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 *  DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package java.lang.invoke;

import jdk.internal.vm.annotation.ForceInline;
import jdk.internal.vm.annotation.Stable;

import java.util.List;
import java.util.function.BiFunction;

An indirect var handle can be thought of as an aggregate of the method handles implementing its supported access modes.
Its varform contains no method name table (given that some of the method handles composing a bound var handle might
not be direct). The set of method handles constituting an indirect var handle are retrieved lazily, to minimize
code spinning (since not all the access modes will be used anyway).
Indirect var handles are useful when constructing var handle adapters - that is, an adapter var handle
can be constructed by extracting the method handles constituting the target var handle, adapting them
(using the method handle combinator API) and then repackaging the adapted method handles into a new, indirect
var handle.
/**
 * An indirect var handle can be thought of as an aggregate of the method handles implementing its supported access modes.
 * Its varform contains no method name table (given that some of the method handles composing a bound var handle might
 * not be direct). The set of method handles constituting an indirect var handle are retrieved lazily, to minimize
 * code spinning (since not all the access modes will be used anyway).
 * Indirect var handles are useful when constructing var handle adapters - that is, an adapter var handle
 * can be constructed by extracting the method handles constituting the target var handle, adapting them
 * (using the method handle combinator API) and then repackaging the adapted method handles into a new, indirect
 * var handle.
 */
/* package */ class IndirectVarHandle extends VarHandle {

    @Stable
    private final MethodHandle[] handleMap = new MethodHandle[AccessMode.values().length];
    private final VarHandle directTarget; // cache, for performance reasons
    private final VarHandle target;
    private final BiFunction<AccessMode, MethodHandle, MethodHandle> handleFactory;
    private final Class<?> value;
    private final Class<?>[] coordinates;

    IndirectVarHandle(VarHandle target, Class<?> value, Class<?>[] coordinates, BiFunction<AccessMode, MethodHandle, MethodHandle> handleFactory) {
        this(target, value, coordinates, handleFactory, new VarForm(value, coordinates), false);
    }

    private IndirectVarHandle(VarHandle target, Class<?> value, Class<?>[] coordinates,
                      BiFunction<AccessMode, MethodHandle, MethodHandle> handleFactory, VarForm form, boolean exact) {
        super(form, exact);
        this.handleFactory = handleFactory;
        this.target = target;
        this.directTarget = target.asDirect();
        this.value = value;
        this.coordinates = coordinates;
    }

    @Override
    public Class<?> varType() {
        return value;
    }

    @Override
    public List<Class<?>> coordinateTypes() {
        return List.of(coordinates);
    }

    @Override
    MethodType accessModeTypeUncached(AccessType at) {
        return at.accessModeType(null, value, coordinates);
    }

    @Override
    boolean isDirect() {
        return false;
    }

    @Override
    VarHandle asDirect() {
        return directTarget;
    }

    VarHandle target() {
        return target;
    }

    @Override
    public VarHandle withInvokeExactBehavior() {
        return hasInvokeExactBehavior()
            ? this
            : new IndirectVarHandle(target, value, coordinates, handleFactory, vform, true);
    }

    @Override
    public VarHandle withInvokeBehavior() {
        return !hasInvokeExactBehavior()
            ? this
            : new IndirectVarHandle(target, value, coordinates, handleFactory, vform, false);
    }

    @Override
    @ForceInline
    MethodHandle getMethodHandle(int mode) {
        MethodHandle handle = handleMap[mode];
        if (handle == null) {
            MethodHandle targetHandle = target.getMethodHandle(mode); // might throw UOE of access mode is not supported, which is ok
            handle = handleMap[mode] = handleFactory.apply(AccessMode.values()[mode], targetHandle);
        }
        return handle;
    }

    @Override
    public MethodHandle toMethodHandle(AccessMode accessMode) {
        return getMethodHandle(accessMode.ordinal()).bindTo(directTarget);
    }
}