parseToUnits function

BigInt parseToUnits(String amount, int decimals)

Parse a decimal string to smallest-unit BigInt (pure BigInt, no float).

Implementation

BigInt parseToUnits(String amount, int decimals) {
  if (decimals < 0) {
    throw ArgumentError('Invalid decimals: $decimals');
  }

  if (!_amountRegex.hasMatch(amount)) {
    throw ArgumentError('Invalid amount: "$amount"');
  }

  final negative = amount.startsWith('-');
  final stripped = negative ? amount.substring(1) : amount;

  final parts = stripped.split('.');
  final whole = parts[0];
  final fraction = parts.length > 1 ? parts[1] : '';

  if (fraction.length > decimals) {
    throw ArgumentError(
      'Too many decimal places: "$amount" has ${fraction.length} but max is $decimals',
    );
  }

  final paddedFraction = fraction.padRight(decimals, '0');
  final wholePart = whole.isEmpty ? BigInt.zero : BigInt.parse(whole);
  final fractionPart = paddedFraction.isEmpty
      ? BigInt.zero
      : BigInt.parse(paddedFraction);
  final result = wholePart * BigInt.from(10).pow(decimals) + fractionPart;

  return negative ? -result : result;
}