/*
 * Copyright 2013 Red Hat, Inc. and/or its affiliates.
 *
 * 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.jbpm.process.core.impl;

import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import javax.script.ScriptEngineFactory;
import javax.script.ScriptEngineManager;

import org.jbpm.process.core.transformation.JavaScriptingDataTransformer;
import org.jbpm.process.core.transformation.MVELDataTransformer;
import org.kie.api.runtime.process.DataTransformer;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Registry for all available on runtime <code>DataTransformer</code>s for performing
 * data input and output transformation. Be default it discovers and registers all 
 * available JSR 223 compliant scripting languages wrapped with 
 * <code>JavaScriptingDataTransformer</code>.<br/>
 * Discovery is based on <code>ScriptEngineManager.getEngineFactories()</code> thus
 * any scripting engines should follow instructions for Java Scripting.<br/>
 * Each Java Scripting engine will get dedicated instance of <code>JavaScriptingDataTransformer</code>
 * which will be registered under one or more key in the registry. The key will be built as follows>
 * <ul>
 * 	<li>constant prefix for URI like syntax : http://www.java.com/</li>
 * 	<li>names provided by given ScriptEngineFactory - JavaScript, js,....</li>
 * </ul>
 * For example default JavaScript scripting engine will be registered under following keys:
 * <ul>
 * 	<li>http://www.java.com/js</li>
 * 	<li>http://www.java.com/rhino</li>
 * 	<li>http://www.java.com/JavaScript</li>
 * 	<li>http://www.java.com/javascript</li>
 * 	<li>http://www.java.com/ECMAScript</li>
 * 	<li>http://www.java.com/ecmascript</li>
 * </ul>
 * when defining the language for transformation that of data input/output the complete key should be provided.
 * <code>
 * 	   <dataInputAssociation><br/>
 *        <sourceRef>s</sourceRef><br/>        
 *        <targetRef>_2_param</targetRef><br/>
 *        <transformation language="http://www.java.com/javascript">s.toUpperCase()</transformation><br/>
 *     </dataInputAssociation><br/>
 * </code>
 * <br/>
 * Besides JSR 223 scripting engine, there is MVEL based transformer available out of the box that is registered under
 * <code>http://www.mvel.org/2.0</code> key.
 * <br/>
 * Custom implementations can be provided and if they are compliant with JSR 223 then follows above registration approach
 * otherwise they need to be registered manually with <code>register</code> method. 
 * @see JavaScriptingDataTransformer
 */
public class DataTransformerRegistry {

	private static final Logger logger = LoggerFactory.getLogger(DataTransformerRegistry.class);
	private static final DataTransformerRegistry INSTANCE = new DataTransformerRegistry();

    private Map<String, DataTransformer> registry;
    
    protected DataTransformerRegistry() {
        this.registry = new ConcurrentHashMap<String, DataTransformer>();
        this.registry.put("http://www.mvel.org/2.0", new MVELDataTransformer());
        ScriptEngineManager manager = new ScriptEngineManager();
        List<ScriptEngineFactory> factories = manager.getEngineFactories();
        for (ScriptEngineFactory factory : factories) {
        	DataTransformer transformer = new JavaScriptingDataTransformer(factory);
        	
        	for (String name : factory.getNames()) {
        		String key = "http://www.java.com/"+name;
        		registry.put(key, transformer);
        		logger.debug("Registered scripting language {} with instance {}", key, transformer);
        	}
        }
    }
    
    public static DataTransformerRegistry get() {
    	return INSTANCE;
    }
    
    public synchronized void register(String language, DataTransformer transformer) {
    	this.registry.put(language, transformer);
    	logger.debug("Manual registration of scripting language {} with instance {}", language, transformer);
    }
    
    public DataTransformer find(String languge) {
    	return this.registry.get(languge);
    }
}