feat: add rate limiter module

src/rateLimiter.js

@@ -0,0 +1,32 @@
+const MAX_REQUESTS_PER_DAY = parseInt(process.env.MAX_REQUESTS_PER_DAY, 10) || 5
+
+const userCounts = new Map()
+let currentDate = new Date().toDateString()
+
+function resetIfNeeded() {
+  const today = new Date().toDateString()
+  if (today !== currentDate) {
+    userCounts.clear()
+    currentDate = today
+    console.log('Rate limiter: daily counters reset')
+  }
+}
+
+function checkLimit(userId) {
+  resetIfNeeded()
+  const count = userCounts.get(userId) || 0
+  return {
+    allowed: count < MAX_REQUESTS_PER_DAY,
+    count,
+    max: MAX_REQUESTS_PER_DAY
+  }
+}
+
+function increment(userId) {
+  resetIfNeeded()
+  const count = (userCounts.get(userId) || 0) + 1
+  userCounts.set(userId, count)
+  return count
+}
+
+module.exports = { checkLimit, increment, MAX_REQUESTS_PER_DAY }