/*
 * Created on Nov 25, 2005
 *
 * 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.
 *
 * Copyright @2005 the original author or authors.
 */
package org.springmodules.cache.util;

import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.lang.reflect.Method;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;

import org.springframework.util.ReflectionUtils;

import org.springmodules.util.Objects;

/**
 * <p>
 * Reflection-related utility methods.
 * </p>
 *
 * @author Omar Irbouh
 * @author Alex Ruiz
 */
public abstract class Reflections {

  private static final int INITIAL_HASH = 7;

  private static final int MULTIPLIER = 31;

  /**
   * <p>
   * This method uses reflection to build a valid hash code.
   * </p>
   *
   * <p>
   * It uses <code>AccessibleObject.setAccessible</code> to gain access to
   * private fields. This means that it will throw a security exception if run
   * under a security manager, if the permissions are not set up correctly. It
   * is also not as efficient as testing explicitly.
   * </p>
   *
   * <p>
   * Transient members will not be used, as they are likely derived fields,
   * and not part of the value of the <code>Object</code>.
   * </p>
   *
   * <p>
   * Static fields will not be tested. Superclass fields will be included.
   * </p>
   *
   * @param obj
   *          the object to create a <code>hashCode</code> for
   * @return the generated hash code, or zero if the given object is
   *         <code>null</code>
   */
  public static int reflectionHashCode(Object obj) {
    if (obj == null)
      return 0;

    Class targetClass = obj.getClass();
    if (Objects.isArrayOfPrimitives(obj)
        || Objects.isPrimitiveOrWrapper(targetClass)) {
      return Objects.nullSafeHashCode(obj);
    }

    if (targetClass.isArray()) {
      return reflectionHashCode((Object[]) obj);
    }

    if (obj instanceof Collection) {
      return reflectionHashCode((Collection) obj);
    }

    if (obj instanceof Map) {
      return reflectionHashCode((Map) obj);
    }

		// determine whether the object's class declares hashCode() or has a
		// superClass other than java.lang.Object that declares hashCode()
		Class clazz = (obj instanceof Class)? (Class) obj : obj.getClass();
		Method hashCodeMethod = ReflectionUtils.findMethod(clazz,
				"hashCode", new Class[0]);

		if (hashCodeMethod != null) {
			return obj.hashCode();
		}

		// could not find a hashCode other than the one declared by java.lang.Object
		int hash = INITIAL_HASH;

    try {
      while (targetClass != null) {
        Field[] fields = targetClass.getDeclaredFields();
        AccessibleObject.setAccessible(fields, true);

        for (int i = 0; i < fields.length; i++) {
          Field field = fields[i];
          int modifiers = field.getModifiers();

          if (!Modifier.isStatic(modifiers) && !Modifier.isTransient(modifiers)) {
            hash = MULTIPLIER * hash + reflectionHashCode(field.get(obj));
          }
        }
        targetClass = targetClass.getSuperclass();
      }
    } catch (IllegalAccessException exception) {
      // ///CLOVER:OFF
      ReflectionUtils.handleReflectionException(exception);
      // ///CLOVER:ON
    }

    return hash;
  }

  private static int reflectionHashCode(Collection collection) {
    int hash = INITIAL_HASH;

    for (Iterator i = collection.iterator(); i.hasNext();) {
      hash = MULTIPLIER * hash + reflectionHashCode(i.next());
    }

    return hash;
  }

  private static int reflectionHashCode(Map map) {
    int hash = INITIAL_HASH;

    for (Iterator i = map.entrySet().iterator(); i.hasNext();) {
      Map.Entry entry = (Map.Entry) i.next();
      hash = MULTIPLIER * hash + reflectionHashCode(entry);
    }

    return hash;
  }

  private static int reflectionHashCode(Map.Entry entry) {
    int hash = INITIAL_HASH;
    hash = MULTIPLIER * hash + reflectionHashCode(entry.getKey());
    hash = MULTIPLIER * hash + reflectionHashCode(entry.getValue());
    return hash;
  }

  private static int reflectionHashCode(Object[] array) {
    int hash = INITIAL_HASH;
    int arraySize = array.length;
    for (int i = 0; i < arraySize; i++) {
      hash = MULTIPLIER * hash + reflectionHashCode(array[i]);
    }

    return hash;
  }
}