/* 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.springframework.security.access.intercept;

import java.util.Collection;
import java.util.HashSet;
import java.util.Set;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationEventPublisherAware;
import org.springframework.context.MessageSource;
import org.springframework.context.MessageSourceAware;
import org.springframework.context.support.MessageSourceAccessor;
import org.springframework.security.access.AccessDecisionManager;
import org.springframework.security.access.AccessDeniedException;
import org.springframework.security.access.ConfigAttribute;
import org.springframework.security.access.SecurityMetadataSource;
import org.springframework.security.access.event.AuthenticationCredentialsNotFoundEvent;
import org.springframework.security.access.event.AuthorizationFailureEvent;
import org.springframework.security.access.event.AuthorizedEvent;
import org.springframework.security.access.event.PublicInvocationEvent;
import org.springframework.security.authentication.AuthenticationCredentialsNotFoundException;
import org.springframework.security.authentication.AuthenticationManager;
import org.springframework.security.core.Authentication;
import org.springframework.security.core.SpringSecurityMessageSource;
import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.util.Assert;

/**
 * Abstract class that implements security interception for secure objects.
 * <p>
 * The <code>AbstractSecurityInterceptor</code> will ensure the proper startup configuration of the security
 * interceptor. It will also implement the proper handling of secure object invocations, namely:
 * <ol>
 * <li>Obtain the {@link Authentication} object from the {@link SecurityContextHolder}.</li>
 * <li>Determine if the request relates to a secured or public invocation by looking up the secure object request
 * against the {@link SecurityMetadataSource}.</li>
 * <li>For an invocation that is secured (there is a list of <code>ConfigAttribute</code>s for the secure
 * object invocation):
 * <ol type="a">
 * <li>If either the {@link org.springframework.security.core.Authentication#isAuthenticated()}
 * returns <code>false</code>, or the {@link #alwaysReauthenticate} is
 * <code>true</code>, authenticate the request against the configured {@link AuthenticationManager}.
 * When authenticated, replace the <code>Authentication</code> object on the
 * <code>SecurityContextHolder</code> with the returned value.</li>
 * <li>Authorize the request against the configured {@link AccessDecisionManager}.</li>
 * <li>Perform any run-as replacement via the configured {@link RunAsManager}.</li>
 * <li>Pass control back to the concrete subclass, which will actually proceed with executing the object.
 * A {@link InterceptorStatusToken} is returned so that after the subclass has finished proceeding with
 * execution of the object, its finally clause can ensure the <code>AbstractSecurityInterceptor</code>
 * is re-called and tidies up correctly.</li>
 * <li>The concrete subclass will re-call the <code>AbstractSecurityInterceptor</code> via the
 * {@link #afterInvocation(InterceptorStatusToken, Object)} method.</li>
 * <li>If the <code>RunAsManager</code> replaced the <code>Authentication</code> object, return the
 * <code>SecurityContextHolder</code> to the object that existed after the call to
 * <code>AuthenticationManager</code>.</li>
 * <li>If an <code>AfterInvocationManager</code> is defined, invoke the
 * invocation manager and allow it to replace the object due to be returned to
 * the caller.</li>
 * </ol>
 * </li>
 * <li>For an invocation that is public (there are no <code>ConfigAttribute</code>s for the secure object
 * invocation):
 * <ol type="a">
 * <li>As described above, the concrete subclass will be returned an <code>InterceptorStatusToken</code> which is
 * subsequently re-presented to the <code>AbstractSecurityInterceptor</code> after the secure object has been executed.
 * The <code>AbstractSecurityInterceptor</code> will take no further action when its
 * {@link #afterInvocation(InterceptorStatusToken, Object)} is called.</li>
 * </ol>
 * </li>
 * <li>Control again returns to the concrete subclass, along with the <code>Object</code> that should be returned to
 * the caller. The subclass will then return that result or exception to the original caller.</li>
 * </ol>
 *
 * @author Ben Alex
 */
public abstract class AbstractSecurityInterceptor implements InitializingBean, ApplicationEventPublisherAware,
        MessageSourceAware {
    //~ Static fields/initializers =====================================================================================

    protected final Log logger = LogFactory.getLog(getClass());

    //~ Instance fields ================================================================================================

    protected MessageSourceAccessor messages = SpringSecurityMessageSource.getAccessor();
    private ApplicationEventPublisher eventPublisher;
    private AccessDecisionManager accessDecisionManager;
    private AfterInvocationManager afterInvocationManager;
    private AuthenticationManager authenticationManager;
    private RunAsManager runAsManager = new NullRunAsManager();

    private boolean alwaysReauthenticate = false;
    private boolean rejectPublicInvocations = false;
    private boolean validateConfigAttributes = true;

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

    public void afterPropertiesSet() throws Exception {
        Assert.notNull(getSecureObjectClass(), "Subclass must provide a non-null response to getSecureObjectClass()");
        Assert.notNull(this.messages, "A message source must be set");
        Assert.notNull(this.authenticationManager, "An AuthenticationManager is required");
        Assert.notNull(this.accessDecisionManager, "An AccessDecisionManager is required");
        Assert.notNull(this.runAsManager, "A RunAsManager is required");
        Assert.notNull(this.obtainSecurityMetadataSource(), "An SecurityMetadataSource is required");
        Assert.isTrue(this.obtainSecurityMetadataSource().supports(getSecureObjectClass()),
                "SecurityMetadataSource does not support secure object class: " + getSecureObjectClass());
        Assert.isTrue(this.runAsManager.supports(getSecureObjectClass()),
                "RunAsManager does not support secure object class: " + getSecureObjectClass());
        Assert.isTrue(this.accessDecisionManager.supports(getSecureObjectClass()),
                "AccessDecisionManager does not support secure object class: " + getSecureObjectClass());

        if (this.afterInvocationManager != null) {
            Assert.isTrue(this.afterInvocationManager.supports(getSecureObjectClass()),
                    "AfterInvocationManager does not support secure object class: " + getSecureObjectClass());
        }

        if (this.validateConfigAttributes) {
            Collection<ConfigAttribute> attributeDefs = this.obtainSecurityMetadataSource().getAllConfigAttributes();

            if (attributeDefs == null) {
                logger.warn("Could not validate configuration attributes as the SecurityMetadataSource did not return "
                        + "any attributes from getAllConfigAttributes()");
                return;
            }

            Set<ConfigAttribute> unsupportedAttrs = new HashSet<ConfigAttribute>();

            for (ConfigAttribute attr : attributeDefs) {
                if (!this.runAsManager.supports(attr) && !this.accessDecisionManager.supports(attr)
                        && ((this.afterInvocationManager == null) || !this.afterInvocationManager.supports(attr))) {
                    unsupportedAttrs.add(attr);
                }
            }

            if (unsupportedAttrs.size() != 0) {
                throw new IllegalArgumentException("Unsupported configuration attributes: " + unsupportedAttrs);
            }

            logger.info("Validated configuration attributes");
        }
    }

    protected InterceptorStatusToken beforeInvocation(Object object) {
        Assert.notNull(object, "Object was null");
        final boolean debug = logger.isDebugEnabled();

        if (!getSecureObjectClass().isAssignableFrom(object.getClass())) {
            throw new IllegalArgumentException("Security invocation attempted for object "
                    + object.getClass().getName()
                    + " but AbstractSecurityInterceptor only configured to support secure objects of type: "
                    + getSecureObjectClass());
        }

        Collection<ConfigAttribute> attributes = this.obtainSecurityMetadataSource().getAttributes(object);

        if (attributes == null || attributes.isEmpty()) {
            if (rejectPublicInvocations) {
                throw new IllegalArgumentException("Secure object invocation " + object +
                        " was denied as public invocations are not allowed via this interceptor. "
                                + "This indicates a configuration error because the "
                                + "rejectPublicInvocations property is set to 'true'");
            }

            if (debug) {
                logger.debug("Public object - authentication not attempted");
            }

            publishEvent(new PublicInvocationEvent(object));

            return null; // no further work post-invocation
        }

        if (debug) {
            logger.debug("Secure object: " + object + "; Attributes: " + attributes);
        }

        if (SecurityContextHolder.getContext().getAuthentication() == null) {
            credentialsNotFound(messages.getMessage("AbstractSecurityInterceptor.authenticationNotFound",
                    "An Authentication object was not found in the SecurityContext"), object, attributes);
        }

        Authentication authenticated = authenticateIfRequired();

        // Attempt authorization
        try {
            this.accessDecisionManager.decide(authenticated, object, attributes);
        }
        catch (AccessDeniedException accessDeniedException) {
            publishEvent(new AuthorizationFailureEvent(object, attributes, authenticated, accessDeniedException));

            throw accessDeniedException;
        }

        if (debug) {
            logger.debug("Authorization successful");
        }

        publishEvent(new AuthorizedEvent(object, attributes, authenticated));

        // Attempt to run as a different user
        Authentication runAs = this.runAsManager.buildRunAs(authenticated, object, attributes);

        if (runAs == null) {
            if (debug) {
                logger.debug("RunAsManager did not change Authentication object");
            }

            // no further work post-invocation
            return new InterceptorStatusToken(authenticated, false, attributes, object);
        } else {
            if (debug) {
                logger.debug("Switching to RunAs Authentication: " + runAs);
            }

            SecurityContextHolder.getContext().setAuthentication(runAs);

            // need to revert to token.Authenticated post-invocation
            return new InterceptorStatusToken(authenticated, true, attributes, object);
        }
    }

    /**
     * Completes the work of the <tt>AbstractSecurityInterceptor</tt> after the secure object invocation has been
     * completed.
     *
     * @param token as returned by the {@link #beforeInvocation(Object)}} method
     * @param returnedObject any object returned from the secure object invocation (may be <tt>null</tt>)
     * @return the object the secure object invocation should ultimately return to its caller (may be <tt>null</tt>)
     */
    protected Object afterInvocation(InterceptorStatusToken token, Object returnedObject) {
        if (token == null) {
            // public object
            return returnedObject;
        }

        if (token.isContextHolderRefreshRequired()) {
            if (logger.isDebugEnabled()) {
                logger.debug("Reverting to original Authentication: " + token.getAuthentication().toString());
            }

            SecurityContextHolder.getContext().setAuthentication(token.getAuthentication());
        }

        if (afterInvocationManager != null) {
            // Attempt after invocation handling
            try {
                returnedObject = afterInvocationManager.decide(token.getAuthentication(), token.getSecureObject(),
                        token.getAttributes(), returnedObject);
            }
            catch (AccessDeniedException accessDeniedException) {
                AuthorizationFailureEvent event = new AuthorizationFailureEvent(token.getSecureObject(),
                        token.getAttributes(), token.getAuthentication(), accessDeniedException);
                publishEvent(event);

                throw accessDeniedException;
            }
        }

        return returnedObject;
    }

    /**
     * Checks the current authentication token and passes it to the AuthenticationManager if
     * {@link org.springframework.security.core.Authentication#isAuthenticated()} returns false or the property
     * <tt>alwaysReauthenticate</tt> has been set to true.
     *
     * @return an authenticated <tt>Authentication</tt> object.
     */
    private Authentication authenticateIfRequired() {
        Authentication authentication = SecurityContextHolder.getContext().getAuthentication();

        if (authentication.isAuthenticated() && !alwaysReauthenticate) {
            if (logger.isDebugEnabled()) {
                logger.debug("Previously Authenticated: " + authentication);
            }

            return authentication;
        }

        authentication = authenticationManager.authenticate(authentication);

        // We don't authenticated.setAuthentication(true), because each provider should do that
        if (logger.isDebugEnabled()) {
            logger.debug("Successfully Authenticated: " + authentication);
        }

        SecurityContextHolder.getContext().setAuthentication(authentication);

        return authentication;
    }

    /**
     * Helper method which generates an exception containing the passed reason,
     * and publishes an event to the application context.
     * <p>
     * Always throws an exception.
     *
     * @param reason        to be provided in the exception detail
     * @param secureObject  that was being called
     * @param configAttribs that were defined for the secureObject
     */
    private void credentialsNotFound(String reason, Object secureObject, Collection<ConfigAttribute> configAttribs) {
        AuthenticationCredentialsNotFoundException exception = new AuthenticationCredentialsNotFoundException(reason);

        AuthenticationCredentialsNotFoundEvent event = new AuthenticationCredentialsNotFoundEvent(secureObject,
                configAttribs, exception);
        publishEvent(event);

        throw exception;
    }

    public AccessDecisionManager getAccessDecisionManager() {
        return accessDecisionManager;
    }

    public AfterInvocationManager getAfterInvocationManager() {
        return afterInvocationManager;
    }

    public AuthenticationManager getAuthenticationManager() {
        return this.authenticationManager;
    }

    public RunAsManager getRunAsManager() {
        return runAsManager;
    }

    /**
     * Indicates the type of secure objects the subclass will be presenting to
     * the abstract parent for processing. This is used to ensure collaborators
     * wired to the {@code AbstractSecurityInterceptor} all support the
     * indicated secure object class.
     *
     * @return the type of secure object the subclass provides services for
     */
    public abstract Class<?> getSecureObjectClass();

    public boolean isAlwaysReauthenticate() {
        return alwaysReauthenticate;
    }

    public boolean isRejectPublicInvocations() {
        return rejectPublicInvocations;
    }

    public boolean isValidateConfigAttributes() {
        return validateConfigAttributes;
    }

    public abstract SecurityMetadataSource obtainSecurityMetadataSource();

    public void setAccessDecisionManager(AccessDecisionManager accessDecisionManager) {
        this.accessDecisionManager = accessDecisionManager;
    }

    public void setAfterInvocationManager(AfterInvocationManager afterInvocationManager) {
        this.afterInvocationManager = afterInvocationManager;
    }

    /**
     * Indicates whether the <code>AbstractSecurityInterceptor</code> should
     * ignore the {@link Authentication#isAuthenticated()} property. Defaults to
     * <code>false</code>, meaning by default the
     * <code>Authentication.isAuthenticated()</code> property is trusted and
     * re-authentication will not occur if the principal has already been
     * authenticated.
     *
     * @param alwaysReauthenticate <code>true</code> to force <code>AbstractSecurityInterceptor</code> to
     * disregard the value of <code>Authentication.isAuthenticated()</code> and always re-authenticate the request
     * (defaults to <code>false</code>).
     */
    public void setAlwaysReauthenticate(boolean alwaysReauthenticate) {
        this.alwaysReauthenticate = alwaysReauthenticate;
    }

    public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
        this.eventPublisher = applicationEventPublisher;
    }

    public void setAuthenticationManager(AuthenticationManager newManager) {
        this.authenticationManager = newManager;
    }

    public void setMessageSource(MessageSource messageSource) {
        this.messages = new MessageSourceAccessor(messageSource);
    }

    /**
     * By rejecting public invocations (and setting this property to <tt>true</tt>), essentially you are ensuring
     * that every secure object invocation advised by <code>AbstractSecurityInterceptor</code> has a configuration
     * attribute defined. This is useful to ensure a "fail safe" mode where undeclared secure objects will be rejected
     * and configuration omissions detected early. An <tt>IllegalArgumentException</tt> will be thrown by the
     * <tt>AbstractSecurityInterceptor</tt> if you set this property to <tt>true</tt> and an attempt is made to invoke
     * a secure object that has no configuration attributes.
     *
     * @param rejectPublicInvocations set to <code>true</code> to reject invocations of secure objects that have no
     * configuration attributes (by default it is <code>false</code> which treats undeclared secure objects
     * as "public" or unauthorized).
     */
    public void setRejectPublicInvocations(boolean rejectPublicInvocations) {
        this.rejectPublicInvocations = rejectPublicInvocations;
    }

    public void setRunAsManager(RunAsManager runAsManager) {
        this.runAsManager = runAsManager;
    }

    public void setValidateConfigAttributes(boolean validateConfigAttributes) {
        this.validateConfigAttributes = validateConfigAttributes;
    }

    private void publishEvent(ApplicationEvent event) {
        if (this.eventPublisher != null) {
            this.eventPublisher.publishEvent(event);
        }
    }
}
