const db = require('../db/db');
const { stripTags } = require('../utils/sanitize');

/* ── валидация URL картинки ────────────────────────────────────────────────
   Принимаем ТОЛЬКО свои загруженные файлы (/uploads/flashcards/<file>) —
   защита от javascript:/data:/внешних URL в src. Всё прочее → пустая строка. */
function safeImg(url) {
  if (typeof url !== 'string') return '';
  const u = url.trim();
  return /^\/uploads\/flashcards\/[A-Za-z0-9._-]+$/.test(u) ? u : '';
}

/* ── SM-2 (Anki-стиль: кнопки различаются) ─────────────────────────────────
   quality: 0/2 = Снова, 3 = Трудно, 4 = Знаю, 5 = Легко.
   В отличие от чистого SM-2, интервал зависит от оценки уже на первых повторах:
   на новой карте Снова/Трудно/Знаю → 1д, Легко → 4д; на зрелых — Трудно ×1.2,
   Знаю ×ef, Легко ×ef×1.3 (easy-бонус). ВАЖНО: клиентское превью
   fcNextInterval() в flashcards.html — точная копия этой логики интервалов.
   ─────────────────────────────────────────────────────────────────────── */
const FC_HARD_MULT = 1.2, FC_EASY_BONUS = 1.3;
function sm2(easeFactor, intervalDays, repetitions, quality) {
  let ef  = easeFactor;
  let n   = repetitions;
  let iv  = intervalDays;

  if (quality < 3) {
    n  = 0;
    iv = 1;                                                  // Снова — сброс
  } else {
    if (n === 0) {
      iv = (quality === 5) ? 4 : 1;                          // выпуск: Легко 4д, иначе 1д
    } else if (n === 1) {
      iv = (quality === 3) ? 3 : (quality === 4) ? 6 : Math.round(6 * FC_EASY_BONUS);
    } else {
      if (quality === 3)      iv = Math.max(iv + 1, Math.round(iv * FC_HARD_MULT));
      else if (quality === 4) iv = Math.round(iv * ef);
      else                    iv = Math.round(iv * ef * FC_EASY_BONUS);
    }
    n++;
  }
  ef = Math.max(1.3, ef + 0.1 - (5 - quality) * (0.08 + (5 - quality) * 0.02));
  const due = new Date(Date.now() + iv * 86400000).toISOString();
  return { easeFactor: ef, intervalDays: iv, repetitions: n, dueAt: due };
}

/* ── GET /api/flashcards/decks ─────────────────────────────────────────── */
function listDecks(req, res) {
  const uid = req.user.id;
  const decks = db.prepare(`
    SELECT d.*,
      (SELECT COUNT(*) FROM flashcard_cards c WHERE c.deck_id = d.id) AS card_count,
      (SELECT COUNT(*) FROM flashcard_cards c
       LEFT JOIN flashcard_reviews r ON r.card_id = c.id AND r.user_id = ?
       WHERE c.deck_id = d.id AND (r.id IS NULL OR r.due_at <= datetime('now'))) AS due_count
    FROM flashcard_decks d
    WHERE d.user_id = ?
    ORDER BY d.created_at DESC
  `).all(uid, uid);
  res.json({ decks });
}

/* ── POST /api/flashcards/decks ────────────────────────────────────────── */
function createDeck(req, res) {
  const uid  = req.user.id;
  const { title, description = '', color = '#9B5DE5' } = req.body;
  if (!title?.trim()) return res.status(400).json({ error: 'Title required' });
  const r = db.prepare(
    `INSERT INTO flashcard_decks (user_id, title, description, color) VALUES (?,?,?,?)`
  ).run(uid, title.trim(), description, color);
  res.json({ id: r.lastInsertRowid, title: title.trim(), description, color, card_count: 0, due_count: 0 });
}

/* ── PUT /api/flashcards/decks/:id ─────────────────────────────────────── */
function updateDeck(req, res) {
  const uid = req.user.id;
  const { title, description, color } = req.body;
  const deck = db.prepare(`SELECT * FROM flashcard_decks WHERE id = ? AND user_id = ?`)
                  .get(req.params.id, uid);
  if (!deck) return res.status(404).json({ error: 'Not found' });
  db.prepare(`UPDATE flashcard_decks SET title=?, description=?, color=? WHERE id=?`)
    .run(title ?? deck.title, description ?? deck.description, color ?? deck.color, deck.id);
  res.json({ ok: true });
}

/* ── DELETE /api/flashcards/decks/:id ──────────────────────────────────── */
function deleteDeck(req, res) {
  const uid = req.user.id;
  const deck = db.prepare(`SELECT id FROM flashcard_decks WHERE id = ? AND user_id = ?`)
                  .get(req.params.id, uid);
  if (!deck) return res.status(404).json({ error: 'Not found' });
  db.prepare(`DELETE FROM flashcard_decks WHERE id = ?`).run(deck.id);
  res.json({ ok: true });
}

/* ── GET /api/flashcards/decks/:id/cards ───────────────────────────────── */
function getCards(req, res) {
  const uid = req.user.id;
  const deck = db.prepare(`SELECT id FROM flashcard_decks WHERE id = ? AND user_id = ?`)
                  .get(req.params.id, uid);
  if (!deck) return res.status(404).json({ error: 'Not found' });
  const cards = db.prepare(`
    SELECT c.*, r.ease_factor, r.interval_days, r.repetitions, r.due_at, r.last_reviewed
    FROM flashcard_cards c
    LEFT JOIN flashcard_reviews r ON r.card_id = c.id AND r.user_id = ?
    WHERE c.deck_id = ?
    ORDER BY c.order_idx, c.id
  `).all(uid, deck.id);
  res.json({ cards });
}

/* ── POST /api/flashcards/decks/:id/cards ──────────────────────────────── */
function addCard(req, res) {
  const uid = req.user.id;
  const deck = db.prepare(`SELECT id FROM flashcard_decks WHERE id = ? AND user_id = ?`)
                  .get(req.params.id, uid);
  if (!deck) return res.status(404).json({ error: 'Not found' });
  const front = stripTags((req.body.front || '').slice(0, 5000));
  const back  = stripTags((req.body.back  || '').slice(0, 5000));
  const front_image = safeImg(req.body.front_image);
  const back_image  = safeImg(req.body.back_image);
  const maxIdx = db.prepare(`SELECT MAX(order_idx) AS m FROM flashcard_cards WHERE deck_id = ?`)
                    .get(deck.id)?.m ?? -1;
  const r = db.prepare(`INSERT INTO flashcard_cards (deck_id, front, back, front_image, back_image, order_idx) VALUES (?,?,?,?,?,?)`)
               .run(deck.id, front, back, front_image, back_image, maxIdx + 1);
  res.json({ id: r.lastInsertRowid, deck_id: deck.id, front, back, front_image, back_image, order_idx: maxIdx + 1 });
}

/* ── POST /api/flashcards/decks/:id/cards/bulk ──────────────────────────── */
function addCardsBulk(req, res) {
  const uid = req.user.id;
  const deck = db.prepare(`SELECT id FROM flashcard_decks WHERE id = ? AND user_id = ?`)
                  .get(req.params.id, uid);
  if (!deck) return res.status(404).json({ error: 'Not found' });
  const { cards } = req.body;
  if (!Array.isArray(cards) || !cards.length) return res.status(400).json({ error: 'cards[] required' });
  const maxIdx = db.prepare(`SELECT MAX(order_idx) AS m FROM flashcard_cards WHERE deck_id = ?`)
                    .get(deck.id)?.m ?? -1;
  const stmt = db.prepare(`INSERT INTO flashcard_cards (deck_id, front, back, front_image, back_image, order_idx) VALUES (?,?,?,?,?,?)`);
  const inserted = [];
  const ins = db.transaction(() => {
    cards.forEach((c, i) => {
      const front = stripTags((c.front || '').slice(0, 5000));
      const back  = stripTags((c.back  || '').slice(0, 5000));
      const fImg  = safeImg(c.front_image);
      const bImg  = safeImg(c.back_image);
      const r = stmt.run(deck.id, front, back, fImg, bImg, maxIdx + 1 + i);
      inserted.push({ id: r.lastInsertRowid, front, back, front_image: fImg, back_image: bImg });
    });
  });
  ins();
  res.json({ inserted });
}

/* ── PUT /api/flashcards/decks/:id/reorder ─────────────────────────────────
   body: { order: [cardId, …] } — переписывает order_idx по позиции в массиве.
   Принимаются только карточки, реально принадлежащие колоде владельца. */
function reorderCards(req, res) {
  const uid = req.user.id;
  const deck = db.prepare(`SELECT id FROM flashcard_decks WHERE id = ? AND user_id = ?`)
                  .get(req.params.id, uid);
  if (!deck) return res.status(404).json({ error: 'Not found' });
  const { order } = req.body;
  if (!Array.isArray(order) || !order.length)
    return res.status(400).json({ error: 'order[] required' });

  const owned = new Set(
    db.prepare(`SELECT id FROM flashcard_cards WHERE deck_id = ?`).all(deck.id).map(r => r.id)
  );
  const stmt = db.prepare(`UPDATE flashcard_cards SET order_idx = ? WHERE id = ? AND deck_id = ?`);
  const run = db.transaction(() => {
    let idx = 0;
    order.forEach(id => { if (owned.has(Number(id))) stmt.run(idx++, Number(id), deck.id); });
  });
  run();
  res.json({ ok: true });
}

/* ── PUT /api/flashcards/cards/:id ─────────────────────────────────────── */
function updateCard(req, res) {
  const uid  = req.user.id;
  const card = db.prepare(`
    SELECT c.* FROM flashcard_cards c
    JOIN flashcard_decks d ON d.id = c.deck_id
    WHERE c.id = ? AND d.user_id = ?
  `).get(req.params.id, uid);
  if (!card) return res.status(404).json({ error: 'Not found' });
  const { front, back } = req.body;
  // Картинки трогаем только если поле реально пришло (пустая строка = очистить).
  const frontImg = ('front_image' in req.body) ? safeImg(req.body.front_image) : card.front_image;
  const backImg  = ('back_image'  in req.body) ? safeImg(req.body.back_image)  : card.back_image;
  db.prepare(`UPDATE flashcard_cards SET front=?, back=?, front_image=?, back_image=? WHERE id=?`)
    .run(front ?? card.front, back ?? card.back, frontImg, backImg, card.id);
  res.json({ ok: true, front_image: frontImg, back_image: backImg });
}

/* ── DELETE /api/flashcards/cards/:id ──────────────────────────────────── */
function deleteCard(req, res) {
  const uid  = req.user.id;
  const card = db.prepare(`
    SELECT c.id FROM flashcard_cards c
    JOIN flashcard_decks d ON d.id = c.deck_id
    WHERE c.id = ? AND d.user_id = ?
  `).get(req.params.id, uid);
  if (!card) return res.status(404).json({ error: 'Not found' });
  db.prepare(`DELETE FROM flashcard_cards WHERE id = ?`).run(card.id);
  res.json({ ok: true });
}

/* ── GET /api/flashcards/decks/:id/study ───────────────────────────────── */
function getStudySession(req, res) {
  const uid = req.user.id;
  const deck = db.prepare(`SELECT id FROM flashcard_decks WHERE id = ? AND user_id = ?`)
                  .get(req.params.id, uid);
  if (!deck) return res.status(404).json({ error: 'Not found' });
  // due cards first, then new cards (no review yet), limit 20
  const cards = db.prepare(`
    SELECT c.id, c.front, c.back, c.front_image, c.back_image,
      COALESCE(r.ease_factor, 2.5) AS ease_factor,
      COALESCE(r.interval_days, 1) AS interval_days,
      COALESCE(r.repetitions, 0)   AS repetitions,
      COALESCE(r.due_at, datetime('now')) AS due_at,
      r.last_reviewed,
      CASE WHEN r.id IS NULL THEN 0 ELSE 1 END AS seen
    FROM flashcard_cards c
    LEFT JOIN flashcard_reviews r ON r.card_id = c.id AND r.user_id = ?
    WHERE c.deck_id = ?
      AND (r.id IS NULL OR r.due_at <= datetime('now'))
    ORDER BY seen ASC, r.due_at ASC
    LIMIT 20
  `).all(uid, deck.id);
  const total_due = db.prepare(`
    SELECT COUNT(*) AS n FROM flashcard_cards c
    LEFT JOIN flashcard_reviews r ON r.card_id = c.id AND r.user_id = ?
    WHERE c.deck_id = ? AND (r.id IS NULL OR r.due_at <= datetime('now'))
  `).get(uid, deck.id).n;
  res.json({ cards, total_due });
}

/* ── POST /api/flashcards/cards/:id/review ─────────────────────────────── */
function submitReview(req, res) {
  const uid     = req.user.id;
  const { quality } = req.body;   // 0..5
  if (quality === undefined || quality < 0 || quality > 5)
    return res.status(400).json({ error: 'quality 0-5 required' });

  const card = db.prepare(`
    SELECT c.id FROM flashcard_cards c
    JOIN flashcard_decks d ON d.id = c.deck_id
    WHERE c.id = ? AND d.user_id = ?
  `).get(req.params.id, uid);
  if (!card) return res.status(404).json({ error: 'Not found' });

  const existing = db.prepare(
    `SELECT * FROM flashcard_reviews WHERE user_id = ? AND card_id = ?`
  ).get(uid, card.id);

  const prev = existing || { ease_factor: 2.5, interval_days: 1, repetitions: 0 };
  const next = sm2(prev.ease_factor, prev.interval_days, prev.repetitions, quality);

  if (existing) {
    db.prepare(`
      UPDATE flashcard_reviews
      SET ease_factor=?, interval_days=?, repetitions=?, due_at=?, last_reviewed=datetime('now')
      WHERE user_id=? AND card_id=?
    `).run(next.easeFactor, next.intervalDays, next.repetitions, next.dueAt, uid, card.id);
  } else {
    db.prepare(`
      INSERT INTO flashcard_reviews (user_id, card_id, ease_factor, interval_days, repetitions, due_at, last_reviewed)
      VALUES (?,?,?,?,?,?,datetime('now'))
    `).run(uid, card.id, next.easeFactor, next.intervalDays, next.repetitions, next.dueAt);
  }
  res.json({ ok: true, next_review: next.dueAt, interval_days: next.intervalDays });
}

/* ── GET /api/flashcards/stats ─────────────────────────────────────────── */
function getStats(req, res) {
  const uid = req.user.id;
  const decks_count = db.prepare(`SELECT COUNT(*) AS n FROM flashcard_decks WHERE user_id=?`).get(uid).n;
  const cards_count = db.prepare(`
    SELECT COUNT(*) AS n FROM flashcard_cards c
    JOIN flashcard_decks d ON d.id = c.deck_id WHERE d.user_id=?
  `).get(uid).n;
  const due_count = db.prepare(`
    SELECT COUNT(*) AS n FROM flashcard_cards c
    JOIN flashcard_decks d ON d.id = c.deck_id
    LEFT JOIN flashcard_reviews r ON r.card_id = c.id AND r.user_id = ?
    WHERE d.user_id = ? AND (r.id IS NULL OR r.due_at <= datetime('now'))
  `).get(uid, uid).n;
  const reviewed_today = db.prepare(`
    SELECT COUNT(*) AS n FROM flashcard_reviews
    WHERE user_id = ? AND date(last_reviewed) = date('now')
  `).get(uid).n;
  res.json({ decks_count, cards_count, due_count, reviewed_today });
}

/* ── POST /api/flashcards/quick — быстрое добавление из любой точки ──────
   Кладёт карточку в указанную колоду (deckId) либо в личную колоду
   «Быстрые карточки» (создаётся при первом обращении). */
const QUICK_DECK_TITLE = 'Быстрые карточки';
function quickAdd(req, res) {
  const uid   = req.user.id;
  const front = stripTags((req.body.front || '').slice(0, 5000)).trim();
  const back  = stripTags((req.body.back  || '').slice(0, 5000)).trim();
  const front_image = safeImg(req.body.front_image);
  const back_image  = safeImg(req.body.back_image);
  if (!front && !front_image) return res.status(400).json({ error: 'Заполни лицевую сторону (текст или картинку)' });

  let deck = null;
  const deckId = Number(req.body.deckId) || 0;
  if (deckId) {
    deck = db.prepare(`SELECT id, title, color FROM flashcard_decks WHERE id = ? AND user_id = ?`)
             .get(deckId, uid);
  }
  if (!deck) {
    deck = db.prepare(`SELECT id, title, color FROM flashcard_decks WHERE user_id = ? AND title = ? ORDER BY id LIMIT 1`)
             .get(uid, QUICK_DECK_TITLE);
    if (!deck) {
      const r = db.prepare(
        `INSERT INTO flashcard_decks (user_id, title, description, color) VALUES (?,?,?,?)`
      ).run(uid, QUICK_DECK_TITLE, 'Карточки, добавленные на лету', '#9B5DE5');
      deck = { id: r.lastInsertRowid, title: QUICK_DECK_TITLE, color: '#9B5DE5', created: true };
    }
  }

  const maxIdx = db.prepare(`SELECT MAX(order_idx) AS m FROM flashcard_cards WHERE deck_id = ?`)
                   .get(deck.id)?.m ?? -1;
  const r = db.prepare(`INSERT INTO flashcard_cards (deck_id, front, back, front_image, back_image, order_idx) VALUES (?,?,?,?,?,?)`)
              .run(deck.id, front, back, front_image, back_image, maxIdx + 1);
  res.json({ id: r.lastInsertRowid, deck_id: deck.id, deck_title: deck.title, deck_color: deck.color, front, back, front_image, back_image });
}

/* ── GET /api/flashcards/random — случайная карточка из всего пула ───────
   Для дашборд-виджета «повтори карточку». */
function getRandom(req, res) {
  const uid = req.user.id;
  const total = db.prepare(`
    SELECT COUNT(*) AS n FROM flashcard_cards c
    JOIN flashcard_decks d ON d.id = c.deck_id WHERE d.user_id = ?
  `).get(uid).n;
  if (!total) return res.json({ card: null, total: 0 });

  const card = db.prepare(`
    SELECT c.id, c.front, c.back, c.front_image, c.back_image, c.deck_id,
           d.title AS deck_title, d.color AS deck_color
    FROM flashcard_cards c
    JOIN flashcard_decks d ON d.id = c.deck_id
    WHERE d.user_id = ?
    ORDER BY RANDOM() LIMIT 1
  `).get(uid);
  res.json({ card, total });
}

/* ── POST /api/flashcards/upload — загрузка картинки для карточки ──────────
   multipart (поле file). Возвращает { url } для сохранения в front_image /
   back_image. Сам файл уже на диске (multer); БД здесь не трогаем. */
function uploadImage(req, res) {
  if (!req.file) return res.status(400).json({ error: 'Файл не получен (только изображения до 5 МБ)' });
  res.json({ url: `/uploads/flashcards/${req.file.filename}` });
}

module.exports = {
  listDecks, createDeck, updateDeck, deleteDeck,
  getCards, addCard, addCardsBulk, updateCard, deleteCard, reorderCards,
  getStudySession, submitReview, getStats,
  quickAdd, getRandom, uploadImage,
};