feat(exam-prep F2): порт браузера вариантов + API /variants + POST /attempts + редирект /exam9

backend/src/routes/exam-prep.js

@@ -41,6 +41,43 @@ const SQL = {
       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 ──
@@ -52,6 +89,7 @@ router.get('/tracks', (_req, res) => {
 
 /* ── 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);
@@ -83,4 +121,96 @@ router.get('/:examKey/info', (req, res) => {
   });
 });
 
+/* ── 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;

backend/src/server.js

@@ -366,9 +366,8 @@ app.get(['/exam-prep/:examKey/:view', '/exam-prep/:examKey/:view/*'], (req, res,
   sendExamPrep(res, file);
 });
 
-// NOTE: /exam9 remains live (served by static middleware as exam9.html) until F2
-// ports the variant browser into /exam-prep/:examKey/variants. The 301 redirect
-// will be added at that point.
+// Legacy /exam9 → new variants browser (F2 port complete)
+app.get('/exam9', (_req, res) => res.redirect(301, '/exam-prep/math9/variants'));
 
 // Serve HTML files without extension  (/dashboard → dashboard.html)
 // In dev: disable cache so edits are always picked up immediately