
);
CREATE INDEX IF NOT EXISTS idx_sessions_expiry ON sessions(expiry);

CREATE INDEX IF NOT EXISTS idx_test_answers_test ON test_answers(test_id);
CREATE INDEX IF NOT EXISTS idx_answers_question ON answers(question_id);
CREATE INDEX IF NOT EXISTS idx_stats_user ON user_question_stats(user_id);