/*
 * Copyright 2004-2012 the original author or authors.
 *
 * 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.springframework.binding.expression.el;

import java.util.List;

import javax.el.ArrayELResolver;
import javax.el.BeanELResolver;
import javax.el.CompositeELResolver;
import javax.el.ELContext;
import javax.el.ELResolver;
import javax.el.ListELResolver;
import javax.el.MapELResolver;
import javax.el.ResourceBundleELResolver;

/**
 * A generic ELResolver to be used as a default when no other ELResolvers have been configured by the client
 * application.
 * 
 * This implementation will resolve the first part of the expression to the pre-configured base object, and will then
 * delegate through the chain of standard resolvers for the rest of the expression.
 * 
 * Note - Requires Java 5 or higher due to the use of generics in the API's basic resolvers.
 * 
 * @author Jeremy Grelle
 */
public class DefaultELResolver extends CompositeELResolver {

	private Object target;

	/**
	 * Creates a new default EL resolver for resolving properties of the root object. Assumes a null target and expect
	 * that the base object has already been resolved by the time this resolver runs.
	 * @param customResolvers the custom resolvers to apply before this resolver
	 */
	public DefaultELResolver(List<? extends ELResolver> customResolvers) {
		this(null, customResolvers);
	}

	/**
	 * Creates a new default EL resolver for resolving properties of the root object.
	 * @param target the target, or "root", object of the expression
	 * @param customResolvers the custom resolvers to apply before this resolver
	 */
	public DefaultELResolver(Object target, List<? extends ELResolver> customResolvers) {
		this.target = target;
		configureResolvers(customResolvers);
	}

	public Object getTarget() {
		return target;
	}

	public Class<?> getType(ELContext context, Object base, Object property) {
		if (base == null) {
			return super.getType(context, target, property);
		} else {
			return super.getType(context, base, property);
		}
	}

	public Object getValue(ELContext context, Object base, Object property) {
		if (base == null) {
			return super.getValue(context, target, property);
		} else {
			return super.getValue(context, base, property);
		}
	}

	public void setValue(ELContext context, Object base, Object property, Object val) {
		if (base == null) {
			super.setValue(context, target, property, val);
		} else {
			super.setValue(context, base, property, val);
		}
	}

	private void configureResolvers(List<? extends ELResolver> customResolvers) {
		if (customResolvers != null) {
			for (ELResolver resolver : customResolvers) {
				add(resolver);
			}
		}
		add(new MapAdaptableELResolver());
		add(new ArrayELResolver());
		add(new ListELResolver());
		add(new MapELResolver());
		add(new ResourceBundleELResolver());
		add(new BeanELResolver());
	}

}