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/*
 * Copyright Terracotta, Inc.
 * Copyright Super iPaaS Integration LLC, an IBM Company 2024
 *
 * 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.terracotta.angela.common.util;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.Closeable;
import java.time.Duration;
import java.util.Collection;
import java.util.Map;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.LinkedTransferQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TransferQueue;
import java.util.concurrent.atomic.AtomicReference;

/**
 * Tracker of inactivity
 *
 * @author Mathieu Carbou
 */
public class ActivityTracker implements Closeable {

  private static final Logger logger = LoggerFactory.getLogger(ActivityTracker.class);

  private final Duration inactivityDelay;
  private final Map> listeners = new ConcurrentHashMap<>();
  private final TransferQueue activity = new LinkedTransferQueue<>();
  private final boolean enabled;
  private final AtomicReference monitor = new AtomicReference<>();

  private ActivityTracker(Duration inactivityDelay) {
    this.enabled = !inactivityDelay.equals(Duration.ZERO);
    this.inactivityDelay = inactivityDelay;
  }


  public Duration getInactivityDelay() {
    return inactivityDelay;
  }

  @Override
  public void close() {
    stop();
  }

  public void onInactivity(Runnable runnable) {
    if (enabled) {
      getListeners("inactivity").add(runnable);
    }
  }

  public void onStart(Runnable runnable) {
    if (enabled) {
      getListeners("start").add(runnable);
    }
  }

  public void onStop(Runnable runnable) {
    if (enabled) {
      getListeners("stop").add(runnable);
    }
  }

  /**
   * Record any activity
   */
  public void touch() {
    if (enabled) {
      activity.tryTransfer(Boolean.TRUE);
    }
  }

  public boolean isRunning() {
    return monitor.get() != null;
  }

  public void stop() {
    internalStop()
        .filter(thread -> thread != Thread.currentThread())
        .ifPresent(thread -> {
          try {
            thread.join();
          } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            throw new RuntimeException(e);
          }
        });
  }

  public void start() {
    if (enabled) {
      CountDownLatch started = new CountDownLatch(1);
      Thread thread = new Thread(() -> {
        Thread currentThread = Thread.currentThread();
        try {
          getListeners("start").forEach(runnable -> {
            try {
              runnable.run();
            } catch (RuntimeException e) {
              logger.error(e.getMessage(), e);
            }
          });
          started.countDown();
          while (monitor.get() == currentThread) {
            if (activity.poll(inactivityDelay.toMillis(), TimeUnit.MILLISECONDS) == null) {
              // timeout and no new element => inactivity
              getListeners("inactivity").forEach(runnable -> {
                try {
                  runnable.run();
                } catch (RuntimeException e) {
                  logger.error(e.getMessage(), e);
                }
              });
            }
          }
        } catch (InterruptedException ignored) {
        } finally {
          getListeners("stop").forEach(runnable -> {
            try {
              runnable.run();
            } catch (RuntimeException e) {
              logger.error(e.getMessage(), e);
            }
          });
          monitor.compareAndSet(currentThread, null);
        }
      });
      thread.setName("ActivityTracker:" + inactivityDelay + ":" + thread.hashCode());
      thread.setDaemon(true);

      if (monitor.compareAndSet(null, thread)) {
        thread.start();
        try {
          started.await();
        } catch (InterruptedException e) {
          Thread.currentThread().interrupt();
        }
      }
    }
  }

  private Optional internalStop() {
    return Optional.ofNullable(monitor.getAndSet(null));
  }

  private Collection getListeners(String event) {
    return listeners.compute(event, (e, listeners) -> listeners != null ? listeners : new CopyOnWriteArrayList<>());
  }

  public static ActivityTracker of(Duration inactivityKillerDelay) {
    return new ActivityTracker(inactivityKillerDelay);
  }
}