chore: initial project import

lib/rate-limit.ts

@@ -0,0 +1,94 @@
+export type RateLimitResult = {
+  allowed: boolean;
+  limit: number;
+  used: number;
+  remaining: number;
+  resetAt: number;
+};
+
+type WindowEntry = {
+  used: number;
+  expiresAt: number;
+};
+
+type RateLimitState = {
+  limit: number;
+  windowMs: number;
+  entries: Map<string, WindowEntry>;
+};
+
+const rateLimitBuckets = new Map<string, RateLimitState>();
+
+function getState(scope: string, limit: number, windowMs: number) {
+  const key = `${scope}|${limit}|${windowMs}`;
+  const existing = rateLimitBuckets.get(key);
+  if (existing) {
+    return existing;
+  }
+
+  const state = { limit, windowMs, entries: new Map<string, WindowEntry>() };
+  rateLimitBuckets.set(key, state);
+  return state;
+}
+
+export function consumeRateLimit(
+  identifier: string,
+  options: {
+    scope: string;
+    limit: number;
+    windowMs: number;
+  }
+): RateLimitResult {
+  const { scope, limit, windowMs } = options;
+  const now = Date.now();
+  const key = `${identifier}`;
+  const state = getState(scope, limit, windowMs);
+  if (state.entries.size > 200) {
+    for (const [storedIdentifier, entry] of state.entries) {
+      if (entry.expiresAt <= now) {
+        state.entries.delete(storedIdentifier);
+      }
+    }
+  }
+
+  const current = state.entries.get(key);
+  if (!current || current.expiresAt <= now) {
+    const fresh = { used: 1, expiresAt: now + windowMs };
+    state.entries.set(key, fresh);
+    return {
+      allowed: true,
+      limit,
+      used: fresh.used,
+      remaining: limit - fresh.used,
+      resetAt: fresh.expiresAt
+    };
+  }
+
+  if (current.used >= limit) {
+    return {
+      allowed: false,
+      limit,
+      used: current.used,
+      remaining: Math.max(0, limit - current.used),
+      resetAt: current.expiresAt
+    };
+  }
+
+  current.used += 1;
+  return {
+    allowed: true,
+    limit,
+    used: current.used,
+    remaining: limit - current.used,
+    resetAt: current.expiresAt
+  };
+}
+
+export function getRateLimitHeaders(result: RateLimitResult) {
+  return {
+    "RateLimit-Limit": String(result.limit),
+    "RateLimit-Remaining": String(result.remaining),
+    "RateLimit-Reset": String(Math.max(0, Math.ceil(result.resetAt / 1000))),
+    "Retry-After": String(Math.max(1, Math.ceil((result.resetAt - Date.now()) / 1000)))
+  };
+}