From 632a1c2fd727dc08aaa6e4bd72a9ec8a838c80b5 Mon Sep 17 00:00:00 2001
From: kmelnikovmh <k.melnikov.mh@proton.me>
Date: Sat, 23 May 2026 17:05:29 +0300
Subject: [PATCH] limiter: initial v1.0

---
 .../lectures/lesson7/limiter/RateLimiter.java | 44 ++++++++++-----
 .../lesson7/limiter/RateLimiterTest.java      | 56 +++++++++++++++++++
 2 files changed, 85 insertions(+), 15 deletions(-)
 create mode 100644 src/test/java/hse/java/lectures/lesson7/limiter/RateLimiterTest.java

diff --git a/src/main/java/hse/java/lectures/lesson7/limiter/RateLimiter.java b/src/main/java/hse/java/lectures/lesson7/limiter/RateLimiter.java
index 08df1b13..99903974 100644
--- a/src/main/java/hse/java/lectures/lesson7/limiter/RateLimiter.java
+++ b/src/main/java/hse/java/lectures/lesson7/limiter/RateLimiter.java
@@ -1,26 +1,40 @@
 package hse.java.lectures.lesson7.limiter;
 
 import java.time.temporal.ChronoUnit;
+import java.util.LinkedList;
 
-/**
- * Скользящий рейтлимитер: не больше заданного числа успешных {@link #check()} за последнюю секунду или минуту.
- */
 public class RateLimiter {
 
-    /**
-     * @param unit        длина окна — только {@link ChronoUnit#SECONDS} или {@link ChronoUnit#MINUTES}
-     *                    (скользящее окно 1 секунда или 1 минута)
-     * @param maxRequests максимум успешных {@link #check()} за окно (должно быть > 0)
-     */
+    private long windowNanos;
+    private int maxRequests;
+    private LinkedList<Long> stamps = new LinkedList<>();
+    private int currentSize = 0;
+
     public RateLimiter(ChronoUnit unit, int maxRequests) {
-        throw new UnsupportedOperationException("Not implemented");
+        if (unit != ChronoUnit.SECONDS && unit != ChronoUnit.MINUTES) {
+            throw new IllegalArgumentException("bad unit");
+        }
+        if (1 > maxRequests) {
+            throw new IllegalArgumentException("bad max");
+        }
+        this.windowNanos = unit.getDuration().toNanos();
+        this.maxRequests = maxRequests;
     }
 
-    /**
-     * Регистрирует попытку и возвращает, разрешена ли она в пределах лимита.
-     */
-    public boolean check() {
-        throw new UnsupportedOperationException("Not implemented");
+    public synchronized boolean check() {
+        long now = System.nanoTime();
+        long border = now - windowNanos;
+        int removed = 0;
+        while (!stamps.isEmpty() && stamps.getFirst() <= border) {
+            stamps.removeFirst();
+            ++removed;
+        }
+        currentSize = currentSize - removed;
+        if (currentSize < maxRequests) {
+            stamps.addLast(now);
+            ++currentSize;
+            return true;
+        }
+        return false;
     }
-
 }
diff --git a/src/test/java/hse/java/lectures/lesson7/limiter/RateLimiterTest.java b/src/test/java/hse/java/lectures/lesson7/limiter/RateLimiterTest.java
new file mode 100644
index 00000000..4e0c1a6b
--- /dev/null
+++ b/src/test/java/hse/java/lectures/lesson7/limiter/RateLimiterTest.java
@@ -0,0 +1,56 @@
+package hse.java.lectures.lesson7.limiter;
+
+import org.junit.jupiter.api.Tag;
+import org.junit.jupiter.api.Test;
+
+import java.time.temporal.ChronoUnit;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+@Tag("limiter")
+class RateLimiterTest {
+
+    @Test
+    void allowsThenRejects() {
+        RateLimiter limiter = new RateLimiter(ChronoUnit.SECONDS, 3);
+        for (int i = 0; i < 3; ++i) {
+            assertTrue(limiter.check());
+        }
+        assertFalse(limiter.check());
+    }
+
+    @Test
+    void rejectedDontTakeSlots() throws InterruptedException {
+        RateLimiter limiter = new RateLimiter(ChronoUnit.SECONDS, 1);
+        assertTrue(limiter.check());
+        for (int i = 0; i < 50; ++i) {
+            assertFalse(limiter.check());
+        }
+        Thread.sleep(1100);
+        assertTrue(limiter.check());
+    }
+
+    @Test
+    void threadSafe() throws Exception {
+        int limit = 5;
+        int threads = 20;
+        RateLimiter limiter = new RateLimiter(ChronoUnit.SECONDS, limit);
+        ExecutorService pool = Executors.newFixedThreadPool(threads);
+        CountDownLatch latch = new CountDownLatch(1);
+        AtomicInteger ok = new AtomicInteger(0);
+        for (int i = 0; i < threads; ++i) {
+            pool.submit(() -> {
+                try { latch.await(); } catch (InterruptedException e) { return; }
+                if (limiter.check()) { ok.incrementAndGet(); }
+            });
+        }
+        latch.countDown();
+        pool.shutdown();
+        while (!pool.isTerminated()) { Thread.sleep(50); }
+        assertEquals(limit, ok.get());
+    }
+}