Format numbers

main.dart

// Format numbers
// https://dartpad.dev/?id=22aa280ffe2d847ca8c074b7eebca969

import 'dart:math' as math;

String formatNumber$1(int number) => number.toString().replaceAllMapped(
      RegExp(r'(\d)(?=(\d{3})+(?!\d))'),
      (match) => '${match[1]} ',
    );

String formatNumber$2(int number) {
  if (number == 0) return '0';
  final isNegative = number.isNegative;
  var temp = number.abs();
  final total = (math.log(temp) / math.log(1000)).floor() + 1;
  final parts = List<String>.filled(total, '', growable: false);
  for (var i = total - 1; i >= 0; i--) {
    final chunk = (temp % 1000).toString();
    temp ~/= 1000;
    parts[i] = temp > 0 ? chunk.padLeft(3, '0') : chunk;
  }
  final result = parts.join(' ');
  return isNegative ? '-$result' : result;
}

String formatNumber$3(int number) {
  final chars =
      number.abs().toString().codeUnits.reversed.toList(growable: false);
  final total = chars.length + (chars.length / 3).ceil();
  final buffer = List.filled(total, ' '.codeUnitAt(0), growable: false);
  for (var i = 0, j = 0; i < chars.length; i++, j++) {
    if ((i % 3) == 0) j++;
    buffer[j] = chars[i];
  }
  final result = String.fromCharCodes(buffer.reversed);
  return number.isNegative ? '-$result' : result;
}

void main() {
  final formatNumber = formatNumber$1; // $1 $2 $3

  print(formatNumber(12_123_123_123_123)); // 12 123 123 123 123
  print(formatNumber(1_234_567_890)); // 1 234 567 890
  print(formatNumber(1_000_000)); // 1 000 000
  print(formatNumber(-9_876_543)); // -9 876 543
  print(formatNumber(123)); // 123
  print(formatNumber(-12)); // -12
  print(formatNumber(-1_234)); // -1 234
  print(formatNumber(0)); // 0
}