/*
    * 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.web.filter.authz;
  
  import org.apache.shiro.util.StringUtils;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import javax.servlet.ServletRequest;
  import javax.servlet.ServletResponse;
  import javax.servlet.http.HttpServletRequest;
  import java.io.IOException;
  import java.util.HashMap;
  import java.util.Map;
  
  /**
   * A filter that translates an HTTP Request's Method (eg GET, POST, etc)
   * into an corresponding action (verb) and uses that verb to construct a permission that will be checked to determine
   * access.
   * <p/>
   * This Filter is primarily provided to support REST environments where the type (Method)
   * of request translates to an action being performed on one or more resources.  This paradigm works well with Shiro's
   * concepts of using permissions for access control and can be leveraged to easily perform permission checks.
   * <p/>
   * This filter functions as follows:
   * <ol>
   * <li>The incoming HTTP request's Method (GET, POST, PUT, DELETE, etc) is discovered.</li>
   * <li>The Method is translated into a more 'application friendly' verb, such as 'create', edit', 'delete', etc.</li>
   * <li>The verb is appended to any configured permissions for the
   * {@link org.apache.shiro.web.filter.PathMatchingFilter currently matching path}.</li>
   * <li>If the current {@code Subject} {@link org.apache.shiro.subject.Subject#isPermitted(String) isPermitted} to
   * perform the resolved action, the request is allowed to continue.</li>
   * </ol>
   * <p/>
   * For example, if the following filter chain was defined, where 'rest' was the name given to a filter instance of
   * this class:
   * <pre>
   * /user/** = rest[user]</pre>
   * Then an HTTP {@code GET} request to {@code /user/1234} would translate to the constructed permission
   * {@code user:read} (GET is mapped to the 'read' action) and execute the permission check
   * <code>Subject.isPermitted(&quot;user:read&quot;)</code> in order to allow the request to continue.
   * <p/>
   * Similarly, an HTTP {@code POST} to {@code /user} would translate to the constructed permission
   * {@code user:create} (POST is mapped to the 'create' action) and execute the permission check
   * <code>Subject.isPermitted(&quot;user:create&quot;)</code> in order to allow the request to continue.
   * <p/>
   * <h3>Method To Verb Mapping</h3>
   * The following table represents the default HTTP Method-to-action verb mapping:
   * <table>
   * <tr><th>HTTP Method</th><th>Mapped Action</th><th>Example Permission</th><th>Runtime Check</th></tr>
   * <tr><td>head</td><td>read</td><td>perm1</td><td>perm1:read</td></tr>
   * <tr><td>get</td><td>read</td><td>perm2</td><td>perm2:read</td></tr>
   * <tr><td>put</td><td>update</td><td>perm3</td><td>perm3:update</td></tr>
   * <tr><td>post</td><td>create</td><td>perm4</td><td>perm4:create</td></tr>
   * <tr><td>mkcol</td><td>create</td><td>perm5</td><td>perm5:create</td></tr>
   * <tr><td>options</td><td>read</td><td>perm6</td><td>perm6:read</td></tr>
   * <tr><td>trace</td><td>read</td><td>perm7</td><td>perm7:read</td></tr>
   * </table>
   *
   * @since 1.0
   */
  public class HttpMethodPermissionFilter extends PermissionsAuthorizationFilter {
  
      /**
       * This class's private logger.
       */
      private static final Logger log = LoggerFactory.getLogger(HttpMethodPermissionFilter.class);
  
      /**
       * Map that contains a mapping between http methods to permission actions (verbs)
       */
      private final Map<String, String> httpMethodActions = new HashMap<String, String>();
  
      //Actions representing HTTP Method values (GET -> read, POST -> create, etc)
      private static final String CREATE_ACTION = "create";
      private static final String READ_ACTION = "read";
      private static final String UPDATE_ACTION = "update";
      private static final String DELETE_ACTION = "delete";
  
      /**
       * Enum of constants for well-defined mapping values.  Used in the Filter's constructor to perform the map instance
       * used at runtime.
       */
     private static enum HttpMethodAction {
 
         DELETE(DELETE_ACTION),
         GET(READ_ACTION),
         HEAD(READ_ACTION),
         MKCOL(CREATE_ACTION), //webdav, but useful here
         OPTIONS(READ_ACTION),
         POST(CREATE_ACTION),
         PUT(UPDATE_ACTION),
         TRACE(READ_ACTION);
 
         private final String action;
 
         private HttpMethodAction(String action) {
             this.action = action;
         }
 
         public String getAction() {
             return this.action;
         }
     }
 
     /**
      * Creates the filter instance with default method-to-action values in the instance's
      * {@link #getHttpMethodActions() http method actions map}.
      */
     public HttpMethodPermissionFilter() {
         for (HttpMethodAction methodAction : HttpMethodAction.values()) {
             httpMethodActions.put(methodAction.name().toLowerCase(), methodAction.getAction());
         }
     }
 
     /**
      * Returns the HTTP Method name (key) to action verb (value) mapping used to resolve actions based on an
      * incoming {@code HttpServletRequest}.  All keys and values are lower-case.  The
      * default key/value pairs are defined in the top class-level JavaDoc.
      *
      * @return the HTTP Method lower-case name (key) to lower-case action verb (value) mapping
      */
     protected Map<String, String> getHttpMethodActions() {
         return this.httpMethodActions;
     }
 
     /**
      * Determines the action (verb) attempting to be performed on the filtered resource by the current request.
      * <p/>
      * This implementation expects the incoming request to be an {@link HttpServletRequest} and returns a mapped
      * action based on the HTTP request {@link javax.servlet.http.HttpServletRequest#getMethod() method}.
      *
      * @param request to pull the method from.
      * @return The string equivalent verb of the http method.
      */
     protected String getHttpMethodAction(ServletRequest request) {
         String method = ((HttpServletRequest) request).getMethod();
         return getHttpMethodAction(method);
     }
 
     /**
      * Determines the corresponding application action that will be performed on the filtered resource based on the
      * specified HTTP method (GET, POST, etc).
      *
      * @param method to be translated into the verb.
      * @return The string equivalent verb of the method.
      */
     protected String getHttpMethodAction(String method) {
         String lc = method.toLowerCase();
         String resolved = getHttpMethodActions().get(lc);
         return resolved != null ? resolved : method;
     }
 
     /**
      * Returns a collection of String permissions with which to perform a permission check to determine if the filter
      * will allow the request to continue.
      * <p/>
      * This implementation merely delegates to {@link #buildPermissions(String[], String)} and ignores the inbound
      * HTTP servlet request, but it can be overridden by subclasses for more complex request-specific building logic
      * if necessary.
      *
      * @param request         the inbound HTTP request - ignored in this implementation, but available to
      *                        subclasses for more complex construction building logic if necessary
      * @param configuredPerms any url-specific permissions mapped to this filter in the URL rules mappings.
      * @param action          the application-friendly action (verb) resolved based on the HTTP Method name.
      * @return a collection of String permissions with which to perform a permission check to determine if the filter
      *         will allow the request to continue.
      */
     protected String[] buildPermissions(HttpServletRequest request, String[] configuredPerms, String action) {
         return buildPermissions(configuredPerms, action);
     }
 
     /**
      * Builds a new array of permission strings based on the original argument, appending the specified action verb
      * to each one per {@link org.apache.shiro.authz.permission.WildcardPermission WildcardPermission} conventions.  The
      * built permission strings will be the ones used at runtime during the permission check that determines if filter
      * access should be allowed to continue or not.
      * <p/>
      * For example, if the {@code configuredPerms} argument contains the following 3 permission strings:
      * <p/>
      * <ol>
      * <li>permission:one</li>
      * <li>permission:two</li>
      * <li>permission:three</li>
      * </ol>
      * And the action is {@code read}, then the return value will be:
      * <ol>
      * <li>permission:one:read</li>
      * <li>permission:two:read</li>
      * <li>permission:three:read</li>
      * </ol>
      * per {@link org.apache.shiro.authz.permission.WildcardPermission WildcardPermission} conventions.  Subclasses
      * are of course free to override this method or the
      * {@link #buildPermissions(javax.servlet.http.HttpServletRequest, String[], String) buildPermissions} request
      * variant for custom building logic or with different permission formats.
      *
      * @param configuredPerms list of configuredPerms to be converted.
      * @param action          the resolved action based on the request method to be appended to permission strings.
      * @return an array of permission strings with each element appended with the action.
      */
     protected String[] buildPermissions(String[] configuredPerms, String action) {
         if (configuredPerms == null || configuredPerms.length <= 0 || !StringUtils.hasText(action)) {
             return configuredPerms;
         }
 
         String[] mappedPerms = new String[configuredPerms.length];
 
         // loop and append :action
         for (int i = 0; i < configuredPerms.length; i++) {
             mappedPerms[i] = configuredPerms[i] + ":" + action;
         }
 
         if (log.isTraceEnabled()) {
             StringBuilder sb = new StringBuilder();
             for (int i = 0; i < mappedPerms.length; i++) {
                 if (i > 0) {
                     sb.append(", ");
                 }
                 sb.append(mappedPerms[i]);
             }
             log.trace("MAPPED '{}' action to permission(s) '{}'", action, sb);
         }
 
         return mappedPerms;
     }
 
     /**
      * Resolves an 'application friendly' action verb based on the {@code HttpServletRequest}'s method, appends that
      * action to each configured permission (the {@code mappedValue} argument is a {@code String[]} array), and
      * delegates the permission check for the newly constructed permission(s) to the superclass
      * {@link PermissionsAuthorizationFilter#isAccessAllowed(javax.servlet.ServletRequest, javax.servlet.ServletResponse, Object) isAccessAllowed}
      * implementation to perform the actual permission check.
      *
      * @param request     the inbound {@code ServletRequest}
      * @param response    the outbound {@code ServletResponse}
      * @param mappedValue the filter-specific config value mapped to this filter in the URL rules mappings.
      * @return {@code true} if the request should proceed through the filter normally, {@code false} if the
      *         request should be processed by this filter's
      *         {@link #onAccessDenied(ServletRequest,ServletResponse,Object)} method instead.
      * @throws IOException
      */
     @Override
     public boolean isAccessAllowed(ServletRequest request, ServletResponse response, Object mappedValue) throws IOException {
         String[] perms = (String[]) mappedValue;
         // append the http action to the end of the permissions and then back to super
         String action = getHttpMethodAction(request);
         String[] resolvedPerms = buildPermissions(perms, action);
         return super.isAccessAllowed(request, response, resolvedPerms);
     }
 }