/**
 *  Copyright 2012-2017 Gunnar Morling (http://www.gunnarmorling.de/)
 *  and/or other contributors as indicated by the @authors tag. See the
 *  copyright.txt file in the distribution for a full listing of all
 *  contributors.
 *
 *  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.mapstruct;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Configures the mapping of source constant value to target constant value.
 * <p>
 * Supported mappings are
 * <ol>
 * <li>Enumeration to Enumeration</li>
 * </ol>
 * <p>
 * <B>Example 1:</B>
 *
 * <pre>
 * <code>
 * public enum OrderType { RETAIL, B2B, EXTRA, STANDARD, NORMAL }
 *
 * public enum ExternalOrderType { RETAIL, B2B, SPECIAL, DEFAULT }
 *
 * @ValueMappings({
 *    @ValueMapping(source = "EXTRA", target = "SPECIAL"),
 *    @ValueMapping(source = "STANDARD", target = "DEFAULT"),
 *    @ValueMapping(source = "NORMAL", target = "DEFAULT")
 * })
 * ExternalOrderType orderTypeToExternalOrderType(OrderType orderType);
 * </code>
 * Mapping result:
 * +---------------------+----------------------------+
 * | OrderType           | ExternalOrderType          |
 * +---------------------+----------------------------+
 * | null                | null                       |
 * | OrderType.EXTRA     | ExternalOrderType.SPECIAL  |
 * | OrderType.STANDARD  | ExternalOrderType.DEFAULT  |
 * | OrderType.NORMAL    | ExternalOrderType.DEFAULT  |
 * | OrderType.RETAIL    | ExternalOrderType.RETAIL   |
 * | OrderType.B2B       | ExternalOrderType.B2B      |
 * +---------------------+----------------------------+
 * </pre>
 *
 * MapStruct will <B>WARN</B> on incomplete mappings. However, if for some reason no match is found an
 * {@link java.lang.IllegalStateException} will be thrown.
 * <p>
 * <B>Example 2:</B>
 *
 * <pre>
 * <code>
 * @ValueMappings({
 *    @ValueMapping( source = "<NULL>", target = "DEFAULT" ),
 *    @ValueMapping( source = "STANDARD", target = "<NULL>" ),
 *    @ValueMapping( source = "<ANY_REMAINING>", target = "SPECIAL" )
 * })
 * ExternalOrderType orderTypeToExternalOrderType(OrderType orderType);
 * </code>
 * Mapping result:
 * +---------------------+----------------------------+
 * | OrderType           | ExternalOrderType          |
 * +---------------------+----------------------------+
 * | null                | ExternalOrderType.DEFAULT  |
 * | OrderType.STANDARD  | null                       |
 * | OrderType.RETAIL    | ExternalOrderType.RETAIL   |
 * | OrderType.B2B       | ExternalOrderType.B2B      |
 * | OrderType.NORMAL    | ExternalOrderType.SPECIAL  |
 * | OrderType.EXTRA     | ExternalOrderType.SPECIAL  |
 * +---------------------+----------------------------+
 * </pre>
 *
 * @author Sjaak Derksen
 */
@Retention(RetentionPolicy.CLASS)
@Target(ElementType.METHOD)
public @interface ValueMapping {

    /**
     * The source value constant to use for this mapping.
     *
     * <p>
     * <b>Valid values:</b>
     * <ol>
     * <li>enum constant name</li>
     * <li>{@link MappingConstants#NULL}</li>
     * <li>{@link MappingConstants#ANY_REMAINING}</li>
     * <li>{@link MappingConstants#ANY_UNMAPPED}</li>
     * </ol>
     * <p>
     * <b>NOTE:</b>When using <ANY_REMAINING>, MapStruct will perform the normal name based mapping, in which
     * source is mapped to target based on enum identifier equality. Using <ANY_UNMAPPED> will not apply name
     * based mapping.
     *
     * @return The source value.
     */
    String source();

    /**
     * The target value constant to use for this mapping.
     *
     * <p>
     * <b>Valid values:</b>
     * <ol>
     * <li>enum constant name</li>
     * <li>{@link MappingConstants#NULL}</li>
     * </ol>
     *
     * @return The target value.
     */
    String target();

}