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package ciphers;

import java.util.*;

/**

* The simple substitution cipher is a cipher that has been in use for many hundreds of years (an

* excellent history is given in Simon Singhs 'the Code Book'). It basically consists of

* substituting every plaintext character for a different ciphertext character. It differs from the

* Caesar cipher in that the cipher alphabet is not simply the alphabet shifted, it is completely

* jumbled.

*

* @author Hassan Elseoudy

*/

public class SimpleSubstitutionCipher {

/**

* Encrypt text by replacing each element with its opposite character.

*

* @param message

* @param cipherSmall

* @return Encrypted message

*/

public static String encode(String message, String cipherSmall) {

String encoded = "";

// This map is used to encode

Map<Character, Character> cipherMap = new HashMap<Character, Character>();

char beginSmallLetter = 'a';

char beginCapitalLetter = 'A';

cipherSmall = cipherSmall.toLowerCase();

String cipherCapital = cipherSmall.toUpperCase();

// To handle Small and Capital letters

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

cipherMap.put(beginSmallLetter++, cipherSmall.charAt(i));

cipherMap.put(beginCapitalLetter++, cipherCapital.charAt(i));

}

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

if (Character.isAlphabetic(message.charAt(i))) encoded += cipherMap.get(message.charAt(i));

else encoded += message.charAt(i);

}

return encoded;

}

/**

* Decrypt message by replacing each element with its opposite character in cipher.

*

* @param encryptedMessage

* @param cipherSmall

* @return message

*/

public static String decode(String encryptedMessage, String cipherSmall) {

String decoded = "";

Map<Character, Character> cipherMap = new HashMap<Character, Character>();

char beginSmallLetter = 'a';

char beginCapitalLetter = 'A';

cipherSmall = cipherSmall.toLowerCase();

String cipherCapital = cipherSmall.toUpperCase();

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

cipherMap.put(cipherSmall.charAt(i), beginSmallLetter++);

cipherMap.put(cipherCapital.charAt(i), beginCapitalLetter++);

}

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

if (Character.isAlphabetic(encryptedMessage.charAt(i)))

decoded += cipherMap.get(encryptedMessage.charAt(i));

else decoded += encryptedMessage.charAt(i);

}

return decoded;

}

/** TODO remove main and make JUnit Testing */

public static void main(String[] args) {

String a = encode("defend the east wall of the castle", "phqgiumeaylnofdxjkrcvstzwb");

String b = decode(a, "phqgiumeaylnofdxjkrcvstzwb");

System.out.println(b);

}

}