feat(exam-prep F3): интерактивный тренажёр — task-card + автопроверка ответа + retry + auto-open решения

frontend/js/exam-prep/answer-check.js

@@ -0,0 +1,88 @@
+'use strict';
+/* ──────────────────────────────────────────────────────────────────
+   Answer normalization + correctness check.
+   Same algorithm runs on user input and stored canonical answer
+   (from /tasks endpoint), then compared.
+
+   Canonical answer forms (produced by backend/scripts/import-exam-tasks.js):
+     MC:        single Cyrillic letter:  "а" | "б" | "в" | "г" | "д"
+     open NUM:  decimal:                 "-2"  "7500"  "1.5"  "0.25"
+     open FRAC: fraction:                "9/4"  "-104/9"  (sign on numerator)
+     open PAIR: two values, ";" sep:     "-2;4"
+   The user can type the answer in many equivalent forms — the normalizer
+   accepts any form and decides equivalence numerically.
+   ────────────────────────────────────────────────────────────────── */
+
+(function () {
+  const EPS = 1e-6;
+
+  // Try to coerce a string to a number; returns NaN on failure.
+  function toNumber(s) {
+    if (s == null) return NaN;
+    let t = String(s).trim().replace(/\$/g, '').replace(/\s+/g, '').replace(',', '.');
+    // Fraction "a/b" → a/b
+    const f = t.match(/^(-?\d+(?:\.\d+)?)\s*\/\s*(-?\d+(?:\.\d+)?)$/);
+    if (f) {
+      const num = Number(f[1]);
+      const den = Number(f[2]);
+      if (!Number.isFinite(num) || !Number.isFinite(den) || den === 0) return NaN;
+      return num / den;
+    }
+    const n = Number(t);
+    return Number.isFinite(n) ? n : NaN;
+  }
+
+  // Parse a "pair" answer "A;B" — accepts ";" or "," or " и " or whitespace
+  function toPair(s) {
+    if (s == null) return null;
+    const t = String(s).trim().replace(/\$/g, '').replace(/\s+и\s+/g, ';');
+    const parts = t.split(/[;,]/).map(p => p.trim()).filter(Boolean);
+    if (parts.length !== 2) return null;
+    const a = toNumber(parts[0]);
+    const b = toNumber(parts[1]);
+    if (Number.isNaN(a) || Number.isNaN(b)) return null;
+    // Order-insensitive comparison: return sorted pair
+    return a <= b ? [a, b] : [b, a];
+  }
+
+  /* Detect form of the canonical answer.
+     Returns: 'mc' | 'pair' | 'numeric' */
+  function detectForm(canonical) {
+    if (canonical == null) return 'numeric';
+    const t = String(canonical).trim();
+    if (/^[а-д]$/.test(t)) return 'mc';
+    if (/^[^;]+;[^;]+$/.test(t)) return 'pair';
+    return 'numeric';
+  }
+
+  /* Main check. Returns true iff user input matches canonical answer.
+     False if either side can't be normalized.
+
+     Both inputs are strings as returned by the form or stored in DB. */
+  function check(userInput, canonical) {
+    if (userInput == null || canonical == null) return false;
+
+    const form = detectForm(canonical);
+
+    if (form === 'mc') {
+      const u = String(userInput).trim().toLowerCase();
+      return u === String(canonical).trim().toLowerCase();
+    }
+
+    if (form === 'pair') {
+      const cp = toPair(canonical);
+      const up = toPair(userInput);
+      if (!cp || !up) return false;
+      return Math.abs(cp[0] - up[0]) < EPS && Math.abs(cp[1] - up[1]) < EPS;
+    }
+
+    // Numeric (integer / decimal / fraction)
+    const c = toNumber(canonical);
+    const u = toNumber(userInput);
+    if (Number.isNaN(c) || Number.isNaN(u)) return false;
+    return Math.abs(c - u) < EPS;
+  }
+
+  window.EP = window.EP || {};
+  window.EP.answer = { check, detectForm, toNumber, toPair };
+})();