/*
    * 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 java.io.IOException;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.concurrent.ScheduledExecutorService;
  import java.util.concurrent.ScheduledThreadPoolExecutor;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicLong;
  import java.util.concurrent.atomic.AtomicReference;
  import org.apache.commons.lang3.concurrent.BasicThreadFactory;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  public class CircuitBreakerMetricsImpl implements CircuitBreakerMetrics {
    private static final Logger logger = LoggerFactory.getLogger(CircuitBreakerMetricsImpl.class);
  
    private final int windowInMS;
    private final List<MetricsListener> listeners;
    private final AtomicReference<SingleWindowMetrics> currentMetrics;
  
    private final ScheduledExecutorService scheduler;
    private static final int SCHEDULER_INITIAL_DELAY = 1000;
    private static final int SCHEDULER_PERIOD = 1000;
  
    public CircuitBreakerMetricsImpl(int windowInSeconds) {
      this.windowInMS = windowInSeconds * 1000;
      this.listeners = new ArrayList<>();
      this.currentMetrics = new AtomicReference<>(new SingleWindowMetrics());
  
      scheduler =
          new ScheduledThreadPoolExecutor(
              1,
              new BasicThreadFactory.Builder()
                  .namingPattern("circuit-breaker-metrics-%d")
                  .daemon(true)
                  .build());
  
      scheduler.scheduleAtFixedRate(
          this::onReachCircuitWindow,
          SCHEDULER_INITIAL_DELAY,
          SCHEDULER_PERIOD,
          TimeUnit.MILLISECONDS);
    }
  
    @Override
    public void recordSuccess() {
      currentMetrics.get().recordSuccess();
    }
  
    @Override
    public void recordFailure() {
      currentMetrics.get().recordFailure();
    }
  
    private void onReachCircuitWindow() {
      SingleWindowMetrics singleWindowMetrics = currentMetrics.get();
      if (System.currentTimeMillis() < singleWindowMetrics.getStartMS() + windowInMS) {
        return;
      }
      if (!currentMetrics.compareAndSet(singleWindowMetrics, new SingleWindowMetrics())) {
        return;
      }
      logger.debug("window timeout, reset SingleWindowMetrics");
      HealthCounts healthCounts = singleWindowMetrics.getHealthCounts();
      for (MetricsListener metricsListener : listeners) {
        metricsListener.onNext(healthCounts);
      }
    }
  
    @Override
    public void addListener(MetricsListener metricsListener) {
      listeners.add(metricsListener);
    }
  
    @Override
    public void close() throws IOException {
      scheduler.shutdown();
    }
  
    /** Instead of using SingleWindowMetrics, it is better to use RollingWindowMetrics. */
    static class SingleWindowMetrics {
     private final long startMS = System.currentTimeMillis();
     private final AtomicLong totalCount = new AtomicLong(0);
     private final AtomicLong errorCount = new AtomicLong(0);
 
     public void recordSuccess() {
       totalCount.incrementAndGet();
     }
 
     public void recordFailure() {
       totalCount.incrementAndGet();
 
       errorCount.incrementAndGet();
     }
 
     public HealthCounts getHealthCounts() {
       return new HealthCounts(totalCount.get(), errorCount.get());
     }
 
     public long getStartMS() {
       return startMS;
     }
   }
 }