/*
 * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.istack.internal.tools;

import java.io.InputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.net.URL;
import java.net.MalformedURLException;
import java.util.Enumeration;

/**
 * Load classes/resources from a side folder, so that
 * classes of the same package can live in a single jar file.
 *
 * <p>
 * For example, with the following jar file:
 * <pre>
 *  /
 *  +- foo
 *     +- X.class
 *  +- bar
 *     +- X.class
 * </pre>
 * <p>
 * {@link ParallelWorldClassLoader}("foo/") would load <tt>X.class<tt> from
 * <tt>/foo/X.class</tt> (note that X is defined in the root package, not
 * <tt>foo.X</tt>.
 *
 * <p>
 * This can be combined with  {@link MaskingClassLoader} to mask classes which are loaded by the parent
 * class loader so that the child class loader
 * classes living in different folders are loaded
 * before the parent class loader loads classes living the jar file publicly
 * visible
 * For example, with the following jar file:
 * <pre>
 *  /
 *  +- foo
 *     +- X.class
 *  +- bar
 *     +-foo
 *        +- X.class
 * </pre>
 * <p>
 * {@link ParallelWorldClassLoader}(MaskingClassLoader.class.getClassLoader()) would load <tt>foo.X.class<tt> from
 * <tt>/bar/foo.X.class</tt> not the <tt>foo.X.class<tt> in the publicly visible place in the jar file, thus
 * masking the parent classLoader from loading the class from  <tt>foo.X.class<tt>
 * (note that X is defined in the  package foo, not
 * <tt>bar.foo.X</tt>.
 *
 * @author Kohsuke Kawaguchi
 */
public class ParallelWorldClassLoader extends ClassLoader {

    /**
     * Strings like "prefix/", "abc/", or "" to indicate
     * classes should be loaded normally.
     */
    private final String prefix;

    public ParallelWorldClassLoader(ClassLoader parent,String prefix) {
        super(parent);
        this.prefix = prefix;
    }

    protected Class findClass(String name) throws ClassNotFoundException {
        StringBuffer sb = new StringBuffer(name.length()+prefix.length()+6);
        sb.append(prefix).append(name.replace('.','/')).append(".class");

        InputStream is = getParent().getResourceAsStream(sb.toString());
        if (is==null)
            throw new ClassNotFoundException(name);

        try {
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            byte[] buf = new byte[1024];
            int len;
            while((len=is.read(buf))>=0)
                baos.write(buf,0,len);

            buf = baos.toByteArray();
            int packIndex = name.lastIndexOf('.');
            if (packIndex != -1) {
                String pkgname = name.substring(0, packIndex);
                // Check if package already loaded.
                Package pkg = getPackage(pkgname);
                if (pkg == null) {
                    definePackage(pkgname, null, null, null, null, null, null, null);
                }
            }
            return defineClass(name,buf,0,buf.length);
        } catch (IOException e) {
            throw new ClassNotFoundException(name,e);
        }
    }

    protected URL findResource(String name) {
        return getParent().getResource(prefix+name);
    }

    protected Enumeration<URL> findResources(String name) throws IOException {
        return getParent().getResources(    prefix+name);
    }

    /**
     * Given the URL inside jar, returns the URL to the jar itself.
     */
    public static URL toJarUrl(URL res) throws ClassNotFoundException, MalformedURLException {
        String url = res.toExternalForm();
        if(!url.startsWith("jar:"))
            throw new ClassNotFoundException("Loaded outside a jar "+url);
        url = url.substring(4); // cut off jar:
        url = url.substring(0,url.lastIndexOf('!'));    // cut off everything after '!'
        return new URL(url);
    }
}