/*
    * 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.mgt;
  
  import org.apache.shiro.session.Session;
  import org.apache.shiro.subject.PrincipalCollection;
  import org.apache.shiro.subject.Subject;
  import org.apache.shiro.subject.support.DefaultSubjectContext;
  import org.apache.shiro.subject.support.DelegatingSubject;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.lang.reflect.Field;
  
  /**
   * Default {@code SubjectDAO} implementation that stores Subject state in the Subject's Session by default (but this
   * can be disabled - see below).  The Subject instance
   * can be re-created at a later time by first acquiring the associated Session (typically from a
   * {@link org.apache.shiro.session.mgt.SessionManager SessionManager}) via a session ID or session key and then
   * building a {@code Subject} instance from {@code Session} attributes.
   * <h2>Controlling how Sessions are used</h2>
   * Whether or not a {@code Subject}'s {@code Session} is used or not to persist its own state is controlled on a
   * <em>per-Subject</em> basis as determined by the configured
   * {@link #setSessionStorageEvaluator(SessionStorageEvaluator) sessionStorageEvaluator}.
   * The default {@code Evaluator} is a {@link DefaultSessionStorageEvaluator}, which supports enabling or disabling
   * session usage for Subject persistence at a global level for all subjects (and defaults to allowing sessions to be
   * used).
   * <h3>Disabling Session Persistence Entirely</h3>
   * Because the default {@code SessionStorageEvaluator} instance is a {@link DefaultSessionStorageEvaluator}, you
   * can disable Session usage for Subject state entirely by configuring that instance directly, e.g.:
   * <pre>
   *     ((DefaultSessionStorageEvaluator)sessionDAO.getSessionStorageEvaluator()).setSessionStorageEnabled(false);
   * </pre>
   * or, for example, in {@code shiro.ini}:
   * <pre>
   *     securityManager.subjectDAO.sessionStorageEvaluator.sessionStorageEnabled = false
   * </pre>
   * but <b>note:</b> ONLY do this your
   * application is 100% stateless and you <em>DO NOT</em> need subjects to be remembered across remote
   * invocations, or in a web environment across HTTP requests.
   * <h3>Supporting Both Stateful and Stateless Subject paradigms</h3>
   * Perhaps your application needs to support a hybrid approach of both stateful and stateless Subjects:
   * <ul>
   * <li>Stateful: Stateful subjects might represent web end-users that need their identity and authentication
   * state to be remembered from page to page.</li>
   * <li>Stateless: Stateless subjects might represent API clients (e.g. REST clients) that authenticate on every
   * request, and therefore don't need authentication state to be stored across requests in a session.</li>
   * </ul>
   * To support the hybrid <em>per-Subject</em> approach, you will need to create your own implementation of the
   * {@link SessionStorageEvaluator} interface and configure it via the
   * {@link #setSessionStorageEvaluator(SessionStorageEvaluator)} method, or, with {@code shiro.ini}:
   * <pre>
   *     myEvaluator = com.my.CustomSessionStorageEvaluator
   *     securityManager.subjectDAO.sessionStorageEvaluator = $myEvaluator
   * </pre>
   * <p/>
   * Unless overridden, the default evaluator is a {@link DefaultSessionStorageEvaluator}, which enables session usage for
   * Subject state by default.
   *
   * @see #isSessionStorageEnabled(org.apache.shiro.subject.Subject)
   * @see SessionStorageEvaluator
   * @see DefaultSessionStorageEvaluator
   * @since 1.2
   */
  public class DefaultSubjectDAO implements SubjectDAO {
  
      private static final Logger log = LoggerFactory.getLogger(DefaultSubjectDAO.class);
  
      /**
       * Evaluator that determines if a Subject's session may be used to store the Subject's own state.
       */
      private SessionStorageEvaluator sessionStorageEvaluator;
  
      public DefaultSubjectDAO() {
          //default implementation allows enabling/disabling session usages at a global level for all subjects:
          this.sessionStorageEvaluator = new DefaultSessionStorageEvaluator();
      }
  
      /**
       * Determines if the subject's session will be used to persist subject state or not.  This implementation
       * merely delegates to the internal {@link SessionStorageEvaluator} (a
       * {@code DefaultSessionStorageEvaluator} by default).
       *
      * @param subject the subject to inspect to determine if the subject's session will be used to persist subject
      *                state or not.
      * @return {@code true} if the subject's session will be used to persist subject state, {@code false} otherwise.
      * @see #setSessionStorageEvaluator(SessionStorageEvaluator)
      * @see DefaultSessionStorageEvaluator
      */
     protected boolean isSessionStorageEnabled(Subject subject) {
         return getSessionStorageEvaluator().isSessionStorageEnabled(subject);
     }
 
     /**
      * Returns the {@code SessionStorageEvaluator} that will determine if a {@code Subject}'s state may be persisted in
      * the Subject's session.  The default instance is a {@link DefaultSessionStorageEvaluator}.
      *
      * @return the {@code SessionStorageEvaluator} that will determine if a {@code Subject}'s state may be persisted in
      *         the Subject's session.
      * @see DefaultSessionStorageEvaluator
      */
     public SessionStorageEvaluator getSessionStorageEvaluator() {
         return sessionStorageEvaluator;
     }
 
     /**
      * Sets the {@code SessionStorageEvaluator} that will determine if a {@code Subject}'s state may be persisted in
      * the Subject's session. The default instance is a {@link DefaultSessionStorageEvaluator}.
      *
      * @param sessionStorageEvaluator the {@code SessionStorageEvaluator} that will determine if a {@code Subject}'s
      *                                state may be persisted in the Subject's session.
      * @see DefaultSessionStorageEvaluator
      */
     public void setSessionStorageEvaluator(SessionStorageEvaluator sessionStorageEvaluator) {
         this.sessionStorageEvaluator = sessionStorageEvaluator;
     }
 
     /**
      * Saves the subject's state to the subject's {@link org.apache.shiro.subject.Subject#getSession() session} only
      * if {@link #isSessionStorageEnabled(Subject) sessionStorageEnabled(subject)}.  If session storage is not enabled
      * for the specific {@code Subject}, this method does nothing.
      * <p/>
      * In either case, the argument {@code Subject} is returned directly (a new Subject instance is not created).
      *
      * @param subject the Subject instance for which its state will be created or updated.
      * @return the same {@code Subject} passed in (a new Subject instance is not created).
      */
     public Subject save(Subject subject) {
         if (isSessionStorageEnabled(subject)) {
             saveToSession(subject);
         } else {
             log.trace("Session storage of subject state for Subject [{}] has been disabled: identity and " +
                     "authentication state are expected to be initialized on every request or invocation.", subject);
         }
 
         return subject;
     }
 
     /**
      * Saves the subject's state (it's principals and authentication state) to its
      * {@link org.apache.shiro.subject.Subject#getSession() session}.  The session can be retrieved at a later time
      * (typically from a {@link org.apache.shiro.session.mgt.SessionManager SessionManager} to be used to recreate
      * the {@code Subject} instance.
      *
      * @param subject the subject for which state will be persisted to its session.
      */
     protected void saveToSession(Subject subject) {
         //performs merge logic, only updating the Subject's session if it does not match the current state:
         mergePrincipals(subject);
         mergeAuthenticationState(subject);
     }
 
     private static boolean isEmpty(PrincipalCollection pc) {
         return pc == null || pc.isEmpty();
     }
 
     /**
      * Merges the Subject's current {@link org.apache.shiro.subject.Subject#getPrincipals()} with whatever may be in
      * any available session.  Only updates the Subject's session if the session does not match the current principals
      * state.
      *
      * @param subject the Subject for which principals will potentially be merged into the Subject's session.
      */
     protected void mergePrincipals(Subject subject) {
         //merge PrincipalCollection state:
 
         PrincipalCollection currentPrincipals = null;
 
         //SHIRO-380: added if/else block - need to retain original (source) principals
         //This technique (reflection) is only temporary - a proper long term solution needs to be found,
         //but this technique allowed an immediate fix that is API point-version forwards and backwards compatible
         //
         //A more comprehensive review / cleaning of runAs should be performed for Shiro 1.3 / 2.0 +
         if (subject.isRunAs() && subject instanceof DelegatingSubject) {
             try {
                 Field field = DelegatingSubject.class.getDeclaredField("principals");
                 field.setAccessible(true);
                 currentPrincipals = (PrincipalCollection)field.get(subject);
             } catch (Exception e) {
                 throw new IllegalStateException("Unable to access DelegatingSubject principals property.", e);
             }
         }
         if (currentPrincipals == null || currentPrincipals.isEmpty()) {
             currentPrincipals = subject.getPrincipals();
         }
 
         Session session = subject.getSession(false);
 
         if (session == null) {
             if (!isEmpty(currentPrincipals)) {
                 session = subject.getSession();
                 session.setAttribute(DefaultSubjectContext.PRINCIPALS_SESSION_KEY, currentPrincipals);
             }
             // otherwise no session and no principals - nothing to save
         } else {
             PrincipalCollection existingPrincipals =
                     (PrincipalCollection) session.getAttribute(DefaultSubjectContext.PRINCIPALS_SESSION_KEY);
 
             if (isEmpty(currentPrincipals)) {
                 if (!isEmpty(existingPrincipals)) {
                     session.removeAttribute(DefaultSubjectContext.PRINCIPALS_SESSION_KEY);
                 }
                 // otherwise both are null or empty - no need to update the session
             } else {
                 if (!currentPrincipals.equals(existingPrincipals)) {
                     session.setAttribute(DefaultSubjectContext.PRINCIPALS_SESSION_KEY, currentPrincipals);
                 }
                 // otherwise they're the same - no need to update the session
             }
         }
     }
 
     /**
      * Merges the Subject's current authentication state with whatever may be in
      * any available session.  Only updates the Subject's session if the session does not match the current
      * authentication state.
      *
      * @param subject the Subject for which principals will potentially be merged into the Subject's session.
      */
     protected void mergeAuthenticationState(Subject subject) {
 
         Session session = subject.getSession(false);
 
         if (session == null) {
             if (subject.isAuthenticated()) {
                 session = subject.getSession();
                 session.setAttribute(DefaultSubjectContext.AUTHENTICATED_SESSION_KEY, Boolean.TRUE);
             }
             //otherwise no session and not authenticated - nothing to save
         } else {
             Boolean existingAuthc = (Boolean) session.getAttribute(DefaultSubjectContext.AUTHENTICATED_SESSION_KEY);
 
             if (subject.isAuthenticated()) {
                 if (existingAuthc == null || !existingAuthc) {
                     session.setAttribute(DefaultSubjectContext.AUTHENTICATED_SESSION_KEY, Boolean.TRUE);
                 }
                 //otherwise authc state matches - no need to update the session
             } else {
                 if (existingAuthc != null) {
                     //existing doesn't match the current state - remove it:
                     session.removeAttribute(DefaultSubjectContext.AUTHENTICATED_SESSION_KEY);
                 }
                 //otherwise not in the session and not authenticated - no need to update the session
             }
         }
     }
 
     /**
      * Removes any existing subject state from the Subject's session (if the session exists).  If the session
      * does not exist, this method does not do anything.
      *
      * @param subject the subject for which any existing subject state will be removed from its session.
      */
     protected void removeFromSession(Subject subject) {
         Session session = subject.getSession(false);
         if (session != null) {
             session.removeAttribute(DefaultSubjectContext.AUTHENTICATED_SESSION_KEY);
             session.removeAttribute(DefaultSubjectContext.PRINCIPALS_SESSION_KEY);
         }
     }
 
     /**
      * Removes any existing subject state from the subject's session (if the session exists).
      *
      * @param subject the Subject instance for which any persistent state should be deleted.
      */
     public void delete(Subject subject) {
         removeFromSession(subject);
     }
 }