/* Copyright 2004, 2005, 2006 Acegi Technology Pty Limited
 *
 * Licensed 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.
 */

package org.acegisecurity.vote;

import org.acegisecurity.Authentication;
import org.acegisecurity.ConfigAttribute;
import org.acegisecurity.ConfigAttributeDefinition;


/**
 * Indicates a class is responsible for voting on authorization decisions.
 * 
 * <p>
 * The coordination of voting (ie polling <code>AccessDecisionVoter</code>s,
 * tallying their responses, and making the final authorization decision) is
 * performed by an {@link org.acegisecurity.AccessDecisionManager}.
 * </p>
 *
 * @author Ben Alex
 * @version $Id$
 */
public interface AccessDecisionVoter {
    //~ Static fields/initializers =====================================================================================

    public static final int ACCESS_GRANTED = 1;
    public static final int ACCESS_ABSTAIN = 0;
    public static final int ACCESS_DENIED = -1;

    //~ Methods ========================================================================================================

    /**
     * Indicates whether this <code>AccessDecisionVoter</code> is able to vote on the passed
     * <code>ConfigAttribute</code>.<p>This allows the <code>AbstractSecurityInterceptor</code> to check every
     * configuration attribute can be consumed by the configured <code>AccessDecisionManager</code> and/or
     * <code>RunAsManager</code> and/or <code>AfterInvocationManager</code>.</p>
     *
     * @param attribute a configuration attribute that has been configured against the
     *        <code>AbstractSecurityInterceptor</code>
     *
     * @return true if this <code>AccessDecisionVoter</code> can support the passed configuration attribute
     */
    public boolean supports(ConfigAttribute attribute);

    /**
     * Indicates whether the <code>AccessDecisionVoter</code> implementation is able to provide access control
     * votes for the indicated secured object type.
     *
     * @param clazz the class that is being queried
     *
     * @return true if the implementation can process the indicated class
     */
    public boolean supports(Class clazz);

    /**
     * Indicates whether or not access is granted.<p>The decision must be affirmative
     * (<code>ACCESS_GRANTED</code>), negative (<code>ACCESS_DENIED</code>) or the <code>AccessDecisionVoter</code>
     * can abstain (<code>ACCESS_ABSTAIN</code>) from voting. Under no circumstances should implementing classes
     * return any other value. If a weighting of results is desired, this should be handled in a custom {@link
     * org.acegisecurity.AccessDecisionManager} instead.</p>
     *  <P>Unless an <code>AccessDecisionVoter</code> is specifically intended to vote on an access control
     * decision due to a passed method invocation or configuration attribute parameter, it must return
     * <code>ACCESS_ABSTAIN</code>. This prevents the coordinating <code>AccessDecisionManager</code> from counting
     * votes from those <code>AccessDecisionVoter</code>s without a legitimate interest in the access control
     * decision.</p>
     *  <p>Whilst the method invocation is passed as a parameter to maximise flexibility in making access
     * control decisions, implementing classes must never modify the behaviour of the method invocation (such as
     * calling <Code>MethodInvocation.proceed()</code>).</p>
     *
     * @param authentication the caller invoking the method
     * @param object the secured object
     * @param config the configuration attributes associated with the method being invoked
     *
     * @return either {@link #ACCESS_GRANTED}, {@link #ACCESS_ABSTAIN} or {@link #ACCESS_DENIED}
     */
    public int vote(Authentication authentication, Object object, ConfigAttributeDefinition config);
}
