AI Implementation feature(863): Challenges Page and Challenge Solve Modal (#45)

backend/src/modules/challenges/scoring.util.ts

@@ -0,0 +1,54 @@
+import { timingSafeEqual } from 'crypto';
+
+export type Difficulty = 'LOW' | 'MEDIUM' | 'HIGH';
+
+export const DIFFICULTY_RANK: Readonly<Record<Difficulty, number>> = {
+  LOW: 0,
+  MEDIUM: 1,
+  HIGH: 2,
+};
+
+export function compareDifficulty(a: Difficulty, b: Difficulty): number {
+  return DIFFICULTY_RANK[a] - DIFFICULTY_RANK[b];
+}
+
+export function computeLivePoints(
+  initial: number,
+  minimum: number,
+  decaySolves: number,
+  currentSolveCount: number,
+): number {
+  if (!Number.isFinite(initial) || !Number.isFinite(minimum)) return minimum;
+  const i = Math.max(0, Math.floor(initial));
+  const m = Math.max(0, Math.floor(minimum));
+  const d = Math.max(0, Math.floor(decaySolves));
+  const c = Math.max(0, Math.floor(currentSolveCount));
+  if (i < m) return Math.max(0, m);
+  if (d <= 0) return i;
+  if (c >= d) return m;
+  const span = i - m;
+  const raw = i - span * (c / d);
+  return Math.max(m, Math.round(raw));
+}
+
+export function rankBonusForPosition(position: number): number {
+  if (!Number.isInteger(position) || position <= 0) return 0;
+  if (position === 1) return 15;
+  if (position === 2) return 10;
+  if (position === 3) return 5;
+  return 0;
+}
+
+export function safeEqualString(a: string, b: string): boolean {
+  const ab = Buffer.from(a, 'utf8');
+  const bb = Buffer.from(b, 'utf8');
+  if (ab.length !== bb.length) {
+    let diff = ab.length ^ bb.length;
+    const max = Math.max(ab.length, bb.length);
+    for (let i = 0; i < max; i += 1) {
+      diff |= (ab[i] ?? 0) ^ (bb[i] ?? 0);
+    }
+    return false;
+  }
+  return timingSafeEqual(ab, bb);
+}