juneau-core/juneau-marshall/src/main/java/org/apache/juneau/http/header/BasicEntityTagHeader.java

// ***************************************************************************************************************************
// * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements.  See the NOTICE file *
// * distributed with this work for additional information regarding copyright ownership.  The ASF licenses this file        *
// * to you 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.apache.juneau.http.header;

import static org.apache.juneau.internal.StringUtils.*;
import static java.util.Optional.*;

import java.util.*;
import java.util.function.*;

/**
 * Category of headers that consist of a single entity validator value.
 *
 * <p>
 * <h5 class='figure'>Example</h5>
 * <p class='bcode w800'>
 * 	ETag: "xyzzy"
 * 	ETag: W/"xyzzy"
 * 	ETag: ""
 * </p>
 *
 * <ul class='seealso'>
 * 	<li class='extlink'>{@doc ExtRFC2616}
 * </ul>
 */
public class BasicEntityTagHeader extends BasicHeader {

	private static final long serialVersionUID = 1L;

	/**
	 * Convenience creator.
	 *
	 * @param name The header name.
	 * @param value
	 * 	The header value.
	 * 	<br>Must be an entity tag value (e.g. <js>"\"xyzzy\""</js>).
	 * 	<br>Can be <jk>null</jk>.
	 * @return A new header bean, or <jk>null</jk> if the name is <jk>null</jk> or empty or the value is <jk>null</jk>.
	 */
	public static BasicEntityTagHeader of(String name, String value) {
		if (isEmpty(name) || value == null)
			return null;
		return new BasicEntityTagHeader(name, value);
	}

	/**
	 * Convenience creator.
	 *
	 * @param name The header name.
	 * @param value
	 * 	The header value.
	 * 	<br>Can be <jk>null</jk>.
	 * @return A new header bean, or <jk>null</jk> if the name is <jk>null</jk> or empty or the value is <jk>null</jk>.
	 */
	public static BasicEntityTagHeader of(String name, EntityTag value) {
		if (isEmpty(name) || value == null)
			return null;
		return new BasicEntityTagHeader(name, value);
	}

	/**
	 * Convenience creator with delayed value.
	 *
	 * <p>
	 * Header value is re-evaluated on each call to {@link #getValue()}.
	 *
	 * @param name The header name.
	 * @param value
	 * 	The supplier of the header value.
	 * 	<br>Can be <jk>null</jk>.
	 * @return A new header bean, or <jk>null</jk> if the name is <jk>null</jk> or empty or the value is <jk>null</jk>.
	 */
	public static BasicEntityTagHeader of(String name, Supplier<EntityTag> value) {
		if (isEmpty(name) || value == null)
			return null;
		return new BasicEntityTagHeader(name, value);
	}

	private final EntityTag value;
	private final Supplier<EntityTag> supplier;

	/**
	 * Constructor.
	 *
	 * @param name The header name.
	 * @param value
	 * 	The header value.
	 * 	<br>Must be an entity tag value (e.g. <js>"\"xyzzy\""</js>).
	 * 	<br>Can be <jk>null</jk>.
	 */
	public BasicEntityTagHeader(String name, String value) {
		super(name, value);
		this.value = parse(value);
		this.supplier = null;
	}

	/**
	 * Constructor.
	 *
	 * @param name The header name.
	 * @param value
	 * 	The header value.
	 * 	<br>Can be <jk>null</jk>.
	 */
	public BasicEntityTagHeader(String name, EntityTag value) {
		super(name, serialize(value));
		this.value = value;
		this.supplier = null;
	}

	/**
	 * Constructor with delayed value.
	 *
	 * <p>
	 * Header value is re-evaluated on each call to {@link #getValue()}.
	 *
	 * @param name The header name.
	 * @param value
	 * 	The supplier of the header value.
	 * 	<br>Can be <jk>null</jk>.
	 */
	public BasicEntityTagHeader(String name, Supplier<EntityTag> value) {
		super(name, null);
		this.value = null;
		this.supplier = value;
	}

	@Override /* Header */
	public String getValue() {
		if (supplier != null)
			return serialize(supplier.get());
		return super.getValue();
	}

	/**
	 * Returns this header as an {@link EntityTag}.
	 *
	 * @return This header as an {@link EntityTag}, or {@link Optional#empty()} if the value is <jk>null</jk>.
	 */
	public Optional<EntityTag> asEntityTag() {
		if (supplier != null)
			return ofNullable(supplier.get());
		return ofNullable(value);
	}

	private static String serialize(EntityTag value) {
		return stringify(value);
	}

	private EntityTag parse(String value) {
		return EntityTag.of(value);
	}
}