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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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package jdk.nashorn.internal.runtime.linker;

import static jdk.nashorn.internal.lookup.Lookup.MH;
import static jdk.nashorn.internal.runtime.ECMAErrors.typeError;
import static jdk.nashorn.internal.runtime.ScriptRuntime.UNDEFINED;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.util.HashMap;
import java.util.Map;
import java.util.function.Supplier;
import jdk.dynalink.CallSiteDescriptor;
import jdk.dynalink.NamedOperation;
import jdk.dynalink.Operation;
import jdk.dynalink.beans.BeansLinker;
import jdk.dynalink.linker.GuardedInvocation;
import jdk.dynalink.linker.GuardingDynamicLinker;
import jdk.dynalink.linker.GuardingTypeConverterFactory;
import jdk.dynalink.linker.LinkRequest;
import jdk.dynalink.linker.LinkerServices;
import jdk.dynalink.linker.support.Lookup;
import jdk.nashorn.internal.codegen.types.Type;
import jdk.nashorn.internal.runtime.ECMAException;
import jdk.nashorn.internal.runtime.JSType;
import jdk.nashorn.internal.runtime.ScriptRuntime;
import jdk.nashorn.internal.runtime.UnwarrantedOptimismException;

Nashorn bottom linker; used as a last-resort catch-all linker for all linking requests that fall through all other linkers (see how Bootstrap class configures the dynamic linker in its static initializer). It will throw appropriate ECMAScript errors for attempts to invoke operations on null, link no-op property getters and setters for Java objects that couldn't be linked by any other linker, and throw appropriate ECMAScript errors for attempts to invoke arbitrary Java objects as functions or constructors. /**
 * Nashorn bottom linker; used as a last-resort catch-all linker for all linking requests that fall through all other
 * linkers (see how {@link Bootstrap} class configures the dynamic linker in its static initializer). It will throw
 * appropriate ECMAScript errors for attempts to invoke operations on {@code null}, link no-op property getters and
 * setters for Java objects that couldn't be linked by any other linker, and throw appropriate ECMAScript errors for
 * attempts to invoke arbitrary Java objects as functions or constructors.
 */
final class NashornBottomLinker implements GuardingDynamicLinker, GuardingTypeConverterFactory {

    @Override
    public GuardedInvocation getGuardedInvocation(final LinkRequest linkRequest, final LinkerServices linkerServices)
            throws Exception {
        final Object self = linkRequest.getReceiver();

        if (self == null) {
            return linkNull(linkRequest);
        }

        // None of the objects that can be linked by NashornLinker should ever reach here. Basically, anything below
        // this point is a generic Java bean. Therefore, reaching here with a ScriptObject is a Nashorn bug.
        assert isExpectedObject(self) : "Couldn't link " + linkRequest.getCallSiteDescriptor() + " for " + self.getClass().getName();

        return linkBean(linkRequest);
    }

    private static final MethodHandle EMPTY_PROP_GETTER =
            MH.dropArguments(MH.constant(Object.class, UNDEFINED), 0, Object.class);
    private static final MethodHandle EMPTY_ELEM_GETTER =
            MH.dropArguments(EMPTY_PROP_GETTER, 0, Object.class);
    private static final MethodHandle EMPTY_PROP_SETTER =
            MH.asType(EMPTY_ELEM_GETTER, EMPTY_ELEM_GETTER.type().changeReturnType(void.class));
    private static final MethodHandle EMPTY_ELEM_SETTER =
            MH.dropArguments(EMPTY_PROP_SETTER, 0, Object.class);

    private static final MethodHandle THROW_STRICT_PROPERTY_SETTER;
    private static final MethodHandle THROW_OPTIMISTIC_UNDEFINED;

    static {
        final Lookup lookup = new Lookup(MethodHandles.lookup());
        THROW_STRICT_PROPERTY_SETTER = lookup.findOwnStatic("throwStrictPropertySetter", void.class, Object.class, Object.class);
        THROW_OPTIMISTIC_UNDEFINED = lookup.findOwnStatic("throwOptimisticUndefined", Object.class, int.class);
    }

    private static GuardedInvocation linkBean(final LinkRequest linkRequest) throws Exception {
        final CallSiteDescriptor desc = linkRequest.getCallSiteDescriptor();
        final Object self = linkRequest.getReceiver();
        switch (NashornCallSiteDescriptor.getStandardOperation(desc)) {
        case NEW:
            if(BeansLinker.isDynamicConstructor(self)) {
                throw typeError("no.constructor.matches.args", ScriptRuntime.safeToString(self));
            }
            if(BeansLinker.isDynamicMethod(self)) {
                throw typeError("method.not.constructor", ScriptRuntime.safeToString(self));
            }
            throw typeError("not.a.function", NashornCallSiteDescriptor.getFunctionErrorMessage(desc, self));
        case CALL:
            if(BeansLinker.isDynamicConstructor(self)) {
                throw typeError("constructor.requires.new", ScriptRuntime.safeToString(self));
            }
            if(BeansLinker.isDynamicMethod(self)) {
                throw typeError("no.method.matches.args", ScriptRuntime.safeToString(self));
            }
            throw typeError("not.a.function", NashornCallSiteDescriptor.getFunctionErrorMessage(desc, self));
        default:
            // Everything else is supposed to have been already handled by Bootstrap.beansLinker
            // delegating to linkNoSuchBeanMember
            throw new AssertionError("unknown call type " + desc);
        }
    }

    static MethodHandle linkMissingBeanMember(final LinkRequest linkRequest, final LinkerServices linkerServices) throws Exception {
        final CallSiteDescriptor desc = linkRequest.getCallSiteDescriptor();
        final String operand = NashornCallSiteDescriptor.getOperand(desc);
        switch (NashornCallSiteDescriptor.getStandardOperation(desc)) {
        case GET:
            if (NashornCallSiteDescriptor.isOptimistic(desc)) {
                return adaptThrower(MethodHandles.insertArguments(THROW_OPTIMISTIC_UNDEFINED, 0, NashornCallSiteDescriptor.getProgramPoint(desc)), desc);
            } else if (operand != null) {
                return getInvocation(EMPTY_PROP_GETTER, linkerServices, desc);
            }
            return getInvocation(EMPTY_ELEM_GETTER, linkerServices, desc);
        case SET:
            final boolean strict = NashornCallSiteDescriptor.isStrict(desc);
            if (strict) {
                return adaptThrower(bindOperand(THROW_STRICT_PROPERTY_SETTER, operand), desc);
            } else if (operand != null) {
                return getInvocation(EMPTY_PROP_SETTER, linkerServices, desc);
            }
            return getInvocation(EMPTY_ELEM_SETTER, linkerServices, desc);
        default:
            throw new AssertionError("unknown call type " + desc);
        }
    }

    private static MethodHandle bindOperand(final MethodHandle handle, final String operand) {
        return operand == null ? handle : MethodHandles.insertArguments(handle, 1, operand);
    }

    private static MethodHandle adaptThrower(final MethodHandle handle, final CallSiteDescriptor desc) {
        final MethodType targetType = desc.getMethodType();
        final int paramCount = handle.type().parameterCount();
        return MethodHandles
                .dropArguments(handle, paramCount, targetType.parameterList().subList(paramCount, targetType.parameterCount()))
                .asType(targetType);
    }

    @SuppressWarnings("unused")
    private static void throwStrictPropertySetter(final Object self, final Object name) {
        throw createTypeError(self, name, "cant.set.property");
    }

    private static ECMAException createTypeError(final Object self, final Object name, final String msg) {
        return typeError(msg, String.valueOf(name), ScriptRuntime.safeToString(self));
    }

    @SuppressWarnings("unused")
    private static Object throwOptimisticUndefined(final int programPoint) {
        throw new UnwarrantedOptimismException(UNDEFINED, programPoint, Type.OBJECT);
    }

    @Override
    public GuardedInvocation convertToType(final Class<?> sourceType, final Class<?> targetType, final Supplier<MethodHandles.Lookup> lookupSupplier) throws Exception {
        final GuardedInvocation gi = convertToTypeNoCast(sourceType, targetType);
        return gi == null ? null : gi.asType(MH.type(targetType, sourceType));
    }

    
Main part of the implementation of GuardingTypeConverterFactory.convertToType that doesn't care about adapting the method signature; that's done by the invoking method. Returns conversion from Object to String/number/boolean (JS primitive types). 
Params:
sourceType – the source type
targetType – the target type
Throws:
Exception – if something goes wrong
Returns:
a guarded invocation that converts from the source type to the target type./**
     * Main part of the implementation of {@link GuardingTypeConverterFactory#convertToType} that doesn't
     * care about adapting the method signature; that's done by the invoking method. Returns conversion
     * from Object to String/number/boolean (JS primitive types).
     * @param sourceType the source type
     * @param targetType the target type
     * @return a guarded invocation that converts from the source type to the target type.
     * @throws Exception if something goes wrong
     */
    private static GuardedInvocation convertToTypeNoCast(final Class<?> sourceType, final Class<?> targetType) throws Exception {
        final MethodHandle mh = CONVERTERS.get(targetType);
        if (mh != null) {
            return new GuardedInvocation(mh);
        }

        return null;
    }

    private static MethodHandle getInvocation(final MethodHandle handle, final LinkerServices linkerServices, final CallSiteDescriptor desc) {
        return linkerServices.asTypeLosslessReturn(handle, desc.getMethodType());
    }

    // Used solely in an assertion to figure out if the object we get here is something we in fact expect. Objects
    // linked by NashornLinker should never reach here.
    private static boolean isExpectedObject(final Object obj) {
        return !(NashornLinker.canLinkTypeStatic(obj.getClass()));
    }

    private static GuardedInvocation linkNull(final LinkRequest linkRequest) {
        final CallSiteDescriptor desc = linkRequest.getCallSiteDescriptor();
        switch (NashornCallSiteDescriptor.getStandardOperation(desc)) {
        case NEW:
        case CALL:
            throw typeError("not.a.function", "null");
        case GET:
            throw typeError(NashornCallSiteDescriptor.isMethodFirstOperation(desc) ? "no.such.function" : "cant.get.property", getArgument(linkRequest), "null");
        case SET:
            throw typeError("cant.set.property", getArgument(linkRequest), "null");
        default:
            throw new AssertionError("unknown call type " + desc);
        }
    }

    private static final Map<Class<?>, MethodHandle> CONVERTERS = new HashMap<>();
    static {
        CONVERTERS.put(boolean.class, JSType.TO_BOOLEAN.methodHandle());
        CONVERTERS.put(double.class, JSType.TO_NUMBER.methodHandle());
        CONVERTERS.put(int.class, JSType.TO_INTEGER.methodHandle());
        CONVERTERS.put(long.class, JSType.TO_LONG.methodHandle());
        CONVERTERS.put(String.class, JSType.TO_STRING.methodHandle());
    }

    private static String getArgument(final LinkRequest linkRequest) {
        final Operation op = linkRequest.getCallSiteDescriptor().getOperation();
        if (op instanceof NamedOperation) {
            return ((NamedOperation)op).getName().toString();
        }
        return ScriptRuntime.safeToString(linkRequest.getArguments()[1]);
    }
}