import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

/// Format: "dd/mm/yyyy"
class DateInputFormatter extends TextInputFormatter {
  @override
  TextEditingValue formatEditUpdate(
      TextEditingValue oldValue, TextEditingValue newValue) {
    if (newValue.text.isEmpty) {
      return newValue;
    }

    String newText = _formatDate(newValue.text, oldValue.text);

    return newValue.copyWith(
      text: newText,
      // Problem: If the user edits the middle of the String, the cursor is moved to the end.
      selection: TextSelection.collapsed(offset: newText.length),
    );
  }

  String _formatDate(String text, String oldText) {
    // Remove non-numeric characters
    text = text.replaceAll(RegExp(r'[^0-9]'), '');

    if (text.length > 8) {
      text = text.substring(0, 8);
    }

    final buffer = StringBuffer();
    for (var i = 0; i < text.length; i++) {
      buffer.write(text[i]);
      if (i == 1 || i == 3) {
        buffer.write('/');
      }
    }
    String newText = buffer.toString();

    // Remove the '/' if backspace is pressed
    if ((newText.length == 3 || newText.length == 6) &&
        (newText.length == oldText.length)) {
      newText = newText.substring(0, newText.length - 1);
    }

    return newText;
  }
}


/// Format: "dd/xxxx..."
class ExpiryDateFormatter extends TextInputFormatter {
  String prevValue = '';

  @override
  TextEditingValue formatEditUpdate(
      TextEditingValue oldValue, TextEditingValue newValue) {
    String text = newValue.text;
    if (text.length == 3) {
      if (text.length > prevValue.length) {
        final cursorPosition = newValue.selection;
        newValue = newValue.copyWith(
          text: '${text.substring(0, 2)}/${text.substring(2)}',
          selection:
              TextSelection.collapsed(offset: cursorPosition.extentOffset + 1),
        );
      } else {
        final cursorPosition = newValue.selection;
        newValue = newValue.copyWith(
            text: text.substring(0, 2),
            selection: TextSelection.collapsed(
                offset: cursorPosition.extentOffset - 1));
      }
    }
    prevValue = newValue.text;
    return newValue;
  }
}