// Copyright 2016 The Bazel Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package com.google.devtools.build.lib.remote;

import static com.google.common.truth.Truth.assertThat;
import static org.junit.Assert.fail;
import static org.mockito.Mockito.never;
import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.when;

import com.google.common.util.concurrent.ListeningScheduledExecutorService;
import com.google.common.util.concurrent.MoreExecutors;
import com.google.devtools.build.lib.remote.Retrier.Backoff;
import com.google.devtools.build.lib.remote.Retrier.CircuitBreaker;
import com.google.devtools.build.lib.remote.Retrier.CircuitBreaker.State;
import com.google.devtools.build.lib.remote.Retrier.CircuitBreakerException;
import com.google.devtools.build.lib.remote.Retrier.RetryException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.Predicate;
import java.util.function.Supplier;
import javax.annotation.concurrent.ThreadSafe;
import org.junit.AfterClass;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;

/**
 * Tests for {@link Retrier}.
 */
@RunWith(JUnit4.class)
public class RetrierTest {

  @Mock
  private CircuitBreaker alwaysOpen;

  private static final Predicate<Exception> RETRY_ALL = (e) -> true;
  private static final Predicate<Exception> RETRY_NONE = (e) -> false;

  private static ListeningScheduledExecutorService retryService;

  @BeforeClass
  public static void beforeEverything() {
    retryService = MoreExecutors.listeningDecorator(Executors.newScheduledThreadPool(1));
  }

  @Before
  public void setup() {
    MockitoAnnotations.initMocks(this);
    when(alwaysOpen.state()).thenReturn(State.ACCEPT_CALLS);
  }

  @AfterClass
  public static void afterEverything() {
    retryService.shutdownNow();
  }

  @Test
  public void retryShouldWork_failure() throws Exception {
    // Test that a call is retried according to the backoff.
    // All calls fail.

    Supplier<Backoff> s  = () -> new ZeroBackoff(/*maxRetries=*/2);
    Retrier r = new Retrier(s, RETRY_ALL, retryService, alwaysOpen);
    try {
      r.execute(() -> {
        throw new Exception("call failed");
      });
      fail("exception expected.");
    } catch (RetryException e) {
      assertThat(e.getAttempts()).isEqualTo(3);
    }

    verify(alwaysOpen, times(3)).recordFailure();
    verify(alwaysOpen, never()).recordSuccess();
  }

  @Test
  public void retryShouldWorkNoRetries_failure() throws Exception {
    // Test that a non-retriable error is not retried.
    // All calls fail.

    Supplier<Backoff> s  = () -> new ZeroBackoff(/*maxRetries=*/2);
    Retrier r = new Retrier(s, RETRY_NONE, retryService, alwaysOpen);
    try {
      r.execute(() -> {
        throw new Exception("call failed");
      });
      fail("exception expected.");
    } catch (RetryException e) {
      assertThat(e.getAttempts()).isEqualTo(1);
    }

    verify(alwaysOpen, times(1)).recordFailure();
    verify(alwaysOpen, never()).recordSuccess();
  }

  @Test
  public void retryShouldWork_success() throws Exception {
    // Test that a call is retried according to the backoff.
    // The last call succeeds.

    Supplier<Backoff> s  = () -> new ZeroBackoff(/*maxRetries=*/2);
    Retrier r = new Retrier(s, RETRY_ALL, retryService, alwaysOpen);
    AtomicInteger numCalls = new AtomicInteger();
    int val = r.execute(() -> {
      numCalls.incrementAndGet();
      if (numCalls.get() == 3) {
        return 1;
      }
      throw new Exception("call failed");
    });
    assertThat(val).isEqualTo(1);

    verify(alwaysOpen, times(2)).recordFailure();
    verify(alwaysOpen, times(1)).recordSuccess();
  }

  @Test
  public void nestedRetriesShouldWork() throws Exception {
    // Test that nested calls using retries compose as expected.

    Supplier<Backoff> s  = () -> new ZeroBackoff(/*maxRetries=*/1);
    Retrier r = new Retrier(s, RETRY_ALL, retryService, alwaysOpen);

    AtomicInteger attemptsLvl0 = new AtomicInteger();
    AtomicInteger attemptsLvl1 = new AtomicInteger();
    AtomicInteger attemptsLvl2 = new AtomicInteger();
    try {
      r.execute(() -> {
        attemptsLvl0.incrementAndGet();
        return r.execute(() -> {
          attemptsLvl1.incrementAndGet();
          return r.execute(() -> {
            attemptsLvl2.incrementAndGet();
            throw new Exception("call failed");
          });
        });
      });
    } catch (RetryException outer) {
      assertThat(outer.getAttempts()).isEqualTo(2);
      assertThat(outer).hasCauseThat().hasMessageThat().isEqualTo("call failed");
      assertThat(attemptsLvl0.get()).isEqualTo(2);
      assertThat(attemptsLvl1.get()).isEqualTo(4);
      assertThat(attemptsLvl2.get()).isEqualTo(8);
    }
  }

  @Test
  public void circuitBreakerShouldTrip() throws Exception {
    // Test that a circuit breaker can trip.

    Supplier<Backoff> s  = () -> new ZeroBackoff(/*maxRetries=*/3);
    TripAfterNCircuitBreaker cb = new TripAfterNCircuitBreaker(/*maxConsecutiveFailures=*/2);
    Retrier r = new Retrier(s, RETRY_ALL, retryService, cb);

    try {
      r.execute(() -> {
        throw new Exception("call failed");
      });
      fail ("exception expected");
    } catch (CircuitBreakerException expected) {
      // Intentionally left empty.
    }

    assertThat(cb.state()).isEqualTo(State.REJECT_CALLS);
    assertThat(cb.consecutiveFailures).isEqualTo(2);
  }

  @Test
  public void circuitBreakerCanRecover() throws Exception {
    // Test that a circuit breaker can recover from REJECT_CALLS to ACCEPT_CALLS by
    // utilizing the TRIAL_CALL state.

    Supplier<Backoff> s  = () -> new ZeroBackoff(/*maxRetries=*/3);
    TripAfterNCircuitBreaker cb = new TripAfterNCircuitBreaker(/*maxConsecutiveFailures=*/2);
    Retrier r = new Retrier(s, RETRY_ALL, retryService, cb);

    cb.trialCall();

    assertThat(cb.state()).isEqualTo(State.TRIAL_CALL);

    int val = r.execute(() -> 10);
    assertThat(val).isEqualTo(10);
    assertThat(cb.state()).isEqualTo(State.ACCEPT_CALLS);
  }

  @Test
  public void circuitBreakerHalfOpenIsNotRetried() throws Exception {
    // Test that a call executed in TRIAL_CALL state is not retried
    // in case of failure.

    Supplier<Backoff> s  = () -> new ZeroBackoff(/*maxRetries=*/3);
    TripAfterNCircuitBreaker cb = new TripAfterNCircuitBreaker(/*maxConsecutiveFailures=*/2);
    Retrier r = new Retrier(s, RETRY_ALL, retryService, cb);

    cb.trialCall();

    try {
      r.execute(() -> {
        throw new Exception("call failed");
      });
    } catch (RetryException expected) {
      // Intentionally left empty.
    }

    assertThat(cb.consecutiveFailures).isEqualTo(1);
  }

  @Test
  public void interruptsShouldNotBeRetried_flag() throws Exception {
    // Test that a call is not executed / retried if the current thread
    // is interrupted.

    Supplier<Backoff> s  = () -> new ZeroBackoff(/*maxRetries=*/3);
    TripAfterNCircuitBreaker cb = new TripAfterNCircuitBreaker(/*maxConsecutiveFailures=*/2);
    Retrier r = new Retrier(s, RETRY_ALL, retryService, cb);

    try {
      Thread.currentThread().interrupt();
      r.execute(() -> 10);
    } catch (InterruptedException expected) {
      // Intentionally left empty.
    }
  }

  @Test
  public void interruptsShouldNotBeRetried_exception() throws Exception {
    // Test that a call is not retried if an InterruptedException is thrown.

    Supplier<Backoff> s  = () -> new ZeroBackoff(/*maxRetries=*/3);
    TripAfterNCircuitBreaker cb = new TripAfterNCircuitBreaker(/*maxConsecutiveFailures=*/2);
    Retrier r = new Retrier(s, RETRY_ALL, retryService, cb);

    try {
      Thread.currentThread().interrupt();
      r.execute(() -> {
        throw new InterruptedException();
      });
    } catch (InterruptedException expected) {
      // Intentionally left empty.
    }
  }

  @Test
  public void asyncRetryShouldWork() throws Exception {
    // Test that a call is retried according to the backoff.
    // All calls fail.

    Supplier<Backoff> s = () -> new ZeroBackoff(/*maxRetries=*/ 2);
    Retrier r = new Retrier(s, RETRY_ALL, retryService, alwaysOpen);
    try {
      r.executeAsync(
              () -> {
                throw new Exception("call failed");
              })
          .get();
      fail("exception expected.");
    } catch (ExecutionException e) {
      assertThat(e.getCause()).isInstanceOf(RetryException.class);
      assertThat(((RetryException) e.getCause()).getAttempts()).isEqualTo(3);
    }
  }

  /**
   * Simple circuit breaker that trips after N consecutive failures.
   */
  @ThreadSafe
  private static class TripAfterNCircuitBreaker implements CircuitBreaker {

    private final int maxConsecutiveFailures;

    private State state = State.ACCEPT_CALLS;
    private int consecutiveFailures;

    TripAfterNCircuitBreaker(int maxConsecutiveFailures) {
      this.maxConsecutiveFailures = maxConsecutiveFailures;
    }

    @Override
    public synchronized State state() {
      return state;
    }

    @Override
    public synchronized void recordFailure() {
      consecutiveFailures++;
      if (consecutiveFailures >= maxConsecutiveFailures) {
        state = State.REJECT_CALLS;
      }
    }

    @Override
    public synchronized void recordSuccess() {
      consecutiveFailures = 0;
      state = State.ACCEPT_CALLS;
    }

    void trialCall() {
      state = State.TRIAL_CALL;
    }
  }

  private static class ZeroBackoff implements Backoff {

    private final int maxRetries;
    private int retries;

    public ZeroBackoff(int maxRetries) {
      this.maxRetries = maxRetries;
    }

    @Override
    public long nextDelayMillis() {
      if (retries >= maxRetries) {
        return -1;
      }
      retries++;
      return 0;
    }

    @Override
    public int getRetryAttempts() {
      return retries;
    }
  }
}