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);
 }

}