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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) 2002-2015 "Neo Technology,"
 * Network Engine for Objects in Lund AB [http://neotechnology.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.graphdb;

import java.util.Iterator;

import org.neo4j.function.Supplier;

/**
 * Find a dependency given a type. This can be the exact type or a super type of
 * the actual dependency.
 */
public interface DependencyResolver
{
    /**
     * Tries to resolve a dependency that matches a given class. No specific
     * {@link SelectionStrategy} is used, so the first encountered matching dependency will be returned.
     *
     * @param type the type of {@link Class} that the returned instance must implement.
     * @param  the type that the returned instance must implement
     * @return the resolved dependency for the given type.
     * @throws IllegalArgumentException if no matching dependency was found.
     */
     T resolveDependency( Class type ) throws IllegalArgumentException;

    /**
     * Tries to resolve a dependency that matches a given class. All candidates are fed to the
     * {@code selector} which ultimately becomes responsible for making the choice between all available candidates.
     *
     * @param type the type of {@link Class} that the returned instance must implement.
     * @param selector {@link SelectionStrategy} which will make the choice of which one to return among
     * matching candidates.
     * @param  the type that the returned instance must implement
     * @return the resolved dependency for the given type.
     * @throws IllegalArgumentException if no matching dependency was found.
     */
     T resolveDependency( Class type, SelectionStrategy selector ) throws IllegalArgumentException;

     Supplier provideDependency( final Class type, final SelectionStrategy selector);

     Supplier provideDependency( final Class type );


    /**
     * Responsible for making the choice between available candidates.
     */
    interface SelectionStrategy
    {
        /**
         * Given a set of candidates, select an appropriate one. Even if there are candidates this
         * method may throw {@link IllegalArgumentException} if there was no suitable candidate.
         *
         * @param type the type of items.
         * @param candidates candidates up for selection, where one should be picked. There might
         * also be no suitable candidate, in which case an exception should be thrown.
         * @param  the type of items
         * @return a suitable candidate among all available.
         * @throws IllegalArgumentException if no suitable candidate was found.
         */
         T select( Class type, Iterable candidates ) throws IllegalArgumentException;
    }

    /**
     * Adapter for {@link DependencyResolver} which will select the first available candidate by default
     * for {@link #resolveDependency(Class)}.
     */
    abstract class Adapter implements DependencyResolver
    {
        private static final SelectionStrategy FIRST = new SelectionStrategy()
        {
            @Override
            public  T select( Class type, Iterable candidates ) throws IllegalArgumentException
            {
                Iterator iterator = candidates.iterator();
                if ( !iterator.hasNext() )
                {
                    throw new IllegalArgumentException( "Could not resolve dependency of type:" + type.getName() );
                }
                return iterator.next();
            }
        };

        @Override
        public  T resolveDependency( Class type ) throws IllegalArgumentException
        {
            return resolveDependency( type, FIRST );
        }

        public  Supplier provideDependency( final Class type, final SelectionStrategy selector)
        {
            return new Supplier()
            {
                @Override
                public T get()
                {
                    return resolveDependency( type, selector );
                }
            };
        }

        public  Supplier provideDependency( final Class type )
        {
            return new Supplier()
            {
                @Override
                public T get()
                {
                    return resolveDependency( type );
                }
            };
        }
    }
}