/*
 * @(#)AttributeValue.java
 *
 * Copyright 2003-2004 Sun Microsystems, Inc. All Rights Reserved.
 *
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 * modification, are permitted provided that the following conditions are met:
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 *      this list of conditions and the following disclaimer.
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 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
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package com.sun.xacml.attr;

import com.sun.xacml.EvaluationCtx;
import com.sun.xacml.Indenter;

import com.sun.xacml.cond.Evaluatable;
import com.sun.xacml.cond.EvaluationResult;

import java.io.OutputStream;
import java.io.PrintStream;

import java.net.URI;

import java.util.Collections;
import java.util.List;


/**
 * The base type for all datatypes used in a policy or request/response,
 * this abstract class represents a value for a given attribute type.
 * All the required types defined in the XACML specification are
 * provided as instances of <code>AttributeValue<code>s. If you want to
 * provide a new type, extend this class and implement the
 * <code>equals(Object)</code> and <code>hashCode</code> methods from
 * <code>Object</code>, which are used for equality checking.
 *
 * @since 1.0
 * @author Seth Proctor
 */
public abstract class AttributeValue implements Evaluatable
{

    // the type of this attribute
    private URI type;
    
    /**
     * Constructor that takes the specific attribute type.
     *
     * @param type the attribute's type
     */
    protected AttributeValue(URI type) {
        this.type = type;
    }

    /**
     * Returns the type of this attribute value. By default this always 
     * returns the type passed to the constructor.
     *
     * @return the attribute's type
     */
    public URI getType() {
        return type;
    }

    /**
     * Returns whether or not this value is actually a bag of values. This
     * is a required interface from <code>Evaluatable</code>, but the
     * more meaningful <code>isBag</code> method is used by
     * <code>AttributeValue</code>s, so this method is declared as final
     * and calls the <code>isBag</code> method for this value.
     *
     * @return true if this is a bag of values, false otherwise
     */
    public final boolean evaluatesToBag() {
       return isBag(); 
    }

    /**
     * Always returns an empty list since values never have children.
     *
     * @return an empty <code>List</code>
     */
    public List getChildren() {
        return Collections.EMPTY_LIST;
    }

    /**
     * Returns whether or not this value is actually a bag of values. By
     * default this returns <code>false</code>. Typically, only the
     * <code>BagAttribute</code> should ever override this to return
     * <code>true</code>.
     *
     * @return true if this is a bag of values, false otherwise
     */
    public boolean isBag() {
        return false;
    }

    /**
     * Implements the required interface from <code>Evaluatable</code>.
     * Since there is nothing to evaluate in an attribute value, the default
     * result is just this instance. Override this method if you want
     * special behavior, like a dynamic value.
     *
     * @param context the representation of the request
     *
     * @return a successful evaluation containing this value
     */
    public EvaluationResult evaluate(EvaluationCtx context) {
        return new EvaluationResult(this);
    }

    /**
     * Encodes the value in a form suitable for including in XML data like
     * a request or an obligation. This must return a value that could in
     * turn be used by the factory to create a new instance with the same
     * value.
     *
     * @return a <code>String</code> form of the value
     */
    public abstract String encode();
    
    /**
     * Encodes this <code>AttributeValue</code> into its XML representation
     * and writes this encoding to the given <code>OutputStream</code> with
     * no indentation. This will always produce the version used in a
     * policy rather than that used in a request, so this is equivalent
     * to calling <code>encodeWithTags(true)</code> and then stuffing that
     * into a stream.
     *
     * @param output a stream into which the XML-encoded data is written
     */
    public void encode(OutputStream output) {
        encode(output, new Indenter(0));
    }

    /**
     * Encodes this <code>AttributeValue</code> into its XML representation
     * and writes this encoding to the given <code>OutputStream</code> with
     * indentation. This will always produce the version used in a
     * policy rather than that used in a request, so this is equivalent
     * to calling <code>encodeWithTags(true)</code> and then stuffing that
     * into a stream.
     *
     * @param output a stream into which the XML-encoded data is written
     * @param indenter an object that creates indentation strings
     */
    public void encode(OutputStream output, Indenter indenter) {
        PrintStream out = new PrintStream(output);
        out.println(indenter.makeString() + encodeWithTags(true));
    }

    /**
     * Encodes the value and includes the AttributeValue XML tags so that
     * the resulting string can be included in a valid XACML policy or
     * Request/Response. The <code>boolean</code> parameter lets you include
     * the DataType attribute, which is required in a policy but not allowed
     * in a Request or Response.
     *
     * @param includeType include the DataType XML attribute if
     *                    <code>true</code>, exclude if <code>false</code>
     *
     * @return a <code>String</code> encoding including the XML tags
     */
    public String encodeWithTags(boolean includeType) {
        if (includeType)
            return "<AttributeValue DataType=\"" + type.toString() + "\">" +
                encode() + "</AttributeValue>";
        else
            return "<AttributeValue>" + encode() + "</AttributeValue>";
    }

}