CipherStreamJava/src/main/java/com/mattrixwv/cipherstream/monosubstitution/Atbash.java

package com.mattrixwv.cipherstream.monosubstitution;


import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.mattrixwv.cipherstream.exceptions.InvalidInputException;


/**
 * Implements the Atbash cipher, a simple substitution cipher where each letter of the alphabet is mapped to its reverse.
 * For example, 'A' is mapped to 'Z', 'B' to 'Y', and so on.
 * This class provides methods to encode and decode strings using the Atbash cipher.
 *
 * <p>
 * The Atbash cipher is symmetric, meaning that encoding and decoding are the same operation.
 * </p>
 */
public final class Atbash{
	private static final Logger logger = LoggerFactory.getLogger(Atbash.class);
	//?Fields
	/** Holds the string that needs encoded or decoded */
	protected String inputString;
	/** The encoded/decoded string */
	protected String outputString;
	//?Settings
	/** Persist capitals in the output string */
	protected boolean preserveCapitals;
	/** Persist whitespace in the output string */
	protected boolean preserveWhitespace;
	/** Persist symbols in the output string */
	protected boolean preserveSymbols;


	/**
	 * Encodes the input string using the Atbash cipher.
	 */
	protected void encode(){
		logger.debug("Encoding");
		StringBuilder output = new StringBuilder();
		//Step through every element in the inputString and shift it the correct amount
		for(int cnt = 0;cnt < inputString.length();++cnt){
			char currentChar = inputString.charAt(cnt);
			logger.debug("Encoding char {}", currentChar);
			//Decode if the letter is alphabetic
			if(Character.isAlphabetic(currentChar)){
				//Use either uppercase or lowercase for the base
				//(letterbase + 25 - (currentChar - letterBase))
				if(Character.isUpperCase(currentChar)){
					logger.debug("Encoding uppercase");

					output.append((char)(155 - currentChar));
				}
				else{
					logger.debug("Encoding lowercase");

					output.append((char)(219 - currentChar));
				}
			}
			//Keep any punctuatio/whitespace the way it is
			else{
				logger.debug("Appending symbol");

				output.append(currentChar);
			}
		}

		//Return the output
		outputString = output.toString();
		logger.debug("Saving output string '{}'", outputString);
	}
	/**
	 * Sets and sanitizes the input string according to the preservation settings.
	 *
	 * @param inputString the string to be processed
	 * @throws InvalidInputException if the input string is null or blank after processing
	 */
	protected void setInputString(String inputString) throws InvalidInputException{
		if(inputString == null){
			throw new InvalidInputException("Input cannot be null");
		}

		logger.debug("Original input string '{}'", inputString);

		if(!preserveCapitals){
			logger.debug("Removing case");

			//Convert all letters to lowercase
			inputString = inputString.toUpperCase();
		}
		if(!preserveWhitespace){
			logger.debug("Removing whitespace");

			//Remove all characters except capital letters
			inputString = inputString.replaceAll("\\s", "");
		}
		if(!preserveSymbols){
			logger.debug("Removing symbols");

			//Remove all non-alpha numeric and whitespace symbols
			inputString = inputString.replaceAll("[^a-zA-Z\\s]", "");
		}

		//Save the string
		this.inputString = inputString;

		logger.debug("Cleaned input string '{}'", inputString);

		if(this.inputString.isBlank()){
			throw new InvalidInputException("Input must contain at least 1 character");
		}
	}


	//?Constructor
	/**
	 * Constructs a new {@code Atbash} instance with default settings:
	 * capitals, symbols, and whitespace are not preserved.
	 */
	public Atbash(){
		reset();
		preserveCapitals = false;
		preserveWhitespace = false;
		preserveSymbols = false;
	}
	/**
	 * Constructs a new {@code Atbash} instance with specified settings for preserving capitals, whitespace, and symbols.
	 *
	 * @param preserveCapitals     whether to preserve capital letters in the output
	 * @param preserveWhitespace   whether to preserve whitespace in the output
	 * @param preserveSymbols      whether to preserve symbols in the output
	 */
	public Atbash(boolean preserveCapitals, boolean preserveWhitespace, boolean preserveSymbols){
		reset();
		this.preserveCapitals = preserveCapitals;
		this.preserveWhitespace = preserveWhitespace;
		this.preserveSymbols = preserveSymbols;
	}

	/**
	 * Encodes the provided input string using the Atbash cipher and returns the encoded result.
	 *
	 * @param inputString the string to be encoded
	 * @return the encoded string
	 * @throws InvalidInputException if the input string is invalid
	 */
	public String encode(String inputString) throws InvalidInputException{
		//Make sure everything is empty before you begin
		reset();
		setInputString(inputString);
		encode();
		return outputString;
	}
	/**
	 * Decodes the provided input string using the Atbash cipher and returns the decoded result.
	 * Since the Atbash cipher is symmetric, this method performs the same operation as encoding.
	 *
	 * @param inputString the string to be decoded
	 * @return the decoded string
	 * @throws InvalidInputException if the input string is invalid
	 */
	public String decode(String inputString) throws InvalidInputException{
		return encode(inputString);
	}

	//?Getters
	/**
	 * Returns the current input string.
	 *
	 * @return the input string
	 */
	public String getInputString(){
		return inputString;
	}
	/**
	 * Returns the current output string.
	 *
	 * @return the output string
	 */
	public String getOutputString(){
		return outputString;
	}
	/**
	 * Resets all fields to their default values.
	 */
	public void reset(){
		logger.debug("Resetting fields");

		inputString = "";
		outputString = "";
	}
}