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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.extension;

import static org.neo4j.internal.helpers.collection.Iterables.stream;

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.List;
import java.util.Objects;
import org.neo4j.collection.Dependencies;
import org.neo4j.common.DependencyResolver;
import org.neo4j.exceptions.UnsatisfiedDependencyException;
import org.neo4j.kernel.extension.context.ExtensionContext;
import org.neo4j.kernel.impl.util.DependenciesProxy;
import org.neo4j.kernel.lifecycle.LifeSupport;
import org.neo4j.kernel.lifecycle.Lifecycle;

public abstract class AbstractExtensions implements DependencyResolver, Lifecycle {
    private final ExtensionContext extensionContext;
    private final List> extensionFactories;
    private final Dependencies dependencies;
    private final LifeSupport life = new LifeSupport();
    private final ExtensionFailureStrategy extensionFailureStrategy;

    AbstractExtensions(
            ExtensionContext extensionContext,
            Iterable> extensionFactories,
            Dependencies dependencies,
            ExtensionFailureStrategy extensionFailureStrategy,
            ExtensionType extensionType) {
        this.extensionContext = extensionContext;
        this.extensionFailureStrategy = extensionFailureStrategy;
        this.extensionFactories = stream(extensionFactories)
                .filter(e -> e.getExtensionType() == extensionType)
                .toList();
        this.dependencies = dependencies;
    }

    @Override
    public void init() {
        for (ExtensionFactory extensionFactory : extensionFactories) {
            try {
                Object extensionDependencies = getExtensionDependencies(extensionFactory);
                Lifecycle dependency = newInstance(extensionContext, extensionFactory, extensionDependencies);
                Objects.requireNonNull(dependency, extensionFactory + " returned a null extension.");
                life.add(dependencies.satisfyDependency(dependency));
            } catch (UnsatisfiedDependencyException exception) {
                extensionFailureStrategy.handle(extensionFactory, exception);
            } catch (Throwable throwable) {
                extensionFailureStrategy.handle(extensionFactory, throwable);
            }
        }

        life.init();
    }

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

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

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

    @Override
    public  T resolveDependency(Class type, SelectionStrategy selector) {
        Iterable typeDependencies = resolveTypeDependencies(type);
        return selector.select(type, typeDependencies);
    }

    @Override
    public  Iterable resolveTypeDependencies(Class type) {
        return life.getLifecycleInstances().stream()
                .filter(type::isInstance)
                .map(type::cast)
                .toList();
    }

    @Override
    public boolean containsDependency(Class type) {
        return life.getLifecycleInstances().stream().anyMatch(type::isInstance);
    }

    private Object getExtensionDependencies(ExtensionFactory factory) {
        // superclass is either ExtensionFactory or it's subclass that can be generic too
        Class factoryType = factory.getClass().getSuperclass();
        Type genericSuperclass = factory.getClass().getGenericSuperclass();
        while (factoryType.getGenericSuperclass() instanceof ParameterizedType) {
            genericSuperclass = factoryType.getGenericSuperclass();
            factoryType = factoryType.getSuperclass();
        }
        Class configurationClass = (Class) ((ParameterizedType) genericSuperclass).getActualTypeArguments()[0];
        return DependenciesProxy.dependencies(dependencies, configurationClass);
    }

    @SuppressWarnings("unchecked")
    private static  Lifecycle newInstance(
            ExtensionContext extensionContext, ExtensionFactory factory, Object dependencies) {
        return factory.newInstance(extensionContext, (T) dependencies);
    }
}