/*
    * Copyright 2012-2013 smartics, Kronseder & Reiner GmbH
    *
    * 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.
   */
  package de.smartics.properties.utils;
  
  import java.lang.reflect.Field;
  import java.lang.reflect.Modifier;
  
  import com.thoughtworks.qdox.model.JavaClass;
  import com.thoughtworks.qdox.model.JavaField;
  
  /**
   * Utilities to instantiate classes and access their runtime information.
   */
  public final class RuntimeUtils
  {
    // ********************************* Fields *********************************
  
    // --- constants ------------------------------------------------------------
  
    // --- members --------------------------------------------------------------
  
    /**
     * The class loader to use to instantiate the referenced class.
     */
    private final ClassLoader classLoader;
  
    // ****************************** Initializer *******************************
  
    // ****************************** Constructors ******************************
  
    /**
     * Default constructor.
     *
     * @param classLoader the class loader to use to instantiate the referenced
     *          class.
     */
    public RuntimeUtils(final ClassLoader classLoader)
    {
      this.classLoader = classLoader;
    }
  
    // ****************************** Inner Classes *****************************
  
    // ********************************* Methods ********************************
  
    // --- init -----------------------------------------------------------------
  
    // --- get&set --------------------------------------------------------------
  
    // --- business -------------------------------------------------------------
  
    /**
     * Loads the instance referenced by the given {@code fieldDoc}.
     *
     * @param fieldDoc the property of a class to be instantiated. This may be an
     *          enumeration element or a constant in a class.
     * @return the instance if {@code fieldDoc} references an enumeration element
     *         or a constant, <code>null</code> otherwise.
     * @throws ClassNotFoundException if the class of the field or any depending
     *           classes cannot be loaded.
     * @throws NullPointerException if {@code fieldDoc} is <code>null</code>.
     */
    public Object loadInstance(final JavaField fieldDoc)
      throws ClassNotFoundException, NullPointerException
    {
      final JavaClass classDoc = fieldDoc.getDeclaringClass();
      final String className = classDoc.getFullyQualifiedName();
      final Class<?> clazz = Class.forName(className, true, classLoader);
      final String fieldName = fieldDoc.getName();
      if (classDoc.isEnum())
      {
        return loadEnumInstance(clazz, fieldName);
      }
      else
      {
        return loadStaticFieldInstance(clazz, fieldName);
      }
    }
  
    /**
     * Loads the class referenced by the given {@code classDoc}.
     *
     * @param classDoc the class documentation to load the class.
     * @return the class instance.
     * @throws NullPointerException if {@code classDoc} is <code>null</code>.
     * @throws ClassNotFoundException if the class of the field or any depending
    *           classes cannot be loaded.
    */
   public Class<?> loadClass(final JavaClass classDoc)
     throws ClassNotFoundException, NullPointerException
   {
     final String className = classDoc.getFullyQualifiedName();
     final Class<?> clazz = Class.forName(className, true, classLoader);
     return clazz;
   }
 
   /**
    * Loads the enumeration element instance with the given identifier from the
    * given class.
    *
    * @param clazz the enumeration class that contains the requested enumeration
    *          element.
    * @param identifier the identifier of the enumeration element to return.
    * @return the enumeration element instance or <code>null</code> if the class
    *         is not an enumeration or the enumeration does not contain an
    *         element with a name matching the given identifier.
    * @throws NullPointerException if <code>clazz</code> or
    *           <code>identifier</code> is <code>null</code>.
    */
   public static Enum<?> loadEnumInstance(final Class<?> clazz,
       final String identifier) throws NullPointerException
   {
     final Enum<?>[] elements = (Enum[]) clazz.getEnumConstants();
     if (elements != null)
     {
       for (Enum<?> element : elements)
       {
         final String elementName = ((Enum<?>) element).name();
         if (identifier.equals(elementName))
         {
           return element;
         }
       }
     }
 
     return null;
   }
 
   /**
    * Loads the static property instance with the given identifier from the given
    * class.
    *
    * @param clazz the class that contains the requested static property.
    * @param identifier the identifier of the static property to return.
    * @return the static property instance or <code>null</code> if the class does
    *         not contain a static property with a name matching the given
    *         identifier.
    * @throws NullPointerException if <code>clazz</code> or
    *           <code>identifier</code> is <code>null</code>.
    */
   public static Object loadStaticFieldInstance(final Class<?> clazz,
       final String identifier) throws NullPointerException
   {
     try
     {
       final Field field = clazz.getDeclaredField(identifier);
       field.setAccessible(true);
       final int modifiers = field.getModifiers();
       if (Modifier.isStatic(modifiers))
       {
         return field.get(null);
       }
     }
     catch (final Exception e)
     {
       // return null at the end.
     }
     return null;
   }
 
   // --- object basics --------------------------------------------------------
 
 }