Functional Question

gistfile1.cs

private IEnumerable<Func<string, Maybe<string>, Outcome<string>>> GetValidators()
{
    // Password cannot be empty
    yield return (password, email) => string.IsNullOrWhiteSpace(password)
                ? Outcome.Failure("Password cannot be empty")
                : Outcome.Success();

    // Password must have at least 8 characters
    yield return (password, email) =>
    {
        const int minimumLength = 8;
        return password.Length < minimumLength
                ? Outcome.Failure(string.Format("Password must be at least {0} characters", minimumLength))
                : Outcome.Success();
    };

    // Password must have no more than 20 characters
    yield return (password, email) =>
    {
        const int maximumLength = 20;
        return password.Length > maximumLength
                ? Outcome.Failure(string.Format("Password cannot be longer than {0} characters", maximumLength))
                : Outcome.Success();
    };

    // Password must not contain a substring of the user's email
    yield return (password, email) => email.HasValue && email.Value.IndexOf(password, StringComparison.InvariantCultureIgnoreCase) > -1
                ? Outcome.Failure("Password cannot contain parts of the email address associated with this account.")
                : Outcome.Success();

    // Password must not contain spaces
    yield return (password, email) => Regex.IsMatch(password, @"\w+")
                ? Outcome.Failure("Password cannot contain spaces")
                : Outcome.Success();

    // Password must not contain prohibited characters
    yield return (password, email) => (Regex.IsMatch(password, @"[^\#\$\%\&\@\*\+\-\=\!\.\?\:\;\(\)\[\]\{\}\^\~_]+"))
                ? Outcome.Failure("Password contains prohibited characters")
                : Outcome.Success();

    // Password must have at least two classes of characters (e.g., letters, digits, "allowed specials").
    yield return (password, email) =>
    {
        var characterClasses = 0;
        characterClasses += Regex.IsMatch(password, @"[a-zA-Z]+") ? 1 : 0;
        characterClasses += Regex.IsMatch(password, @"\d+") ? 1 : 0;
        characterClasses += Regex.IsMatch(password, @"[^\#\$\%\&\@\*\+\-\=\!\.\?\:\;\(\)\[\]\{\}\^\~_]+") ? 1 : 0;
        return characterClasses < 2
                ? Outcome.Failure("Password must contain at least two kinds of characters (letters, numbers or 'allowed special characters'.")
                : Outcome.Success();
    };
}



Outcome<string> IAuthenticationService.ValidatePassword(IDssPrincipal dssPrincipal, string password)
{

    var email = dssPrincipal.Identity.EmailAddress.ToMaybe();
    Outcome<string> result = Outcome.Success();
    GetValidators().Run(validator => result.Combine(validator(password, email)));
    return result;
}