// CS7
//
// Encrypt.java - A small program that uses a simple Caesar
// cipher to encrypt a text file.
// 
// TO RUN THIS FILE:
//   1.  copy it to your java directory
//   2.  verify that the tio package is available
//   3.  create a simple text file (pico can be used for this)
//   4.  run the program as follows:  java Encrypt INPUTFILE OUTPUTFILE
//       (plug in the name of your text file followed by a new file name)
//   5.  enter a key value (pick some small integer)
//   6.  do a listing and cat the new file to look inside
//   7.  it is easy to decrypt as well - do you know how???
//
import java.io.*;
import tio.*;

class Encrypt {

  public static void main(String[] args) throws IOException {
	// first check for proper usage	
	if (args.length < 2) {
	  System.out.println("Usage: java Encrypt clearFile outputFile");
	  System.exit(1);
	}

	// load the source file and create the output file
	ReadInput in = new ReadInput(args[0]);
	PrintWriter out = new PrintWriter(new FileWriter(args[1]));

	// get the key
	System.out.print("Please enter the encryption key (int): ");
	int key = Console.in.readInt();

	// perform the encryption
	System.out.print("Now encrypting " + args[0] + "...");
	encrypt(in, out, key);
	System.out.println("Complete.");
	System.out.println("Output written to " + args[1]);
   
	out.close();
  }// end main()

  // transforms an upper case char into a new one by shifting by
  // key spaces (it wraps around if 'Z' is reached)
  public static int caeserCipher(char c, int key) {
	return (c - 'A' + key) % 26 + 'A';
  }

  // encrypt() takes a source text file, runs through each char it
  // contains and writes the encrypted char to the output file.
  public static void encrypt(ReadInput source, PrintWriter dest, int key) {
	while (source.hasMoreElements()) {
	  char c = (char) source.readChar();
	  if (Character.isLetter(c))		// uses wrapper class to check
	    dest.print((char) caeserCipher(Character.toUpperCase(c),key));
	  else
	    dest.print(c);	// just copy non-letters
	}
  }// end encrypt()

}// end class