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

function _tier(total, correct) {
  if (total === 0) return 'locked';
  const pct = correct / total * 100;
  if (total >= 10 && pct >= 90) return 'platinum';
  if (total >= 5  && pct >= 80) return 'gold';
  if (total >= 3  && pct >= 50) return 'silver';
  if (correct >= 1)             return 'bronze';
  return 'locked';
}

/* ── GET /api/collection ──────────────────────────────────────────────── */
function getCollection(req, res) {
  const rows = db.prepare(`
    SELECT
      t.id   AS topic_id,
      t.name AS topic_name,
      s.name AS subject_name,
      s.slug AS subject_slug,
      s.icon AS subject_icon,
      COALESCE(agg.total_attempts, 0)  AS total_attempts,
      COALESCE(agg.correct_count, 0)   AS correct_count,
      agg.first_seen_at
    FROM topics t
    JOIN subjects s ON s.id = t.subject_id
    LEFT JOIN (
      SELECT q.topic_id,
             COUNT(ua.id)                       AS total_attempts,
             SUM(CASE WHEN ua.is_correct=1 THEN 1 ELSE 0 END) AS correct_count,
             MIN(ua.answered_at)                AS first_seen_at
      FROM user_answers ua
      JOIN questions q ON q.id = ua.question_id
      WHERE ua.session_id IN (
        SELECT id FROM test_sessions WHERE user_id = ? AND status = 'completed'
      )
      GROUP BY q.topic_id
    ) agg ON agg.topic_id = t.id
    ORDER BY s.slug, t.order_index, t.name
  `).all(req.user.id);

  const cards = rows.map(r => ({
    topicId:      r.topic_id,
    topicName:    r.topic_name,
    subjectName:  r.subject_name,
    subjectSlug:  r.subject_slug,
    subjectIcon:  r.subject_icon,
    tier:         _tier(r.total_attempts, r.correct_count),
    totalAttempts: r.total_attempts,
    correctCount:  r.correct_count,
    masteryPct:   r.total_attempts > 0 ? Math.round(r.correct_count / r.total_attempts * 100) : 0,
    firstSeenAt:  r.first_seen_at || null,
  }));

  const unlocked = cards.filter(c => c.tier !== 'locked').length;

  res.json({
    totalTopics:    cards.length,
    unlockedTopics: unlocked,
    platinumCount:  cards.filter(c => c.tier === 'platinum').length,
    goldCount:      cards.filter(c => c.tier === 'gold').length,
    silverCount:    cards.filter(c => c.tier === 'silver').length,
    bronzeCount:    cards.filter(c => c.tier === 'bronze').length,
    cards,
  });
}

module.exports = { getCollection };