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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.kernel.extension;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.List;

import org.neo4j.graphdb.DependencyResolver;
import org.neo4j.helpers.Function;
import org.neo4j.helpers.Predicate;
import org.neo4j.helpers.collection.Iterables;
import org.neo4j.kernel.impl.util.UnsatisfiedDependencyException;
import org.neo4j.kernel.lifecycle.LifeSupport;
import org.neo4j.kernel.lifecycle.Lifecycle;

import static org.neo4j.helpers.collection.Iterables.filter;
import static org.neo4j.helpers.collection.Iterables.map;

public class KernelExtensions extends DependencyResolver.Adapter implements Lifecycle
{
    private final List> kernelExtensionFactories;
    private final DependencyResolver dependencyResolver;
    private final LifeSupport life = new LifeSupport();
    private final UnsatisfiedDependencyStrategy unsatisfiedDepencyStrategy;

    public KernelExtensions( Iterable> kernelExtensionFactories,
            DependencyResolver dependencyResolver, UnsatisfiedDependencyStrategy unsatisfiedDepencyStrategy )
    {
        this.unsatisfiedDepencyStrategy = unsatisfiedDepencyStrategy;
        this.kernelExtensionFactories = Iterables.addAll( new ArrayList>(),
                kernelExtensionFactories );
        this.dependencyResolver = dependencyResolver;
    }

    @Override
    public void init() throws Throwable
    {

        for ( KernelExtensionFactory kernelExtensionFactory : kernelExtensionFactories )
        {
            Object configuration = getKernelExtensionDependencies( kernelExtensionFactory );

            try
            {
                life.add( kernelExtensionFactory.newKernelExtension( configuration) );
            }
            catch ( UnsatisfiedDependencyException e )
            {
                unsatisfiedDepencyStrategy.handle( kernelExtensionFactory, e );
            }
        }

        life.init();
    }

    @Override
    public void start() throws Throwable
    {
        life.start();
    }

    @Override
    public void stop() throws Throwable
    {
        life.stop();
    }

    @Override
    public void shutdown() throws Throwable
    {
        life.shutdown();
    }

    public boolean isRegistered( Class kernelExtensionFactoryClass )
    {
        for ( KernelExtensionFactory kernelExtensionFactory : kernelExtensionFactories )
        {
            if ( kernelExtensionFactoryClass.isInstance( kernelExtensionFactory ) )
            {
                return true;
            }
        }
        return false;
    }

    @Override
    public  T resolveDependency( final Class type, SelectionStrategy selector ) throws IllegalArgumentException
    {
        Iterable filtered = filter( new TypeFilter( type ), life.getLifecycleInstances() );
        Iterable casted = map( new CastFunction( type ), filtered );
        return selector.select( type, casted );
    }

    private Object getKernelExtensionDependencies( KernelExtensionFactory factory )
    {
        Class configurationClass = (Class) ((ParameterizedType) factory.getClass().getGenericSuperclass())
                .getActualTypeArguments()[0];
        return Proxy.newProxyInstance( configurationClass.getClassLoader(), new Class[]{configurationClass},
                new KernelExtensionHandler() );
    }

    public Iterable> listFactories()
    {
        return kernelExtensionFactories;
    }

    private static class TypeFilter implements Predicate
    {
        private final Class type;

        public TypeFilter( Class type )
        {
            this.type = type;
        }

        @Override
        public boolean accept( Object extension )
        {
            return type.isInstance( extension );
        }
    }

    private class KernelExtensionHandler
            implements InvocationHandler
    {
        @Override
        public Object invoke( Object proxy, Method method, Object[] args ) throws Throwable
        {
            try
            {
                return dependencyResolver.resolveDependency( method.getReturnType() );
            }
            catch ( IllegalArgumentException e )
            {
                throw new UnsatisfiedDependencyException( e );
            }
        }
    }

    private class CastFunction implements Function
    {
        private final Class type;

        public CastFunction( Class type )
        {
            this.type = type;
        }

        @Override
        public T apply( Object o )
        {
            return type.cast( o );
        }
    }
}