formatter

class DecimalFormatter extends TextInputFormatter {
  final int decimalDigits;

  DecimalFormatter({this.decimalDigits = 2}) : assert(decimalDigits >= 0);

  @override
  TextEditingValue formatEditUpdate(
    TextEditingValue oldValue,
    TextEditingValue newValue,
  ) {
    String newText;

    if (decimalDigits == 0) {
      newText = newValue.text.replaceAll(RegExp('[^0-9]'), '');
    } else {
      newText = newValue.text.replaceAll(RegExp('[^0-9\.]'), '');
    }

    if (newText.contains('.')) {
      //in case if user's first input is "."
      if (newText.trim() == '.') {
        return newValue.copyWith(
          text: '0.',
          selection: const TextSelection.collapsed(offset: 2),
        );
      }
      //in case if user tries to input multiple "."s or tries to input
      //more than the decimal place
      else if ((newText.split(".").length > 2) ||
          (newText.split(".")[1].length > decimalDigits)) {
        return oldValue;
      } else {
        return newValue;
      }
    }

    //in case if input is empty or zero
    if (newText.trim() == '' || newText.trim() == '0') {
      return newValue.copyWith(text: '');
    } else if (int.parse(newText) < 1) {
      return newValue.copyWith(text: '');
    }

    double newDouble = double.parse(newText);
    var selectionIndexFromTheRight =
        newValue.text.length - newValue.selection.end;

    String newString = NumberFormat("#,##0.##").format(newDouble);
    // String formattedString = "$newString.00";
    return TextEditingValue(
      text: newString,
      selection: TextSelection.collapsed(
        offset: newString.length - selectionIndexFromTheRight,
      ),
    );
  }
}