Main.java

import java.io.*;
import java.nio.file.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws IOException {
        Cipher.runTests();
        Scanner scanner = new Scanner(System.in);

        // Question for users:
        System.out.print("Do you want to encrypt or decrypt (E/D): ");
        String choice = scanner.nextLine().toUpperCase();

        System.out.print("Filename: ");
        String inputFileName = scanner.nextLine();

        System.out.print("Secret key (7 characters): ");
        String secretKey = scanner.nextLine();
        if (secretKey.length() != 7) {
            System.out.println("Error: key must be 7 characters (56 bits).");
            return;
        }

        System.out.print("Output file: ");
        String outputFileName = scanner.nextLine();

        // read file and convert into Binary:
        String fileContent = new String(Files.readAllBytes(Paths.get(inputFileName)));
        String binaryInput = toBinary(fileContent);

        binaryInput = padBinary(binaryInput);

        String resultBinary;
        if (choice.equals("E")) {
            resultBinary = Cipher.encrypt(binaryInput, secretKey);
        } else if (choice.equals("D")) {
            resultBinary = Cipher.decrypt(binaryInput, secretKey);
            resultBinary = toText(resultBinary);
        } else {
            System.out.println("Invalid.");
            return;
        }

        // get output file
        Files.write(Paths.get(outputFileName), resultBinary.getBytes());
        System.out.println("Output saved to " + outputFileName);
    }

    //// convert plain text to a binary string
    public static String toBinary(String text) {
        StringBuilder binary = new StringBuilder();
        for (char ch : text.toCharArray()) {
            binary.append(String.format("%8s", Integer.toBinaryString(ch)).replace(' ', '0'));
        }
        return binary.toString();
    }

    // // convert a binary string back to readable text
    public static String toText(String binary) {
        StringBuilder text = new StringBuilder();
        for (int i = 0; i < binary.length(); i += 8) {
            text.append((char) Integer.parseInt(binary.substring(i, i + 8), 2));
        }
        return text.toString();
    }

    public static String padBinary(String binary) {
        int remainder = binary.length() % 64;
        if (remainder != 0) {
            int padding = 64 - remainder;
            binary += "0".repeat(padding);
        }
        return binary;
    }

    public static String binaryToTextKey(String binary) {
        StringBuilder key = new StringBuilder();
        for (int i = 0; i < 56; i += 8) {
            int ascii = Integer.parseInt(binary.substring(i, i + 8), 2);
            key.append((char) ascii);
        }
        return key.toString(); // returns 7 char key
    }

}