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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

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 * accompanied this code).

 *

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package java.lang.invoke;

import sun.invoke.util.Wrapper;

import static java.lang.invoke.MethodHandleNatives.mapLookupExceptionToError;

import static java.util.Objects.requireNonNull;

/**

 * Bootstrap methods for dynamically-computed constants.

 *

 * <p>The bootstrap methods in this class will throw a

 * {@code NullPointerException} for any reference argument that is {@code null},

 * unless the argument is specified to be unused or specified to accept a

 * {@code null} value.

 *

 * @since 11

 */

public final class ConstantBootstraps {

    // implements the upcall from the JVM, MethodHandleNatives.linkDynamicConstant:

    /*non-public*/

    static Object makeConstant(MethodHandle bootstrapMethod,

                               // Callee information:

                               String name, Class<?> type,

                               // Extra arguments for BSM, if any:

                               Object info,

                               // Caller information:

                               Class<?> callerClass) {

        // Restrict bootstrap methods to those whose first parameter is Lookup

        // The motivation here is, in the future, to possibly support BSMs

        // that do not accept the meta-data of lookup/name/type, thereby

        // allowing the co-opting of existing methods to be used as BSMs as

        // long as the static arguments can be passed as method arguments

        MethodType mt = bootstrapMethod.type();

        if (mt.parameterCount() < 2 ||

            !MethodHandles.Lookup.class.isAssignableFrom(mt.parameterType(0))) {

            throw new BootstrapMethodError(

                    "Invalid bootstrap method declared for resolving a dynamic constant: " + bootstrapMethod);

        }

        // BSMI.invoke handles all type checking and exception translation.

        // If type is not a reference type, the JVM is expecting a boxed

        // version, and will manage unboxing on the other side.

        return BootstrapMethodInvoker.invoke(

                type, bootstrapMethod, name, type, info, callerClass);

    }

    /**

     * Returns a {@code null} object reference for the reference type specified

     * by {@code type}.

     *

     * @param lookup unused

     * @param name unused

     * @param type a reference type

     * @return a {@code null} value

     * @throws IllegalArgumentException if {@code type} is not a reference type

     */

    public static Object nullConstant(MethodHandles.Lookup lookup, String name, Class<?> type) {

        if (requireNonNull(type).isPrimitive()) {

            throw new IllegalArgumentException(String.format("not reference: %s", type));

        }

        return null;

    }

    /**

     * Returns a {@link Class} mirror for the primitive type whose type

     * descriptor is specified by {@code name}.

     *

     * @param lookup unused

     * @param name the descriptor (JVMS 4.3) of the desired primitive type

     * @param type the required result type (must be {@code Class.class})

     * @return the {@link Class} mirror

     * @throws IllegalArgumentException if the name is not a descriptor for a

     * primitive type or the type is not {@code Class.class}

     */

    public static Class<?> primitiveClass(MethodHandles.Lookup lookup, String name, Class<?> type) {

        requireNonNull(name);

        requireNonNull(type);

        if (type != Class.class) {

            throw new IllegalArgumentException();

        }

        if (name.length() != 1) {

            throw new IllegalArgumentException(String.format("not primitive: %s", name));

        }

        return Wrapper.forPrimitiveType(name.charAt(0)).primitiveType();

    }

    /**

     * Returns an {@code enum} constant of the type specified by {@code type}

     * with the name specified by {@code name}.

     *

     * @param lookup the lookup context describing the class performing the

     * operation (normally stacked by the JVM)

     * @param name the name of the constant to return, which must exactly match

     * an enum constant in the specified type.

     * @param type the {@code Class} object describing the enum type for which

     * a constant is to be returned

     * @param <E> The enum type for which a constant value is to be returned

     * @return the enum constant of the specified enum type with the

     * specified name

     * @throws IllegalAccessError if the declaring class or the field is not

     * accessible to the class performing the operation

     * @throws IllegalArgumentException if the specified enum type has

     * no constant with the specified name, or the specified

     * class object does not represent an enum type

     * @see Enum#valueOf(Class, String)

     */

    public static <E extends Enum<E>> E enumConstant(MethodHandles.Lookup lookup, String name, Class<E> type) {

        requireNonNull(lookup);

        requireNonNull(name);

        requireNonNull(type);

        validateClassAccess(lookup, type);

        return Enum.valueOf(type, name);

    }

    /**

     * Returns the value of a static final field.

     *

     * @param lookup the lookup context describing the class performing the

     * operation (normally stacked by the JVM)

     * @param name the name of the field

     * @param type the type of the field

     * @param declaringClass the class in which the field is declared

     * @return the value of the field

     * @throws IllegalAccessError if the declaring class or the field is not

     * accessible to the class performing the operation

     * @throws NoSuchFieldError if the specified field does not exist

     * @throws IncompatibleClassChangeError if the specified field is not

     * {@code final}

     */

    public static Object getStaticFinal(MethodHandles.Lookup lookup, String name, Class<?> type,

                                        Class<?> declaringClass) {

        requireNonNull(lookup);

        requireNonNull(name);

        requireNonNull(type);

        requireNonNull(declaringClass);

        MethodHandle mh;

        try {

            mh = lookup.findStaticGetter(declaringClass, name, type);

            MemberName member = mh.internalMemberName();

            if (!member.isFinal()) {

                throw new IncompatibleClassChangeError("not a final field: " + name);

            }

        }

        catch (ReflectiveOperationException ex) {

            throw mapLookupExceptionToError(ex);

        }

        // Since mh is a handle to a static field only instances of

        // VirtualMachineError are anticipated to be thrown, such as a

        // StackOverflowError or an InternalError from the j.l.invoke code

        try {

            return mh.invoke();

        }

        catch (RuntimeException | Error e) {

            throw e;

        }

        catch (Throwable e) {

            throw new LinkageError("Unexpected throwable", e);

        }

    }

    /**

     * Returns the value of a static final field declared in the class which

     * is the same as the field's type (or, for primitive-valued fields,

     * declared in the wrapper class.)  This is a simplified form of

     * {@link #getStaticFinal(MethodHandles.Lookup, String, Class, Class)}

     * for the case where a class declares distinguished constant instances of

     * itself.

     *

     * @param lookup the lookup context describing the class performing the

     * operation (normally stacked by the JVM)

     * @param name the name of the field

     * @param type the type of the field

     * @return the value of the field

     * @throws IllegalAccessError if the declaring class or the field is not

     * accessible to the class performing the operation

     * @throws NoSuchFieldError if the specified field does not exist

     * @throws IncompatibleClassChangeError if the specified field is not

     * {@code final}

     * @see #getStaticFinal(MethodHandles.Lookup, String, Class, Class)

     */

    public static Object getStaticFinal(MethodHandles.Lookup lookup, String name, Class<?> type) {

        requireNonNull(type);

        Class<?> declaring = type.isPrimitive()

                             ? Wrapper.forPrimitiveType(type).wrapperType()

                             : type;

        return getStaticFinal(lookup, name, type, declaring);

    }

    /**

     * Returns the result of invoking a method handle with the provided

     * arguments.

     * <p>

     * This method behaves as if the method handle to be invoked is the result

     * of adapting the given method handle, via {@link MethodHandle#asType}, to

     * adjust the return type to the desired type.

     *

     * @param lookup unused

     * @param name unused

     * @param type the desired type of the value to be returned, which must be

     * compatible with the return type of the method handle

     * @param handle the method handle to be invoked

     * @param args the arguments to pass to the method handle, as if with

     * {@link MethodHandle#invokeWithArguments}.  Each argument may be

     * {@code null}.

     * @return the result of invoking the method handle

     * @throws WrongMethodTypeException if the handle's method type cannot be

     * adjusted to take the given number of arguments, or if the handle's return

     * type cannot be adjusted to the desired type

     * @throws ClassCastException if an argument or the result produced by

     * invoking the handle cannot be converted by reference casting

     * @throws Throwable anything thrown by the method handle invocation

     */

    public static Object invoke(MethodHandles.Lookup lookup, String name, Class<?> type,

                                MethodHandle handle, Object... args) throws Throwable {

        requireNonNull(type);

        requireNonNull(handle);

        requireNonNull(args);

        if (type != handle.type().returnType()) {

            // Adjust the return type of the handle to be invoked while

            // preserving variable arity if present

            handle = handle.asType(handle.type().changeReturnType(type)).

                    withVarargs(handle.isVarargsCollector());

        }

        return handle.invokeWithArguments(args);

    }

    /**

     * Finds a {@link VarHandle} for an instance field.

     *

     * @param lookup the lookup context describing the class performing the

     * operation (normally stacked by the JVM)

     * @param name the name of the field

     * @param type the required result type (must be {@code Class<VarHandle>})

     * @param declaringClass the class in which the field is declared

     * @param fieldType the type of the field

     * @return the {@link VarHandle}

     * @throws IllegalAccessError if the declaring class or the field is not

     * accessible to the class performing the operation

     * @throws NoSuchFieldError if the specified field does not exist

     * @throws IllegalArgumentException if the type is not {@code VarHandle}

     */

    public static VarHandle fieldVarHandle(MethodHandles.Lookup lookup, String name, Class<VarHandle> type,

                                           Class<?> declaringClass, Class<?> fieldType) {

        requireNonNull(lookup);

        requireNonNull(name);

        requireNonNull(type);

        requireNonNull(declaringClass);

        requireNonNull(fieldType);

        if (type != VarHandle.class) {

            throw new IllegalArgumentException();

        }

        try {

            return lookup.findVarHandle(declaringClass, name, fieldType);

        }

        catch (ReflectiveOperationException e) {

            throw mapLookupExceptionToError(e);

        }

    }

    /**

     * Finds a {@link VarHandle} for a static field.

     *

     * @param lookup the lookup context describing the class performing the

     * operation (normally stacked by the JVM)

     * @param name the name of the field

     * @param type the required result type (must be {@code Class<VarHandle>})

     * @param declaringClass the class in which the field is declared

     * @param fieldType the type of the field

     * @return the {@link VarHandle}

     * @throws IllegalAccessError if the declaring class or the field is not

     * accessible to the class performing the operation

     * @throws NoSuchFieldError if the specified field does not exist

     * @throws IllegalArgumentException if the type is not {@code VarHandle}

     */

    public static VarHandle staticFieldVarHandle(MethodHandles.Lookup lookup, String name, Class<VarHandle> type,

                                                 Class<?> declaringClass, Class<?> fieldType) {

        requireNonNull(lookup);

        requireNonNull(name);

        requireNonNull(type);

        requireNonNull(declaringClass);

        requireNonNull(fieldType);

        if (type != VarHandle.class) {

            throw new IllegalArgumentException();

        }

        try {

            return lookup.findStaticVarHandle(declaringClass, name, fieldType);

        }

        catch (ReflectiveOperationException e) {

            throw mapLookupExceptionToError(e);

        }

    }

    /**

     * Finds a {@link VarHandle} for an array type.

     *

     * @param lookup the lookup context describing the class performing the

     * operation (normally stacked by the JVM)

     * @param name unused

     * @param type the required result type (must be {@code Class<VarHandle>})

     * @param arrayClass the type of the array

     * @return the {@link VarHandle}

     * @throws IllegalAccessError if the component type of the array is not

     * accessible to the class performing the operation

     * @throws IllegalArgumentException if the type is not {@code VarHandle}

     */

    public static VarHandle arrayVarHandle(MethodHandles.Lookup lookup, String name, Class<VarHandle> type,

                                           Class<?> arrayClass) {

        requireNonNull(lookup);

        requireNonNull(type);

        requireNonNull(arrayClass);

        if (type != VarHandle.class) {

            throw new IllegalArgumentException();

        }

        return MethodHandles.arrayElementVarHandle(validateClassAccess(lookup, arrayClass));

    }

    private static <T> Class<T> validateClassAccess(MethodHandles.Lookup lookup, Class<T> type) {

        try {

            lookup.accessClass(type);

            return type;

        }

        catch (ReflectiveOperationException ex) {

            throw mapLookupExceptionToError(ex);

        }

    }

}