/*
    * Copyright 2021 TiKV Project Authors.
    *
    * 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 org.tikv.service.failsafe;
  
  import io.prometheus.client.Counter;
  import java.io.IOException;
  import java.util.concurrent.atomic.AtomicLong;
  import java.util.concurrent.atomic.AtomicReference;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  import org.tikv.common.TiConfiguration;
  
  public class CircuitBreakerImpl implements CircuitBreaker {
    private static final Logger logger = LoggerFactory.getLogger(CircuitBreakerImpl.class);
  
    private static final Counter CIRCUIT_BREAKER_ATTEMPT_COUNTER =
        Counter.build()
            .name("client_java_circuit_breaker_attempt_counter")
            .help("client circuit breaker attempt counter.")
            .labelNames("type", "cluster")
            .register();
  
    private final Long clusterId;
    private final boolean enable;
    private final int windowInSeconds;
    private final int errorThresholdPercentage;
    private final int requestVolumeThreshold;
    private final int sleepWindowInSeconds;
    private final int attemptRequestCount;
  
    private final AtomicLong circuitOpened = new AtomicLong(-1);
    private final AtomicReference<Status> status = new AtomicReference<>(Status.CLOSED);
    private final AtomicLong attemptCount = new AtomicLong(0);
    private final AtomicLong attemptSuccessCount = new AtomicLong(0);
  
    private final CircuitBreakerMetrics metrics;
  
    public CircuitBreakerImpl(TiConfiguration conf, long clusterId) {
      this(
          conf.isCircuitBreakEnable(),
          conf.getCircuitBreakAvailabilityWindowInSeconds(),
          conf.getCircuitBreakAvailabilityErrorThresholdPercentage(),
          conf.getCircuitBreakAvailabilityRequestVolumnThreshold(),
          conf.getCircuitBreakSleepWindowInSeconds(),
          conf.getCircuitBreakAttemptRequestCount(),
          clusterId);
    }
  
    public CircuitBreakerImpl(
        boolean enable,
        int windowInSeconds,
        int errorThresholdPercentage,
        int requestVolumeThreshold,
        int sleepWindowInSeconds,
        int attemptRequestCount,
        long clusterId) {
      this.enable = enable;
      this.clusterId = clusterId;
      this.windowInSeconds = windowInSeconds;
      this.errorThresholdPercentage = errorThresholdPercentage;
      this.requestVolumeThreshold = requestVolumeThreshold;
      this.sleepWindowInSeconds = sleepWindowInSeconds;
      this.attemptRequestCount = attemptRequestCount;
      this.metrics =
          enable ? new CircuitBreakerMetricsImpl(windowInSeconds) : new NoOpCircuitBreakerMetrics();
      this.metrics.addListener(getMetricsListener());
    }
  
    private MetricsListener getMetricsListener() {
      return hc -> {
        logger.debug("onNext " + hc.toString());
        // check if we are past the requestVolumeThreshold
        if (hc.getTotalRequests() < requestVolumeThreshold) {
          // we are not past the minimum volume threshold for the stat window,
          // so no change to circuit status.
          // if it was CLOSED, it stays CLOSED
          // if it was half-open, we need to wait for some successful command executions
          // if it was open, we need to wait for sleep window to elapse
        } else {
          if (hc.getErrorPercentage() < errorThresholdPercentage) {
            // we are not past the minimum error threshold for the stat window,
            // so no change to circuit status.
            // if it was CLOSED, it stays CLOSED
            // if it was half-open, we need to wait for some successful command executions
           // if it was open, we need to wait for sleep window to elapse
         } else {
           // our failure rate is too high, we need to set the state to OPEN
           close2Open();
         }
       }
     };
   }
 
   @Override
   public CircuitBreakerMetrics getMetrics() {
     return metrics;
   }
 
   @Override
   public boolean allowRequest() {
     if (!enable) {
       return true;
     }
     return !isOpen();
   }
 
   boolean isOpen() {
     return circuitOpened.get() >= 0;
   }
 
   Status getStatus() {
     return status.get();
   }
 
   @Override
   public void recordAttemptSuccess() {
     CIRCUIT_BREAKER_ATTEMPT_COUNTER.labels("success", clusterId.toString()).inc();
     if (attemptSuccessCount.incrementAndGet() >= this.attemptRequestCount) {
       halfOpen2Close();
     }
   }
 
   @Override
   public void recordAttemptFailure() {
     CIRCUIT_BREAKER_ATTEMPT_COUNTER.labels("failure", clusterId.toString()).inc();
     halfOpen2Open();
   }
 
   @Override
   public boolean attemptExecution() {
     if (allowRequest()) {
       return true;
     } else {
       if (isAfterSleepWindow()) {
         // only the `attemptRequestCount` requests after sleep window should execute
         // if all the executing commands succeed, the status will transition to CLOSED
         // if some of the executing commands fail, the status will transition to OPEN
         open2HalfOpen();
         return attemptCount.incrementAndGet() <= attemptRequestCount;
       } else {
         return false;
       }
     }
   }
 
   private boolean isAfterSleepWindow() {
     final long circuitOpenTime = circuitOpened.get();
     final long currentTime = System.currentTimeMillis();
     final long sleepWindowTime = (long) sleepWindowInSeconds * 1000;
     return currentTime >= circuitOpenTime + sleepWindowTime;
   }
 
   private void close2Open() {
     if (status.compareAndSet(Status.CLOSED, Status.OPEN)) {
       // This thread wins the race to open the circuit
       // it sets the start time for the sleep window
       circuitOpened.set(System.currentTimeMillis());
       logger.info("CLOSED => OPEN");
     }
   }
 
   private void halfOpen2Close() {
     if (status.compareAndSet(Status.HALF_OPEN, Status.CLOSED)) {
       // This thread wins the race to close the circuit
       circuitOpened.set(-1L);
       logger.info("HALF_OPEN => CLOSED");
     }
   }
 
   private void open2HalfOpen() {
     if (status.compareAndSet(Status.OPEN, Status.HALF_OPEN)) {
       // This thread wins the race to half close the circuit
       // it resets the attempt count
       attemptCount.set(0);
       attemptSuccessCount.set(0);
       logger.info("OPEN => HALF_OPEN");
     }
   }
 
   private void halfOpen2Open() {
     if (status.compareAndSet(Status.HALF_OPEN, Status.OPEN)) {
       // This thread wins the race to re-open the circuit
       // it resets the start time for the sleep window
       circuitOpened.set(System.currentTimeMillis());
       logger.info("HALF_OPEN => OPEN");
     }
   }
 
   @Override
   public void close() throws IOException {
     metrics.close();
   }
 }