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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.util;

import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.cp.elements.lang.FluentApiExtension;
import org.cp.elements.lang.StringUtils;
import org.cp.elements.lang.annotation.FluentApi;

/**
 * The {@link CollectionExtensions} class provides methods to write natural language expressions for performing various
 * {@link Collection}-oriented operations.
 *
 * @author John J. Blum
 * @see java.util.Arrays
 * @see java.util.Collection
 * @see java.util.Collections
 * @see java.util.List
 * @see java.util.Set
 * @see org.cp.elements.lang.FluentApiExtension
 * @see org.cp.elements.lang.annotation.FluentApi
 * @since 1.0.0
 */
@SuppressWarnings("unused")
public class CollectionExtensions {

  /**
   * The {@literal from} operator performs conversions on the given array and it's elements.
   *
   * For instance, the array can be converted into an ordered {@link List} of elements,
   * or a unique {@link Set} of elements originating from the array.
   *
   * @param  {@link Class} type of the elements in the array.
   * @param array array of elements all of {@link Class} type T to be converted.
   * @return a {@link From} operator to perform the conversions.
   * @see org.cp.elements.lang.annotation.FluentApi
   */
  @FluentApi
  @SafeVarargs
  public static  From from(T... array) {
    return new FromExpression<>(array);
  }

  /**
   * The {@link From} interface defines operations for conversion of array to a {@link List}, {@link Set}
   * or {@link String}.
   *
   * @param  {@link Class} type of elements in the {@link List} or {@link Set}.
   * @see org.cp.elements.lang.FluentApiExtension
   */
  public interface From extends FluentApiExtension {

    /**
     * Converts an object array to a List.
     *
     * @return a List implementation containing all the elements in the given object array to the from operator.
     * @see java.util.List
     */
    List toList();

    /**
     * Converts an object array to a Set.
     *
     * @return a Set implementation containing all the elements of the given object array to the from operator.
     * @see java.util.Set
     */
    Set toSet();

  }

  /**
   * The FromExpression class is an implementation of the From interface, from operator.
   *
   * @param  the element type of items in the List or Set.
   * @see org.cp.elements.util.CollectionExtensions.From
   */
  private static final class FromExpression implements From {

    private final T[] array;

    @SafeVarargs
    public FromExpression(T... array) {
      this.array = array;
    }

    @SuppressWarnings("unchecked")
    public List toList() {
      return (this.array == null ? Collections.emptyList()
        : (this.array.length == 1 ? Collections.singletonList(this.array[0])
          : Arrays.asList(array)));
    }

    public Set toSet() {
      return (this.array == null ? Collections.emptySet()
        : (this.array.length == 1 ? Collections.singleton(this.array[0])
          : new HashSet<>(toList())));
    }

    @Override
    public String toString() {

      StringBuilder buffer = new StringBuilder("[");

      if (this.array != null) {
        for (int index = 0; index < this.array.length; index++) {
          buffer.append(index > 0 ? StringUtils.COMMA_SPACE_DELIMITER : StringUtils.EMPTY_STRING);
          buffer.append(this.array[index]);
        }
      }

      return buffer.append("]").toString();
    }
  }
}