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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.data.conversion;

import static org.cp.elements.lang.ElementsExceptionsFactory.newConversionException;

import org.cp.elements.lang.Constants;

/**
 * The {@link DefaultableConverter} class is an abstract {@link Converter} implementation supporting
 * the use {@link Object default values} if the {@link Object value} to convert is {@literal null}.
 *
 * @author John Blum
 * @see org.cp.elements.data.conversion.AbstractConverter
 * @since 1.0.0
 */
@SuppressWarnings("unused")
public abstract class DefaultableConverter extends AbstractConverter {

  private T defaultValue;

  /**
   * Sets the {@link Object default value} to use if the {@link Object value} to convert is {@literal null}.
   *
   * @param defaultValue {@link Object default value} returned if the {@link Object value} to convert
   * is {@literal null}.
   */
  public void setDefaultValue(T defaultValue) {
    this.defaultValue = defaultValue;
  }

  /**
   * Returns the {@link Object default value} used if the {@link Object value} to convert is {@literal null}.
   *
   * @return the {@link Object default value} used if the {@link Object value} to convert is {@literal null}.
   */
  protected T getDefaultValue() {
    return this.defaultValue;
  }

  /**
   * Determines whether this {@link Converter} can convert {@link Object Objects}
   * {@link Class from type} {@link Class to type}.
   *
   * @param fromType {@link Class type} to convert from.
   * @param toType {@link Class type} to convert to.
   * @return a boolean indicating whether this {@link Converter} can convert {@link Object Objects}
   * {@link Class from type} {@link Class to type}.
   * @see org.cp.elements.data.conversion.ConversionService#canConvert(Class, Class)
   */
  @Override
  public boolean canConvert(Class fromType, Class toType) {
    return (fromType == null && getDefaultValue() != null);
  }

  /**
   * Converts an {@link Object} of {@link Class type S} into an {@link Object} of {@link Class type T}.
   *
   * @param value {@link Object} of {@link Class type S} to convert.
   * @return the converted {@link Object} of {@link Class type T}.
   * @throws ConversionException if the {@link Object} cannot be converted.
   * @see org.cp.elements.data.conversion.ConversionService#convert(Object, Class)
   * @see #convert(Object, Class)
   */
  @Override
  public T convert(S value) {

    T defaultValue = getDefaultValue();

    if (value == null && defaultValue != null) {
      return defaultValue;
    }

    throw newConversionException("Cannot convert [%1$s] to [%2$s]",
      value, getTargetType().map(Class::getName).orElse(Constants.UNKNOWN));
  }

  /**
   * Builder method used to set the {@link Object default value} to use
   * if the {@link Object value} to convert is {@literal null}.
   *
   * @param  {@link Class type} of this {@link Converter}.
   * @param defaultValue {@link Object default value} returned if the {@link Object value} to convert
   * is {@literal null}.
   * @return this {@link Converter}.
   * @see #setDefaultValue(Object)
   */
  @SuppressWarnings("unchecked")
  public > CONVERTER withDefaultValue(T defaultValue) {
    setDefaultValue(defaultValue);
    return (CONVERTER) this;
  }
}