/*--------------------------------------------------------
*   Main Program: Encrypting/Decrypting a text file
*---------------------------------------------------------
*   Date: 8 Febuary 2012
*   @author Chris Wallace
*/
import java.util.Scanner;
import java.io.*;
public class Enigma{
    public static void main(String[] args){
        Scanner keyboard = new Scanner(System.in);
        System.out.println("Enigma Program- Main Menu");
        System.out.println("\t e: Encrypt a File");
        System.out.println("\t d: Decrypt a File");
        System.out.println("\t q: Quit");
        System.out.print("Please Enter A Command: ");
        char command = (keyboard.next()).charAt(0);
        keyboard.nextLine();
        while (command != 'q'){
            String fileName = getFileName(keyboard,command);
            String fileOutName = getOutFileName(keyboard);
            try{
                File fileobject = new File(fileName);
                FileReader inputFile = new FileReader(fileobject);
                PrintWriter outputFile = new PrintWriter(fileOutName);
                if (command == 'e'){
                    encryptFile(inputFile, outputFile);
                    System.out.println("Encryption Complete.");
                }
                else if (command == 'd'){
                    decryptFile(inputFile, outputFile);
                    System.out.println("Decryption Complete.");
                }
                inputFile.close();
                outputFile.close();
            }
            catch(IOException e){
                System.out.println("An Error occured during file input/output");
            }
            System.out.println("\n-------------------------\nEnigma Program- Main Menu");
            System.out.println("\t e: Encrypt a File");
            System.out.println("\t d: Decrypt a File");
            System.out.println("\t q: Quit");
            System.out.print("Please Enter A Command: ");
            command = (keyboard.next()).charAt(0);
            keyboard.nextLine();
        }
        System.out.println("\nGoodbye!");
    }

    public static String getFileName(Scanner keyboard, char command){
        if (command == 'e'){
            System.out.print("Please enter the File Name to Encrypt: ");
        }
        else{
            System.out.print("Please enter the File Name to Decrypt: ");
        }
        return keyboard.nextLine();
    }


    public static String getOutFileName(Scanner keyboard){
        System.out.print("Please enter the File Name of the file to Output: ");
        return keyboard.nextLine();
    }

    public static char[] initRotor(int offset){
        int ascii_size = 128;
        char[] a = new char[ascii_size];
        // add all ASCII characters to the rotor
        for(int rotor_pos = 0; rotor_pos < (ascii_size); rotor_pos++)
        {
            a[rotor_pos] = (char)((rotor_pos + offset) % ascii_size);
        }
        return a;
    }
    public static int charIsAt(char a[], char ch){
        int x = 0;
        boolean cont = true;
        for (int i = 0; (i < 128 && cont); i++){
            if (a[i] == ch){
                cont = false;
                x = i;
            }
        }
        return x;
    }
    public static void encryptFile(FileReader inputFile, PrintWriter outputFile) throws IOException{
        char[] rotor1 = initRotor(0);
        char[] rotor2 = initRotor(7);
        char[] backplate = initRotor(13);
        int rotor1Count = 0, rotor2Count = 0;
        char ch = (char)inputFile.read();;
        while(ch != (char)-1){
            int i = 0;
            //take next input char
            i = charIsAt(rotor1, ch) + rotor1Count;
            if (i >= 128){
                i = i - 128;
            }
            ch = backplate[i];
            i = charIsAt(rotor2, ch) + rotor2Count;
            if (i >= 128){
                i = i - 128;
            }
            ch = backplate[i];
            //write single character
            outputFile.print(ch);
            ch = (char)inputFile.read();
            //advance rotor
            rotor1Count++;
            if (rotor1Count > 127){
                rotor1Count = 0;
                rotor2Count++;
                if (rotor2Count > 127){
                    rotor2Count = 0;
                }
            }
        }
    }
    public static void decryptFile(FileReader inputFile, PrintWriter outputFile) throws IOException{
        char[] rotor1 = initRotor(0);
        char[] rotor2 = initRotor(7);
        char[] backplate = initRotor(13);
        int rotor1Count = 0, rotor2Count = 0;
        char ch = (char)inputFile.read();;
        while(ch != (char)-1){
            int i = 0;
            //take next input char
            i = charIsAt(backplate, ch) - rotor2Count;
            if (i < 0){
                i = i + 128;
            }
            ch = rotor2[i];
            i = charIsAt(backplate, ch) - rotor1Count;
            if (i < 0){
                i = i + 128;
            }
            ch = rotor1[i];
            //write single character
            outputFile.print(ch);
            ch = (char)inputFile.read();
            //advance rotor
            rotor1Count++;
            if (rotor1Count > 127){
                rotor1Count = 0;
                rotor2Count++;
                if (rotor2Count > 127){
                    rotor2Count = 0;
                }
            }
        }
    }
}