public string EncryptMessage(string plainText, CaesarCipherKey cipherKey)
{
if (string.IsNullOrWhiteSpace(plainText))
{
throw new ArgumentNullException(nameof(plainText));
}
var sb = new StringBuilder(string.Empty);
foreach (var character in plainText.ToUpper())
{
if (!cipherKey.Alphabet.Contains(character.ToString()))
{
sb.Append(character);
continue;
}
var encryptedCharacterIndex = (cipherKey.Alphabet.IndexOf(character) + cipherKey.Shift) %
cipherKey.Alphabet.Length;
char encryptedCharacter;
if (encryptedCharacterIndex >= 0)
{
encryptedCharacter = cipherKey.Alphabet[encryptedCharacterIndex];
}
else
{
var adjustedIndex = cipherKey.Alphabet.Length +
(encryptedCharacterIndex % -cipherKey.Alphabet.Length);
encryptedCharacter = cipherKey.Alphabet.ElementAt(adjustedIndex);
}
sb.Append(encryptedCharacter);
}
return(sb.ToString());
}
public string DecryptMessage(string cipherText, CaesarCipherKey cipherKey)
{
cipherKey.Shift = -cipherKey.Shift;
return(EncryptMessage(cipherText, cipherKey).ToLower());
}