private void ValidateUsername(string username)
{
if (repository.GetAccountByUsername(username) != null)
{ // Username already exists in the database.
throw new ValidationException("Username already exists!");
}
if (TextValidator.IsNullEmptyOrWhiteSpace(username))
{ // Username empty or not provided.
throw new ValidationException("Username can't be empty!");
}
if (!TextValidator.ContainsBetweenXAndYCharacters(username, 8, 32))
{ // Username doesn't contain between 8 and 32 characters.
throw new ValidationException("Username must contain between 8 and 32 characters!");
}
if (!TextValidator.ContainsLetters(username))
{ // Username doesn't contain any letters (only numbers or symbols).
throw new ValidationException("Username must contain at least one letter!");
}
}