public static void optimize()

in src/org/intellij/grammar/refactor/BnfExpressionOptimizer.java [25:75]
50 lines of code
21 McCabe index (conditional complexity)

  public static void optimize(@NotNull Project project, @NotNull PsiElement element) {
    LinkedList<PsiElement> list = new LinkedList<>();
    list.add(element.getParent());
    list.add(element);
    while (!list.isEmpty()) {
      PsiElement cur = list.removeLast();
      PsiElement parent = cur.getParent();
      if (isTrivial(cur)) {
        mergeChildrenTo(parent, cur, list);
      }
      else if (cur instanceof BnfParenOptExpression && isTrivialOrSingular(((BnfParenOptExpression)cur).getExpression())) {
        // currently, <expr> + ? expressions are not supported, thus:
        BnfExpression child = ((BnfParenOptExpression)cur).getExpression();
        IElementType type = ParserGeneratorUtil.getEffectiveType(child);
        if (type == BnfTypes.BNF_OP_OPT || type == BnfTypes.BNF_OP_ZEROMORE) {
          list.add(cur.replace(child));
        }
        else if (type == BnfTypes.BNF_OP_ONEMORE) {
          String replacement = ((BnfQuantified)child).getExpression().getText() + "*";
          list.add(cur.replace(BnfElementFactory.createExpressionFromText(project, replacement)));
        }
        else {
          String replacement = child.getText() + "?";
          list.add(cur.replace(BnfElementFactory.createExpressionFromText(project, replacement)));
        }
      }
      else if (cur instanceof BnfChoice &&
               !(parent instanceof BnfParenthesized) &&
               (parent instanceof BnfSequence || parent instanceof BnfQuantified)) {
        String replacement = "(" + cur.getText() + ")";
        cur.replace(BnfElementFactory.createExpressionFromText(project, replacement));
      }
      else if (isOptMany(cur) && isOptMany(PsiTreeUtil.getChildOfType(cur, BnfExpression.class))) {
        BnfExpression child = PsiTreeUtil.getChildOfType(cur, BnfExpression.class);
        IElementType type1 = ParserGeneratorUtil.getEffectiveType(cur);
        IElementType type2 = ParserGeneratorUtil.getEffectiveType(child);
        if (type1 == type2) {
          list.add(cur.replace(child));
        }
        else if (type1 == BnfTypes.BNF_OP_OPT && type2 == BnfTypes.BNF_OP_ONEMORE ||
                 type2 == BnfTypes.BNF_OP_OPT && type1 == BnfTypes.BNF_OP_ONEMORE ||
                 type1 == BnfTypes.BNF_OP_ZEROMORE || type2 == BnfTypes.BNF_OP_ZEROMORE
          ) {
          BnfExpression childOfChild = PsiTreeUtil.getChildOfType(child, BnfExpression.class);
          String childText = childOfChild == null? "" : childOfChild.getText();
          String replacement = (child instanceof BnfParenthesized? "(" + childText + ")" : childText) + "*";
          cur.replace(BnfElementFactory.createExpressionFromText(project, replacement)); //
        }
      }
    }
  }