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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package jdk.javadoc.internal.doclets.toolkit.taglets;

import java.util.EnumSet;
import javax.lang.model.element.Element;
import javax.lang.model.element.VariableElement;

import com.sun.source.doctree.DocTree;
import jdk.javadoc.internal.doclets.toolkit.BaseConfiguration;
import jdk.javadoc.internal.doclets.toolkit.Content;
import jdk.javadoc.internal.doclets.toolkit.Messages;
import jdk.javadoc.internal.doclets.toolkit.util.CommentHelper;
import jdk.javadoc.internal.doclets.toolkit.util.Utils;

import static com.sun.source.doctree.DocTree.Kind.VALUE;

An inline Taglet representing the value tag. This tag should only be used with
constant fields that have a value.  It is used to access the value of constant
fields.  This inline tag has an optional field name parameter.  If the name is
specified, the constant value is retrieved from the specified field.  A link
is also created to the specified field.  If a name is not specified, the value
is retrieved for the field that the inline tag appears on.  The name is specifed
in the following format:  [fully qualified class name]#[constant field name].
 
This is NOT part of any supported API.
 If you write code that depends on this, you do so at your own risk.
 This code and its internal interfaces are subject to change or
 deletion without notice.
Author:
Jamie Ho/**
 * An inline Taglet representing the value tag. This tag should only be used with
 * constant fields that have a value.  It is used to access the value of constant
 * fields.  This inline tag has an optional field name parameter.  If the name is
 * specified, the constant value is retrieved from the specified field.  A link
 * is also created to the specified field.  If a name is not specified, the value
 * is retrieved for the field that the inline tag appears on.  The name is specifed
 * in the following format:  [fully qualified class name]#[constant field name].
 *
 *  <p><b>This is NOT part of any supported API.
 *  If you write code that depends on this, you do so at your own risk.
 *  This code and its internal interfaces are subject to change or
 *  deletion without notice.</b>
 *
 * @author Jamie Ho
 */

public class ValueTaglet extends BaseTaglet {

    
Construct a new ValueTaglet.
/**
     * Construct a new ValueTaglet.
     */
    public ValueTaglet() {
        super(VALUE.tagName, true, EnumSet.allOf(Site.class));
    }

    
Returns the referenced field or a null if the value tag
is empty or the reference is invalid.
Params:
holder – the tag holder.
config – the  configuration of the doclet.
tag – the value tag.
Returns:
the referenced field or null./**
     * Returns the referenced field or a null if the value tag
     * is empty or the reference is invalid.
     *
     * @param holder the tag holder.
     * @param config the  configuration of the doclet.
     * @param tag the value tag.
     *
     * @return the referenced field or null.
     */
    private VariableElement getVariableElement(Element holder, BaseConfiguration config, DocTree tag) {
        CommentHelper ch = config.utils.getCommentHelper(holder);
        String signature = ch.getReferencedSignature(tag);

        Element e = signature == null
                ? holder
                : ch.getReferencedMember(config, tag);

        return (e != null && config.utils.isVariableElement(e))
                ? (VariableElement) e
                : null;
    }

    @Override
    public Content getTagletOutput(Element holder, DocTree tag, TagletWriter writer) {
        Utils utils = writer.configuration().utils;
        Messages messages = writer.configuration().getMessages();
        VariableElement field = getVariableElement(holder, writer.configuration(), tag);
        if (field == null) {
            if (tag.toString().isEmpty()) {
                //Invalid use of @value
                messages.warning(holder,
                        "doclet.value_tag_invalid_use");
            } else {
                //Reference is unknown.
                messages.warning(holder,
                        "doclet.value_tag_invalid_reference", tag.toString());
            }
        } else if (field.getConstantValue() != null) {
            return writer.valueTagOutput(field,
                utils.constantValueExpresion(field),
                // TODO: investigate and cleanup
                // in the j.l.m world, equals will not be accurate
                // !field.equals(tag.holder())
                !utils.elementsEqual(field, holder)
            );
        } else {
            //Referenced field is not a constant.
            messages.warning(holder,
                "doclet.value_tag_invalid_constant", utils.getSimpleName(field));
        }
        return writer.getOutputInstance();
    }
}