insertSpaces method

String insertSpaces(String str)

Returns a String with spaces added according to SI guidelines.

Implementation

String insertSpaces(String str) {
  // Remove any exponent piece and add it back in after spaces are added.
  final expIndex = _exponentIndex(str);
  final numStr = expIndex != -1 ? str.substring(0, expIndex) : str;

  final decimalIndex = numStr.indexOf('.');
  final preCount = decimalIndex != -1 ? decimalIndex : numStr.length;
  final postCount = decimalIndex != -1 ? numStr.length - decimalIndex - 1 : 0;

  final buf = StringBuffer();

  // Pre-decimal.
  if (preCount > 4) {
    final preStr =
        decimalIndex != -1 ? numStr.substring(0, decimalIndex) : numStr;
    final fullGroups = preStr.length ~/ 3;
    var cursor = preStr.length - fullGroups * 3;
    if (cursor != 0) buf.write(preStr.substring(0, cursor));
    while (cursor + 3 <= preStr.length) {
      if (cursor != 0) buf.write(unicode ? '\u{2009}' : ' ');
      buf.write(preStr.substring(cursor, cursor + 3));
      cursor += 3;
    }
  } else {
    if (decimalIndex != -1) {
      buf.write(numStr.substring(0, decimalIndex));
    } else {
      buf.write(numStr);
    }
  }

  // Decimal and post-decimal.
  if (decimalIndex != -1) {
    buf.write('.');
    if (postCount > 4) {
      // Insert a space after each grouping of 3.
      buf.write(numStr.substring(decimalIndex + 1, decimalIndex + 4));
      var cursor = 3;
      while (cursor < postCount) {
        buf
          ..write(unicode ? '\u{2009}' : ' ')
          ..write(numStr.substring(decimalIndex + 1 + cursor,
              min(decimalIndex + 4 + cursor, numStr.length)));
        cursor += 3;
      }
    } else {
      buf.write(numStr.substring(decimalIndex + 1));
    }
  }

  if (expIndex != -1) buf.write(str.substring(expIndex));

  return buf.toString();
}