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package org.apache.juneau.http.header;

import java.util.function.*;

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

/**
 * Represents a parsed <l>Accept</l> HTTP request header.
 *
 * <p>
 * Content-Types that are acceptable for the response.
 *
 * <h5 class='figure'>Example</h5>
 * <p class='bcode'>
 * 	Accept: text/plain
 * </p>
 *
 * <h5 class='topic'>RFC2616 Specification</h5>
 *
 * The Accept request-header field can be used to specify certain media types which are acceptable for the response.
 * Accept headers can be used to indicate that the request is specifically limited to a small set of desired types, as
 * in the case of a request for an in-line image.
 *
 * <p class='bcode'>
 * 	 Accept         = "Accept" ":
 * 							#( media-range [ accept-params ] )
 *
 * 	 media-range    = ( "* /*"
 * 							| ( type "/" "*" )
 * 							| ( type "/" subtype )
 * 							) *( ";" parameter )
 * 	 accept-params  = ";" "q" "=" qvalue *( accept-extension )
 * 	 accept-extension = ";" token [ "=" ( token | quoted-string ) ]
 * </p>
 *
 * <p>
 * The asterisk "*" character is used to group media types into ranges, with "* /*" indicating all media types and
 * "type/*" indicating all subtypes of that type.
 * The media-range MAY include media type parameters that are applicable to that range.
 *
 * <p>
 * Each media-range MAY be followed by one or more accept-params, beginning with the "q" parameter for indicating a
 * relative quality factor.
 * The first "q" parameter (if any) separates the media-range parameter(s) from the accept-params.
 * Quality factors allow the user or user agent to indicate the relative degree of preference for that media-range,
 * using the qvalue scale from 0 to 1 (section 3.9).
 * The default value is q=1.
 *
 * <p>
 * Note: Use of the "q" parameter name to separate media type parameters from Accept extension parameters is due to
 * historical practice.
 * Although this prevents any media type parameter named "q" from being used with a media range, such an event is
 * believed to be unlikely given the lack of any "q" parameters in the IANA
 * media type registry and the rare usage of any media type parameters in Accept.
 * Future media types are discouraged from registering any parameter named "q".
 *
 * <p>
 * The example
 * <p class='bcode'>
 * 	Accept: audio/*; q=0.2, audio/basic
 * </p>
 * <p>
 * SHOULD be interpreted as "I prefer audio/basic, but send me any audio type if it is the best available after an 80%
 * mark-down in quality."
 *
 * <p>
 * If no Accept header field is present, then it is assumed that the client accepts all media types.
 *
 * <p>
 * If an Accept header field is present, and if the server cannot send a response which is acceptable according to the
 * combined Accept field value, then the server SHOULD send a 406 (not acceptable) response.
 *
 * <p>
 * A more elaborate example is
 * <p class='bcode'>
 * 	Accept: text/plain; q=0.5, text/html,
 * 	        text/x-dvi; q=0.8, text/x-c
 * </p>
 *
 * <p>
 * Verbally, this would be interpreted as "text/html and text/x-c are the preferred media types, but if they do not
 * exist, then send the
 * text/x-dvi entity, and if that does not exist, send the text/plain entity."
 *
 * <p>
 * Media ranges can be overridden by more specific media ranges or specific media types.
 * If more than one media range applies to a given type, the most specific reference has precedence.
 * For example,
 * <p class='bcode'>
 * 	Accept: text/ *, text/html, text/html;level=1, * /*
 * </p>
 * <p>
 * have the following precedence:
 * <ol>
 * 	<li>text/html;level=1
 * 	<li>text/html
 * 	<li>text/*
 * 	<li>* /*
 * </ol>
 *
 * <p>
 * The media type quality factor associated with a given type is determined by finding the media range with the highest
 * precedence which matches that type.
 * For example,
 * <p class='bcode'>
 * 	Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
 * 	        text/html;level=2;q=0.4, * /*;q=0.5
 * </p>
 * <p>
 * would cause the following values to be associated:
 * <p class='bcode'>
 * 	text/html;level=1         = 1
 * 	text/html                 = 0.7
 * 	text/plain                = 0.3
 * 	image/jpeg                = 0.5
 * 	text/html;level=2         = 0.4
 * 	text/html;level=3         = 0.7
 * </p>
 *
 * <p>
 * Note: A user agent might be provided with a default set of quality values for certain media ranges.
 * However, unless the user agent is a closed system which cannot interact with other rendering agents, this default
 * set ought to be configurable by the user.
 *
 * <ul class='seealso'>
 * 	<li class='link'>{@doc jm.HttpParts}
 * 	<li class='extlink'>{@doc ext.RFC2616}
 * 	<li class='extlink'>{@source}
 * </ul>
 *
 * @serial exclude
 */
@Header("Accept")
public class Accept extends BasicMediaRangesHeader {

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

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

	private static final Cache<String,Accept> CACHE = Cache.of(String.class, Accept.class).build();

	// Constants
	@SuppressWarnings("javadoc")
	public static final Accept
		APPLICATION_ATOM_XML = of("application/atom+xml"),
		APPLICATION_FORM_URLENCODED = of("application/x-www-form-urlencoded"),
		APPLICATION_JSON = of("application/json"),
		APPLICATION_OCTET_STREAM = of("application/octet-stream"),
		APPLICATION_SOAP_XML = of("application/soap+xml"),
		APPLICATION_SVG_XML = of("application/svg+xml"),
		APPLICATION_XHTML_XML = of("application/xhtml+xml"),
		APPLICATION_XML = of("application/xml"),
		IMAGE_BMP = of("image/bmp"),
		IMAGE_GIF = of("image/gif"),
		IMAGE_JPEG = of("image/jpeg"),
		IMAGE_PNG = of("image/png"),
		IMAGE_SVG = of("image/svg+xml"),
		IMAGE_TIFF = of("image/tiff"),
		IMAGE_WEBP = of("image/webp"),
		MULTIPART_FORM_DATA = of("multipart/form-data"),
		TEXT_HTML = of("text/html"),
		TEXT_PLAIN = of("text/plain"),
		TEXT_XML = of("text/xml"),
		WILDCARD = of("*/*"),
		NULL = new Accept((String)null);

	/**
	 * Static creator.
	 *
	 * @param value
	 * 	The header value.
	 * 	<br>Must be parsable by {@link MediaRanges#of(String)}.
	 * 	<br>Can be <jk>null</jk>.
	 * @return A new header bean, or <jk>null</jk> if the value is <jk>null</jk>.
	 */
	public static Accept of(String value) {
		return value == null ? null : CACHE.get(value, ()->new Accept(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 Accept of(MediaRanges value) {
		return value == null ? null : new Accept(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 Accept of(MediaType value) {
		return value == null ? null : new Accept(value.toString());
	}

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

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

	/**
	 * Constructor.
	 *
	 * @param value
	 * 	The header value.
	 * 	<br>Must be parsable by {@link MediaRanges#of(String)}.
	 * 	<br>Can be <jk>null</jk>.
	 */
	public Accept(String value) {
		super(NAME, value);
	}

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