MongoDB.Bson.IO.JsonScanner.GetRegularExpressionToken C# (CSharp) Метод

        private static JsonToken GetRegularExpressionToken(JsonBuffer buffer)
        {
            // opening slash has already been read
            var start = buffer.Position - 1;
            var state = RegularExpressionState.InPattern;
            while (true)
            {
                var c = buffer.Read();
                switch (state)
                {
                    case RegularExpressionState.InPattern:
                        switch (c)
                        {
                            case '/': state = RegularExpressionState.InOptions; break;
                            case '\\': state = RegularExpressionState.InEscapeSequence; break;
                            default: state = RegularExpressionState.InPattern; break;
                        }
                        break;
                    case RegularExpressionState.InEscapeSequence:
                        state = RegularExpressionState.InPattern;
                        break;
                    case RegularExpressionState.InOptions:
                        switch (c)
                        {
                            case 'i':
                            case 'm':
                            case 'x':
                            case 's':
                                state = RegularExpressionState.InOptions;
                                break;
                            case ',':
                            case '}':
                            case ']':
                            case ')':
                            case -1:
                                state = RegularExpressionState.Done;
                                break;
                            default:
                                if (char.IsWhiteSpace((char)c))
                                {
                                    state = RegularExpressionState.Done;
                                }
                                else
                                {
                                    state = RegularExpressionState.Invalid;
                                }
                                break;
                        }
                        break;
                }

                switch (state)
                {
                    case RegularExpressionState.Done:
                        buffer.UnRead(c);
                        var lexeme = buffer.Substring(start, buffer.Position - start);
                        var regex = new BsonRegularExpression(lexeme);
                        return new RegularExpressionJsonToken(lexeme, regex);
                    case RegularExpressionState.Invalid:
                        throw new Exception(FormatMessage("Invalid JSON regular expression", buffer, start));
                }
            }
        }