/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.click.service;

import java.io.IOException;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import javax.servlet.ServletContext;

import org.apache.click.util.ClassLoaderCache;
import org.apache.click.util.PropertyUtils;
import org.mvel2.MVEL;

/**
 * Provides an MVEL based property services.
 */
public class MVELPropertyService implements PropertyService {

    // Expression cache with support for multiple classloader caching
    private static final ClassLoaderCache<Map<String, Serializable>>
        EXPRESSION_CL_CACHE = new ClassLoaderCache<Map<String, Serializable>>();

    // Public Methods --------------------------------------------------------

    /**
     * @see PropertyService#onInit(ServletContext)
     *
     * @param servletContext the application servlet context
     * @throws IOException if an IO error occurs initializing the service
     */
    public void onInit(ServletContext servletContext) throws IOException {
    }

    /**
     * @see PropertyService#onDestroy()
     */
    public void onDestroy() {
    }

    /**
     * @see PropertyService#getValue(Object, String)
     *
     * @param source the source object
     * @param name the name of the property
     * @return the property value for the given source object and property name
     */
    public Object getValue(Object source, String name) {
        return PropertyUtils.getValue(source, name);
    }

    /**
     * @see PropertyService#getValue(Object, String, Map)
     *
     * @param source the source object
     * @param name the name of the property
     * @param cache the cache of reflected property Method objects, do NOT modify
     * this cache
     * @return the property value for the given source object and property name
     */
    public Object getValue(Object source, String name, Map<?, ?> cache) {
        return PropertyUtils.getValue(source, name, cache);
    }

    /**
     * Set the named property value on the target object using the MVEL library.
     *
     * @see PropertyService#setValue(Object, String, Object)
     *
     * @param target the target object to set the property of
     * @param name the name of the property to set
     * @param value the property value to set
     */
    public void setValue(Object target, String name, Object value) {

        String expression = target.getClass().getSimpleName() + "." + name + " = value";

        Serializable compiledExpression = getExpressionCache().get(expression);

        if (compiledExpression == null) {
            compiledExpression = MVEL.compileExpression(expression);
            getExpressionCache().put(expression, compiledExpression);
        }

        Map<String, Object> vars = new HashMap<String, Object>();
        vars.put(target.getClass().getSimpleName(), target);
        vars.put("value", value);

        MVEL.executeExpression(compiledExpression, vars);
    }

    // Private Methods --------------------------------------------------------

    private static Map<String, Serializable> getExpressionCache() {
        Map<String, Serializable> expressionCache = EXPRESSION_CL_CACHE.get();
        if (expressionCache == null) {
            expressionCache = new ConcurrentHashMap<String, Serializable>();
            EXPRESSION_CL_CACHE.put(expressionCache);
        }

        return expressionCache;
    }

}