/*****************************************************************************
 *                                                                           *
 *  This file is part of the BeanShell Java Scripting distribution.          *
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 *  Sun Public License Notice:                                               *
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 *  The contents of this file are subject to the Sun Public License Version  *
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 *  The Original Code is BeanShell. The Initial Developer of the Original    *
 *  Code is Pat Niemeyer. Portions created by Pat Niemeyer are Copyright     *
 *  (C) 2000.  All Rights Reserved.                                          *
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 *  GNU Public License Notice:                                               *
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 *                                                                           *
 *  Patrick Niemeyer (pat@pat.net)                                           *
 *  Author of Learning Java, O'Reilly & Associates                           *
 *  http://www.pat.net/~pat/                                                 *
 *                                                                           *
 *****************************************************************************/


package org.gjt.sp.jedit.bsh;

import java.lang.reflect.*;
import java.lang.reflect.InvocationHandler;
import java.util.Hashtable;

/**
    XThis is a dynamically loaded extension which extends This.java and adds
    support for the generalized interface proxy mechanism introduced in
    JDK1.3.  XThis allows bsh scripted objects to implement arbitrary
    interfaces (be arbitrary event listener types).

    Note: This module relies on new features of JDK1.3 and will not compile
    with JDK1.2 or lower.  For those environments simply do not compile this
    class.

    Eventually XThis should become simply This, but for backward compatability
    we will maintain This without requiring support for the proxy mechanism.

    XThis stands for "eXtended This" (I had to call it something).

    @see org.gjt.sp.jedit.bsh.JThis	JThis
    See also JThis with explicit JFC support for compatability.
    @see org.gjt.sp.jedit.bsh.This This
*/
public class XThis extends This
    {
    /**
        A cache of proxy interface handlers.
        Currently just one per interface.
    */
    Hashtable interfaces;

    InvocationHandler invocationHandler = new Handler();

    public XThis( NameSpace namespace, Interpreter declaringInterp ) {
        super( namespace, declaringInterp );
    }

    public String toString() {
        return "'this' reference (XThis) to Bsh object: " + namespace;
    }

    /**
        Get dynamic proxy for interface, caching those it creates.
    */
    public Object getInterface( Class clas )
    {
        return getInterface( new Class[] { clas } );
    }

    /**
        Get dynamic proxy for interface, caching those it creates.
    */
    public Object getInterface( Class [] ca )
    {
        if ( interfaces == null )
            interfaces = new Hashtable();

        // Make a hash of the interface hashcodes in order to cache them
        int hash = 21;
        for(int i=0; i<ca.length; i++)
            hash *= ca[i].hashCode() + 3;
        Object hashKey = new Integer(hash);

        Object interf = interfaces.get( hashKey );

        if ( interf == null )
        {
            ClassLoader classLoader = ca[0].getClassLoader(); // ?
            interf = Proxy.newProxyInstance(
                classLoader, ca, invocationHandler );
            interfaces.put( hashKey, interf );
        }

        return interf;
    }

    /**
        This is the invocation handler for the dynamic proxy.
        <p>

        Notes:
        Inner class for the invocation handler seems to shield this unavailable
        interface from JDK1.2 VM...

        I don't understand this.  JThis works just fine even if those
        classes aren't there (doesn't it?)  This class shouldn't be loaded
        if an XThis isn't instantiated in NameSpace.java, should it?
    */
    class Handler implements InvocationHandler, java.io.Serializable
    {
        public Object invoke( Object proxy, Method method, Object[] args )
            throws Throwable
        {
            try {
                return invokeImpl( proxy, method, args );
            } catch ( TargetError te ) {
                // Unwrap target exception.  If the interface declares that
                // it throws the ex it will be delivered.  If not it will be
                // wrapped in an UndeclaredThrowable
                throw te.getTarget();
            } catch ( EvalError ee ) {
                // Ease debugging...
                // XThis.this refers to the enclosing class instance
                if ( Interpreter.DEBUG )
                    Interpreter.debug( "EvalError in scripted interface: "
                    + XThis.this.toString() + ": "+ ee );
                throw ee;
            }
        }

        public Object invokeImpl( Object proxy, Method method, Object[] args )
            throws EvalError
        {
            String methodName = method.getName();
            CallStack callstack = new CallStack( namespace );

            /*
                If equals() is not explicitly defined we must override the
                default implemented by the This object protocol for scripted
                object.  To support XThis equals() must test for equality with
                the generated proxy object, not the scripted bsh This object;
                otherwise callers from outside in Java will not see a the
                proxy object as equal to itself.
            */
            BshMethod equalsMethod = null;
            try {
                equalsMethod = namespace.getMethod(
                    "equals", new Class [] { Object.class } );
            } catch ( UtilEvalError e ) {/*leave null*/ }
            if ( methodName.equals("equals" ) && equalsMethod == null ) {
                Object obj = args[0];
                return new Boolean( proxy == obj );
            }

            /*
                If toString() is not explicitly defined override the default
                to show the proxy interfaces.
            */
            BshMethod toStringMethod = null;
            try {
                toStringMethod =
                    namespace.getMethod( "toString", new Class [] { } );
            } catch ( UtilEvalError e ) {/*leave null*/ }

            if ( methodName.equals("toString" ) && toStringMethod == null)
            {
                Class [] ints = proxy.getClass().getInterfaces();
                // XThis.this refers to the enclosing class instance
                StringBuilder sb = new StringBuilder(
                    XThis.this.toString() + "\nimplements:" );
                for(int i=0; i<ints.length; i++)
                    sb.append( " "+ ints[i].getName()
                        + ((ints.length > 1)?",":"") );
                return sb.toString();
            }

            Class [] paramTypes = method.getParameterTypes();
            return Primitive.unwrap(
                invokeMethod( methodName, Primitive.wrap(args, paramTypes) ) );
        }
    };
}



