/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
/*
 * Copyright 2005 Sun Microsystems, Inc. All rights reserved.
 */
/*
 * $Id: Reference.java 1092655 2011-04-15 10:24:18Z coheigea $
 */
package javax.xml.crypto.dsig;

import javax.xml.crypto.Data;
import javax.xml.crypto.URIReference;
import javax.xml.crypto.XMLStructure;
import java.io.InputStream;
import java.util.List;

/**
 * A representation of the <code>Reference</code> element as defined in the 
 * <a href="http://www.w3.org/TR/xmldsig-core/">
 * W3C Recommendation for XML-Signature Syntax and Processing</a>. 
 * The XML schema is defined as: 
 * <code><pre>
 * &lt;element name="Reference" type="ds:ReferenceType"/&gt;
 * &lt;complexType name="ReferenceType"&gt;
 *   &lt;sequence&gt;
 *     &lt;element ref="ds:Transforms" minOccurs="0"/&gt;
 *     &lt;element ref="ds:DigestMethod"/&gt;
 *     &lt;element ref="ds:DigestValue"/&gt;
 *   &lt;/sequence&gt;
 *   &lt;attribute name="Id" type="ID" use="optional"/&gt;
 *   &lt;attribute name="URI" type="anyURI" use="optional"/&gt;
 *   &lt;attribute name="Type" type="anyURI" use="optional"/&gt;
 * &lt;/complexType&gt;
 *
 * &lt;element name="DigestValue" type="ds:DigestValueType"/&gt;
 * &lt;simpleType name="DigestValueType"&gt;
 *   &lt;restriction base="base64Binary"/&gt;
 * &lt;/simpleType&gt;
 * </pre></code>
 *
 * <p>A <code>Reference</code> instance may be created by invoking one of the 
 * {@link XMLSignatureFactory#newReference newReference} methods of the
 * {@link XMLSignatureFactory} class; for example:
 *
 * <pre>
 *   XMLSignatureFactory factory = XMLSignatureFactory.getInstance("DOM");
 *   Reference ref = factory.newReference
 *     ("http://www.ietf.org/rfc/rfc3275.txt", 
 *	factory.newDigestMethod(DigestMethod.SHA1, null));
 * </pre>
 *
 * @author Sean Mullan
 * @author Erwin van der Koogh 
 * @author JSR 105 Expert Group
 * @see XMLSignatureFactory#newReference(String, DigestMethod)
 * @see XMLSignatureFactory#newReference(String, DigestMethod, List, String, String)
 */
public interface Reference extends URIReference, XMLStructure {

    /**
     * Returns an {@link java.util.Collections#unmodifiableList unmodifiable 
     * list} of {@link Transform}s that are contained in this 
     * <code>Reference</code>.
     *
     * @return an unmodifiable list of <code>Transform</code>s
     *    (may be empty but never <code>null</code>)
     */
    List getTransforms();

    /**
     * Returns the digest method of this <code>Reference</code>.
     *
     * @return the digest method
     */
    DigestMethod getDigestMethod();

    /**
     * Returns the optional <code>Id</code> attribute of this 
     * <code>Reference</code>, which permits this reference to be 
     * referenced from elsewhere.
     *
     * @return the <code>Id</code> attribute (may be <code>null</code> if not 
     *    specified) 
     */
    String getId();

    /**
     * Returns the digest value of this <code>Reference</code>.
     * 
     * @return the raw digest value, or <code>null</code> if this reference has
     *    not been digested yet. Each invocation of this method returns a new
     *    clone to protect against subsequent modification.
     */
    byte[] getDigestValue();

    /**
     * Returns the calculated digest value of this <code>Reference</code>
     * after a validation operation. This method is useful for debugging if
     * the reference fails to validate.
     * 
     * @return the calculated digest value, or <code>null</code> if this 
     *    reference has not been validated yet. Each invocation of this method 
     *    returns a new clone to protect against subsequent modification.
     */
    byte[] getCalculatedDigestValue();

    /**
     * Validates this reference. This method verifies the digest of this 
     * reference.
     *
     * <p>This method only validates the reference the first time it is 
     * invoked. On subsequent invocations, it returns a cached result.
     *
     * @return <code>true</code> if this reference was validated successfully;
     *    <code>false</code> otherwise
     * @param validateContext the validating context
     * @throws NullPointerException if <code>validateContext</code> is 
     *    <code>null</code>
     * @throws XMLSignatureException if an unexpected exception occurs while 
     *    validating the reference 
     */
    boolean validate(XMLValidateContext validateContext) 
        throws XMLSignatureException;

    /**
     * Returns the dereferenced data, if 
     * <a href="XMLSignContext.html#Supported Properties">reference caching</a>
     * is enabled. This is the result of dereferencing the URI of this 
     * reference during a validation or generation operation. 
     *
     * @return the dereferenced data, or <code>null</code> if reference 
     *    caching is not enabled or this reference has not been generated or
     *    validated
     */
    Data getDereferencedData();

    /**
     * Returns the pre-digested input stream, if
     * <a href="XMLSignContext.html#Supported Properties">reference caching</a>
     * is enabled. This is the input to the digest operation during a
     * validation or signing operation. 
     *
     * @return an input stream containing the pre-digested input, or
     *    <code>null</code> if reference caching is not enabled or this
     *    reference has not been generated or validated
     */
    InputStream getDigestInputStream();
}
