<?php
declare(strict_types=1);

namespace App\Services;

/** Grades one immutable server snapshot; no client-supplied answer key. */
final class RemediationAttemptGrader
{
    public static function grade(array $questionIds, array $answerKey, array $answers): int
    {
        if (count($questionIds) !== 3 || count(array_unique($questionIds)) !== 3 ||
            count($answerKey) !== 3 || array_keys($answers) !== [0, 1, 2]) {
            throw new \InvalidArgumentException('Invalid quiz shape');
        }
        $correct = 0;
        foreach ($questionIds as $index => $questionId) {
            $key = $answerKey[$index] ?? null;
            $selected = $answers[$index];
            if (!is_array($key) || !is_int($selected) || $selected <= 0 ||
                (int)($key['question_id'] ?? 0) !== (int)$questionId ||
                !is_array($key['option_ids'] ?? null) ||
                !in_array($selected, $key['option_ids'], true) ||
                !in_array((int)($key['correct_option_id'] ?? 0), $key['option_ids'], true)) {
                throw new \InvalidArgumentException('Answer does not belong to the attempt');
            }
            if ($selected === (int)$key['correct_option_id']) $correct++;
        }
        return $correct;
    }
}