// This will do mandatory call
const MAX_ATTEMPTS = 10;
const ATTEMPT_WINDOW_HOURS = 24;
const COOLDOWN_MINUTES = 60;

// Fisher-Yates shuffle of each question's options. Pure — returns new
// arrays/objects, never mutates input. Grading is unaffected since
// submitUnitQuiz/submitCourseAssessment always re-fetch questions fresh
// from the DB and never trust shuffled client-facing order.
function shuffleOptions(questions) {
  return questions.map((q) => {
    const options = [...(q.options ?? [])];
    for (let i = options.length - 1; i > 0; i--) {
      const j = Math.floor(Math.random() * (i + 1));
      [options[i], options[j]] = [options[j], options[i]];
    }
    return { ...q, options };
  });
}

// Single source of truth for both the GET-time info fields and the
// submit-time enforcement check. Doesn't care about input order —
// derives best/most-recent itself, so callers can just fetch attempts
// with no ORDER BY.
function getAttemptStatus(attempts) {
  const now = new Date();
  const windowStart = new Date(now.getTime() - ATTEMPT_WINDOW_HOURS * 60 * 60 * 1000);
  const attemptsInWindow = attempts.filter((a) => new Date(a.createdAt) >= windowStart);

  const attempt_count = attempts.length; // lifetime — still used for has_passed/best_attempt
  const has_passed = attempts.some((a) => a.passed);

  const best_attempt = attempts.reduce(
    (best, a) => (!best || a.score > best.score ? a : best),
    null
  );

  const most_recent = attempts.reduce(
    (latest, a) => (!latest || new Date(a.createdAt) > new Date(latest.createdAt) ? a : latest),
    null
  );

  let cooldown_until = null;
  if (most_recent) {
    const unlockAt = new Date(new Date(most_recent.createdAt).getTime() + COOLDOWN_MINUTES * 60000);
    if (unlockAt > now) cooldown_until = unlockAt.toISOString();
  }

  const attempts_remaining = Math.max(0, MAX_ATTEMPTS - attemptsInWindow.length);

  let window_reset_at = null;
  if (attempts_remaining === 0 && attemptsInWindow.length > 0) {
    const oldestInWindow = attemptsInWindow.reduce(
      (oldest, a) => (!oldest || new Date(a.createdAt) < new Date(oldest.createdAt) ? a : oldest),
      null
    );
    window_reset_at = new Date(
      new Date(oldestInWindow.createdAt).getTime() + ATTEMPT_WINDOW_HOURS * 60 * 60 * 1000
    ).toISOString();
  }

  const can_attempt = attempts_remaining > 0 && !cooldown_until;

  return { attempt_count, has_passed, best_attempt, attempts_remaining, cooldown_until, window_reset_at, can_attempt };
}

module.exports = { MAX_ATTEMPTS, ATTEMPT_WINDOW_HOURS, COOLDOWN_MINUTES, shuffleOptions, getAttemptStatus };