/*

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

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * 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

 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,

 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,

 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR

 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF

 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING

 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS

 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

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.CompositeOperation;

import jdk.dynalink.NamedOperation;

import jdk.dynalink.Operation;

import jdk.dynalink.StandardOperation;

import jdk.dynalink.beans.BeansLinker;

import jdk.dynalink.linker.GuardingDynamicLinker;

import jdk.dynalink.linker.GuardingDynamicLinkerExporter;

import jdk.dynalink.linker.GuardedInvocation;

import jdk.dynalink.linker.TypeBasedGuardingDynamicLinker;

import jdk.dynalink.linker.LinkRequest;

import jdk.dynalink.linker.LinkerServices;

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(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));

    }

    // locate the first standard operation from the call descriptor

    private static StandardOperation getFirstStandardOperation(final CallSiteDescriptor desc) {

        final Operation base = NamedOperation.getBaseOperation(desc.getOperation());

        if (base instanceof StandardOperation) {

            return (StandardOperation)base;

        } else if (base instanceof CompositeOperation) {

            final CompositeOperation cop = (CompositeOperation)base;

            for(int i = 0; i < cop.getOperationCount(); ++i) {

                final Operation op = cop.getOperation(i);

                if (op instanceof StandardOperation) {

                    return (StandardOperation)op;

                }

            }

        }

        return null;

    }

    @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(LinkRequest request,

                LinkerServices linkerServices) throws Exception {

                final Object self = request.getReceiver();

                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.

                    boolean isGetMethod = getFirstStandardOperation(desc) == StandardOperation.GET_METHOD;

                    Object name = NamedOperation.getName(desc.getOperation());

                    if (isGetMethod && name instanceof String) {

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

                        GuardedInvocation inv;

                        try {

                            inv = javaLinker.getGuardedInvocation(request, linkerServices);

                        } catch (final Throwable th) {

                            inv = null;

                        }

                        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

                            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.

                    boolean isCall = getFirstStandardOperation(desc) == 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;

    }

}