Swing/SelectWordAction のバックアップ(No.8)

// @see javax.swint.text.Utilities.getWordStart(...)
int getWordStart(JTextComponent c, int offs) throws BadLocationException {
  Element line = Optional.ofNullable(Utilities.getParagraphElement(c, offs))
      .orElseThrow(() -> new BadLocationException("No word at " + offs, offs));
  Document doc = c.getDocument();
  int lineStart = line.getStartOffset();
  int lineEnd = Math.min(line.getEndOffset(), doc.getLength());
  int offs2 = offs;
  Segment seg = SegmentCache.getSharedSegment();
  doc.getText(lineStart, lineEnd - lineStart, seg);
  if (seg.count > 0) {
    BreakIterator words = BreakIterator.getWordInstance(c.getLocale());
    words.setText(seg);
    int wordPosition = seg.offset + offs - lineStart;
    if (wordPosition >= words.last()) {
      wordPosition = words.last() - 1;
      words.following(wordPosition);
      offs2 = lineStart + words.previous() - seg.offset;
    } else {
      words.following(wordPosition);
      offs2 = lineStart + words.previous() - seg.offset;
      for (int i = offs; i > offs2; i--) {
        char ch = seg.charAt(i - seg.offset);
        if (ch == '_' || ch == '-') {
          offs2 = i + 1;
          break;
        }
      }
    }
  }
  SegmentCache.releaseSharedSegment(seg);
  return offs2;
}