package org.codehaus.plexus.util.introspection;
   
   /*
    * Copyright The Codehaus Foundation.
    *
    * 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.
   */
  
  import java.lang.ref.WeakReference;
  import java.lang.reflect.Array;
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.util.List;
  import java.util.Map;
  import java.util.WeakHashMap;
  
  import org.codehaus.plexus.util.StringUtils;
  
  /**
   * <p>
   * Using simple dotted expressions to extract the values from an Object instance, For example we might want to extract a
   * value like: <code>project.build.sourceDirectory</code>
   * </p>
   * <p>
   * The implementation supports indexed, nested and mapped properties similar to the JSP way.
   * </p>
   * 
   * @author <a href="mailto:jason@maven.org">Jason van Zyl </a>
   * @author <a href="mailto:vincent.siveton@gmail.com">Vincent Siveton</a>
   *
   * @see <a href=
   *      "http://struts.apache.org/1.x/struts-taglib/indexedprops.html">http://struts.apache.org/1.x/struts-taglib/indexedprops.html</a>
   */
  public class ReflectionValueExtractor
  {
      private static final Class<?>[] CLASS_ARGS = new Class[0];
  
      private static final Object[] OBJECT_ARGS = new Object[0];
  
      /**
       * Use a WeakHashMap here, so the keys (Class objects) can be garbage collected. This approach prevents permgen
       * space overflows due to retention of discarded classloaders.
       */
      private static final Map<Class<?>, WeakReference<ClassMap>> classMaps =
          new WeakHashMap<Class<?>, WeakReference<ClassMap>>();
  
      static final int EOF = -1;
  
      static final char PROPERTY_START = '.';
  
      static final char INDEXED_START = '[';
  
      static final char INDEXED_END = ']';
  
      static final char MAPPED_START = '(';
  
      static final char MAPPED_END = ')';
  
      static class Tokenizer
      {
          final String expression;
  
          int idx;
  
          public Tokenizer( String expression )
          {
              this.expression = expression;
          }
  
          public int peekChar()
          {
              return idx < expression.length() ? expression.charAt( idx ) : EOF;
          }
  
          public int skipChar()
          {
              return idx < expression.length() ? expression.charAt( idx++ ) : EOF;
          }
  
          public String nextToken( char delimiter )
          {
              int start = idx;
  
              while ( idx < expression.length() && delimiter != expression.charAt( idx ) )
              {
                  idx++;
              }
  
              // delimiter MUST be present
             if ( idx <= start || idx >= expression.length() )
             {
                 return null;
             }
 
             return expression.substring( start, idx++ );
         }
 
         public String nextPropertyName()
         {
             final int start = idx;
 
             while ( idx < expression.length() && Character.isJavaIdentifierPart( expression.charAt( idx ) ) )
             {
                 idx++;
             }
 
             // property name does not require delimiter
             if ( idx <= start || idx > expression.length() )
             {
                 return null;
             }
 
             return expression.substring( start, idx );
         }
 
         public int getPosition()
         {
             return idx < expression.length() ? idx : EOF;
         }
 
         // to make tokenizer look pretty in debugger
         @Override
         public String toString()
         {
             return idx < expression.length() ? expression.substring( idx ) : "<EOF>";
         }
     }
 
     private ReflectionValueExtractor()
     {
     }
 
     /**
      * <p>The implementation supports indexed, nested and mapped properties.</p>
      * 
      * <ul>
      * <li>nested properties should be defined by a dot, i.e. "user.address.street"</li>
      * <li>indexed properties (java.util.List or array instance) should be contains <code>(\\w+)\\[(\\d+)\\]</code>
      * pattern, i.e. "user.addresses[1].street"</li>
      * <li>mapped properties should be contains <code>(\\w+)\\((.+)\\)</code> pattern, i.e.
      * "user.addresses(myAddress).street"</li>
      * </ul>
      * 
      * @param expression not null expression
      * @param root not null object
      * @return the object defined by the expression
      * @throws Exception if any
      */
     public static Object evaluate( String expression, Object root )
         throws Exception
     {
         return evaluate( expression, root, true );
     }
 
     /**
      * <p>The implementation supports indexed, nested and mapped properties.</p>
      * 
      * <ul>
      * <li>nested properties should be defined by a dot, i.e. "user.address.street"</li>
      * <li>indexed properties (java.util.List or array instance) should be contains <code>(\\w+)\\[(\\d+)\\]</code>
      * pattern, i.e. "user.addresses[1].street"</li>
      * <li>mapped properties should be contains <code>(\\w+)\\((.+)\\)</code> pattern, i.e.
      * "user.addresses(myAddress).street"</li>
      * </ul>
      * 
      * @param expression not null expression
      * @param root not null object
      * @param trimRootToken  root start
      * @return the object defined by the expression
      * @throws Exception if any
      */
     // TODO: don't throw Exception
     public static Object evaluate( String expression, final Object root, final boolean trimRootToken )
         throws Exception
     {
         Object value = root;
 
         // ----------------------------------------------------------------------
         // Walk the dots and retrieve the ultimate value desired from the
         // MavenProject instance.
         // ----------------------------------------------------------------------
 
         if ( StringUtils.isEmpty( expression ) || !Character.isJavaIdentifierStart( expression.charAt( 0 ) ) )
         {
             return null;
         }
 
         boolean hasDots = expression.indexOf( PROPERTY_START ) >= 0;
 
         final Tokenizer tokenizer;
         if ( trimRootToken && hasDots )
         {
             tokenizer = new Tokenizer( expression );
             tokenizer.nextPropertyName();
             if ( tokenizer.getPosition() == EOF )
             {
                 return null;
             }
         }
         else
         {
             tokenizer = new Tokenizer( "." + expression );
         }
 
         int propertyPosition = tokenizer.getPosition();
         while ( value != null && tokenizer.peekChar() != EOF )
         {
             switch ( tokenizer.skipChar() )
             {
                 case INDEXED_START:
                     value = getIndexedValue( expression, propertyPosition, tokenizer.getPosition(), value,
                                              tokenizer.nextToken( INDEXED_END ) );
                     break;
                 case MAPPED_START:
                     value = getMappedValue( expression, propertyPosition, tokenizer.getPosition(), value,
                                             tokenizer.nextToken( MAPPED_END ) );
                     break;
                 case PROPERTY_START:
                     propertyPosition = tokenizer.getPosition();
                     value = getPropertyValue( value, tokenizer.nextPropertyName() );
                     break;
                 default:
                     // could not parse expression
                     return null;
             }
         }
 
         return value;
     }
 
     private static Object getMappedValue( final String expression, final int from, final int to, final Object value,
                                           final String key )
         throws Exception
     {
         if ( value == null || key == null )
         {
             return null;
         }
 
         if ( value instanceof Map )
         {
             Object[] localParams = new Object[] { key };
             ClassMap classMap = getClassMap( value.getClass() );
             Method method = classMap.findMethod( "get", localParams );
             return method.invoke( value, localParams );
         }
 
         final String message =
             String.format( "The token '%s' at position '%d' refers to a java.util.Map, but the value seems is an instance of '%s'",
                            expression.subSequence( from, to ), from, value.getClass() );
 
         throw new Exception( message );
     }
 
     private static Object getIndexedValue( final String expression, final int from, final int to, final Object value,
                                            final String indexStr )
         throws Exception
     {
         try
         {
             int index = Integer.parseInt( indexStr );
 
             if ( value.getClass().isArray() )
             {
                 return Array.get( value, index );
             }
 
             if ( value instanceof List )
             {
                 ClassMap classMap = getClassMap( value.getClass() );
                 // use get method on List interface
                 Object[] localParams = new Object[] { index };
                 Method method = classMap.findMethod( "get", localParams );
                 return method.invoke( value, localParams );
             }
         }
         catch ( NumberFormatException e )
         {
             return null;
         }
         catch ( InvocationTargetException e )
         {
             // catch array index issues gracefully, otherwise release
             if ( e.getCause() instanceof IndexOutOfBoundsException )
             {
                 return null;
             }
 
             throw e;
         }
 
         final String message =
             String.format( "The token '%s' at position '%d' refers to a java.util.List or an array, but the value seems is an instance of '%s'",
                            expression.subSequence( from, to ), from, value.getClass() );
 
         throw new Exception( message );
     }
 
     private static Object getPropertyValue( Object value, String property )
         throws Exception
     {
         if ( value == null || property == null )
         {
             return null;
         }
 
         ClassMap classMap = getClassMap( value.getClass() );
         String methodBase = StringUtils.capitalizeFirstLetter( property );
         String methodName = "get" + methodBase;
         Method method = classMap.findMethod( methodName, CLASS_ARGS );
 
         if ( method == null )
         {
             // perhaps this is a boolean property??
             methodName = "is" + methodBase;
 
             method = classMap.findMethod( methodName, CLASS_ARGS );
         }
 
         if ( method == null )
         {
             return null;
         }
 
         try
         {
             return method.invoke( value, OBJECT_ARGS );
         }
         catch ( InvocationTargetException e )
         {
             throw e;
         }
     }
 
     private static ClassMap getClassMap( Class<?> clazz )
     {
 
         WeakReference<ClassMap> softRef = classMaps.get( clazz );
 
         ClassMap classMap;
 
         if ( softRef == null || ( classMap = softRef.get() ) == null )
         {
             classMap = new ClassMap( clazz );
 
             classMaps.put( clazz, new WeakReference<ClassMap>( classMap ) );
         }
 
         return classMap;
     }
 }