const db = require('../db/db');

/* Вопросы теста без зафиксированного правильного ответа (нет верного варианта И
 * нет correct_text). matching исключаем (там ответ — пары match_pair).
 * Такой вопрос нельзя оценить → не пускаем тест к ученикам. */
function unanswerableInTest(testId) {
  return db.prepare(`
    SELECT tq.question_id AS id FROM test_questions tq JOIN questions q ON q.id = tq.question_id
     WHERE tq.test_id = ? AND q.type <> 'matching'
       AND (q.correct_text IS NULL OR TRIM(q.correct_text) = '')
       AND NOT EXISTS (SELECT 1 FROM options o WHERE o.question_id = q.id AND o.is_correct = 1)
  `).all(testId).map(r => r.id);
}

/* ── GET /api/tests ─────────────────────────────────────────────────────── */
function list(req, res) {
  const { subject } = req.query;
  const { role, id: uid } = req.user;
  const args = [];
  let where = '1=1';
  if (subject) { where += ' AND t.subject_slug = ?'; args.push(subject); }
  const isStudent = role === 'student' || role === 'free_student';
  // Ученик видит каталог тестов, помеченных доступными; учитель — только свои; админ — все.
  if (isStudent)             { where += ' AND t.available_to_students = 1'; }
  else if (role !== 'admin') { where += ' AND t.created_by = ?'; args.push(uid); }
  // Экзаменационные варианты — это служебные строки в tests (см. import-exam9.js),
  // не показываем их во вкладке «Тесты (шаблоны)» админки.
  where += ' AND t.id NOT IN (SELECT test_id FROM exam9_variant_tests)';

  let rows = db.prepare(`
    SELECT t.id, t.title, t.subject_slug, t.description, t.created_at, t.available_to_students,
           u.name AS creator_name,
           COUNT(tq.question_id) AS question_count
    FROM tests t
    JOIN users u ON u.id = t.created_by
    LEFT JOIN test_questions tq ON tq.test_id = t.id
    WHERE ${where}
    GROUP BY t.id ORDER BY t.created_at DESC
  `).all(...args);
  if (isStudent) rows = rows.filter(r => r.question_count > 0);   // пустые тесты ученику не показываем
  res.json(rows);
}

/* ── POST /api/tests ─────────────────────────────────────────────────────── */
function create(req, res) {
  const { title, subject_slug, description, show_answers = 1, time_limit, available_to_students = 0 } = req.body;
  if (!title?.trim())  return res.status(400).json({ error: 'title required' });
  if (!subject_slug)   return res.status(400).json({ error: 'subject_slug required' });
  const tl = time_limit ? Math.max(1, Math.min(600, Number(time_limit))) : null;
  const r = db.prepare(
    'INSERT INTO tests (title, subject_slug, description, show_answers, time_limit, available_to_students, created_by) VALUES (?, ?, ?, ?, ?, ?, ?)'
  ).run(title.trim(), subject_slug, description?.trim() || null, show_answers ? 1 : 0, tl, available_to_students ? 1 : 0, req.user.id);
  res.status(201).json({ id: r.lastInsertRowid });
}

/* ── GET /api/tests/:id ──────────────────────────────────────────────────── */
function getOne(req, res) {
  const t = db.prepare(`
    SELECT t.*, u.name AS creator_name
    FROM tests t JOIN users u ON u.id = t.created_by WHERE t.id = ?
  `).get(req.params.id);
  if (!t) return res.status(404).json({ error: 'Not found' });

  // Доступ как в list(): ученик видит только помеченные доступными и не служебные
  // экзамен-варианты; учитель — только свои; админ — все. Иначе по id можно было бы
  // прочитать тексты заданий из черновиков/вариантов.
  const { role, id: uid } = req.user;
  const isStudent = role === 'student' || role === 'free_student';
  if (isStudent) {
    const isVariant = db.prepare('SELECT 1 FROM exam9_variant_tests WHERE test_id = ?').get(t.id);
    if (!t.available_to_students || isVariant) return res.status(404).json({ error: 'Not found' });
  } else if (role !== 'admin' && t.created_by !== uid) {
    return res.status(404).json({ error: 'Not found' });
  }

  const questions = db.prepare(`
    SELECT q.id, q.text, q.type, q.difficulty, q.explanation,
           tp.name AS topic, s.name AS subject_name,
           (SELECT json_group_array(json_object('id',o.id,'text',o.text,'is_correct',o.is_correct,'order_index',o.order_index,'match_pair',o.match_pair) ORDER BY o.order_index)
            FROM options o WHERE o.question_id = q.id) AS options_json,
           tq.order_index
    FROM test_questions tq
    JOIN questions q ON q.id = tq.question_id
    LEFT JOIN topics tp ON tp.id = q.topic_id
    LEFT JOIN subjects s ON s.id = q.subject_id
    WHERE tq.test_id = ? ORDER BY tq.order_index
  `).all(req.params.id).map(r => ({
    ...r,
    options: JSON.parse(r.options_json || '[]'),
    options_json: undefined,
  }));

  // Hide is_correct from students — only teachers/admins see correct answers
  const isPrivileged = req.user.role === 'teacher' || req.user.role === 'admin';
  if (!isPrivileged) {
    questions.forEach(q => {
      q.options.forEach(o => { delete o.is_correct; });
      delete q.explanation;
    });
  }

  res.json({ ...t, questions });
}

/* ── PUT /api/tests/:id ──────────────────────────────────────────────────── */
function update(req, res) {
  const b = req.body;
  const t = req.resource; // ownership verified by requireOwnership middleware
  // Частичный апдейт: НЕ переданные поля сохраняем из текущей строки (иначе toggleTstAvail,
  // присылающий только available_to_students, обнулил бы title/subject и т.п.).
  const title        = b.title        !== undefined ? (b.title?.trim() || t.title) : t.title;
  const subject_slug = b.subject_slug !== undefined ? b.subject_slug : t.subject_slug;
  const description  = b.description  !== undefined ? (b.description?.trim() || null) : t.description;
  const show_answers = b.show_answers !== undefined ? (b.show_answers ? 1 : 0) : t.show_answers;
  const time_limit   = b.time_limit   !== undefined ? (b.time_limit ? Math.max(1, Math.min(600, Number(b.time_limit))) : null) : t.time_limit;
  const available    = b.available_to_students !== undefined ? (b.available_to_students ? 1 : 0) : t.available_to_students;
  // Гард целостности: нельзя публиковать тест ученикам с вопросами без правильного ответа.
  if (available === 1) {
    const broken = unanswerableInTest(t.id);
    if (broken.length) return res.status(400).json({ error: `Нельзя опубликовать: ${broken.length} вопрос(ов) без правильного ответа. Исправьте их в банке.`, brokenQuestions: broken });
  }
  db.prepare('UPDATE tests SET title = ?, subject_slug = ?, description = ?, show_answers = ?, time_limit = ?, available_to_students = ? WHERE id = ?')
    .run(title, subject_slug, description, show_answers, time_limit, available, t.id);
  res.json({ ok: true });
}

/* ── DELETE /api/tests/:id ───────────────────────────────────────────────── */
function remove(req, res) {
  db.prepare('DELETE FROM tests WHERE id = ?').run(req.resource.id);
  res.json({ ok: true });
}

/* ── POST /api/tests/:id/questions ──────────────────────────────────────── */
function addQuestions(req, res) {
  const { question_ids } = req.body;
  if (!Array.isArray(question_ids) || !question_ids.length)
    return res.status(400).json({ error: 'question_ids[] required' });

  const testId = req.resource.id; // ownership verified by requireOwnership middleware

  const { mx } = db.prepare(
    'SELECT COALESCE(MAX(order_index), -1) AS mx FROM test_questions WHERE test_id = ?'
  ).get(testId);

  let idx = mx + 1;
  const ins = db.prepare(
    'INSERT OR IGNORE INTO test_questions (test_id, question_id, order_index) VALUES (?, ?, ?)'
  );
  try {
    db.transaction(() => { question_ids.forEach(qid => ins.run(testId, qid, idx++)); })();
  } catch (e) {
    console.error('[testController] addQuestions error:', e.message);
    return res.status(500).json({ error: 'Ошибка добавления вопросов' });
  }
  res.json({ ok: true });
}

/* ── DELETE /api/tests/:id/questions/:qid ───────────────────────────────── */
function removeQuestion(req, res) {
  db.prepare('DELETE FROM test_questions WHERE test_id = ? AND question_id = ?')
    .run(req.resource.id, req.params.qid);
  res.json({ ok: true });
}

/* ── PATCH /api/tests/:id/questions/reorder  { ids: [qid, qid, ...] } ──── */
function reorderQuestions(req, res) {
  const { ids } = req.body;
  if (!Array.isArray(ids) || !ids.length)
    return res.status(400).json({ error: 'ids[] required' });

  const testId = req.resource.id;
  const upd = db.prepare(
    'UPDATE test_questions SET order_index = ? WHERE test_id = ? AND question_id = ?'
  );
  try {
    db.transaction(() => {
      ids.forEach((qid, i) => upd.run(i, testId, qid));
    })();
  } catch (e) {
    console.error('[testController] reorderQuestions error:', e.message);
    return res.status(500).json({ error: 'Ошибка сортировки' });
  }
  res.json({ ok: true });
}

module.exports = { list, create, getOne, update, remove, addQuestions, removeQuestion, reorderQuestions };