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Java Simplified. Extensions and Useful Constructs for the Java Platform. Codeprimate Elements (a.k.a. cp-elements) is a Java library and micro-framework used to simplify the development of software applications written in Java. Elements packages several APIs into one library in order to address various application concerns and aspects of software design and development collectively and conveniently. Elements is a highly simple, yet robust and proven library built on solid OO principles, software design patterns and best practices to effectively solve common and reoccurring problems in software development.

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/*
 * Copyright 2016 Author or 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.cp.elements.lang.support;

import org.cp.elements.lang.Assert;

/**
 * The ComposableRunnable class is an implementation of the Runnable interface and the Composite Design Pattern to
 * compose multiple Runnable objects and treat it as a single instance of Runnable.
 *
 * @author John J. Blum
 * @see java.lang.Runnable
 * @since 1.0.0
 */
@SuppressWarnings("unused")
public final class ComposableRunnable implements Runnable {

  private final Runnable leftRunnable;
  private final Runnable rightRunnable;

  /**
   * Constructs an instance of the ComposableRunnable class composed an initialized with 2 Runnable objects.
   *
   * @param leftRunnable the left Runnable node in the composed graph.
   * @param rightRunnable the right Runnable node in the composed graph.
   * @throws NullPointerException if either the left or right Runnable object is null.
   */
  private ComposableRunnable(final Runnable leftRunnable, final Runnable rightRunnable) {
    Assert.notNull(leftRunnable, "The left node Runnable object cannot be null!");
    Assert.notNull(rightRunnable, "The right node Runnable object cannot be null!");

    this.leftRunnable = leftRunnable;
    this.rightRunnable = rightRunnable;
  }

  /**
   * Composes 2 Runnable objects into a single, compound Runnable object.  Returns the left Runnable if the right is
   * null and the right if the left is null.
   *
   * @param leftRunnable the left Runnable node in the composed graph.
   * @param rightRunnable the right Runnable node in the composed graph.
   * @return a Runnable object composed with the left and right Runnable objects.
   * @see #compose(Runnable...)
   */
  public static Runnable compose(final Runnable leftRunnable, final Runnable rightRunnable) {
    return (rightRunnable == null ? leftRunnable : (leftRunnable == null ? rightRunnable
      : new ComposableRunnable(leftRunnable, rightRunnable)));
  }

  /**
   * Composes the array of Runnable objects into a single, compound Runnable object that are run in the order the
   * Runnable objects are contained in the array.
   *
   * @param runnables an array of Runnable objects to compose into a single, compound Runnable object.
   * @return a Runnable object composed with the Runnable objects contained in the array.
   * @see #compose(Runnable, Runnable)
   */
  public static Runnable compose(final Runnable... runnables) {
    Runnable currentRunnable = null;

    if (runnables != null) {
      for (Runnable runnable : runnables) {
        currentRunnable = compose(currentRunnable, runnable);
      }
    }

    return currentRunnable;
  }

  /**
   * Runs the left and right Runnable objects/nodes in the graph.
   *
   * @see java.lang.Runnable#run()
   */
  @Override
  public void run() {
    leftRunnable.run();
    rightRunnable.run();
  }

}