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Neo4j kernel is a lightweight, embedded Java database designed to store data structured as graphs rather than tables. For more information, see http://neo4j.org.

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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [https://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.kernel.impl.util;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Proxy;
import java.util.function.Supplier;
import org.neo4j.common.DependencyResolver;
import org.neo4j.exceptions.UnsatisfiedDependencyException;

/**
 * Used to create dynamic proxies that implement dependency interfaces. Each method should have no arguments
 * and return the type of the dependency desired. It will be mapped to a lookup in the provided {@link DependencyResolver}.
 * Methods may also use a {@link Supplier} type for deferred lookups.
 */
public class DependenciesProxy {
    private DependenciesProxy() {
        throw new AssertionError(); // no instances
    }

    /**
     * Create a dynamic proxy that implements the given interface and backs invocation with lookups into the given
     * dependency resolver.
     *
     * @param dependencyResolver original resolver to proxy
     * @param dependenciesInterface interface to proxy
     * @param  type of the interface
     * @return a proxied {@link DependencyResolver} that will lookup dependencies in {@code dependencyResolver} based
     * on method names in the provided {@code dependenciesInterface}
     */
    public static  T dependencies(DependencyResolver dependencyResolver, Class dependenciesInterface) {
        return dependenciesInterface.cast(Proxy.newProxyInstance(
                dependenciesInterface.getClassLoader(),
                new Class[] {dependenciesInterface},
                new ProxyHandler(dependencyResolver)));
    }

    private static class ProxyHandler implements InvocationHandler {
        private final DependencyResolver dependencyResolver;

        ProxyHandler(DependencyResolver dependencyResolver) {
            this.dependencyResolver = dependencyResolver;
        }

        @Override
        public Object invoke(Object proxy, Method method, Object[] args) {
            try {
                if (method.getReturnType().equals(Supplier.class)) {
                    return dependencyResolver.provideDependency(
                            (Class) ((ParameterizedType) method.getGenericReturnType()).getActualTypeArguments()[0]);
                } else {
                    return dependencyResolver.resolveDependency(method.getReturnType());
                }
            } catch (IllegalArgumentException e) {
                throw new UnsatisfiedDependencyException(e);
            }
        }
    }
}