starr-philproperties/utils/courses/grading.util.js

"use strict";

/**
 * Grades a submission against the stored correct answers.
 *
 * The breakdown returned here is what gets sent back to the client, so it
 * deliberately never includes which option(s) were correct — only whether
 * the user's own answer for each question was right or wrong. Explanation
 * text is included only when the question was answered correctly, since
 * showing it for a wrong answer would effectively reveal the correct one.
 *
 * @param {Array}  questions - QuizQuestion rows w/ .options (incl. is_correct), already fetched
 * @param {Object} answers   - { [question_id]: optionId | optionId[] } submitted by the client
 */
function gradeSubmission(questions, answers = {}) {
  let totalPoints = 0;
  let earnedPoints = 0;

  const breakdown = questions.map((q) => {
    const points = q.points ?? 1;
    totalPoints += points;

    const correctIds = (q.options ?? [])
      .filter((o) => o.is_correct)
      .map((o) => o.option_id);

    const submitted = answers[q.question_id];
    const submittedIds = Array.isArray(submitted)
      ? submitted
      : (submitted !== undefined && submitted !== null ? [submitted] : []);

    const isCorrect =
      submittedIds.length === correctIds.length &&
      correctIds.every((id) => submittedIds.includes(id));

    if (isCorrect) earnedPoints += points;

    return {
      question_id: q.question_id,
      type: q.type,
      question: q.question,
      points,
      is_correct: isCorrect,
      selected_option_ids: submittedIds,
      explanation: isCorrect ? (q.explanation ?? null) : null,
      options: (q.options ?? []).map((o) => ({
        option_id: o.option_id,
        text: o.text,
      })),
    };
  });

  const score = totalPoints > 0 ? Math.round((earnedPoints / totalPoints) * 100) : 0;
  return { totalPoints, earnedPoints, score, breakdown };
}

module.exports = { gradeSubmission };