CSC-151 Project 3

ArgumentParser.java

/**
 * Argument parser for the FileUtilities class
 *
 * @author Jake Eaton
 */
public class ArgumentParser {

    private static String helpLine =
"Usage: java FileUtilities COMMAND SHIFT FILE [-verbose]\n" +
"Encrypt/decrypt files using the shift cipher.\n\n" +
"  COMMAND            encrypt or decrypt\n" +
"  SHIFT              how many letters to shift\n" +
"  FILE               the file to be encrypted/decrypted\n" +
"  -h, --help         show this message\n" +
"  -v, --verbose      write the encrypted/decrypted text to stdout in addition to FILE";

    private static final int VERBOSE   = 1,
                             FILE_NAME = 2,
                             SHIFT     = 4,
                             TYPE      = 8;

    public boolean verbose = false;
    public String fileName;
    public int shift;
    public boolean encrypt;

    public static void printHelp() {
        System.out.println(helpLine);
    }

    public static void fail() {
        System.err.println("Try 'java FileUtilities --help' for more information.");
        System.exit(-1);
    }

    public ArgumentParser(final String[] args) {
        int mask = 0;
        for (final String e: args) {
            if (e.equals("-h") || e.equals("--help")) {
                printHelp();
                System.exit(0);
            }
        }
        for (final String e: args) {
            if (e.equals("-v") || e.equals("--verbose")) {
                verbose = true;
                mask |= VERBOSE;
            } else if ((mask & SHIFT) == 0 &&
                       e.matches("^\\s*-?(0|[1-9][0-9]*)\\s*$")) {
                shift = Integer.valueOf(e);
                mask |= SHIFT;
            } else if ((mask & TYPE) == 0 &&
                       e.matches("^(de|en)crypt$")) {
                encrypt = e.equals("encrypt");
                mask |= TYPE;
            } else {
                if (e.indexOf('-') == 0) {
                    System.err.printf("Unexpected option: %s\n", e);
                    fail();
                }
                if ((mask & FILE_NAME) != 0) {
                    System.err.printf("Unexpected argument: %s\n", e);
                    fail();
                }
                mask |= FILE_NAME;
                fileName = e;
            }
        }
        shift *= encrypt ? -1 : 1;
        if ((mask & ~VERBOSE) != (FILE_NAME | SHIFT | TYPE)) {
            System.err.println("Invalid usage.");
            fail();
        }
    }

}

FileUtilities.java

import java.io.IOException;
import java.io.FileOutputStream;
import java.nio.file.Paths;
import java.nio.file.Files;

public class FileUtilities {

    public static byte encodeLetter(byte letter, int shift) {
        return (letter < 'A' || letter > 'z' || letter > 'Z' && letter < 'a') ? (letter) :
            (byte) ('A' + (letter & 32) + (letter - 39 + shift % 26 - (letter & 32)) % 26);
    }

    public static void main(String[] args) {
        final ArgumentParser parser = new ArgumentParser(args);
        byte[] data = null;
        try {
            data = Files.readAllBytes(Paths.get(parser.fileName));
        } catch (IOException e) {
            System.err.printf("Error reading file: %s\n", parser.fileName);
            System.exit(-1);
        }
        for (int i = 0; i < data.length; i++) {
            data[i] = encodeLetter(data[i], parser.shift);
        }
        if (parser.verbose) {
            System.out.println(new String(data).replaceFirst("\n+$", ""));
        }
        FileOutputStream fileOut = null;
        try {
            fileOut = new FileOutputStream(parser.fileName);
        } catch (IOException e) {
            System.err.printf("Error opening file for output: %s\n",
                    parser.fileName);
            System.exit(-1);
        }
        try {
            fileOut.write(data);
            fileOut.close();
        } catch (IOException e) {
            System.err.printf("Error writing file: %s\n",
                    parser.fileName);
            System.exit(-1);
        }
    }

}