private string ModifyString(
string?source,
string?key,
EncryptionModificationMethod modificationMethod)
{
VerifyModificationMethod(modificationMethod);
if (string.IsNullOrEmpty(source) || string.IsNullOrEmpty(key))
{
return(source ?? "");
}
StringBuilder resultString = new StringBuilder();
for (int i = 0; i < source.Length; i++)
{
ushort sourceCharCode = Convert.ToUInt16(source[i]);
ushort keyCharCode = Convert.ToUInt16(key[i % key.Length]);
ushort resultCharCode;
if (modificationMethod == EncryptionModificationMethod.Encrypt)
{
resultCharCode = (ushort)unchecked (sourceCharCode + keyCharCode);
}
else
{
resultCharCode = (ushort)unchecked (sourceCharCode - keyCharCode);
}
char resultCharacter = Convert.ToChar(resultCharCode);
resultString.Append(resultCharacter);
}
return(resultString.ToString());
}
private void VerifyModificationMethod(EncryptionModificationMethod modificationMethod)
{
if (modificationMethod != EncryptionModificationMethod.Encrypt &&
modificationMethod != EncryptionModificationMethod.Decrypt)
{
throw new ArgumentException(
"modifictionMethod parameter should be " +
$"\"Encrypt\" or \"Decrypt\"");
}
}
private IEnumerable <string> ModifyCollection(
IEnumerable <string>?source,
string?key,
EncryptionModificationMethod modificationMethod)
{
if (source == null || source.Count() == 0)
{
yield return("");
}
else
{
int limitOfBufferLength = byte.MaxValue;
var bufferSource = source.Take(limitOfBufferLength);
foreach (string str in bufferSource)
{
yield return(ModifyString(str, key, modificationMethod));
}
}
}
