/*
 * 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.clerezza.platform.scripting;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import javax.script.Bindings;
import javax.script.ScriptContext;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineFactory;
import javax.script.ScriptException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.clerezza.platform.content.DiscobitsHandler;
import org.apache.clerezza.platform.graphprovider.content.ContentGraphProvider;
import org.apache.clerezza.rdf.core.LiteralFactory;
import org.apache.clerezza.rdf.core.MGraph;
import org.apache.clerezza.rdf.core.NonLiteral;
import org.apache.clerezza.rdf.core.Resource;
import org.apache.clerezza.rdf.core.TypedLiteral;
import org.apache.clerezza.rdf.core.UriRef;
import org.apache.clerezza.rdf.core.access.TcManager;
import org.apache.clerezza.rdf.core.serializedform.Parser;
import org.apache.clerezza.rdf.ontologies.SCRIPT;
import org.apache.clerezza.rdf.utils.GraphNode;

/**
 * This class executes scripts, binds {@code ScriptEngineFactory}ies
 * of installed {@code ScriptEngine}s.
 *
 * It provides a facade to the installed {@code ScriptEngine}s
 * that implement {@code javax.script.ScriptEngine}.
 *
 * The services {@code ContentGraphProvider}, {@code DiscobitsHandler}, and
 * {@code TcManager} are provided to the ScriptEngine's eval method through
 * the parameter {@code Bindings}. In a script, they are accessible under the
 * names contentGraphProvider, contentHandler, and tcManager respectively.
 *
 * @scr.component
 * @scr.service
 *        interface="org.apache.clerezza.platform.scripting.ScriptExecution"
 * @scr.reference name="scriptEngineFactory" cardinality="0..n"
 *        interface="javax.script.ScriptEngineFactory"
 *
 * @author hasan, daniel
 *
 * @see javax.script.ScriptEngineManager
 * @see javax.script.ScriptEngine
 */
public class ScriptExecution {

    /**
     * @scr.reference
     */
    private ContentGraphProvider cgProvider;
    
    /**
     * @scr.reference
     */
    private DiscobitsHandler contentHandler;

    /**
     * @scr.reference
     */
    private TcManager tcManager;
    
    /**
     * @scr.reference
     */
    private Parser parser;

    private Map<ScriptLanguageDescription, List<ScriptEngineFactory>>
            languageToFactoryMap =
            new HashMap<ScriptLanguageDescription, List<ScriptEngineFactory>>();

    private static final Logger logger = LoggerFactory.getLogger(ScriptExecution.class);

    /**
     * @see #execute(org.apache.clerezza.rdf.core.NonLiteral, javax.script.Bindings)
     */
    public Object execute(NonLiteral scriptResource)
            throws ScriptException, NoEngineException {
        return execute(scriptResource, null);
    }

    /**
     * Executes the specified {@code scriptResource}.
     *
     * The output is either a GraphNode or a response with
     * the media type specified by the producedType property
     * of the associated script.
     *
     * GraphNodes can be rendered by Renderlets registered for the type
     * of the GraphNode.
     *
     * @param scriptResource
     *                The resource (URI).
     * @param bindings
     *                Name/Value pairs of Java {@code Object}s made accessible
     *                to script
     * @return
     *                The value returned from the execution of the script.
     *                Either a GraphNode or a Response.
     * @throws ScriptException
     *                If an error occurrs in the script.
     * @throws NoEngineException
     *                If no engine can be found
     *
     * @see org.apache.clerezza.rdf.ontologies.SCRIPT#Script
     * @see org.apache.clerezza.rdf.ontologies.SCRIPT#producedType
     * @see org.apache.clerezza.platform.typerendering.Renderlet
     */
    public Object execute(NonLiteral scriptResource, Bindings bindings)
            throws ScriptException, NoEngineException {

        MGraph contentGraph = cgProvider.getContentGraph();

        String scriptString = null;
        String scriptLanguage = null;
        String scriptLanguageVersion = null;
        String scriptProducedType = "text/plain";

        GraphNode scriptNode = new GraphNode(scriptResource, contentGraph);
        Iterator<Resource> it = scriptNode.getObjects(SCRIPT.scriptLanguage);
        scriptLanguage = LiteralFactory.getInstance().createObject(
                        String.class, (TypedLiteral) it.next());

        it = scriptNode.getObjects(SCRIPT.scriptLanguageVersion);
        scriptLanguageVersion = LiteralFactory.getInstance().createObject(
                        String.class, (TypedLiteral) it.next());

        it = scriptNode.getObjects(SCRIPT.producedType);
        if(it.hasNext()) {
            scriptProducedType = LiteralFactory.getInstance().createObject(
                            String.class, (TypedLiteral) it.next());
        }

        scriptString = new String(
                contentHandler.getData((UriRef) scriptResource));

        Object result = execute(
                scriptString, bindings, scriptLanguage, scriptLanguageVersion);
        if (result instanceof GraphNode) {
            return result;
        }
        return Response.ok(result, MediaType.valueOf(scriptProducedType)).build();
    }

    /**
     * Executes the specified {@code script} with the {@code ScriptEngine}
     * that is registered for {@code language} and {@code languageVersion}.
     * <p>
     *    The default {@link ScriptContext} for the {@link ScriptEngine} is used.
     *  It uses {@code bindings} as the {@link ScriptContext#ENGINE_SCOPE}
     *    Bindings of the ScriptEngine during the script execution.
     *  Three new attributes are added to the bindings: contentGraphProvider,
     *  contentHandler, and tcManager.
     *    The Reader, Writer and non-ENGINE_SCOPE Bindings of the default
     *    ScriptContext are used. The ENGINE_SCOPE Bindings of the ScriptEngine
     *    is not changed, and its mappings are unaltered by the script execution.
     * </p>
     *
     * @param script
     *                The script language source to be executed.
     * @param bindings
     *                 The Bindings of attributes to be used for script execution.
     * @param language
     *                The script language.
     *                It is used to determine the ScriptEngine.
     * @param languageVersion
     *                The version of the script language.
     *                It is used to determine the ScriptEngine.
     * @return
     *                The value returned from the execution of {@code script}.
     * @throws ScriptException
     *                If an error occurrs in the script.
     * @throws NoEngineException
     *                If no engine can be found for the specified language
     *
     * @see javax.script.ScriptEngine#eval(java.lang.String, javax.script.Bindings)
     */
    public Object execute(String script, Bindings bindings,
            String language, String languageVersion)
            throws ScriptException, NoEngineException {
        ScriptEngine engine = getScriptEngine(language, languageVersion);
        if (engine == null) {
            logger.warn("Cannot execute script: " +
                    "No engine available for language {}({})",
                    language, languageVersion);
            throw new NoEngineException(new ScriptLanguageDescription(language,
                    languageVersion));
        }
        if (bindings == null) {
            bindings = engine.createBindings();
        }
        addBindings(bindings);
        return engine.eval(script, bindings);
    }

    private void addBindings(Bindings bindings) {
        bindings.put("contentGraphProvider", cgProvider);
        bindings.put("contentHandler", contentHandler);
        bindings.put("tcManager", tcManager);
        bindings.put("parser", parser);
    }

    private ScriptEngine getScriptEngine(String language, String languageVersion) {
        List<ScriptEngineFactory> factoryList = null;

        try {
            factoryList = languageToFactoryMap.get(
                    new ScriptLanguageDescription(language, languageVersion));
        } catch (IllegalArgumentException ex) {
            return null;
        }

        if (factoryList == null || factoryList.isEmpty()) {
            return null;
        }
        return factoryList.get(factoryList.size() - 1).getScriptEngine();
    }

    /**
     * Returns all installed script language descriptions.
     *
     * @return
     *                All script language descriptions
     *                of the currently installed script engines.
     *
     * @see ScriptLanguageDescription
     */
    public Iterator<ScriptLanguageDescription> getInstalledScriptLanguages() {
        return languageToFactoryMap.keySet().iterator();
    }

    /**
     * Binds a ScriptEngineFactory.
     * If script engine factories for the same language and/or language version
     * already exist, they are shadowed.
     *
     * @param factory
     *        the script engine factory to bind
     */
    protected void bindScriptEngineFactory(ScriptEngineFactory factory) {
        String language = factory.getLanguageName();
        String languageVersion = factory.getLanguageVersion();

        addScriptEngineFactory(
                new ScriptLanguageDescription(language, languageVersion),
                factory);
    }

    private void addScriptEngineFactory(ScriptLanguageDescription language, 
            ScriptEngineFactory factory) {

        List<ScriptEngineFactory> factoryList = languageToFactoryMap.get(language);
        if (factoryList == null) {
            factoryList = new ArrayList<ScriptEngineFactory>();
        } else {
            if (factoryList.contains(factory)) {
                return;
            }
        }
        factoryList.add(factory);
        languageToFactoryMap.put(language, factoryList);
    }

    /**
     * Unbinds a ScriptEngineFactory.
     *
     * @param factory
     *        the script engine factory to unbind
     */
    protected void unbindScriptEngineFactory(ScriptEngineFactory factory) {
        String language = factory.getLanguageName();
        String languageVersion = factory.getLanguageVersion();

        removeScriptEngineFactory(
                new ScriptLanguageDescription(language, languageVersion),
                factory);
    }

    private void removeScriptEngineFactory(ScriptLanguageDescription language, 
            ScriptEngineFactory factory) {

        List<ScriptEngineFactory> factoryList = languageToFactoryMap.get(language);
        if (factoryList != null) {
            factoryList.remove(factory);
            if (factoryList.isEmpty()) {
                languageToFactoryMap.remove(language);
            }
        }
    }
}