using System;
using System.IO;
using System.Text;

class FileIOTest {
    public static int Main(String[] args) {
        int ret = 0;
        if (args.Length == 0) {
            Console.WriteLine("Missing file name");
            return 1;
        }
        if (args.Length < 2) {
            Console.WriteLine("Missing key string");
            return 1;
        }

        FileStream stream = null;
        BinaryReader reader = null;
        BinaryWriter writer = null;
        try {
            stream = new FileStream(
                args[0], FileMode.Open, FileAccess.ReadWrite
            );
            reader = new BinaryReader(stream);
            writer = new BinaryWriter(stream);

            byte[] buffer = new byte[1024];
            byte[] key = new ASCIIEncoding().GetBytes(args[1]);
            int keyLen = key.Length;

            long fileSize = stream.Length;
            long processed = 0;
            long pos = 0;

            while (processed < fileSize) {
                int requested = 1024;
                if (requested > fileSize - processed)
                    requested = (int)(fileSize - processed);
                int bytesRead = reader.Read(buffer, 0, requested);
                if (bytesRead <= 0)
                    break;
                for (int i = 0; i < bytesRead; i++) {
                    buffer[i] ^= key[(pos + i) % keyLen];
                }
                stream.Seek(pos, SeekOrigin.Begin);
                writer.Write(buffer, 0, bytesRead);
                processed += bytesRead;
                pos += bytesRead;
            }
        } catch (Exception e) {
            Console.WriteLine(e.Message);
            ret = 1;
        } finally {
            if (stream != null) {
                stream.Close();
            }
        }
        return ret;
    }
}