/*

 * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package javax.script;

import java.util.*;

import java.security.*;

import java.util.ServiceLoader;

import java.util.ServiceConfigurationError;

/**

 * The <code>ScriptEngineManager</code> implements a discovery and instantiation

 * mechanism for <code>ScriptEngine</code> classes and also maintains a

 * collection of key/value pairs storing state shared by all engines created

 * by the Manager. This class uses the service provider mechanism described in the

 * {@link java.util.ServiceLoader} class to enumerate all the

 * implementations of <code>ScriptEngineFactory</code>. <br><br>

 * The <code>ScriptEngineManager</code> provides a method to return a list of all these factories

 * as well as utility methods which look up factories on the basis of language name, file extension

 * and mime type.

 * <p>

 * The <code>Bindings</code> of key/value pairs, referred to as the "Global Scope"  maintained

 * by the manager is available to all instances of <code>ScriptEngine</code> created

 * by the <code>ScriptEngineManager</code>.  The values in the <code>Bindings</code> are

 * generally exposed in all scripts.

 *

 * @author Mike Grogan

 * @author A. Sundararajan

 * @since 1.6

 */

public class ScriptEngineManager  {

    private static final boolean DEBUG = false;

    /**

     * The effect of calling this constructor is the same as calling

     * <code>ScriptEngineManager(Thread.currentThread().getContextClassLoader())</code>.

     *

     * @see java.lang.Thread#getContextClassLoader

     */

    public ScriptEngineManager() {

        ClassLoader ctxtLoader = Thread.currentThread().getContextClassLoader();

        init(ctxtLoader);

    }

    /**

     * This constructor loads the implementations of

     * <code>ScriptEngineFactory</code> visible to the given

     * <code>ClassLoader</code> using the service provider mechanism.<br><br>

     * If loader is <code>null</code>, the script engine factories that are

     * bundled with the platform are loaded. <br>

     *

     * @param loader ClassLoader used to discover script engine factories.

     */

    public ScriptEngineManager(ClassLoader loader) {

        init(loader);

    }

    private void init(final ClassLoader loader) {

        globalScope = new SimpleBindings();

        engineSpis = new TreeSet<ScriptEngineFactory>(Comparator.comparing(

            ScriptEngineFactory::getEngineName,

            Comparator.nullsLast(Comparator.naturalOrder()))

        );

        nameAssociations = new HashMap<String, ScriptEngineFactory>();

        extensionAssociations = new HashMap<String, ScriptEngineFactory>();

        mimeTypeAssociations = new HashMap<String, ScriptEngineFactory>();

        initEngines(loader);

    }

    private ServiceLoader<ScriptEngineFactory> getServiceLoader(final ClassLoader loader) {

        if (loader != null) {

            return ServiceLoader.load(ScriptEngineFactory.class, loader);

        } else {

            return ServiceLoader.loadInstalled(ScriptEngineFactory.class);

        }

    }

    private void initEngines(final ClassLoader loader) {

        Iterator<ScriptEngineFactory> itr = null;

        try {

            ServiceLoader<ScriptEngineFactory> sl = AccessController.doPrivileged(

                new PrivilegedAction<ServiceLoader<ScriptEngineFactory>>() {

                    @Override

                    public ServiceLoader<ScriptEngineFactory> run() {

                        return getServiceLoader(loader);

                    }

                });

            itr = sl.iterator();

        } catch (ServiceConfigurationError err) {

            System.err.println("Can't find ScriptEngineFactory providers: " +

                          err.getMessage());

            if (DEBUG) {

                err.printStackTrace();

            }

            // do not throw any exception here. user may want to

            // manage his/her own factories using this manager

            // by explicit registratation (by registerXXX) methods.

            return;

        }

        try {

            while (itr.hasNext()) {

                try {

                    ScriptEngineFactory fact = itr.next();

                    engineSpis.add(fact);

                } catch (ServiceConfigurationError err) {

                    System.err.println("ScriptEngineManager providers.next(): "

                                 + err.getMessage());

                    if (DEBUG) {

                        err.printStackTrace();

                    }

                    // one factory failed, but check other factories...

                    continue;

                }

            }

        } catch (ServiceConfigurationError err) {

            System.err.println("ScriptEngineManager providers.hasNext(): "

                            + err.getMessage());

            if (DEBUG) {

                err.printStackTrace();

            }

            // do not throw any exception here. user may want to

            // manage his/her own factories using this manager

            // by explicit registratation (by registerXXX) methods.

            return;

        }

    }

    /**

     * <code>setBindings</code> stores the specified <code>Bindings</code>

     * in the <code>globalScope</code> field. ScriptEngineManager sets this

     * <code>Bindings</code> as global bindings for <code>ScriptEngine</code>

     * objects created by it.

     *

     * @param bindings The specified <code>Bindings</code>

     * @throws IllegalArgumentException if bindings is null.

     */

    public void setBindings(Bindings bindings) {

        if (bindings == null) {

            throw new IllegalArgumentException("Global scope cannot be null.");

        }

        globalScope = bindings;

    }

    /**

     * <code>getBindings</code> returns the value of the <code>globalScope</code> field.

     * ScriptEngineManager sets this <code>Bindings</code> as global bindings for

     * <code>ScriptEngine</code> objects created by it.

     *

     * @return The globalScope field.

     */

    public Bindings getBindings() {

        return globalScope;

    }

    /**

     * Sets the specified key/value pair in the Global Scope.

     * @param key Key to set

     * @param value Value to set.

     * @throws NullPointerException if key is null.

     * @throws IllegalArgumentException if key is empty string.

     */

    public void put(String key, Object value) {

        globalScope.put(key, value);

    }

    /**

     * Gets the value for the specified key in the Global Scope

     * @param key The key whose value is to be returned.

     * @return The value for the specified key.

     */

    public Object get(String key) {

        return globalScope.get(key);

    }

    /**

     * Looks up and creates a <code>ScriptEngine</code> for a given  name.

     * The algorithm first searches for a <code>ScriptEngineFactory</code> that has been

     * registered as a handler for the specified name using the <code>registerEngineName</code>

     * method.

     * <br><br> If one is not found, it searches the set of <code>ScriptEngineFactory</code> instances

     * stored by the constructor for one with the specified name.  If a <code>ScriptEngineFactory</code>

     * is found by either method, it is used to create instance of <code>ScriptEngine</code>.

     * @param shortName The short name of the <code>ScriptEngine</code> implementation.

     * returned by the <code>getNames</code> method of its <code>ScriptEngineFactory</code>.

     * @return A <code>ScriptEngine</code> created by the factory located in the search.  Returns null

     * if no such factory was found.  The <code>ScriptEngineManager</code> sets its own <code>globalScope</code>

     * <code>Bindings</code> as the <code>GLOBAL_SCOPE</code> <code>Bindings</code> of the newly

     * created <code>ScriptEngine</code>.

     * @throws NullPointerException if shortName is null.

     */

    public ScriptEngine getEngineByName(String shortName) {

        if (shortName == null) throw new NullPointerException();

        //look for registered name first

        Object obj;

        if (null != (obj = nameAssociations.get(shortName))) {

            ScriptEngineFactory spi = (ScriptEngineFactory)obj;

            try {

                ScriptEngine engine = spi.getScriptEngine();

                engine.setBindings(getBindings(), ScriptContext.GLOBAL_SCOPE);

                return engine;

            } catch (Exception exp) {

                if (DEBUG) exp.printStackTrace();

            }

        }

        for (ScriptEngineFactory spi : engineSpis) {

            List<String> names = null;

            try {

                names = spi.getNames();

            } catch (Exception exp) {

                if (DEBUG) exp.printStackTrace();

            }

            if (names != null) {

                for (String name : names) {

                    if (shortName.equals(name)) {

                        try {

                            ScriptEngine engine = spi.getScriptEngine();

                            engine.setBindings(getBindings(), ScriptContext.GLOBAL_SCOPE);

                            return engine;

                        } catch (Exception exp) {

                            if (DEBUG) exp.printStackTrace();

                        }

                    }

                }

            }

        }

        return null;

    }

    /**

     * Look up and create a <code>ScriptEngine</code> for a given extension.  The algorithm

     * used by <code>getEngineByName</code> is used except that the search starts

     * by looking for a <code>ScriptEngineFactory</code> registered to handle the

     * given extension using <code>registerEngineExtension</code>.

     * @param extension The given extension

     * @return The engine to handle scripts with this extension.  Returns <code>null</code>

     * if not found.

     * @throws NullPointerException if extension is null.

     */

    public ScriptEngine getEngineByExtension(String extension) {

        if (extension == null) throw new NullPointerException();

        //look for registered extension first

        Object obj;

        if (null != (obj = extensionAssociations.get(extension))) {

            ScriptEngineFactory spi = (ScriptEngineFactory)obj;

            try {

                ScriptEngine engine = spi.getScriptEngine();

                engine.setBindings(getBindings(), ScriptContext.GLOBAL_SCOPE);

                return engine;

            } catch (Exception exp) {

                if (DEBUG) exp.printStackTrace();

            }

        }

        for (ScriptEngineFactory spi : engineSpis) {

            List<String> exts = null;

            try {

                exts = spi.getExtensions();

            } catch (Exception exp) {

                if (DEBUG) exp.printStackTrace();

            }

            if (exts == null) continue;

            for (String ext : exts) {

                if (extension.equals(ext)) {

                    try {

                        ScriptEngine engine = spi.getScriptEngine();

                        engine.setBindings(getBindings(), ScriptContext.GLOBAL_SCOPE);

                        return engine;

                    } catch (Exception exp) {

                        if (DEBUG) exp.printStackTrace();

                    }

                }

            }

        }

        return null;

    }

    /**

     * Look up and create a <code>ScriptEngine</code> for a given mime type.  The algorithm

     * used by <code>getEngineByName</code> is used except that the search starts

     * by looking for a <code>ScriptEngineFactory</code> registered to handle the

     * given mime type using <code>registerEngineMimeType</code>.

     * @param mimeType The given mime type

     * @return The engine to handle scripts with this mime type.  Returns <code>null</code>

     * if not found.

     * @throws NullPointerException if mimeType is null.

     */

    public ScriptEngine getEngineByMimeType(String mimeType) {

        if (mimeType == null) throw new NullPointerException();

        //look for registered types first

        Object obj;

        if (null != (obj = mimeTypeAssociations.get(mimeType))) {

            ScriptEngineFactory spi = (ScriptEngineFactory)obj;

            try {

                ScriptEngine engine = spi.getScriptEngine();

                engine.setBindings(getBindings(), ScriptContext.GLOBAL_SCOPE);

                return engine;

            } catch (Exception exp) {

                if (DEBUG) exp.printStackTrace();

            }

        }

        for (ScriptEngineFactory spi : engineSpis) {

            List<String> types = null;

            try {

                types = spi.getMimeTypes();

            } catch (Exception exp) {

                if (DEBUG) exp.printStackTrace();

            }

            if (types == null) continue;

            for (String type : types) {

                if (mimeType.equals(type)) {

                    try {

                        ScriptEngine engine = spi.getScriptEngine();

                        engine.setBindings(getBindings(), ScriptContext.GLOBAL_SCOPE);

                        return engine;

                    } catch (Exception exp) {

                        if (DEBUG) exp.printStackTrace();

                    }

                }

            }

        }

        return null;

    }

    /**

     * Returns a list whose elements are instances of all the <code>ScriptEngineFactory</code> classes

     * found by the discovery mechanism.

     * @return List of all discovered <code>ScriptEngineFactory</code>s.

     */

    public List<ScriptEngineFactory> getEngineFactories() {

        List<ScriptEngineFactory> res = new ArrayList<ScriptEngineFactory>(engineSpis.size());

        for (ScriptEngineFactory spi : engineSpis) {

            res.add(spi);

        }

        return Collections.unmodifiableList(res);

    }

    /**

     * Registers a <code>ScriptEngineFactory</code> to handle a language

     * name.  Overrides any such association found using the Discovery mechanism.

     * @param name The name to be associated with the <code>ScriptEngineFactory</code>.

     * @param factory The class to associate with the given name.

     * @throws NullPointerException if any of the parameters is null.

     */

    public void registerEngineName(String name, ScriptEngineFactory factory) {

        if (name == null || factory == null) throw new NullPointerException();

        nameAssociations.put(name, factory);

    }

    /**

     * Registers a <code>ScriptEngineFactory</code> to handle a mime type.

     * Overrides any such association found using the Discovery mechanism.

     *

     * @param type The mime type  to be associated with the

     * <code>ScriptEngineFactory</code>.

     *

     * @param factory The class to associate with the given mime type.

     * @throws NullPointerException if any of the parameters is null.

     */

    public void registerEngineMimeType(String type, ScriptEngineFactory factory) {

        if (type == null || factory == null) throw new NullPointerException();

        mimeTypeAssociations.put(type, factory);

    }

    /**

     * Registers a <code>ScriptEngineFactory</code> to handle an extension.

     * Overrides any such association found using the Discovery mechanism.

     *

     * @param extension The extension type  to be associated with the

     * <code>ScriptEngineFactory</code>.

     * @param factory The class to associate with the given extension.

     * @throws NullPointerException if any of the parameters is null.

     */

    public void registerEngineExtension(String extension, ScriptEngineFactory factory) {

        if (extension == null || factory == null) throw new NullPointerException();

        extensionAssociations.put(extension, factory);

    }

    /** Set of script engine factories discovered. */

    private TreeSet<ScriptEngineFactory> engineSpis;

    /** Map of engine name to script engine factory. */

    private HashMap<String, ScriptEngineFactory> nameAssociations;

    /** Map of script file extension to script engine factory. */

    private HashMap<String, ScriptEngineFactory> extensionAssociations;

    /** Map of script MIME type to script engine factory. */

    private HashMap<String, ScriptEngineFactory> mimeTypeAssociations;

    /** Global bindings associated with script engines created by this manager. */

    private Bindings globalScope;

}