StepFactory.cs

using System;
using System.Collections.Generic;

namespace Ara3D.StepParser
{

    public static unsafe class StepFactory
    {
        public static StepList GetAttributes(this StepRawInstance inst, byte* lineEnd)
        {
            if (!inst.IsValid())
                return default;
            var ptr = inst.Type.End();
            var token = StepTokenizer.ParseToken(ptr, lineEnd);
            // TODO: there is a potential bug here when the line is split across multiple line
            return CreateAggregate(ref token, lineEnd);
        }

        public static StepValue Create(ref StepToken token, byte* end)
        {
            switch (token.Type)
            {
                case StepTokenType.String:
                    return StepString.Create(token);

                case StepTokenType.Symbol:
                    return StepSymbol.Create(token);

                case StepTokenType.Id:
                    return StepId.Create(token);

                case StepTokenType.Redeclared:
                    return StepRedeclared.Create(token);

                case StepTokenType.Unassigned:
                    return StepUnassigned.Create(token);

                case StepTokenType.Number:
                    return StepNumber.Create(token);

                case StepTokenType.Ident:
                    var span = token.Span;
                    StepTokenizer.ParseNextToken(ref token, end);
                    var attr = CreateAggregate(ref token, end);
                    return new StepEntity(span, attr);

                case StepTokenType.BeginGroup:
                    return CreateAggregate(ref token, end);

                case StepTokenType.None:
                case StepTokenType.Whitespace:
                case StepTokenType.Comment:
                case StepTokenType.Unknown:
                case StepTokenType.LineBreak:
                case StepTokenType.EndOfLine:
                case StepTokenType.Definition:
                case StepTokenType.Separator:
                case StepTokenType.EndGroup:
                default:
                    throw new Exception($"Cannot convert token type {token.Type} to a StepValue");
            }
        }

        public static StepList CreateAggregate(ref StepToken token, byte* end)
        {
            var values = new List<StepValue>();
            StepTokenizer.EatWSpace(ref token, end);
            if (token.Type != StepTokenType.BeginGroup)
                throw new Exception("Expected '('");

            while (StepTokenizer.ParseNextToken(ref token, end))
            {
                switch (token.Type)
                {
                    // Advance past comments, whitespace, and commas 
                    case StepTokenType.Comment:
                    case StepTokenType.Whitespace:
                    case StepTokenType.LineBreak:
                    case StepTokenType.Separator:
                    case StepTokenType.None:
                        continue;

                    // Expected end of group 
                    case StepTokenType.EndGroup:
                        return new StepList(values);    
                }

                var curValue = Create(ref token, end);
                values.Add(curValue);
            }

            throw new Exception("Unexpected end of input");
        }
    }
}