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/*
 * =========================================================================================
 * Copyright © 2013-2018 the kamon project 
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the
 * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific language governing permissions
 * and limitations under the License.
 * =========================================================================================
 */

package kanela.agent.util.classloader;

import lombok.EqualsAndHashCode;
import lombok.Value;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;


/**
 * This class is a ClassLoader that loads classes before delegating to a parent.
 */
@Value
@EqualsAndHashCode(callSuper = false)
public class ChildFirstURLClassLoader extends URLClassLoader {

    static {
        registerAsParallelCapable();
    }

    private ClassLoader system;

    ChildFirstURLClassLoader(URL[] classpath, ClassLoader parent) {
        super(classpath, parent);
        system = getSystemClassLoader();
    }

    @Override
    protected synchronized Class loadClass(String name, boolean resolve) throws ClassNotFoundException {
        // First, check if the class has already been loaded
        Class c = findLoadedClass(name);
        if (c == null) {
            if (system != null) {
                try {
                    // checking system: jvm classes, endorsed, cmd classpath, etc.
                    c = system.loadClass(name);
                }catch (ClassNotFoundException ignored) {}
            }
            if (c == null) {
                try {
                    // checking local
                    c = findClass(name);
                } catch (ClassNotFoundException e) {
                    // checking parent
                    // This call to loadClass may eventually call findClass again, in case the parent doesn't find anything.
                    c = super.loadClass(name, resolve);
                }
            }
        }
        if (resolve) {
            resolveClass(c);
        }
        return c;
    }

    @Override
    public URL getResource(String name) {
        URL url = null;
        if (system != null) {
            url = system.getResource(name);
        }
        if (url == null) {
            url = findResource(name);
            if (url == null) {
                // This call to getResource may eventually call findResource again, in case the parent doesn't find anything.
                url = super.getResource(name);
            }
        }
        return url;
    }

    @Override
    public Enumeration getResources(String name) throws IOException {
        /**
         * Similar to super, but local resources are enumerated before parent resources
         */
        Enumeration systemUrls = null;
        if (system != null) {
            systemUrls = system.getResources(name);
        }
        Enumeration localUrls = findResources(name);
        Enumeration parentUrls = null;
        if (getParent() != null) {
            parentUrls = getParent().getResources(name);
        }
        final List urls = new ArrayList();
        if (systemUrls != null) {
            while(systemUrls.hasMoreElements()) {
                urls.add(systemUrls.nextElement());
            }
        }
        if (localUrls != null) {
            while (localUrls.hasMoreElements()) {
                urls.add(localUrls.nextElement());
            }
        }
        if (parentUrls != null) {
            while (parentUrls.hasMoreElements()) {
                urls.add(parentUrls.nextElement());
            }
        }
        return new Enumeration() {
            Iterator iter = urls.iterator();

            public boolean hasMoreElements() {
                return iter.hasNext();
            }
            public URL nextElement() {
                return iter.next();
            }
        };
    }

    @Override
    public InputStream getResourceAsStream(String name) {
        URL url = getResource(name);
        try {
            return url != null ? url.openStream() : null;
        } catch (IOException ignored) {}
        return null;
    }

}