/**
 * This file is part of Graylog.
 *
 * Graylog 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.
 *
 * Graylog 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 Graylog.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.graylog2.shared.plugins;

import com.google.common.collect.ImmutableList;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;

public class ChainingClassLoader extends ClassLoader {
    public static final Logger LOG = LoggerFactory.getLogger(ChainingClassLoader.class);

    private final List<ClassLoader> classLoaders = new CopyOnWriteArrayList<>();

    public ChainingClassLoader(ClassLoader parent) {
        classLoaders.add(parent);
    }

    @Override
    protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
        Class<?> cls = null;
        for (ClassLoader classLoader : classLoaders) {
            try {
                cls = classLoader.loadClass(name);
            } catch (ClassNotFoundException e) {
                LOG.trace("Class " + name + " not found", e);
            }

            if (cls != null) {
                break;
            }
        }

        if (cls == null) {
            throw new ClassNotFoundException("Class " + name + " not found.");
        }

        return cls;
    }

    @Override
    public URL getResource(String name) {
        URL url = null;
        for (ClassLoader classLoader : classLoaders) {
            url = classLoader.getResource(name);

            if (url != null) {
                break;
            }
        }

        if (url == null && LOG.isTraceEnabled()) {
            LOG.trace("Resource " + name + " not found.");
        }

        return url;
    }

    @Override
    public Enumeration<URL> getResources(String name) throws IOException {
        final List<URL> urls = new ArrayList<>();
        for (ClassLoader classLoader : classLoaders) {
            final Enumeration<URL> resources = classLoader.getResources(name);

            if (resources.hasMoreElements()) {
                urls.addAll(Collections.list(resources));
            }
        }

        if (urls.isEmpty() && LOG.isTraceEnabled()) {
            LOG.trace("Resource " + name + " not found.");
        }

        return Collections.enumeration(urls);
    }

    @Override
    public InputStream getResourceAsStream(String name) {
        InputStream stream = null;
        for (ClassLoader classLoader : classLoaders) {
            stream = classLoader.getResourceAsStream(name);

            if (stream != null) {
                break;
            }
        }

        if (stream == null && LOG.isTraceEnabled()) {
            LOG.trace("Resource " + name + " not found.");
        }

        return stream;
    }

    public List<ClassLoader> getClassLoaders() {
        return ImmutableList.copyOf(classLoaders);
    }

    public boolean addClassLoader(ClassLoader classLoader) {
        return classLoaders.add(classLoader);
    }
}