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package org.apache.juneau.http.header;

import java.util.function.*;

import org.apache.juneau.http.annotation.*;

/**
 * Represents a parsed <l>ETag</l> HTTP response header.
 *
 * <p>
 * An identifier for a specific version of a resource, often a message digest.
 *
 * <h5 class='figure'>Example</h5>
 * <p class='bcode'>
 * 	ETag: "737060cd8c284d8af7ad3082f209582d"
 * </p>
 *
 * <h5 class='topic'>RFC2616 Specification</h5>
 *
 * The ETag response-header field provides the current value of the entity tag for the requested variant.
 * The headers used with entity tags are described in sections 14.24, 14.26 and 14.44.
 * The entity tag MAY be used for comparison with other entities from the same resource (see section 13.3.3).
 *
 * <p class='bcode'>
 * 	ETag = "ETag" ":" entity-tag
 * </p>
 *
 * <p>
 * Examples:
 * <p class='bcode'>
 * 	ETag: "xyzzy"
 * 	ETag: W/"xyzzy"
 * 	ETag: ""
 * </p>
 *
 * <ul class='seealso'>
 * 	<li class='link'>{@doc jm.HttpParts}
 * 	<li class='extlink'>{@doc ext.RFC2616}
 * 	<li class='extlink'>{@source}
 * </ul>
 *
 * @serial exclude
 */
@Header("ETag")
public class ETag extends BasicEntityTagHeader {

	//-----------------------------------------------------------------------------------------------------------------
	// Static
	//-----------------------------------------------------------------------------------------------------------------

	private static final long serialVersionUID = 1L;
	private static final String NAME = "ETag";

	/**
	 * Static creator.
	 *
	 * @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 value is <jk>null</jk>.
	 */
	public static ETag of(String value) {
		return value == null ? null : new ETag(value);
	}

	/**
	 * Static creator.
	 *
	 * @param value
	 * 	The header value.
	 * 	<br>Can be <jk>null</jk>.
	 * @return A new header bean, or <jk>null</jk> if the value is <jk>null</jk>.
	 */
	public static ETag of(EntityTag value) {
		return value == null ? null : new ETag(value);
	}

	/**
	 * Static creator with delayed value.
	 *
	 * <p>
	 * Header value is re-evaluated on each call to {@link #getValue()}.
	 *
	 * @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 value is <jk>null</jk>.
	 */
	public static ETag of(Supplier<EntityTag> value) {
		return value == null ? null : new ETag(value);
	}

	//-----------------------------------------------------------------------------------------------------------------
	// Static
	//-----------------------------------------------------------------------------------------------------------------

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

	/**
	 * Constructor.
	 *
	 * @param value
	 * 	The header value.
	 * 	<br>Can be <jk>null</jk>.
	 */
	public ETag(EntityTag value) {
		super(NAME, value);
	}

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