import 'package:flutter/services.dart';

class FrequencyInputFormatter extends TextInputFormatter {
  @override
  TextEditingValue formatEditUpdate(
    TextEditingValue oldValue,
    TextEditingValue newValue,
  ) {
    // Skip formatting if deleting
    if (oldValue.text.length > newValue.text.length) {
      return newValue;
    }

    // Allow only numbers and decimal point
    String filteredText = newValue.text.replaceAll(RegExp(r'[^\d.]'), '');

    // Only allow one decimal point
    if (filteredText.split('.').length > 2) {
      return oldValue;
    }

    // Format for three decimal places and auto-insert decimal point
    if (filteredText.contains('.')) {
      List<String> parts = filteredText.split('.');
      String whole = parts[0];
      String fraction = parts[1];

      // Limit to three decimal places
      if (fraction.length > 3) {
        fraction = fraction.substring(0, 3);
      }
      
      // Reconstruct the text
      filteredText = "$whole.$fraction";
    } else {
      // Auto-insert decimal point after the third digit
      if (filteredText.length > 3) {
        String whole = filteredText.substring(0, 3);
        String fraction = filteredText.substring(3);
        
        // Limit fraction to three digits
        if (fraction.length > 3) {
          fraction = fraction.substring(0, 3);
        }
        
        filteredText = "$whole.$fraction";
      }
    }

    return TextEditingValue(
      text: filteredText,
      selection: TextSelection.collapsed(offset: filteredText.length),
    );
  }
}