import java.io.FileInputStream;
import java.io.FileOutputStream;

public class DumbCrypt {

    private int generator;

    public void setKey(int key){
        generator = key;
    }

    public byte[] crypt(byte[] input){
        byte[] output = new byte[input.length];
        // generate some pseudo-random bytes
        for(int i = 0; i < input.length; i++){
            generator *= 314159;
            generator += 2718;
            output[i] = (byte) generator;
        }
        // then exclusive-or each with an input byte
        for(int i = 0; i < input.length; i++){
            output[i] ^= input[i];
        }
        return output;
    }

    public static void main(String args[]) throws Exception {
        if(args.length < 2 || args.length > 3){
            System.err.println("usage: java DumbCrypt inFile outFile [key]");
            System.exit(1);
        } else if(args.length < 3){
            System.err.println("Key recovery feature not yet written.\n");
            System.exit(1);
        } else {
            DumbCrypt crypter = new DumbCrypt();
            crypter.setKey(Integer.parseInt(args[2]));
            FileInputStream inStream = new FileInputStream(args[0]);
            byte[] input = new byte[inStream.available()];
            inStream.read(input);
            FileOutputStream outStream = new FileOutputStream(args[1]);
            outStream.write(crypter.crypt(input));
        }
    }
}