/*
 * Copyright (C) 2011 The Android Open Source 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 dalvik.system;

import java.io.File;
import java.net.URL;
import java.util.Enumeration;

/**
 * Base class for common functionality between various dex-based
 * {@link ClassLoader} implementations.
 */
public class BaseDexClassLoader extends ClassLoader {
    /** originally specified path (just used for {@code toString()}) */
    private final String originalPath;

    /** originally specified library path (just used for {@code toString()}) */
    private final String originalLibraryPath;

    /** structured lists of path elements */
    private final DexPathList pathList;

    /**
     * Constructs an instance.
     *
     * @param dexPath the list of jar/apk files containing classes and
     * resources, delimited by {@code File.pathSeparator}, which
     * defaults to {@code ":"} on Android
     * @param optimizedDirectory directory where optimized dex files
     * should be written; may be {@code null}
     * @param libraryPath the list of directories containing native
     * libraries, delimited by {@code File.pathSeparator}; may be
     * {@code null}
     * @param parent the parent class loader
     */
    public BaseDexClassLoader(String dexPath, File optimizedDirectory,
            String libraryPath, ClassLoader parent) {
        super(parent);

        this.originalPath = dexPath;
        this.originalLibraryPath = libraryPath;
        this.pathList =
            new DexPathList(this, dexPath, libraryPath, optimizedDirectory);
    }

    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        Class clazz = pathList.findClass(name);

        if (clazz == null) {
            throw new ClassNotFoundException("Didn't find class \"" + name + "\" on path: " + originalPath);
        }

        return clazz;
    }

    @Override
    protected URL findResource(String name) {
        return pathList.findResource(name);
    }

    @Override
    protected Enumeration<URL> findResources(String name) {
        return pathList.findResources(name);
    }

    @Override
    public String findLibrary(String name) {
        return pathList.findLibrary(name);
    }

    /**
     * Returns package information for the given package.
     * Unfortunately, instances of this class don't really have this
     * information, and as a non-secure {@code ClassLoader}, it isn't
     * even required to, according to the spec. Yet, we want to
     * provide it, in order to make all those hopeful callers of
     * {@code myClass.getPackage().getName()} happy. Thus we construct
     * a {@code Package} object the first time it is being requested
     * and fill most of the fields with dummy values. The {@code
     * Package} object is then put into the {@code ClassLoader}'s
     * package cache, so we see the same one next time. We don't
     * create {@code Package} objects for {@code null} arguments or
     * for the default package.
     *
     * <p>There is a limited chance that we end up with multiple
     * {@code Package} objects representing the same package: It can
     * happen when when a package is scattered across different JAR
     * files which were loaded by different {@code ClassLoader}
     * instances. This is rather unlikely, and given that this whole
     * thing is more or less a workaround, probably not worth the
     * effort to address.
     *
     * @param name the name of the class
     * @return the package information for the class, or {@code null}
     * if there is no package information available for it
     */
    @Override
    protected synchronized Package getPackage(String name) {
        if (name != null && !name.isEmpty()) {
            Package pack = super.getPackage(name);

            if (pack == null) {
                pack = definePackage(name, "Unknown", "0.0", "Unknown",
                        "Unknown", "0.0", "Unknown", null);
            }

            return pack;
        }

        return null;
    }

    @Override
    public String toString() {
        return getClass().getName()
                + "[dexPath=" + originalPath + ",libraryPath=" + originalLibraryPath + "]";
    }
}