import java.util.*;
import java.net.*;
import java.io.*;

// Le class loader !
class ProgramLoader extends ClassLoader {
	// the base directory for loading local classes
	String basedir;
	boolean url;
	// The cache for name binding.
	Hashtable cache = new Hashtable();
	// --------------------
	// Private method to read an input strean until the end
	private int read(InputStream ds, byte zone[]) throws IOException {
		int n,off=0,len=zone.length;
		while (len>0) {
			n = ds.read(zone, off, len);
			if (n == -1) return off;
			len -= n; off +=n;
		}
		return len;
	}
	// --------------------
	// Private method that read a class from a local file.
	private byte loadClassDataFromFile (String name)[] {
		File class_file;
		FileInputStream class_stream;
		long len = 0;
		class_file = new File(basedir+"/"+name+".class");
		if (!class_file.exists()) return null;
		len = class_file.length();
		byte data[] = new byte[(int)len];
		try {
			class_stream = new FileInputStream(class_file);
			int x = read(class_stream, data);
			return data;
		} catch (FileNotFoundException ex) {
			System.out.println("loadClassDataFromFile: "+ex);
			return null;
		} catch (IOException ex) {
			System.out.println("loadClassDataFromFile: "+ex);
			return null;
		}
	}
	// --------------------
	// Private method that read a class from a web server.
	// Sorry, I can't do better !!!
	// I can't get the size of the remote file before I read it ...
	private byte loadClassDataFromURL (String name)[] {
		try {
			//System.out.println("basedir : "+basedir);
			//System.out.println("name : "+name);
			URL remloc = new URL(basedir+"/"+name+".class");
			DataInputStream dis = new DataInputStream(remloc.openStream());
			byte data[] = new byte[50000];
			int x = read(dis, data);
			byte data2[] = new byte[x];
			for (int i = 0;i<x;i++) data2[i] = data[i];
			return data2;
		} catch (MalformedURLException ex) {
			System.out.println("loadClassDataFromURL: "+ex);
			return null;
		} catch (IOException ex) {
			System.out.println("loadClassDataFromURL: "+ex);
			return null;
		}
	}
	// --------------------
	// the class constructor
	public ProgramLoader(String dir) {
		basedir = dir;
		if (dir.startsWith("http")) url = true;
		else url = false;
	}
	// --------------------
	// The main entry point of the class which allows class names to be
	// bound and classes to be loaded if needed.
	public synchronized Class loadClass(String name) {
		Class  theclass;
		System.out.println(" ------------> Load Class "+name);
		// First case: the name is already resolved in the cache.
		theclass = (Class)cache.get(name);
		if (theclass != null) {
			//System.out.println("Class "+name+" found in the cache");
			return theclass;
		}	
		try {
			theclass = findSystemClass(name);
			//System.out.println("	Class "+name+" is a system class");
			cache.put(name,theclass);
			return theclass;
		} catch (ClassNotFoundException ex) {
			// Try to load it as a class from a file or web server
			byte data[];
			if (url)
				data = loadClassDataFromURL(name);
			else
				data = loadClassDataFromFile(name);
			if (data != null) {
				try {
					//System.out.println("	+++++Class "+name+" is loaded remotly");
					theclass = defineClass(name,data,0,data.length);
					cache.put(name,theclass);
					return theclass;
				} catch (ClassFormatError ex1) {
					System.out.println("loadClass: "+ex1);
					return null;
				}
			}
		}
		System.out.println("loadClass: class "+name+" not found");
		return null;
	}
}