/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.iotdb.db.utils.stats;

import io.airlift.units.Duration;

import java.lang.management.ManagementFactory;
import java.lang.management.ThreadMXBean;

import static com.google.common.base.MoreObjects.toStringHelper;
import static java.util.concurrent.TimeUnit.NANOSECONDS;

/**
 * this class is copied from
 * https://github.com/airlift/airlift/blob/214/stats/src/main/java/io/airlift/stats/CpuTimer.java as
 * it doesn't support Java8.
 */
public class CpuTimer {
  private static final ThreadMXBean THREAD_MX_BEAN = ManagementFactory.getThreadMXBean();

  private final long wallStartTime;
  private final long cpuStartTime;
  private final long userStartTime;

  private long intervalWallStart;
  private long intervalCpuStart;
  private long intervalUserStart;

  public CpuTimer() {
    wallStartTime = System.nanoTime();
    cpuStartTime = THREAD_MX_BEAN.getCurrentThreadCpuTime();
    userStartTime = THREAD_MX_BEAN.getCurrentThreadUserTime();

    intervalWallStart = wallStartTime;
    intervalCpuStart = cpuStartTime;
    intervalUserStart = userStartTime;
  }

  public CpuDuration startNewInterval() {
    long currentWallTime = System.nanoTime();
    long currentCpuTime = THREAD_MX_BEAN.getCurrentThreadCpuTime();
    long currentUserTime = THREAD_MX_BEAN.getCurrentThreadUserTime();

    CpuDuration cpuDuration =
        new CpuDuration(
            nanosBetween(intervalWallStart, currentWallTime),
            nanosBetween(intervalCpuStart, currentCpuTime),
            nanosBetween(intervalUserStart, currentUserTime));

    intervalWallStart = currentWallTime;
    intervalCpuStart = currentCpuTime;
    intervalUserStart = currentUserTime;

    return cpuDuration;
  }

  public CpuDuration elapsedIntervalTime() {
    long currentWallTime = System.nanoTime();
    long currentCpuTime = THREAD_MX_BEAN.getCurrentThreadCpuTime();
    long currentUserTime = THREAD_MX_BEAN.getCurrentThreadUserTime();

    return new CpuDuration(
        nanosBetween(intervalWallStart, currentWallTime),
        nanosBetween(intervalCpuStart, currentCpuTime),
        nanosBetween(intervalUserStart, currentUserTime));
  }

  public CpuDuration elapsedTime() {
    long currentWallTime = System.nanoTime();
    long currentCpuTime = THREAD_MX_BEAN.getCurrentThreadCpuTime();
    long currentUserTime = THREAD_MX_BEAN.getCurrentThreadUserTime();

    return new CpuDuration(
        nanosBetween(wallStartTime, currentWallTime),
        nanosBetween(cpuStartTime, currentCpuTime),
        nanosBetween(userStartTime, currentUserTime));
  }

  private static Duration nanosBetween(long start, long end) {
    return new Duration(Math.abs(end - start), NANOSECONDS);
  }

  public static class CpuDuration {
    private final Duration wall;
    private final Duration cpu;
    private final Duration user;

    public CpuDuration() {
      this.wall = new Duration(0, NANOSECONDS);
      this.cpu = new Duration(0, NANOSECONDS);
      this.user = new Duration(0, NANOSECONDS);
    }

    public CpuDuration(Duration wall, Duration cpu, Duration user) {
      this.wall = wall;
      this.cpu = cpu;
      this.user = user;
    }

    public Duration getWall() {
      return wall;
    }

    public Duration getCpu() {
      return cpu;
    }

    public Duration getUser() {
      return user;
    }

    public CpuDuration add(CpuDuration cpuDuration) {
      return new CpuDuration(
          addDurations(wall, cpuDuration.wall),
          addDurations(cpu, cpuDuration.cpu),
          addDurations(user, cpuDuration.user));
    }

    public CpuDuration subtract(CpuDuration cpuDuration) {
      return new CpuDuration(
          subtractDurations(wall, cpuDuration.wall),
          subtractDurations(cpu, cpuDuration.cpu),
          subtractDurations(user, cpuDuration.user));
    }

    private static Duration addDurations(Duration a, Duration b) {
      return new Duration(a.getValue(NANOSECONDS) + b.getValue(NANOSECONDS), NANOSECONDS);
    }

    private static Duration subtractDurations(Duration a, Duration b) {
      return new Duration(
          Math.max(0, a.getValue(NANOSECONDS) - b.getValue(NANOSECONDS)), NANOSECONDS);
    }

    @Override
    public String toString() {
      return toStringHelper(this).add("wall", wall).add("cpu", cpu).add("user", user).toString();
    }
  }
}
