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  package org.apache.hc.client5.http.impl.classic;
  
  
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.junit.jupiter.api.Assertions.assertTrue;
  
  import java.time.Instant;
  import java.util.Map;
  import java.util.Random;
  import java.util.concurrent.BrokenBarrierException;
  import java.util.concurrent.CountDownLatch;
  import java.util.concurrent.CyclicBarrier;
  
  import org.apache.hc.client5.http.HttpRoute;
  import org.apache.hc.client5.http.classic.BackoffManager;
  import org.apache.hc.core5.http.HttpHost;
  import org.apache.hc.core5.util.TimeValue;
  import org.junit.jupiter.api.BeforeEach;
  import org.junit.jupiter.api.Test;
  
  class TestAIMDBackoffManager {
  
      private AIMDBackoffManager impl;
      private MockConnPoolControl connPerRoute;
      private HttpRoute route;
      private static final long DEFAULT_COOL_DOWN_MS = 10; // Adjust this value to match the default cooldown period in AIMDBackoffManager
  
  
      @BeforeEach
      void setUp() {
          connPerRoute = new MockConnPoolControl();
          route = new HttpRoute(new HttpHost("localhost", 80));
          impl = new AIMDBackoffManager(connPerRoute);
          impl.setPerHostConnectionCap(10);
          impl.setCoolDown(TimeValue.ofMilliseconds(DEFAULT_COOL_DOWN_MS));
  
      }
  
      @Test
      void isABackoffManager() {
          assertTrue(impl instanceof BackoffManager);
      }
  
      @Test
      void halvesConnectionsOnBackoff() {
          connPerRoute.setMaxPerRoute(route, 4);
          impl.backOff(route);
          assertEquals(2, connPerRoute.getMaxPerRoute(route));
      }
  
      @Test
      void doesNotBackoffBelowOneConnection() {
          connPerRoute.setMaxPerRoute(route, 1);
          impl.backOff(route);
          assertEquals(1, connPerRoute.getMaxPerRoute(route));
      }
  
      @Test
      void increasesByOneOnProbe() {
          connPerRoute.setMaxPerRoute(route, 2);
          impl.probe(route);
          assertEquals(3, connPerRoute.getMaxPerRoute(route));
      }
  
      @Test
      void doesNotIncreaseBeyondPerHostMaxOnProbe() {
          connPerRoute.setDefaultMaxPerRoute(5);
          connPerRoute.setMaxPerRoute(route, 5);
          impl.setPerHostConnectionCap(5);
          impl.probe(route);
          assertEquals(5, connPerRoute.getMaxPerRoute(route));
      }
  
     @Test
     void backoffDoesNotAdjustDuringCoolDownPeriod() {
         // Arrange
         connPerRoute.setMaxPerRoute(route, 4);
 
         // Act
         impl.backOff(route);
         final long max1 = connPerRoute.getMaxPerRoute(route);
 
         // Manipulate lastRouteBackoffs to simulate that not enough time has passed
         final Map<HttpRoute, Instant> lastRouteBackoffs = impl.getLastRouteBackoffs();
         lastRouteBackoffs.put(route, Instant.now().minusMillis(1));
 
         // Act again
         impl.backOff(route);
         final long max2 = connPerRoute.getMaxPerRoute(route);
 
         // Assert
         assertEquals(max1, max2);
     }
 
 
     @Test
     void backoffStillAdjustsAfterCoolDownPeriod() {
         // Arrange: Initialize the maximum number of connections for a route to 8
         connPerRoute.setMaxPerRoute(route, 8);
 
         // Act: Perform the first backoff operation
         impl.backOff(route);
         final long initialMax = connPerRoute.getMaxPerRoute(route);
 
         // Act: Simulate that the cooldown period has passed
         final Map<HttpRoute, Instant> lastRouteBackoffs = impl.getLastRouteBackoffs();
         lastRouteBackoffs.put(route, Instant.now().minusMillis(DEFAULT_COOL_DOWN_MS + 1));
 
         // Act: Perform the second backoff operation
         impl.backOff(route);
         final long finalMax = connPerRoute.getMaxPerRoute(route);
 
         // Assert: Verify that the maximum number of connections has decreased or reached the minimum limit (1)
         if (initialMax != 1) {
             assertTrue(finalMax < initialMax, "Max connections should decrease after cooldown");
         } else {
             assertEquals(1, finalMax, "Max connections should remain 1 if it's already at the minimum");
         }
     }
 
 
     @Test
     void probeDoesNotAdjustDuringCooldownPeriod() {
         // Arrange
         connPerRoute.setMaxPerRoute(route, 4);
 
         // First probe
         impl.probe(route);
         final long max1 = connPerRoute.getMaxPerRoute(route);
 
         // Manipulate lastRouteProbes to simulate that not enough time has passed
         final Map<HttpRoute, Instant> lastRouteProbes = impl.getLastRouteProbes();
         lastRouteProbes.put(route, Instant.now().minusMillis(1));
 
         // Second probe
         impl.probe(route);
         final long max2 = connPerRoute.getMaxPerRoute(route);
 
         // Assert
         assertEquals(max1, max2);
     }
 
 
     @Test
     void probeStillAdjustsAfterCoolDownPeriod() {
         connPerRoute.setMaxPerRoute(route, 8);
 
         // First probe
         impl.probe(route);
         final long max = connPerRoute.getMaxPerRoute(route);
 
         // Manipulate lastRouteProbes to simulate that enough time has passed for the cooldown period
         final Map<HttpRoute, Instant> lastRouteProbes = impl.getLastRouteProbes();
         lastRouteProbes.put(route, Instant.now().minusMillis(DEFAULT_COOL_DOWN_MS + 1));
 
         // Second probe
         impl.probe(route);
 
         // Assert that the max connections have increased
         assertTrue(max < connPerRoute.getMaxPerRoute(route));
     }
 
 
     @Test
     void willBackoffImmediatelyEvenAfterAProbe() {
         connPerRoute.setMaxPerRoute(route, 8);
         impl.probe(route);
         final long max = connPerRoute.getMaxPerRoute(route);
         impl.backOff(route);
         assertTrue(connPerRoute.getMaxPerRoute(route) < max);
     }
 
     @Test
     void backOffFactorIsConfigurable() {
         connPerRoute.setMaxPerRoute(route, 10);
         impl.setBackoffFactor(0.9);
         impl.backOff(route);
         assertEquals(9, connPerRoute.getMaxPerRoute(route));
     }
 
     @Test
     void coolDownPeriodIsConfigurable() {
         final long cd = new Random().nextInt(500) + 500; // Random cooldown period between 500 and 1000 milliseconds
         impl.setCoolDown(TimeValue.ofMilliseconds(cd));
 
         // Probe and check if the connection count remains the same during the cooldown period
         impl.probe(route);
         final int max0 = connPerRoute.getMaxPerRoute(route);
 
         // Manipulate lastRouteProbes to simulate that not enough time has passed
         final Map<HttpRoute, Instant> lastRouteProbes = impl.getLastRouteProbes();
         lastRouteProbes.put(route, Instant.now().minusMillis(cd / 2));
 
         // Probe again
         impl.probe(route);
         assertEquals(max0, connPerRoute.getMaxPerRoute(route));
 
         // Manipulate lastRouteProbes to simulate that enough time has passed
         lastRouteProbes.put(route, Instant.now().minusMillis(cd + 1));
 
         // Probe again
         impl.probe(route);
         assertTrue(max0 < connPerRoute.getMaxPerRoute(route));
     }
 
     @Test
     void testConcurrency() throws InterruptedException {
         final int initialMaxPerRoute = 10;
         final int numberOfThreads = 20;
         final int numberOfOperationsPerThread = 100;  // reduced operations
 
         // Create a cyclic barrier that will wait for all threads to be ready before proceeding
         final CyclicBarrier barrier = new CyclicBarrier(numberOfThreads);
 
         final CountDownLatch latch = new CountDownLatch(numberOfThreads);
 
         for (int i = 0; i < numberOfThreads; i++) {
             final HttpRoute threadRoute = new HttpRoute(new HttpHost("localhost", 8080 + i)); // Each thread gets its own route
             connPerRoute.setMaxPerRoute(threadRoute, initialMaxPerRoute);
 
             new Thread(() -> {
                 try {
                     // Wait for all threads to be ready
                     barrier.await();
 
                     // Run operations
                     for (int j = 0; j < numberOfOperationsPerThread; j++) {
                         if (Math.random() < 0.5) {
                             impl.backOff(threadRoute);
                         } else {
                             impl.probe(threadRoute);
                         }
                     }
                 } catch (InterruptedException | BrokenBarrierException e) {
                     Thread.currentThread().interrupt();
                 } finally {
                     latch.countDown();
                 }
             }).start();
         }
 
         latch.await();
 
         // Check that the final value for each route is within an acceptable range
         for (int i = 0; i < numberOfThreads; i++) {
             final HttpRoute threadRoute = new HttpRoute(new HttpHost("localhost", 8080 + i));
             final int finalMaxPerRoute = connPerRoute.getMaxPerRoute(threadRoute);
             assertTrue(finalMaxPerRoute >= 1 && finalMaxPerRoute <= initialMaxPerRoute + 7);  // more permissive check
         }
     }
 }