/*
 * @(#)ScriptEngineManager.java	1.6 06/04/21 17:44:33
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTAIL. Use is subject to license terms.
 */

package javax.script;
import java.util.*;
import java.net.URL;
import java.io.*;
import java.security.*;
import sun.misc.Service;
import sun.misc.ServiceConfigurationError;
import sun.reflect.Reflection;
import sun.security.util.SecurityConstants;

/**
 * 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 <a href="../../../technotes/guides/jar/jar.html#Service%20Provider">service provider</a> mechanism to enumerate all the 
 * implementations of <code>ScriptEngineFactory</code>. <br><br>
 * The <code>ScriptEngineManager</code> provides a method to return an array 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;
    /**
     * If the thread context ClassLoader can be accessed by the caller, 
     * then the effect of calling this constructor is the same as calling 
     * <code>ScriptEngineManager(Thread.currentThread().getContextClassLoader())</code>.
     * Otherwise, the effect is the same as calling <code>ScriptEngineManager(null)</code>.
     *
     * @see java.lang.Thread#getContextClassLoader
     */
    public ScriptEngineManager() {
        ClassLoader ctxtLoader = Thread.currentThread().getContextClassLoader();
        if (canCallerAccessLoader(ctxtLoader)) {
            if (DEBUG) System.out.println("using " + ctxtLoader);
            init(ctxtLoader);
        } else {
            if (DEBUG) System.out.println("using bootstrap loader");
            init(null);
        }
    }
    
    /**
     * This constructor loads the implementations of 
     * <code>ScriptEngineFactory</code> visible to the given 
     * <code>ClassLoader</code> using the <a href="../../../technotes/guides/jar/jar.html#Service%20Provider">service provider</a> mechanism.<br><br>
     * If loader is <code>null</code>, the script engine factories that are 
     * bundled with the platform and that are in the usual extension 
     * directories (installed extensions) are loaded. <br><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 HashSet<ScriptEngineFactory>();
        nameAssociations = new HashMap<String, ScriptEngineFactory>();
        extensionAssociations = new HashMap<String, ScriptEngineFactory>();
        mimeTypeAssociations = new HashMap<String, ScriptEngineFactory>();
        AccessController.doPrivileged(new PrivilegedAction() {
            public Object run() {
                initEngines(loader);
                return null;
            }
        });
    }

    private void initEngines(final ClassLoader loader) {
        Iterator itr = null;
        try {
            if (loader != null) {
                itr = Service.providers(ScriptEngineFactory.class, loader);
            } else {
                itr = Service.installedProviders(ScriptEngineFactory.class);
            }
        } 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