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package com.thealgorithms.ciphers;

/**

* A Java implementation of Caesar Cipher. /It is a type of substitution cipher

* in which each letter in the plaintext is replaced by a letter some fixed

* number of positions down the alphabet. /

*

* @author FAHRI YARDIMCI

* @author khalil2535

*/

public class Caesar {

private static char normalizeShift(final int shift) {

return (char) (shift % 26);

}

/**

* Encrypt text by shifting every Latin char by add number shift for ASCII

* Example : A + 1 -> B

*

* @return Encrypted message

*/

public String encode(String message, int shift) {

StringBuilder encoded = new StringBuilder();

final char shiftChar = normalizeShift(shift);

final int length = message.length();

for (int i = 0; i < length; i++) {

// int current = message.charAt(i); //using char to shift characters because

// ascii

// is in-order latin alphabet

char current = message.charAt(i); // Java law : char + int = char

if (isCapitalLatinLetter(current)) {

current += shiftChar;

encoded.append((char) (current > 'Z' ? current - 26 : current)); // 26 = number of latin letters

} else if (isSmallLatinLetter(current)) {

current += shiftChar;

encoded.append((char) (current > 'z' ? current - 26 : current)); // 26 = number of latin letters

} else {

encoded.append(current);

}

}

return encoded.toString();

}

/**

* Decrypt message by shifting back every Latin char to previous the ASCII

* Example : B - 1 -> A

*

* @return message

*/

public String decode(String encryptedMessage, int shift) {

StringBuilder decoded = new StringBuilder();

final char shiftChar = normalizeShift(shift);

final int length = encryptedMessage.length();

for (int i = 0; i < length; i++) {

char current = encryptedMessage.charAt(i);

if (isCapitalLatinLetter(current)) {

current -= shiftChar;

decoded.append((char) (current < 'A' ? current + 26 : current)); // 26 = number of latin letters

} else if (isSmallLatinLetter(current)) {

current -= shiftChar;

decoded.append((char) (current < 'a' ? current + 26 : current)); // 26 = number of latin letters

} else {

decoded.append(current);

}

}

return decoded.toString();

}

/**

* @return true if character is capital Latin letter or false for others

*/

private static boolean isCapitalLatinLetter(char c) {

return c >= 'A' && c <= 'Z';

}

/**

* @return true if character is small Latin letter or false for others

*/

private static boolean isSmallLatinLetter(char c) {

return c >= 'a' && c <= 'z';

}

/**

* @return string array which contains all the possible decoded combination.

*/

public String[] bruteforce(String encryptedMessage) {

String[] listOfAllTheAnswers = new String[27];

for (int i = 0; i <= 26; i++) {

listOfAllTheAnswers[i] = decode(encryptedMessage, i);

}

return listOfAllTheAnswers;

}

}