/*
 *  Copyright 2008 biaoping.yin
 *
 *  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 org.frameworkset.util;

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.WildcardType;



/**
 * <p>Title: TypeUtils.java</p> 
 * <p>Description: </p>
 * <p>bboss workgroup</p>
 * <p>Copyright (c) 2008</p>
 * @Date 2010-9-24
 * @author biaoping.yin
 * @version 1.0
 */
public abstract class TypeUtils {
	/**
	 * Check if the right-hand side type may be assigned to the left-hand side
	 * type following the Java generics rules.
	 * @param lhsType the target type
	 * @param rhsType	the value type that should be assigned to the target type
	 * @return true if rhs is assignable to lhs
	 */
	public static boolean isAssignable(Type lhsType, Type rhsType) {
		Assert.notNull(lhsType, "Left-hand side type must not be null");
		Assert.notNull(rhsType, "Right-hand side type must not be null");
		if (lhsType.equals(rhsType)) {
			return true;
		}
		if (lhsType instanceof Class && rhsType instanceof Class) {
			return ClassUtils.isAssignable((Class) lhsType, (Class) rhsType);
		}
		if (lhsType instanceof ParameterizedType && rhsType instanceof ParameterizedType) {
			return isAssignable((ParameterizedType) lhsType, (ParameterizedType) rhsType);
		}
		if (lhsType instanceof WildcardType) {
			return isAssignable((WildcardType) lhsType, rhsType);
		}
		return false;
	}

	private static boolean isAssignable(ParameterizedType lhsType, ParameterizedType rhsType) {
		if (lhsType.equals(rhsType)) {
			return true;
		}
		Type[] lhsTypeArguments = lhsType.getActualTypeArguments();
		Type[] rhsTypeArguments = rhsType.getActualTypeArguments();
		if (lhsTypeArguments.length != rhsTypeArguments.length) {
			return false;
		}
		for (int size = lhsTypeArguments.length, i = 0; i < size; ++i) {
			Type lhsArg = lhsTypeArguments[i];
			Type rhsArg = rhsTypeArguments[i];
			if (!lhsArg.equals(rhsArg) &&
					!(lhsArg instanceof WildcardType && isAssignable((WildcardType) lhsArg, rhsArg))) {
				return false;
			}
		}
		return true;
	}

	private static boolean isAssignable(WildcardType lhsType, Type rhsType) {
		Type[] upperBounds = lhsType.getUpperBounds();
		Type[] lowerBounds = lhsType.getLowerBounds();
		for (int size = upperBounds.length, i = 0; i < size; ++i) {
			if (!isAssignable(upperBounds[i], rhsType)) {
				return false;
			}
		}
		for (int size = lowerBounds.length, i = 0; i < size; ++i) {
			if (!isAssignable(rhsType, lowerBounds[i])) {
				return false;
			}
		}
		return true;
	}

}
