/*
    * 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.
   */
  package org.apache.shiro.subject.support;
  
  import org.apache.shiro.authc.AuthenticationException;
  import org.apache.shiro.authc.AuthenticationToken;
  import org.apache.shiro.authc.HostAuthenticationToken;
  import org.apache.shiro.authz.AuthorizationException;
  import org.apache.shiro.authz.Permission;
  import org.apache.shiro.authz.UnauthenticatedException;
  import org.apache.shiro.mgt.SecurityManager;
  import org.apache.shiro.session.InvalidSessionException;
  import org.apache.shiro.session.ProxiedSession;
  import org.apache.shiro.session.Session;
  import org.apache.shiro.session.SessionException;
  import org.apache.shiro.session.mgt.DefaultSessionContext;
  import org.apache.shiro.session.mgt.SessionContext;
  import org.apache.shiro.subject.ExecutionException;
  import org.apache.shiro.subject.PrincipalCollection;
  import org.apache.shiro.subject.Subject;
  import org.apache.shiro.util.CollectionUtils;
  import org.apache.shiro.util.StringUtils;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.util.Collection;
  import java.util.List;
  import java.util.concurrent.Callable;
  import java.util.concurrent.CopyOnWriteArrayList;
  
  /**
   * Implementation of the {@code Subject} interface that delegates
   * method calls to an underlying {@link org.apache.shiro.mgt.SecurityManager SecurityManager} instance for security checks.
   * It is essentially a {@code SecurityManager} proxy.
   * <p/>
   * This implementation does not maintain state such as roles and permissions (only {@code Subject}
   * {@link #getPrincipals() principals}, such as usernames or user primary keys) for better performance in a stateless
   * architecture.  It instead asks the underlying {@code SecurityManager} every time to perform
   * the authorization check.
   * <p/>
   * A common misconception in using this implementation is that an EIS resource (RDBMS, etc) would
   * be &quot;hit&quot; every time a method is called.  This is not necessarily the case and is
   * up to the implementation of the underlying {@code SecurityManager} instance.  If caching of authorization
   * data is desired (to eliminate EIS round trips and therefore improve database performance), it is considered
   * much more elegant to let the underlying {@code SecurityManager} implementation or its delegate components
   * manage caching, not this class.  A {@code SecurityManager} is considered a business-tier component,
   * where caching strategies are better managed.
   * <p/>
   * Applications from large and clustered to simple and JVM-local all benefit from
   * stateless architectures.  This implementation plays a part in the stateless programming
   * paradigm and should be used whenever possible.
   *
   * @since 0.1
   */
  public class DelegatingSubject implements Subject {
  
      private static final Logger log = LoggerFactory.getLogger(DelegatingSubject.class);
  
      private static final String RUN_AS_PRINCIPALS_SESSION_KEY =
              DelegatingSubject.class.getName() + ".RUN_AS_PRINCIPALS_SESSION_KEY";
  
      protected PrincipalCollection principals;
      protected boolean authenticated;
      protected String host;
      protected Session session;
      /**
       * @since 1.2
       */
      protected boolean sessionCreationEnabled;
  
      protected transient SecurityManager securityManager;
  
      public DelegatingSubject(SecurityManager securityManager) {
          this(null, false, null, null, securityManager);
      }
  
      public DelegatingSubject(PrincipalCollection principals, boolean authenticated, String host,
                               Session session, SecurityManager securityManager) {
          this(principals, authenticated, host, session, true, securityManager);
      }
  
      //since 1.2
      public DelegatingSubject(PrincipalCollection principals, boolean authenticated, String host,
                              Session session, boolean sessionCreationEnabled, SecurityManager securityManager) {
         if (securityManager == null) {
             throw new IllegalArgumentException("SecurityManager argument cannot be null.");
         }
         this.securityManager = securityManager;
         this.principals = principals;
         this.authenticated = authenticated;
         this.host = host;
         if (session != null) {
             this.session = decorate(session);
         }
         this.sessionCreationEnabled = sessionCreationEnabled;
     }
 
     protected Session../../../../../org/apache/shiro/session/Session.html#Session">Session decorate(Session session) {
         if (session == null) {
             throw new IllegalArgumentException("session cannot be null");
         }
         return new StoppingAwareProxiedSession(session, this);
     }
 
     public SecurityManager getSecurityManager() {
         return securityManager;
     }
 
     private static boolean isEmpty(PrincipalCollection pc) {
         return pc == null || pc.isEmpty();
     }
 
     protected boolean hasPrincipals() {
         return !isEmpty(getPrincipals());
     }
 
     /**
      * Returns the host name or IP associated with the client who created/is interacting with this Subject.
      *
      * @return the host name or IP associated with the client who created/is interacting with this Subject.
      */
     public String getHost() {
         return this.host;
     }
 
     private Object getPrimaryPrincipal(PrincipalCollection principals) {
         if (!isEmpty(principals)) {
             return principals.getPrimaryPrincipal();
         }
         return null;
     }
 
     /**
      * @see Subject#getPrincipal()
      */
     public Object getPrincipal() {
         return getPrimaryPrincipal(getPrincipals());
     }
 
     public PrincipalCollection getPrincipals() {
         List<PrincipalCollection> runAsPrincipals = getRunAsPrincipalsStack();
         return CollectionUtils.isEmpty(runAsPrincipals) ? this.principals : runAsPrincipals.get(0);
     }
 
     public boolean isPermitted(String permission) {
         return hasPrincipals() && securityManager.isPermitted(getPrincipals(), permission);
     }
 
     public boolean isPermitted(Permission permission) {
         return hasPrincipals() && securityManager.isPermitted(getPrincipals(), permission);
     }
 
     public boolean[] isPermitted(String... permissions) {
         if (hasPrincipals()) {
             return securityManager.isPermitted(getPrincipals(), permissions);
         } else {
             return new boolean[permissions.length];
         }
     }
 
     public boolean[] isPermitted(List<Permission> permissions) {
         if (hasPrincipals()) {
             return securityManager.isPermitted(getPrincipals(), permissions);
         } else {
             return new boolean[permissions.size()];
         }
     }
 
     public boolean isPermittedAll(String... permissions) {
         return hasPrincipals() && securityManager.isPermittedAll(getPrincipals(), permissions);
     }
 
     public boolean isPermittedAll(Collection<Permission> permissions) {
         return hasPrincipals() && securityManager.isPermittedAll(getPrincipals(), permissions);
     }
 
     protected void assertAuthzCheckPossible() throws AuthorizationException {
         if (!hasPrincipals()) {
             String msg = "This subject is anonymous - it does not have any identifying principals and " +
                     "authorization operations require an identity to check against.  A Subject instance will " +
                     "acquire these identifying principals automatically after a successful login is performed " +
                     "be executing " + Subject.class.getName() + ".login(AuthenticationToken) or when 'Remember Me' " +
                     "functionality is enabled by the SecurityManager.  This exception can also occur when a " +
                     "previously logged-in Subject has logged out which " +
                     "makes it anonymous again.  Because an identity is currently not known due to any of these " +
                     "conditions, authorization is denied.";
             throw new UnauthenticatedException(msg);
         }
     }
 
     public void checkPermission(String permission) throws AuthorizationException {
         assertAuthzCheckPossible();
         securityManager.checkPermission(getPrincipals(), permission);
     }
 
     public void checkPermission(Permission permission) throws AuthorizationException {
         assertAuthzCheckPossible();
         securityManager.checkPermission(getPrincipals(), permission);
     }
 
     public void checkPermissions(String... permissions) throws AuthorizationException {
         assertAuthzCheckPossible();
         securityManager.checkPermissions(getPrincipals(), permissions);
     }
 
     public void checkPermissions(Collection<Permission> permissions) throws AuthorizationException {
         assertAuthzCheckPossible();
         securityManager.checkPermissions(getPrincipals(), permissions);
     }
 
     public boolean hasRole(String roleIdentifier) {
         return hasPrincipals() && securityManager.hasRole(getPrincipals(), roleIdentifier);
     }
 
     public boolean[] hasRoles(List<String> roleIdentifiers) {
         if (hasPrincipals()) {
             return securityManager.hasRoles(getPrincipals(), roleIdentifiers);
         } else {
             return new boolean[roleIdentifiers.size()];
         }
     }
 
     public boolean hasAllRoles(Collection<String> roleIdentifiers) {
         return hasPrincipals() && securityManager.hasAllRoles(getPrincipals(), roleIdentifiers);
     }
 
     public void checkRole(String role) throws AuthorizationException {
         assertAuthzCheckPossible();
         securityManager.checkRole(getPrincipals(), role);
     }
 
     public void checkRoles(String... roleIdentifiers) throws AuthorizationException {
         assertAuthzCheckPossible();
         securityManager.checkRoles(getPrincipals(), roleIdentifiers);
     }
 
     public void checkRoles(Collection<String> roles) throws AuthorizationException {
         assertAuthzCheckPossible();
         securityManager.checkRoles(getPrincipals(), roles);
     }
 
     public void login(AuthenticationToken token) throws AuthenticationException {
         clearRunAsIdentitiesInternal();
         Subject subject = securityManager.login(this, token);
 
         PrincipalCollection principals;
 
         String host = null;
 
         if (subject instanceof DelegatingSubject) {
             DelegatingSubjectorg/apache/shiro/subject/support/DelegatingSubject.html#DelegatingSubject">DelegatingSubject delegating = (DelegatingSubject) subject;
             //we have to do this in case there are assumed identities - we don't want to lose the 'real' principals:
             principals = delegating.principals;
             host = delegating.host;
         } else {
             principals = subject.getPrincipals();
         }
 
         if (principals == null || principals.isEmpty()) {
             String msg = "Principals returned from securityManager.login( token ) returned a null or " +
                     "empty value.  This value must be non null and populated with one or more elements.";
             throw new IllegalStateException(msg);
         }
         this.principals = principals;
         this.authenticated = true;
         if (token instanceof HostAuthenticationToken) {
             host = ((HostAuthenticationToken) token).getHost();
         }
         if (host != null) {
             this.host = host;
         }
         Session session = subject.getSession(false);
         if (session != null) {
             this.session = decorate(session);
         } else {
             this.session = null;
         }
     }
 
     public boolean isAuthenticated() {
         return authenticated && hasPrincipals();
     }
 
     public boolean isRemembered() {
         PrincipalCollection principals = getPrincipals();
         return principals != null && !principals.isEmpty() && !isAuthenticated();
     }
 
     /**
      * Returns {@code true} if this Subject is allowed to create sessions, {@code false} otherwise.
      *
      * @return {@code true} if this Subject is allowed to create sessions, {@code false} otherwise.
      * @since 1.2
      */
     protected boolean isSessionCreationEnabled() {
         return this.sessionCreationEnabled;
     }
 
     public Session getSession() {
         return getSession(true);
     }
 
     public Session getSession(boolean create) {
         if (log.isTraceEnabled()) {
             log.trace("attempting to get session; create = " + create +
                     "; session is null = " + (this.session == null) +
                     "; session has id = " + (this.session != null && session.getId() != null));
         }
 
         if (this.session == null && create) {
 
             //added in 1.2:
             if (!isSessionCreationEnabled()) {
                 String msg = "Session creation has been disabled for the current subject.  This exception indicates " +
                         "that there is either a programming error (using a session when it should never be " +
                         "used) or that Shiro's configuration needs to be adjusted to allow Sessions to be created " +
                         "for the current Subject.  See the " + DisabledSessionException.class.getName() + " JavaDoc " +
                         "for more.";
                 throw new DisabledSessionException(msg);
             }
 
             log.trace("Starting session for host {}", getHost());
             SessionContext sessionContext = createSessionContext();
             Session session = this.securityManager.start(sessionContext);
             this.session = decorate(session);
         }
         return this.session;
     }
 
     protected SessionContext createSessionContext() {
         SessionContext sessionContext = new DefaultSessionContext();
         if (StringUtils.hasText(host)) {
             sessionContext.setHost(host);
         }
         return sessionContext;
     }
 
     private void clearRunAsIdentitiesInternal() {
         //try/catch added for SHIRO-298
         try {
             clearRunAsIdentities();
         } catch (SessionException se) {
             log.debug("Encountered session exception trying to clear 'runAs' identities during logout.  This " +
                     "can generally safely be ignored.", se);
         }
     }
 
     public void logout() {
         try {
             clearRunAsIdentitiesInternal();
             this.securityManager.logout(this);
         } finally {
             this.session = null;
             this.principals = null;
             this.authenticated = false;
             //Don't set securityManager to null here - the Subject can still be
             //used, it is just considered anonymous at this point.  The SecurityManager instance is
             //necessary if the subject would log in again or acquire a new session.  This is in response to
             //https://issues.apache.org/jira/browse/JSEC-22
             //this.securityManager = null;
         }
     }
 
     private void sessionStopped() {
         this.session = null;
     }
 
     public <V> V execute(Callable<V> callable) throws ExecutionException {
         Callable<V> associated = associateWith(callable);
         try {
             return associated.call();
         } catch (Throwable t) {
             throw new ExecutionException(t);
         }
     }
 
     public void execute(Runnable runnable) {
         Runnable associated = associateWith(runnable);
         associated.run();
     }
 
     public <V> Callable<V> associateWith(Callable<V> callable) {
         return new SubjectCallable<V>(this, callable);
     }
 
     public Runnable associateWith(Runnable runnable) {
         if (runnable instanceof Thread) {
             String msg = "This implementation does not support Thread arguments because of JDK ThreadLocal " +
                     "inheritance mechanisms required by Shiro.  Instead, the method argument should be a non-Thread " +
                     "Runnable and the return value from this method can then be given to an ExecutorService or " +
                     "another Thread.";
             throw new UnsupportedOperationException(msg);
         }
         return new SubjectRunnable(this, runnable);
     }
 
     private class StoppingAwareProxiedSession extends ProxiedSession {
 
         private final DelegatingSubject owner;
 
         private StoppingAwareProxiedSession(Session target, DelegatingSubject owningSubject) {
             super(target);
             owner = owningSubject;
         }
 
         public void stop() throws InvalidSessionException {
             super.stop();
             owner.sessionStopped();
         }
     }
 
 
     // ======================================
     // 'Run As' support implementations
     // ======================================
 
     public void runAs(PrincipalCollection principals) {
         if (!hasPrincipals()) {
             String msg = "This subject does not yet have an identity.  Assuming the identity of another " +
                     "Subject is only allowed for Subjects with an existing identity.  Try logging this subject in " +
                     "first, or using the " + Subject.Builder.class.getName() + " to build ad hoc Subject instances " +
                     "with identities as necessary.";
             throw new IllegalStateException(msg);
         }
         pushIdentity(principals);
     }
 
     public boolean isRunAs() {
         List<PrincipalCollection> stack = getRunAsPrincipalsStack();
         return !CollectionUtils.isEmpty(stack);
     }
 
     public PrincipalCollection getPreviousPrincipals() {
         PrincipalCollection previousPrincipals = null;
         List<PrincipalCollection> stack = getRunAsPrincipalsStack();
         int stackSize = stack != null ? stack.size() : 0;
         if (stackSize > 0) {
             if (stackSize == 1) {
                 previousPrincipals = this.principals;
             } else {
                 //always get the one behind the current:
                 assert stack != null;
                 previousPrincipals = stack.get(1);
             }
         }
         return previousPrincipals;
     }
 
     public PrincipalCollection releaseRunAs() {
         return popIdentity();
     }
 
     @SuppressWarnings("unchecked")
     private List<PrincipalCollection> getRunAsPrincipalsStack() {
         Session session = getSession(false);
         if (session != null) {
             return (List<PrincipalCollection>) session.getAttribute(RUN_AS_PRINCIPALS_SESSION_KEY);
         }
         return null;
     }
 
     private void clearRunAsIdentities() {
         Session session = getSession(false);
         if (session != null) {
             session.removeAttribute(RUN_AS_PRINCIPALS_SESSION_KEY);
         }
     }
 
     private void pushIdentity(PrincipalCollection principals) throws NullPointerException {
         if (isEmpty(principals)) {
             String msg = "Specified Subject principals cannot be null or empty for 'run as' functionality.";
             throw new NullPointerException(msg);
         }
         List<PrincipalCollection> stack = getRunAsPrincipalsStack();
         if (stack == null) {
             stack = new CopyOnWriteArrayList<PrincipalCollection>();
         }
         stack.add(0, principals);
         Session session = getSession();
         session.setAttribute(RUN_AS_PRINCIPALS_SESSION_KEY, stack);
     }
 
     private PrincipalCollection popIdentity() {
         PrincipalCollection popped = null;
 
         List<PrincipalCollection> stack = getRunAsPrincipalsStack();
         if (!CollectionUtils.isEmpty(stack)) {
             popped = stack.remove(0);
             Session session;
             if (!CollectionUtils.isEmpty(stack)) {
                 //persist the changed stack to the session
                 session = getSession();
                 session.setAttribute(RUN_AS_PRINCIPALS_SESSION_KEY, stack);
             } else {
                 //stack is empty, remove it from the session:
                 clearRunAsIdentities();
             }
         }
 
         return popped;
     }
 }