/*

 * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * 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).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

/*

 * This file is available under and governed by the GNU General Public

 * License version 2 only, as published by the Free Software Foundation.

 * However, the following notice accompanied the original version of this

 * file, and Oracle licenses the original version of this file under the BSD

 * license:

 */

/*

   Copyright 2009-2013 Attila Szegedi

*/

package jdk.dynalink.linker;

import java.lang.invoke.MethodHandles;

import java.util.function.Supplier;

import jdk.dynalink.SecureLookupSupplier;

import jdk.dynalink.beans.BeansLinker;

import jdk.dynalink.linker.support.TypeUtilities;

/**

 * Optional interface that can be implemented by {@link GuardingDynamicLinker}

 * implementations to provide language-specific type conversion capabilities.

 * Note that if you implement this interface, you will very likely want to

 * implement {@link ConversionComparator} interface too, as your additional

 * language-specific conversions, in absence of a strategy for prioritizing

 * these conversions, will cause more ambiguity for {@link BeansLinker} in

 * selecting the correct overload when trying to link to an overloaded Java

 * method.

 */

public interface GuardingTypeConverterFactory {

    /**

     * Returns a guarded type conversion that receives a value of the specified

     * source type and returns a value converted to the specified target type.

     * Value types can be either primitives or reference types, including

     * interfaces, so you can even provide converters for converting your

     * language's objects to Java interfaces and classes by generating adapters

     * for them.

     * <p>

     * The type of the invocation is <code>(sourceType)&rarr;targetType</code>, while the

     * type of the guard is <code>(sourceType)&rarr;boolean</code>. You are allowed to

     * return unconditional invocations (with no guard) if the source type is

     * specific to your runtime and your runtime only.

     * <p>Note that this method will never be invoked for

     * {@link TypeUtilities#isMethodInvocationConvertible(Class, Class) method

     * invocation conversions} as those can be automatically applied by

     * {@link java.lang.invoke.MethodHandle#asType(MethodType)}.

     * An implementation can assume it is never requested to produce a

     * converter for those conversions. If a language runtime needs to customize

     * method invocation conversions, it should

     * {@link jdk.dynalink.DynamicLinkerFactory#setAutoConversionStrategy(MethodTypeConversionStrategy)

     * set an autoconversion strategy in the dynamic linker factory} instead.

     * <p>Dynalink is at liberty to either cache some of the returned converters

     * or to repeatedly request the converter factory to create the same

     * conversion.

     *

     * @param sourceType source type

     * @param targetType the target type.

     * @param lookupSupplier a supplier for retrieving the lookup of the class

     * on whose behalf a type converter is requested. When a converter is

     * requested as part of linking an {@code invokedynamic} instruction the

     * supplier will return the lookup passed to the bootstrap method, otherwise

     * if the method is invoked from within a

     * {@link LinkerServices#getWithLookup(Supplier, jdk.dynalink.SecureLookupSupplier)}

     * it will delegate to the secure lookup supplier. In any other case,

     * it will return the public lookup. A typical case where the lookup might

     * be needed is when the converter creates a Java adapter class on the fly

     * (e.g. to convert some object from the dynamic language into a Java

     * interface for interoperability). Invoking the {@link Supplier#get()}

     * method on the passed supplier will be subject to the same security checks

     * as {@link SecureLookupSupplier#getLookup()}. An implementation should avoid

     * retrieving the lookup if it is not needed so as to avoid the expense of

     * {@code AccessController.doPrivileged} call.

     * @return a guarded invocation that can take an object (if it passes guard)

     * and return another object that is its representation coerced into the

     * target type. In case the factory is certain it is unable to handle a

     * conversion, it can return null. In case the factory is certain that it

     * can always handle the conversion, it can return an unconditional

     * invocation (one whose guard is null).

     * @throws Exception if there was an error during creation of the converter

     * @see LinkerServices#getWithLookup(Supplier, SecureLookupSupplier)

     */

    public GuardedInvocation convertToType(Class<?> sourceType, Class<?> targetType, Supplier<MethodHandles.Lookup> lookupSupplier) throws Exception;

}