/*

 * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.

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 * are met:

 *

 *   - Redistributions of source code must retain the above copyright

 *     notice, this list of conditions and the following disclaimer.

 *

 *   - Redistributions in binary form must reproduce the above copyright

 *     notice, this list of conditions and the following disclaimer in the

 *     documentation and/or other materials provided with the distribution.

 *

 *   - Neither the name of Oracle nor the names of its

 *     contributors may be used to endorse or promote products derived

 *     from this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS

 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,

 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR

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 */

import java.lang.invoke.MethodHandle;

import java.lang.invoke.MethodHandles;

import java.lang.invoke.MethodType;

import java.util.ArrayList;

import java.util.List;

import jdk.dynalink.CallSiteDescriptor;

import jdk.dynalink.NamedOperation;

import jdk.dynalink.NamespaceOperation;

import jdk.dynalink.Operation;

import jdk.dynalink.StandardNamespace;

import jdk.dynalink.StandardOperation;

import jdk.dynalink.beans.BeansLinker;

import jdk.dynalink.linker.GuardedInvocation;

import jdk.dynalink.linker.GuardingDynamicLinker;

import jdk.dynalink.linker.GuardingDynamicLinkerExporter;

import jdk.dynalink.linker.LinkRequest;

import jdk.dynalink.linker.LinkerServices;

import jdk.dynalink.linker.TypeBasedGuardingDynamicLinker;

import jdk.dynalink.linker.support.Guards;

import jdk.dynalink.linker.support.Lookup;

/**

 * This is a dynalink pluggable linker (see http://openjdk.java.net/jeps/276).

 * This linker routes missing methods to Smalltalk-style doesNotUnderstand method.

 * Object of any Java class that implements MissingMethodHandler is handled by this linker.

 * For any method call, if a matching Java method is found, it is called. If there is no

 * method by that name, then MissingMethodHandler.doesNotUnderstand is called.

 */

public final class MissingMethodLinkerExporter extends GuardingDynamicLinkerExporter {

    static {

        System.out.println("pluggable dynalink missing method linker loaded");

    }

    // represents a MissingMethod - just stores as name and also serves a guard type

    public static class MissingMethod {

        private final String name;

        public MissingMethod(final String name) {

            this.name = name;

        }

        public String getName() {

            return name;

        }

    }

    // MissingMethodHandler.doesNotUnderstand method

    private static final MethodHandle DOES_NOT_UNDERSTAND;

    // type of MissingMethodHandler - but "this" and String args are flipped

    private static final MethodType FLIPPED_DOES_NOT_UNDERSTAND_TYPE;

    // "is this a MissingMethod?" guard

    private static final MethodHandle IS_MISSING_METHOD;

    // MissingMethod object->it's name filter

    private static final MethodHandle MISSING_METHOD_TO_NAME;

    static {

        DOES_NOT_UNDERSTAND = Lookup.PUBLIC.findVirtual(

            MissingMethodHandler.class,

            "doesNotUnderstand",

            MethodType.methodType(Object.class, String.class, Object[].class));

        FLIPPED_DOES_NOT_UNDERSTAND_TYPE =

            MethodType.methodType(Object.class, String.class, MissingMethodHandler.class, Object[].class);

        IS_MISSING_METHOD = Guards.isOfClass(MissingMethod.class,

            MethodType.methodType(Boolean.TYPE, Object.class));

        MISSING_METHOD_TO_NAME = Lookup.PUBLIC.findVirtual(MissingMethod.class,

            "getName", MethodType.methodType(String.class));

    }

    @Override

    public List<GuardingDynamicLinker> get() {

        final ArrayList<GuardingDynamicLinker> linkers = new ArrayList<>();

        final BeansLinker beansLinker = new BeansLinker();

        linkers.add(new TypeBasedGuardingDynamicLinker() {

            // only handles MissingMethodHandler and MissingMethod objects

            @Override

            public boolean canLinkType(final Class<?> type) {

                return

                    MissingMethodHandler.class.isAssignableFrom(type) ||

                    type == MissingMethod.class;

            }

            @Override

            public GuardedInvocation getGuardedInvocation(final LinkRequest request,

                final LinkerServices linkerServices) throws Exception {

                final Object self = request.getReceiver();

                final CallSiteDescriptor desc = request.getCallSiteDescriptor();

                // any method call is done by two steps. Step (1) GET_METHOD and (2) is CALL

                // For step (1), we check if GET_METHOD can succeed by Java linker, if so

                // we return that method object. If not, we return a MissingMethod object.

                if (self instanceof MissingMethodHandler) {

                    // Check if this is a named GET_METHOD first.

                    final Operation namedOp = desc.getOperation();

                    final Operation namespaceOp = NamedOperation.getBaseOperation(namedOp);

                    final Operation op = NamespaceOperation.getBaseOperation(namespaceOp);

                    final boolean isGetMethod = op == StandardOperation.GET && StandardNamespace.findFirst(namespaceOp) == StandardNamespace.METHOD;

                    final Object name = NamedOperation.getName(namedOp);

                    if (isGetMethod && name instanceof String) {

                        final GuardingDynamicLinker javaLinker = beansLinker.getLinkerForClass(self.getClass());

                        GuardedInvocation inv;

                        try {

                            inv = javaLinker.getGuardedInvocation(request, linkerServices);

                        } catch (final Throwable th) {

                            inv = null;

                        }

                        final String nameStr = name.toString();

                        if (inv == null) {

                            // use "this" for just guard and drop it -- return a constant Method handle

                            // that returns a newly created MissingMethod object

                            final MethodHandle mh = MethodHandles.constant(Object.class, new MissingMethod(nameStr));

                            inv = new GuardedInvocation(

                                MethodHandles.dropArguments(mh, 0, Object.class),

                                Guards.isOfClass(self.getClass(), MethodType.methodType(Boolean.TYPE, Object.class)));

                        }

                        return inv;

                    }

                } else if (self instanceof MissingMethod) {

                    // This is step (2). We call MissingMethodHandler.doesNotUnderstand here

                    // Check if this is this a CALL first.

                    final boolean isCall = NamedOperation.getBaseOperation(desc.getOperation()) == StandardOperation.CALL;

                    if (isCall) {

                        MethodHandle mh = DOES_NOT_UNDERSTAND;

                        // flip "this" and method name (String)

                        mh = MethodHandles.permuteArguments(mh, FLIPPED_DOES_NOT_UNDERSTAND_TYPE, 1, 0, 2);

                        // collect rest of the arguments as vararg

                        mh = mh.asCollector(Object[].class, desc.getMethodType().parameterCount() - 2);

                        // convert MissingMethod object to it's name

                        mh = MethodHandles.filterArguments(mh, 0, MISSING_METHOD_TO_NAME);

                        return new GuardedInvocation(mh, IS_MISSING_METHOD);

                    }

                }

                return null;

            }

        });

        return linkers;

    }

}