'use strict';
const router = require('express').Router();
const db = require('../db/db');
const { authMiddleware } = require('../middleware/auth');

router.use(authMiddleware);

/* ── Statements (prepared once) ────────────────────────────────── */
const SQL = {
  listTracks: db.prepare(`
    SELECT exam_key, title, subject_slug, grade, duration_min,
           tasks_per_variant, variants_count, intro_html, sort_order
      FROM exam_tracks
     WHERE enabled = 1
     ORDER BY sort_order, exam_key
  `),
  getTrack: db.prepare(`
    SELECT exam_key, title, subject_slug, grade, duration_min,
           tasks_per_variant, variants_count, scoring_json, intro_html
      FROM exam_tracks
     WHERE exam_key = ? AND enabled = 1
  `),
  countTasks: db.prepare(`
    SELECT
      COUNT(*) AS total,
      COALESCE(SUM(CASE WHEN task_type = 'mc'   THEN 1 ELSE 0 END), 0) AS mc,
      COALESCE(SUM(CASE WHEN task_type = 'open' THEN 1 ELSE 0 END), 0) AS open,
      COALESCE(SUM(CASE WHEN task_type = 'long' THEN 1 ELSE 0 END), 0) AS long
      FROM exam_tasks
     WHERE exam_key = ?
  `),
  /* For each (user, task) — was the most-recent attempt correct?
     A task counts as «solved» iff at least one historical attempt is_correct = 1. */
  userProgress: db.prepare(`
    SELECT
      COUNT(DISTINCT exam_task_id) AS tasks_attempted,
      COUNT(DISTINCT CASE WHEN is_correct = 1 THEN exam_task_id END) AS tasks_solved,
      COUNT(*) AS total_attempts,
      COALESCE(SUM(CASE WHEN is_correct = 1 THEN 1 ELSE 0 END), 0) AS correct_attempts
      FROM exam_attempts a
      JOIN exam_tasks t ON t.id = a.exam_task_id
     WHERE a.user_id = ? AND t.exam_key = ?
  `),

  /* Variants list + per-user counts. One row per variant.
     - total:        tasks in variant
     - solved:       distinct tasks where user has ≥1 correct attempt
     - viewed_sol:   distinct tasks where user opened the solution */
  listVariants: db.prepare(`
    SELECT
      t.variant,
      COUNT(*) AS total,
      COUNT(DISTINCT CASE WHEN a.is_correct = 1 THEN t.id END) AS solved,
      COUNT(DISTINCT CASE WHEN a.solution_viewed = 1 THEN t.id END) AS viewed_sol
      FROM exam_tasks t
      LEFT JOIN exam_attempts a
        ON a.exam_task_id = t.id AND a.user_id = ?
     WHERE t.exam_key = ?
     GROUP BY t.variant
     ORDER BY t.variant
  `),

  getVariantTasks: db.prepare(`
    SELECT
      id, task_idx, task_type, text_html, figure_html, opts_json,
      answer, solution_html, topic, subtopic
      FROM exam_tasks
     WHERE exam_key = ? AND variant = ?
     ORDER BY task_idx
  `),

  /* For attempt save: confirm the task belongs to a known track + user */
  getTaskExamKey: db.prepare(`SELECT exam_key FROM exam_tasks WHERE id = ?`),

  insertAttempt: db.prepare(`
    INSERT INTO exam_attempts
      (user_id, exam_task_id, user_answer, is_correct, time_ms,
       mode, session_id, hint_used, solution_viewed, created_at)
    VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
  `),
};

/* ── GET /api/exam-prep/tracks ──
   Public list of enabled exam tracks (for a future landing page). */
router.get('/tracks', (_req, res) => {
  const tracks = SQL.listTracks.all();
  res.json({ tracks });
});

/* ── GET /api/exam-prep/:examKey/info ──
   Track metadata + global counts + this user's aggregate progress. */
// @public-by-design: router-level authMiddleware (line 6) covers this route
router.get('/:examKey/info', (req, res) => {
  const { examKey } = req.params;
  const track = SQL.getTrack.get(examKey);
  if (!track) return res.status(404).json({ error: 'Unknown exam track' });

  const counts   = SQL.countTasks.get(examKey);
  const progress = SQL.userProgress.get(req.user.id, examKey);

  // Parse scoring grid (JSON in DB). Tolerant of malformed values.
  let scoring = null;
  if (track.scoring_json) {
    try { scoring = JSON.parse(track.scoring_json); } catch { scoring = null; }
  }

  res.json({
    track: {
      exam_key: track.exam_key,
      title:    track.title,
      subject:  track.subject_slug,
      grade:    track.grade,
      duration_min:      track.duration_min,
      tasks_per_variant: track.tasks_per_variant,
      variants_count:    track.variants_count,
      intro_html:        track.intro_html,
      scoring,
    },
    counts,
    progress,
  });
});

/* ── GET /api/exam-prep/:examKey/variants ──
   List of variants with per-user progress aggregates. */
// @public-by-design: router-level authMiddleware (line 6) covers this route
router.get('/:examKey/variants', (req, res) => {
  const { examKey } = req.params;
  if (!SQL.getTrack.get(examKey)) return res.status(404).json({ error: 'Unknown exam track' });
  const rows = SQL.listVariants.all(req.user.id, examKey);
  const variants = rows.map(r => ({
    n: r.variant,
    label: `Вариант ${r.variant}`,
    total: r.total,
    solved: r.solved,
    viewed_sol: r.viewed_sol,
  }));
  res.json({ variants });
});

/* ── GET /api/exam-prep/:examKey/variants/:n/tasks ──
   All tasks of a specific variant. Includes answer + solution_html
   (variants view = same UX as old /exam9: read condition + reveal solution).
   In F3, the task-card will also use `answer` to auto-check user input. */
// @public-by-design: router-level authMiddleware (line 6) covers this route
router.get('/:examKey/variants/:n/tasks', (req, res) => {
  const { examKey } = req.params;
  const n = parseInt(req.params.n, 10);
  if (!Number.isFinite(n) || n < 1) return res.status(400).json({ error: 'Bad variant number' });

  const rows = SQL.getVariantTasks.all(examKey, n);
  if (!rows.length) return res.status(404).json({ error: 'Variant not found or empty' });

  const tasks = rows.map(r => ({
    id:        r.id,
    idx:       r.task_idx,
    type:      r.task_type,
    text:      r.text_html,
    figure:    r.figure_html,
    opts:      r.opts_json ? safeJson(r.opts_json) : null,
    answer:    r.answer,
    solution:  r.solution_html,
    topic:     r.topic,
    subtopic:  r.subtopic,
  }));
  res.json({ variant: n, tasks });
});

function safeJson(s) { try { return JSON.parse(s); } catch { return null; } }

/* ── POST /api/exam-prep/attempts ──
   Save a single attempt. Used by the variants view (F2) for "solution viewed"
   markers, and by the practice / mock views (F3+) for actual answer checking.

   Body: {
     exam_task_id   (required, integer)
     user_answer    (string|null)        — what the user typed/selected
     is_correct     (0|1|null)           — null for solution-viewed-only events
     time_ms        (integer|null)
     mode           ('practice'|'variant'|'topic'|'mock')
     session_id     (integer|null)
     hint_used      (0|1)
     solution_viewed (0|1)
   }
   The server does NOT recompute is_correct from `user_answer` here — that's
   the client's responsibility (it has the `answer` from /tasks). Server only
   validates ownership and records the event. */
router.post('/attempts', (req, res) => {
  const b = req.body || {};
  const taskId = Number(b.exam_task_id);
  if (!Number.isFinite(taskId)) return res.status(400).json({ error: 'exam_task_id required' });

  const task = SQL.getTaskExamKey.get(taskId);
  if (!task) return res.status(404).json({ error: 'Task not found' });

  const mode = String(b.mode || '');
  if (!['practice', 'variant', 'topic', 'mock'].includes(mode)) {
    return res.status(400).json({ error: 'invalid mode' });
  }

  const userAnswer     = b.user_answer != null ? String(b.user_answer).slice(0, 500) : null;
  const isCorrect      = b.is_correct === 1 || b.is_correct === 0 ? b.is_correct : null;
  const timeMs         = Number.isFinite(b.time_ms) ? Math.max(0, Math.min(b.time_ms, 24 * 60 * 60 * 1000)) : null;
  const sessionId      = Number.isFinite(b.session_id) ? b.session_id : null;
  const hintUsed       = b.hint_used ? 1 : 0;
  const solutionViewed = b.solution_viewed ? 1 : 0;

  const result = SQL.insertAttempt.run(
    req.user.id, taskId, userAnswer, isCorrect, timeMs,
    mode, sessionId, hintUsed, solutionViewed, Date.now()
  );

  res.json({ id: Number(result.lastInsertRowid) });
});

module.exports = router;