private static()

in src/Core/Parsers/EntitySourceNamesParser.cs [114:218]
60 lines of code
18 McCabe index (conditional complexity)

        private static (string?, string?) GetTokenAndNextToken(string input, int startIndex = 0)
        {
            bool startsWithBracket = input[startIndex] == '[';
            int i = startIndex;
            while (i < input.Length)
            {
                if (!startsWithBracket)
                {
                    if (input[i] == '.')
                    {
                        // ^ is startIndex and i is current index
                        // Ex: abc.xyz
                        //     ^  i
                        // Return "abc" as the token and the index of x as the next starting index
                        //
                        return (input[startIndex..i], input.Substring(i + 1));
                    }

                    if (input[i] == ']' || input[i] == '[')
                    {
                        // ^ is startIndex and i is current index
                        // Ex: abc]xyz
                        //     ^  i
                        // Return exception because we encountered a ']' or '[',  and the token was not surrounded by "[" and "]".
                        //
                        throw new DataApiBuilderException(message: "Token is not surrounded by '[' and ']'.",
                                                       statusCode: HttpStatusCode.ServiceUnavailable,
                                                       subStatusCode: DataApiBuilderException.SubStatusCodes.ErrorInInitialization);
                    }
                } // close of if of !startsWithBracket
                else
                {
                    if (input[i] == ']' && i + 1 < input.Length && input[i + 1] == '.')
                    {
                        // ^ is startIndex and i is current index
                        // Ex: [ab.c].xyz
                        //     ^    i
                        // Return "ab.c" as the token and the index of x as the next starting index
                        //
                        return (input[(startIndex + 1)..i], input.Substring(i + 2));
                    }
                    else if (input[i] == ']' && i + 1 < input.Length && input[i + 1] == ']')
                    {
                        if (i + 2 >= input.Length)
                        {
                            // ^ is startIndex and i is current index
                            // Ex: [abc]]
                            //     ^   i
                            // Return exception because we encountered ]] at the end of the string, and there is no closing "]"
                            throw new DataApiBuilderException(message: "Token does not have closing ']'.",
                                                           statusCode: HttpStatusCode.ServiceUnavailable,
                                                           subStatusCode: DataApiBuilderException.SubStatusCodes.ErrorInInitialization);
                        }

                        // We increase by 2 so that we skip over the escaped "]"
                        i += 2;

                        continue;
                    }
                    else if (input[i] == ']' && i + 1 < input.Length && input[i + 1] != ']')
                    {
                        // ^ is startIndex and i is current index
                        // Ex: [abc]xyz
                        //     ^   i
                        // Return exception because we encountered "]" and the character after "]" is not a "."
                        throw new DataApiBuilderException(message: "Token has invalid character next to ']'. Allowed characters are '.' and ']'.",
                                                       statusCode: HttpStatusCode.ServiceUnavailable,
                                                       subStatusCode: DataApiBuilderException.SubStatusCodes.ErrorInInitialization);
                    }
                }  // close of else of !startsWithBracket

                i += 1;
            }  // close of while loop

            // Special cases for parsing tokens at the end of the string.
            if (startsWithBracket)
            {
                if (!input.EndsWith(']'))
                {
                    // ^ is startIndex and i is current index
                    // Ex: [abcdef
                    //     ^   i
                    // Return exception because there is no corresponding closing "]".
                    //
                    throw new DataApiBuilderException(message: "Token does not have corresponding closing ']'.",
                                                   statusCode: HttpStatusCode.ServiceUnavailable,
                                                   subStatusCode: DataApiBuilderException.SubStatusCodes.ErrorInInitialization);
                }
                // ^ is startIndex and i is current index
                // Ex: xyz.[abc.def]
                //         ^        i
                // Return "abc.def" as the token and the input length as the index of the next token (it wont look for more tokens after this)
                //
                return (input[(startIndex + 1)..(input.Length - 1)], null);
            }
            else
            {
                // ^ is startIndex and i is current index
                // Ex: abc.def
                //         ^  i
                // Return "def" as the token and the input length as the index of the next token (it wont look for more tokens after this)
                //
                return (input[startIndex..(input.Length)], null);
            }
        }