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package org.apache.juneau.http.header;

import java.util.function.*;

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

/**
 * Represents a parsed <l>User-Agent</l> HTTP request header.
 *
 * <p>
 * The user agent string of the user agent.
 *
 * <h5 class='figure'>Example</h5>
 * <p class='bcode'>
 * 	User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20100101 Firefox/21.0
 * </p>
 *
 * <h5 class='topic'>RFC2616 Specification</h5>
 *
 * The User-Agent request-header field contains information about the user agent originating the request.
 * This is for statistical purposes, the tracing of protocol violations, and automated recognition of user agents for
 * the sake of tailoring responses to avoid particular user agent limitations.
 * User agents SHOULD include this field with requests.
 * The field can contain multiple product tokens (section 3.8) and comments identifying the agent and any sub-products
 * which form a significant part of the user agent.
 * By convention, the product tokens are listed in order of their significance for identifying the application.
 *
 * <p class='bcode'>
 * 	User-Agent     = "User-Agent" ":" 1*( product | comment )
 * </p>
 *
 * <p>
 * Example:
 * <p class='bcode'>
 * 	User-Agent: CERN-LineMode/2.15 libwww/2.17b3
 * </p>
 *
 * <ul class='seealso'>
 * 	<li class='link'>{@doc jm.HttpParts}
 * 	<li class='extlink'>{@doc ext.RFC2616}
 * 	<li class='extlink'>{@source}
 * </ul>
 *
 * @serial exclude
 */
@Header("User-Agent")
public class UserAgent extends BasicStringHeader {

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

	private static final long serialVersionUID = 1L;
	private static final String NAME = "User-Agent";

	/**
	 * 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 UserAgent of(String value) {
		return value == null ? null : new UserAgent(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 UserAgent of(Supplier<String> value) {
		return value == null ? null : new UserAgent(value);
	}

	//-----------------------------------------------------------------------------------------------------------------
	// Instance
	//-----------------------------------------------------------------------------------------------------------------

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