/**

 * 

 */

package stx.libjava.tools.environment.internal;

import java.lang.reflect.Field;

import java.util.Iterator;

import java.util.Vector;

/**

 * <code>ReflectiveClassLoader</code> is a simple wrapper on a {@link java.lang.ClassLoader} that provides

 * reflective features standard {@link java.lang.ClassLoader} doesn't.

 * In particular, it provides {@link #isPackage(String)} which is used

 * by {@link stx.libjava.tools.environment.ReflectiveEnvironment}.

 * 

 * The way {@link java.lang.ClassLoader} accesses and loads classes differ

 * so specialised subclasses exists for individual {@link java.lang.ClassLoader}

 * instances in order to provide more accurate answers. Therefore use method 

 * {@link #forClassLoader(ClassLoader)} to create an instance of a 

 * <code>ReflectiveClassLoader</code> 

 *  

 * @author Jan Vrany <jan.vrany [at] fit.cvut.cz>

 *

 */

@stx.libjava.annotation.Package("stx:libjava/tools")

public class ReflectiveClassLoader {

    /** 

     * Shared cached {@link ReflectiveClassLoader} representing primordial class loader. 

     * Primordial class loader is not to change during the life-span of a JVM, so it can be

     * safely cached.  

     * 

     */

    protected static ReflectiveClassLoader PRIMORDIAL = new ReflectiveURLClassLoader(null, sun.misc.Launcher.getBootstrapClassPath().getURLs());

    /**

     * Cached {@link Field} to access normally inaccessible field {@link java.lang.ClassLoader#classes}. 

     * On OpenJDK based libraries, this field contains a list of loaded classes. This list is used

     * to check for loaded classes as a short-circuit (or as the only way for generic class loaders) 

     */

    protected static Field FIELD_ClassLoader_Classes;

    /**

     * A real {@link ClassLoader} this {@link ReflectiveClassLoader} reflects on. 

     * For primordial class loader the value is <code>null</code>.

     */

    protected ClassLoader realClassLoader;

    /**

     * A cached {@link ReflectiveClassLoader} representing a parent class loader of

     * this object. For primordial class loader the value is <code>null</code>.

     */

    protected ReflectiveClassLoader parent;

    protected ReflectiveClassLoader(ClassLoader loader) {

        realClassLoader = loader;

    }

    static {

        try {

            FIELD_ClassLoader_Classes = ClassLoader.class.getDeclaredField("classes");

            FIELD_ClassLoader_Classes.setAccessible(true);

        } catch (NoSuchFieldException e) {

            FIELD_ClassLoader_Classes = null;

        } catch (SecurityException e) {

            FIELD_ClassLoader_Classes = null;

        }

    }

    /**

     * Returns a suitable {@link ReflectiveClassLoader} for given (real) {@link ClassLoader}.

     * 

     * @param loader a {@link ClassLoader} on which to reflect.

     * @return a {@link ReflectiveClassLoader} for given @param loader. 

     */

    public static ReflectiveClassLoader forClassLoader(ClassLoader loader) {

        if (loader == null) {

            return PRIMORDIAL;

        }

        /* This is kind of ugly, we should provide a way to register custom subclasses,

         * but for now, keep it simple. We'll see if this machinery proves usable at all. 

         */

        if (loader instanceof java.net.URLClassLoader) {

            return new ReflectiveURLClassLoader((java.net.URLClassLoader)loader);

        }

        return new ReflectiveClassLoader(loader);

    }

    public ReflectiveClassLoader getParent() {

        if (realClassLoader == null) return null;

        if (parent == null) {

            parent = ReflectiveClassLoader.forClassLoader(realClassLoader.getParent());

        }

        return parent;

    }

    /**

     * Return <code>true</code> is package with name @param packageName exists under

     * this class loader, <code>false</code> otherwise.  

     * 

     * A package is considered to exist if there's at least one class in that package. 

     * However, individual {@link ReflectiveClassLoader}s may extend the definition of

     * {@link #isPackage(String)} For example {@link ReflectiveURLClassLoader} may return

     * <code>true</code> if a directory exists along it's class path.  

     * 

     * @param packageName a name of the package

     * @return <code>true</code> if such package exists, <code>false</code> otherwise

     */

    public boolean isPackage(String packageName) {

        // First, check parent class loader

        if (realClassLoader != null) {

            if (realClassLoader.getParent() == null) {

                if (PRIMORDIAL.isPackage(packageName)) {

                    return true;

                }

            } else {

                if (getParent().isPackage(packageName)) {

                    return true;

                }

            }

        }

        // Second, consult list of already loaded classes.

        if (realClassLoader != null && FIELD_ClassLoader_Classes != null) {

            int packageNameLen = packageName.length();

            Vector<Class<?>> classes;

            try {

                classes = (Vector<Class<?>>)FIELD_ClassLoader_Classes.get(realClassLoader);

                if (classes.size() > 0) {

                    Iterator<Class<?>> i = classes.iterator();

                    while (i.hasNext()) {                    

                        String className = i.next().getName();

                        int classNameLen = className.length();                  

                        if ((classNameLen > packageNameLen) &&

                            (className.charAt(packageNameLen) == '.') &&

                            (className.startsWith(packageName))) {

                            return true;

                        } else if ((classNameLen == packageNameLen) &&

                                    className.equals(packageName)) {

                            return false;

                        }

                    }

                }

            } catch (IllegalArgumentException e) {

                // If we're for whatever reason fobidden access to classes field,

                // well, just ignore it. 

            } catch (IllegalAccessException e) {

                // same as above. 

            }

        }

        // Last, we don't know. For generic ClassLoader, there's no other way

        // to figure out what packages are there or not. So be conservative...

        return false;

    }

    public ClassLoader getRealClassLoader() {

        return realClassLoader;

    }

}