performShaping method Null safety

List<int> performShaping(List<int> text)

3.5 Shaping Implements rules R1-R7 and rules L1-L3 of section 8.2 (Persian) of the Unicode standard.

Implementation

// TODO - this code is very special-cased.
List<int> performShaping(List<int> text) {
  _ShapeJoiningType lastJt = _ShapeJoiningType.U;
  _LetterForm lastForm = _LetterForm.Isolated;
  int lastPos = 0;
  var lastChar = _BidiChars.NotAChar;
  final letterForms =
      List<_LetterForm>.filled(text.length, _LetterForm.Initial);

  for (int currPos = 0; currPos < text.length; ++currPos) {
    var ch = text[currPos];
    //string chStr = (ch).toString("X4");

    final jt = _getShapeJoiningType(ch);

    if ((jt == _ShapeJoiningType.R ||
            jt == _ShapeJoiningType.D ||
            jt == _ShapeJoiningType.C) &&
        (lastJt == _ShapeJoiningType.L ||
            lastJt == _ShapeJoiningType.D ||
            lastJt == _ShapeJoiningType.C)) {
      if (lastForm == _LetterForm.Isolated &&
          (lastJt == _ShapeJoiningType.D || lastJt == _ShapeJoiningType.L)) {
        letterForms[lastPos] = _LetterForm.Initial;
      } else if (lastForm == _LetterForm.Final &&
          lastJt == _ShapeJoiningType.D) {
        letterForms[lastPos] = _LetterForm.Medial;
      }
      letterForms[currPos] = _LetterForm.Final;
      lastForm = _LetterForm.Final;
      lastJt = jt;
      lastPos = currPos;
      lastChar = ch;
    } else if (jt != _ShapeJoiningType.T) {
      letterForms[currPos] = _LetterForm.Isolated;
      lastForm = _LetterForm.Isolated;
      lastJt = jt;
      lastPos = currPos;
      lastChar = ch;
    } else {
      letterForms[currPos] = _LetterForm.Isolated;
    }
  }

  lastChar = _BidiChars.NotAChar;
  lastPos = 0;
  int insertPos = 0;

  final sb = <int>[];

  for (int currPos = 0; currPos < text.length; ++currPos) {
    var ch = text[currPos];
    //string chStr = (ch).toString("X4");
    final jt = _getShapeJoiningType(ch);

    if (lastChar == _BidiChars.ARABIC_LAM &&
        ch != _BidiChars.ARABIC_ALEF &&
        ch != _BidiChars.ARABIC_ALEF_MADDA_ABOVE &&
        ch != _BidiChars.ARABIC_ALEF_HAMZA_ABOVE &&
        ch != _BidiChars.ARABIC_ALEF_HAMZA_BELOW &&
        jt != _ShapeJoiningType.T) {
      lastChar = _BidiChars.NotAChar;
    } else if (ch == _BidiChars.ARABIC_LAM) {
      lastChar = ch;
      lastPos = currPos;
      insertPos = sb.length;
    }

    if (lastChar == _BidiChars.ARABIC_LAM) {
      if (letterForms[lastPos] == _LetterForm.Medial) {
        switch (ch) {
          case _BidiChars.ARABIC_ALEF:
            sb[insertPos] = _BidiChars.ARABIC_LAM_ALEF_FINAL;
            _charLengths.removeAt(insertPos);
            continue;

          case _BidiChars.ARABIC_ALEF_MADDA_ABOVE:
            sb[insertPos] = _BidiChars.ARABIC_LAM_ALEF_MADDA_ABOVE_FINAL;
            _charLengths.removeAt(insertPos);
            _charLengths[insertPos] = _charLengths[insertPos] + 1;
            continue;

          case _BidiChars.ARABIC_ALEF_HAMZA_ABOVE:
            sb[insertPos] = _BidiChars.ARABIC_LAM_ALEF_HAMZA_ABOVE_FINAL;
            _charLengths.removeAt(insertPos);
            continue;

          case _BidiChars.ARABIC_ALEF_HAMZA_BELOW:
            sb[insertPos] = _BidiChars.ARABIC_LAM_ALEF_HAMZA_BELOW_FINAL;
            _charLengths.removeAt(insertPos);
            continue;
        }
      } else if (letterForms[lastPos] == _LetterForm.Initial) {
        switch (ch) {
          case _BidiChars.ARABIC_ALEF:
            sb[insertPos] = _BidiChars.ARABIC_LAM_ALEF_ISOLATED;
            _charLengths.removeAt(insertPos);
            continue;

          case _BidiChars.ARABIC_ALEF_MADDA_ABOVE:
            sb[insertPos] = _BidiChars.ARABIC_LAM_ALEF_MADDA_ABOVE_ISOLATED;
            _charLengths.removeAt(insertPos);
            _charLengths[insertPos] = _charLengths[insertPos] + 1;
            continue;

          case _BidiChars.ARABIC_ALEF_HAMZA_ABOVE:
            sb[insertPos] = _BidiChars.ARABIC_LAM_ALEF_HAMZA_ABOVE_ISOLATED;
            _charLengths.removeAt(insertPos);
            continue;

          case _BidiChars.ARABIC_ALEF_HAMZA_BELOW:
            sb[insertPos] = _BidiChars.ARABIC_LAM_ALEF_HAMZA_BELOW_ISOLATED;
            _charLengths.removeAt(insertPos);
            continue;
        }
      }
    }

    sb.add(_getCharacterByLetterForm(ch, letterForms[currPos]));
  }

  return sb;
}