Catrobat.IDE.Core.Formulas.FormulaInterpreter.CompleteBrackets C# (CSharp) Method

        private IEnumerable<IFormulaToken> CompleteBrackets(IEnumerable<IFormulaToken> tokens, bool forward = true)
        {
            var parenthesesTokens = new Stack<List<IFormulaToken>>();
            var parentheses = new Stack<IFormulaToken>();
            foreach (var context in tokens.WithContext())
            {
                var previousToken = context[0];
                var token = context[1];

                var parenthesisToken = token as FormulaTokenParenthesis;
                if (parenthesisToken != null)
                {
                    if (forward ? parenthesisToken.IsOpening : parenthesisToken.IsClosing)
                    {
                        parenthesesTokens.Push(new List<IFormulaToken>());
                        parenthesesTokens.Peek().Add(token);
                        parentheses.Push(FormulaTreeFactory.CreateParenthesesNode(null));
                    }
                    else
                    {
                        // unmatched bracket
                        if (parenthesesTokens.Count == 0) yield break;

                        parenthesesTokens.Peek().Add(token);

                        var commonToken = parentheses.Pop();
                        CompleteChildren(commonToken, parenthesesTokens.Pop());
                        if (parenthesesTokens.Count != 0)
                        {
                            parenthesesTokens.Peek().Add(commonToken);
                        }
                        else
                        {
                            yield return commonToken;
                        }
                    }
                    continue;
                }

                // complete incomplete parentheses
                if (token == null)
                {
                    while (parenthesesTokens.Count != 0)
                    {
                        parenthesesTokens.Peek().Add(previousToken);

                        var commonToken = parentheses.Pop();
                        CompleteChildren(commonToken, parenthesesTokens.Pop());
                        if (parenthesesTokens.Count != 0)
                        {
                            parenthesesTokens.Peek().Add(commonToken);
                        }
                        else
                        {
                            yield return commonToken;
                        }
                    }
                    continue;
                }

                // dismiss tokens inside parentheses
                if (parenthesesTokens.Count != 0) continue;

                // yield any token outside parentheses
                yield return token;
            }
        }