public class NotBeginsWithFunction : ICustomFunctionDisplayAttributes {
  public const string FunctionName = "NotBeginsWith";
  static readonly NotBeginsWithFunction instance = new NotBeginsWithFunction();
  public static void Register() {
    CriteriaOperator.RegisterCustomFunction(instance);
  }
  public static bool Unregister() {
    return CriteriaOperator.UnregisterCustomFunction(instance);
  }

  public string Name => FunctionName;
  public string DisplayName => "Does not begin with";
  public object Image => "FontSizeDecrease;Office2013";
  public string Description => "Hides records when the field begins with the given value";
  public FunctionCategory Category => FunctionCategory.Text;

  public int MinOperandCount => 2;
  public int MaxOperandCount => 2;
  public bool IsValidOperandCount(int count) => count == 2;
  public bool IsValidOperandType(int operandIndex, int operandCount, Type type) =>
    typeof(string);
  public Type ResultType(params Type[] operands) => typeof(bool);

  public object Evaluate(params object[] operands) {
    if(operands[0] != null && operands[1] != null) {
      string str1 = operands[0].ToString();
      string str2 = operands[1].ToString();
      return !str1.StartsWith(str2, StringComparison.InvariantCultureIgnoreCase);
    }
    return false;
  }
}