/*
    * 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.commons.jexl3.introspection;
  
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  
  /**
   * A sandbox describes permissions on a class by explicitly allowing or forbidding
   * access to methods and properties through "allowlists" and "blocklists".
   *
   * <p>A <b>allowlist</b> explicitly allows methods/properties for a class;</p>
   *
   * <ul>
   *   <li>If a allowlist is empty and thus does not contain any names,
   *       all properties/methods are allowed for its class.</li>
   *   <li>If it is not empty, the only allowed properties/methods are the ones contained.</li>
   * </ul>
   *
   * <p>A <b>blocklist</b> explicitly forbids methods/properties for a class;</p>
   *
   * <ul>
   *   <li>If a blocklist is empty and thus does not contain any names,
   *       all properties/methods are forbidden for its class.</li>
   *   <li>If it is not empty, the only forbidden properties/methods are the ones contained.</li>
   * </ul>
   *
   * <p>Permissions are composed of three lists, read, write, execute, each being
   * "allow" or "block":</p>
   *
   * <ul>
   *   <li><b>read</b> controls readable properties </li>
   *   <li><b>write</b> controls writable properties</li>
   *   <li><b>execute</b> controls executable methods and constructor</li>
   * </ul>
   *
   * <p>When specified, permissions - allow or block lists - can be created inheritable
   * on interfaces or classes and thus applicable to their implementations or derived
   * classes; the sandbox must be created with the 'inheritable' flag for this behavior
   * to be triggered. Note that even in this configuration, it is still possible to
   * add non-inheritable permissions.
   * Adding inheritable lists to a non inheritable sandbox has no added effect;
   * permissions only apply to their specified class.</p>
   *
   * <p>Note that a JexlUberspect always uses a <em>copy</em> of the JexlSandbox
   * used to built it preventing permission changes after its instantiation.</p>
   *
   * @since 3.0
   */
  public final class JexlSandbox {
      /**
       * The marker string for explicitly disallowed null properties.
       */
      public static final String NULL = "?";
      /**
       * The map from class names to permissions.
       */
      private final Map<String, Permissions> sandbox;
      /**
       * Whether permissions can be inherited (through implementation or extension).
       */
      private final boolean inherit;
      /**
       * Default behavior, block or allow.
       */
      private final boolean allow;
  
      /**
       * Creates a new default sandbox.
       * <p>In the absence of explicit permissions on a class, the
       * sandbox is a allow-box, allow-listing that class for all permissions (read, write and execute).
       */
      public JexlSandbox() {
          this(true, false, null);
      }
  
      /**
       * Creates a new default sandbox.
       * <p>A allow-box considers no permissions as &quot;everything is allowed&quot; when
       * a block-box considers no permissions as &quot;nothing is allowed&quot;.
       * @param ab whether this sandbox is allow (true) or block (false)
      * if no permission is explicitly defined for a class.
      * @since 3.1
      */
     public JexlSandbox(final boolean ab) {
         this(ab, false, null);
     }
 
     /**
      * Creates a sandbox.
      * @param ab whether this sandbox is allow (true) or block (false)
      * @param inh whether permissions on interfaces and classes are inherited (true) or not (false)
      * @since 3.2
      */
     public JexlSandbox(final boolean ab, final boolean inh) {
         this(ab, inh, null);
     }
 
     /**
      * Creates a sandbox based on an existing permissions map.
      * @param map the permissions map
      */
     @Deprecated
     protected JexlSandbox(final Map<String, Permissions> map) {
         this(true, false, map);
     }
 
     /**
      * Creates a sandbox based on an existing permissions map.
      * @param ab whether this sandbox is allow (true) or block (false)
      * @param map the permissions map
      * @since 3.1
      */
     @Deprecated
     protected JexlSandbox(final boolean ab, final Map<String, Permissions> map) {
         this(ab, false, map);
     }
 
     /**
      * Creates a sandbox based on an existing permissions map.
      * @param ab whether this sandbox is allow (true) or block (false)
      * @param inh whether permissions are inherited, default false
      * @param map the permissions map
      * @since 3.2
      */
     protected JexlSandbox(final boolean ab, final boolean inh, final Map<String, Permissions> map) {
         allow = ab;
         inherit = inh;
         sandbox = map != null? map : new HashMap<>();
     }
 
     /**
      * @return a copy of this sandbox
      */
     public JexlSandbox copy() {
         // modified concurrently at runtime so...
         final Map<String, Permissions> map = new ConcurrentHashMap<>();
         for (final Map.Entry<String, Permissions> entry : sandbox.entrySet()) {
             map.put(entry.getKey(), entry.getValue().copy());
         }
         return new JexlSandbox(allow, inherit, map);
     }
 
     /**
      * Gets a class by name, crude mechanism for backwards (&lt;3.2 ) compatibility.
      * @param cname the class name
      * @return the class
      */
     static Class<?> forName(final String cname) {
         try {
             return Class.forName(cname);
         } catch(final Exception xany) {
             return null;
         }
     }
 
     /**
      * Gets the read permission value for a given property of a class.
      *
      * @param clazz the class
      * @param name the property name
      * @return null (or NULL if name is null) if not allowed, the name of the property to use otherwise
      */
     public String read(final Class<?> clazz, final String name) {
         return get(clazz).read().get(name);
     }
 
     /**
      * Gets the read permission value for a given property of a class.
      *
      * @param clazz the class name
      * @param name the property name
      * @return null if not allowed, the name of the property to use otherwise
      */
     @Deprecated
     public String read(final String clazz, final String name) {
         return get(clazz).read().get(name);
     }
 
     /**
      * Gets the write permission value for a given property of a class.
      *
      * @param clazz the class
      * @param name the property name
      * @return null (or NULL if name is null) if not allowed, the name of the property to use otherwise
      */
     public String write(final Class<?> clazz, final String name) {
         return get(clazz).write().get(name);
     }
 
     /**
      * Gets the write permission value for a given property of a class.
      *
      * @param clazz the class name
      * @param name the property name
      * @return null if not allowed, the name of the property to use otherwise
      */
     @Deprecated
     public String write(final String clazz, final String name) {
         return get(clazz).write().get(name);
     }
 
     /**
      * Gets the execute permission value for a given method of a class.
      *
      * @param clazz the class
      * @param name the method name
      * @return null if not allowed, the name of the method to use otherwise
      */
     public String execute(final Class<?> clazz, final String name) {
         final String m = get(clazz).execute().get(name);
         return "".equals(name) && m != null? clazz.getName() : m;
     }
 
     /**
      * Gets the execute permission value for a given method of a class.
      *
      * @param clazz the class name
      * @param name the method name
      * @return null if not allowed, the name of the method to use otherwise
      */
     @Deprecated
     public String execute(final String clazz, final String name) {
         final String m = get(clazz).execute().get(name);
         return "".equals(name) && m != null? clazz : m;
     }
 
     /**
      * A base set of names.
      */
     public abstract static class Names {
 
         /**
          * Adds a name to this set.
          *
          * @param name the name to add
          * @return  true if the name was really added, false if not
          */
         public abstract boolean add(String name);
 
         /**
          * Adds an alias to a name to this set.
          * <p>This only has an effect on allow lists.</p>
          *
          * @param name the name to alias
          * @param alias the alias
          * @return  true if the alias was added, false if it was already present
          */
         public boolean alias(final String name, final String alias) {
             return false;
         }
 
         /**
          * Whether a given name is allowed or not.
          *
          * @param name the method/property name to check
          * @return null (or NULL if name is null) if not allowed, the actual name to use otherwise
          */
         public String get(final String name) {
             return name;
         }
 
         /**
          * @return a copy of these Names
          */
         protected Names copy() {
             return this;
         }
     }
 
     /**
      * The pass-thru name set.
      */
     private static final Names ALLOW_NAMES = new Names() {
         @Override
         public boolean add(final String name) {
             return false;
         }
 
         @Override
         protected Names copy() {
             return this;
         }
     };
 
     /**
      * The block-all name set.
      */
     private static final Names BLOCK_NAMES = new Names() {
         @Override
         public boolean add(final String name) {
             return false;
         }
 
         @Override
         protected Names copy() {
             return this;
         }
 
         @Override
         public String get(final String name) {
             return name == null? NULL : null;
         }
     };
 
     /**
      * A allow set of names.
      */
     static class AllowSet extends Names {
         /** The map of controlled names and aliases. */
         private Map<String, String> names = null;
 
         @Override
         protected Names copy() {
             final AllowSet copy = new AllowSet();
             copy.names = names == null ? null : new HashMap<>(names);
             return copy;
         }
 
         @Override
         public boolean add(final String name) {
             if (names == null) {
                 names = new HashMap<>();
             }
             return names.put(name, name) == null;
         }
 
         @Override
         public boolean alias(final String name, final String alias) {
             if (names == null) {
                 names = new HashMap<>();
             }
             return names.put(alias, name) == null;
         }
 
         @Override
         public String get(final String name) {
             if (names == null) {
                 return name;
             }
             final String actual = names.get(name);
             // if null is not explicitly allowed, explicit null aka NULL
             if (name == null && actual == null && !names.containsKey(null)) {
                 return JexlSandbox.NULL;
             }
             return actual;
         }
     }
 
     /**
      * A block set of names.
      */
     static class BlockSet extends Names {
         /** The set of controlled names. */
         private Set<String> names = null;
 
         @Override
         protected Names copy() {
             final BlockSet copy = new BlockSet();
             copy.names = names == null ? null : new HashSet<>(names);
             return copy;
         }
 
         @Override
         public boolean add(final String name) {
             if (names == null) {
                 names = new HashSet<>();
             }
             return names.add(name);
         }
 
         @Override
         public String get(final String name) {
             // if name is null and contained in set, explicit null aka NULL
             return names != null && !names.contains(name) ? name : name != null? null : NULL;
         }
     }
 
     /**
      * @deprecated since 3.2, use {@link AllowSet}
      */
     @Deprecated
     public static final class WhiteSet extends AllowSet {}
 
     /**
      * @deprecated since 3.2, use {@link BlockSet}
      */
     @Deprecated
     public static final class BlackSet extends BlockSet {}
 
     /**
      * Contains the allow or block lists for properties and methods for a given class.
      */
     public static final class Permissions {
         /** Whether these permissions are inheritable, ie can be used by derived classes. */
         private final boolean inheritable;
         /** The controlled readable properties. */
         private final Names read;
         /** The controlled  writable properties. */
         private final Names write;
         /** The controlled methods. */
         private final Names execute;
 
         /**
          * Creates a new permissions instance.
          *
          * @param inherit whether these permissions are inheritable
          * @param readFlag whether the read property list is allow or block
          * @param writeFlag whether the write property list is allow or block
          * @param executeFlag whether the method list is allow of block
          */
         Permissions(final boolean inherit, final boolean readFlag, final boolean writeFlag, final boolean executeFlag) {
             this(inherit,
                     readFlag ? new AllowSet() : new BlockSet(),
                     writeFlag ? new AllowSet() : new BlockSet(),
                     executeFlag ? new AllowSet() : new BlockSet());
         }
 
         /**
          * Creates a new permissions instance.
          *
          * @param inherit whether these permissions are inheritable
          * @param nread the read set
          * @param nwrite the write set
          * @param nexecute the method set
          */
         Permissions(final boolean inherit, final Names nread, final Names nwrite, final Names nexecute) {
             this.read = nread != null ? nread : ALLOW_NAMES;
             this.write = nwrite != null ? nwrite : ALLOW_NAMES;
             this.execute = nexecute != null ? nexecute : ALLOW_NAMES;
             this.inheritable = inherit;
         }
 
         /**
          * @return a copy of these permissions
          */
         Permissions copy() {
             return new Permissions(inheritable, read.copy(), write.copy(), execute.copy());
         }
 
         /**
          * @return whether these permissions applies to derived classes.
          */
         public boolean isInheritable() {
             return inheritable;
         }
 
         /**
          * Adds a list of readable property names to these permissions.
          *
          * @param pnames the property names
          * @return this instance of permissions
          */
         public Permissions read(final String... pnames) {
             for (final String pname : pnames) {
                 read.add(pname);
             }
             return this;
         }
 
         /**
          * Adds a list of writable property names to these permissions.
          *
          * @param pnames the property names
          * @return this instance of permissions
          */
         public Permissions write(final String... pnames) {
             for (final String pname : pnames) {
                 write.add(pname);
             }
             return this;
         }
 
         /**
          * Adds a list of executable methods names to these permissions.
          * <p>The constructor is denoted as the empty-string, all other methods by their names.</p>
          *
          * @param mnames the method names
          * @return this instance of permissions
          */
         public Permissions execute(final String... mnames) {
             for (final String mname : mnames) {
                 execute.add(mname);
             }
             return this;
         }
 
         /**
          * Gets the set of readable property names in these permissions.
          *
          * @return the set of property names
          */
         public Names read() {
             return read;
         }
 
         /**
          * Gets the set of writable property names in these permissions.
          *
          * @return the set of property names
          */
         public Names write() {
             return write;
         }
 
         /**
          * Gets the set of method names in these permissions.
          *
          * @return the set of method names
          */
         public Names execute() {
             return execute;
         }
     }
 
     /**
      * The pass-thru permissions.
      */
     private static final Permissions ALLOW_ALL = new Permissions(false, ALLOW_NAMES, ALLOW_NAMES, ALLOW_NAMES);
     /**
      * The block-all permissions.
      */
     private static final Permissions BLOCK_ALL = new Permissions(false, BLOCK_NAMES, BLOCK_NAMES, BLOCK_NAMES);
 
     /**
      * Creates the set of permissions for a given class.
      * <p>The sandbox inheritance property will apply to the permissions created by this method
      *
      * @param clazz the class for which these permissions apply
      * @param readFlag whether the readable property list is allow - true - or block - false -
      * @param writeFlag whether the writable property list is allow - true - or block - false -
      * @param executeFlag whether the executable method list is allow - true - or block - false -
      * @return the set of permissions
      */
     public Permissions permissions(final String clazz,
                                    final boolean readFlag,
                                    final boolean writeFlag,
                                    final boolean executeFlag) {
         return permissions(clazz, inherit, readFlag, writeFlag, executeFlag);
     }
 
     /**
      * Creates the set of permissions for a given class.
      *
      * @param clazz the class for which these permissions apply
      * @param inhf whether these permissions are inheritable
      * @param readf whether the readable property list is allow - true - or block - false -
      * @param writef whether the writable property list is allow - true - or block - false -
      * @param execf whether the executable method list is allow - true - or block - false -
      * @return the set of permissions
      */
     public Permissions permissions(final String clazz,
                                    final boolean inhf,
                                    final boolean readf,
                                    final boolean writef,
                                    final boolean execf) {
         final Permissions box = new Permissions(inhf, readf, writef, execf);
         sandbox.put(clazz, box);
         return box;
     }
 
     /**
      * Creates a new set of permissions based on allow lists for methods and properties for a given class.
      * <p>The sandbox inheritance property will apply to the permissions created by this method
      *
      * @param clazz the allowed class name
      * @return the permissions instance
      */
     public Permissions allow(final String clazz) {
         return permissions(clazz, true, true, true);
     }
     /**
      * Use allow() instead.
      * @param clazz the allowed class name
      * @return the permissions instance
      */
     @Deprecated
     public Permissions white(final String clazz) {
         return allow(clazz);
     }
 
     /**
      * Creates a new set of permissions based on block lists for methods and properties for a given class.
      * <p>The sandbox inheritance property will apply to the permissions created by this method
      *
      * @param clazz the blocked class name
      * @return the permissions instance
      */
     public Permissions block(final String clazz) {
         return permissions(clazz, false, false, false);
     }
 
     /**
      * Use block() instead.
      * @param clazz the allowed class name
      * @return the permissions instance
      */
     @Deprecated
     public Permissions black(final String clazz) {
         return block(clazz);
     }
 
     /**
      * Gets the set of permissions associated to a class.
      *
      * @param clazz the class name
      * @return the defined permissions or an all-allow permission instance if none were defined
      */
     public Permissions get(final String clazz) {
         if (inherit) {
             return get(forName(clazz));
         }
         final Permissions permissions = sandbox.get(clazz);
         if (permissions == null) {
             return allow ? ALLOW_ALL : BLOCK_ALL;
         }
         return permissions;
     }
 
     /**
      * Get the permissions associated to a class.
      * @param clazz the class
      * @return the permissions
      */
     @SuppressWarnings("null") // clazz can not be null since permissions would be not null and block;
     public Permissions get(final Class<?> clazz) {
         Permissions permissions = clazz == null ? BLOCK_ALL : sandbox.get(clazz.getName());
         if (permissions == null) {
             if (inherit) {
                 // find first inherited interface that defines permissions
                 for (final Class<?> inter : clazz.getInterfaces()) {
                     permissions = sandbox.get(inter.getName());
                     if (permissions != null) {
                         if (permissions.isInheritable()) {
                             break;
                         }
                         permissions = null;
                     }
                 }
                 // nothing defined yet, find first superclass that defines permissions
                 if (permissions == null) {
                     // lets walk all super classes
                     Class<?> zuper = clazz.getSuperclass();
                     // walk all superclasses
                     while (zuper != null) {
                         permissions = sandbox.get(zuper.getName());
                         if (permissions != null) {
                             if (permissions.isInheritable()) {
                                 break;
                             }
                             permissions = null;
                         }
                         zuper = zuper.getSuperclass();
                     }
                 }
                 // nothing was inheritable
                 if (permissions == null) {
                     permissions = allow ? ALLOW_ALL : BLOCK_ALL;
                 }
                 // store the info to avoid doing this costly look up
                 sandbox.put(clazz.getName(), permissions);
             } else {
                 permissions = allow ? ALLOW_ALL : BLOCK_ALL;
             }
         }
         return permissions;
     }
 
 }