toWords method

Implementation

String toWords() {
  if (this == 0) return 'zero';

  final units = [
    '',
    'one',
    'two',
    'three',
    'four',
    'five',
    'six',
    'seven',
    'eight',
    'nine',
    'ten',
    'eleven',
    'twelve',
    'thirteen',
    'fourteen',
    'fifteen',
    'sixteen',
    'seventeen',
    'eighteen',
    'nineteen',
  ];
  final tens = [
    '',
    '',
    'twenty',
    'thirty',
    'forty',
    'fifty',
    'sixty',
    'seventy',
    'eighty',
    'ninety',
  ];
  final scales = ['', 'thousand', 'million', 'billion'];

  String convertLessThanThousand(int num) {
    if (num == 0) return '';

    if (num < 20) return units[num];

    if (num < 100) {
      return tens[num ~/ 10] + (num % 10 != 0 ? '-${units[num % 10]}' : '');
    }

    return '${units[num ~/ 100]} hundred'
        '${num % 100 != 0 ? ' and ${convertLessThanThousand(num % 100)}' : ''}';
  }

  int absNum = this.abs(); // Handle negative numbers
  String result = '';
  int scaleIndex = 0;

  while (absNum > 0) {
    int chunk = absNum % 1000;
    if (chunk > 0) {
      String chunkWords = convertLessThanThousand(chunk);
      if (scaleIndex > 0 && chunkWords.isNotEmpty) {
        chunkWords += ' ${scales[scaleIndex]}';
      }
      result = '$chunkWords ${result.trim()}';
    }
    absNum ~/= 1000;
    scaleIndex++;
  }

  return (this < 0 ? 'negative ' : '') + result.trim();
}