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/**
 * Copyright (C) cedarsoft GmbH.
 *
 * Licensed under the GNU General Public License version 3 (the "License")
 * with Classpath Exception; you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at
 *
 *         http://www.cedarsoft.org/gpl3ce
 *         (GPL 3 with Classpath Exception)
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 3 only, as
 * published by the Free Software Foundation. cedarsoft GmbH designates this
 * particular file as subject to the "Classpath" exception as provided
 * by cedarsoft GmbH in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 3 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 3 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact cedarsoft GmbH, 72810 Gomaringen, Germany,
 * or visit www.cedarsoft.com if you need additional information or
 * have any questions.
 */
package com.cedarsoft.concurrent;

import com.cedarsoft.annotations.NonBlocking;
import com.cedarsoft.annotations.NonUiThread;
import com.cedarsoft.annotations.UiThread;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.GuardedBy;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * Abstract base class for async execution of scheduled runnables.
 * Only the latest runnable is executed
 *
 * @author Johannes Schneider ([email protected])
 */
public abstract class AbstractAsync {
  @Nonnull
  private final ReadWriteLock lock = new ReentrantReadWriteLock();

  @GuardedBy("lock")
  @Nonnull
  private final Map scheduledRunnables = new HashMap<>();

  /**
   * Asynchronously calls only the last added runnable.
   */
  @NonUiThread
  @UiThread
  public void last(@Nonnull final Runnable runnable) {
    last(runnable.getClass(), runnable);
  }

  /**
   * Asynchronously calls only the last runnable.
   */
  @NonUiThread
  @UiThread
  public void last(@Nonnull final Object key, @Nonnull final Runnable runnable) {
    lock.writeLock().lock();
    try {
      if (scheduledRunnables.put(key, runnable) != null) {
        //There is another job scheduled, so we do not have to reschedule it
        return;
      }
    } finally {
      lock.writeLock().unlock();
    }

    //There has no other event been scheduled
    runInTargetThread(() -> get(key).run());
  }

  /**
   * Returns the runnable for the given key
   */
  @UiThread
  @Nonnull
  private Runnable get(@Nonnull Object key) {
    lock.writeLock().lock();
    try {
      @Nullable
      Runnable found = scheduledRunnables.remove(key);
      if (found == null) {
        throw new IllegalStateException("No job found for <" + key + ">");
      }
      return found;
    } finally {
      lock.writeLock().unlock();
    }
  }

  /**
   * Run in target thread
   */
  @NonBlocking
  protected abstract void runInTargetThread(@Nonnull Runnable runnable);
}