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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. Write better Java!

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/*
 * Copyright 2011-Present 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.Optional;

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

/**
 * Java {@link FunctionalInterface} defining a contract for implementing objects
 * used to generate unique identifiers (IDs) for uniquely identifying some {@link Object} or {@literal entity}.
 *
 * @author John J. Blum
 * @param  {@link Comparable} {@link Class type} of the {@literal identifying value}.
 * @see java.lang.Comparable
 * @see java.lang.FunctionalInterface
 * @see org.cp.elements.lang.Identifiable
 * @since 1.0.0
 */
@FunctionalInterface
@SuppressWarnings("unused")
public interface IdentifierSequence> {

  /**
   * Generates the next {@link T unique ID} in sequence.
   *
   * @return the next {@link T unique ID} of {@link Class type T} in the sequence.
   */
  T nextId();

  /**
   * Sets the {@link T identifier} for the given {@link Identifiable object} if not set.
   *
   * @param  {@link Class type} of {@link Identifiable object}.
   * @param identifiable {@link Identifiable object} to identify (set the ID).
   * @return the given {@link Identifiable} object.
   * @see org.cp.elements.lang.Identifiable
   * @see #nextId()
   */
  @NullSafe
  default @Nullable > S identify(@Nullable S identifiable) {

    return Optional.ofNullable(identifiable)
      .filter(Identifiable::isNew)
      .map(it -> it.identifiedBy(nextId()))
      .orElse(identifiable);
  }
}