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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;

import java.util.Iterator;
import java.util.Optional;

import org.cp.elements.lang.annotation.NullSafe;

/**
 * The {@link Registry} interface defines a contract for implementing {@link Object objects} that can register
 * and unregister other interesting {@link Object Objects}.
 *
 * @author John Blum
 * @see java.lang.Iterable
 * @since 1.0.0
 */
@SuppressWarnings("unused")
public interface Registry extends Iterable {

  /**
   * Determines whether the {@link Object} is registered with this {@link Registry}.
   *
   * @param obj {@link Object} to evaluate.
   * @return a boolean value indicating whether the {@link Object} is registered with this {@link Registry}.
   * @see #register(Object)
   */
  @NullSafe
  default boolean isRegistered(T obj) {

    return Optional.ofNullable(obj)
      .map(it -> {

        for (T registeredObject : this) {
          if (it.equals(registeredObject)) {
            return true;
          }
        }

        return false;

      })
      .orElse(false);
  }

  /**
   * Registers the {@link Object} with this {@link Registry}.
   *
   * @param  {@link Class concrete type} of this {@link Registry} implementation.
   * @param obj {@link Object} to register.
   * @return this {@link Registry}.
   * @see #unregister(Object)
   */
  > R register(T obj);

  /**
   * Unregisters the {@link Object} from this {@link Registry}.
   *
   * @param  {@link Class concrete type} of this {@link Registry} implementation.
   * @param obj {@link Object} to unregister.
   * @return this {@link Registry}.
   * @see #register(Object)
   */
  @NullSafe
  @SuppressWarnings("unchecked")
  default > R unregister(T obj) {

    Iterator registeredObjects = this.iterator();

    while (registeredObjects.hasNext()) {
      if (registeredObjects.next().equals(obj)) {
        registeredObjects.remove();
      }
    }

    return (R) this;
  }
}