StepValue.cs

using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using Ara3D.Buffers;
using Ara3D.Utils;

namespace Ara3D.StepParser
{
    /// <summary>
    /// The base class of the different type of value items that can be found in a STEP file.
    /// * Entity
    /// * List
    /// * String
    /// * Symbol
    /// * Unassigned token
    /// * Redeclared token
    /// * Number
    /// </summary>
    public class StepValue;

    public class StepEntity : StepValue
    {
        public readonly ByteSpan EntityType;
        public readonly StepList Attributes;

        public StepEntity(ByteSpan entityType, StepList attributes)
        {
            Debug.Assert(!entityType.IsNull());
            EntityType = entityType;
            Attributes = attributes;
        }

        public override string ToString()
            => $"{EntityType}{Attributes}";
    }

    public class StepList : StepValue
    {
        public readonly List<StepValue> Values;

        public StepList(List<StepValue> values)
            => Values = values;

        public override string ToString()
            => $"({Values.JoinStringsWithComma()})";

        public static StepList Default = new(new List<StepValue>());
    }

    public class StepString : StepValue
    {
        public readonly ByteSpan Value;

        public static StepString Create(StepToken token)
        {
            var span = token.Span;
            Debug.Assert(token.Type == StepTokenType.String);
            Debug.Assert(span.Length >= 2);
            Debug.Assert(span.First() == '\'' || span.First() == '"');
            Debug.Assert(span.Last() == '\'' || span.Last() == '"');
            return new StepString(span.Trim(1, 1));
        }

        public StepString(ByteSpan value)
            => Value = value;

        public override string ToString()
            => $"'{Value}'";
    }

    public class StepSymbol : StepValue
    {
        public readonly ByteSpan Name;

        public StepSymbol(ByteSpan name)
            => Name = name;

        public override string ToString()
            => $".{Name}.";

        public static StepSymbol Create(StepToken token)
        {
            Debug.Assert(token.Type == StepTokenType.Symbol);
            var span = token.Span;
            Debug.Assert(span.Length >= 2);
            Debug.Assert(span.First() == '.');
            Debug.Assert(span.Last() == '.');
            return new StepSymbol(span.Trim(1, 1));
        }
    }

    public class StepNumber : StepValue
    {
        public readonly ByteSpan Span;
        public double Value => Span.ToDouble();

        public StepNumber(ByteSpan span)
            => Span = span;

        public override string ToString()
            => $"{Value}";

        public static StepNumber Create(StepToken token)
        {
            Debug.Assert(token.Type == StepTokenType.Number);
            var span = token.Span;
            return new(span);
        }
    }

    public class StepId : StepValue
    {
        public readonly uint Id;

        public StepId(uint id)
            => Id = id;

        public override string ToString()
            => $"#{Id}";

        public static unsafe StepId Create(StepToken token)
        {
            Debug.Assert(token.Type == StepTokenType.Id);
            var span = token.Span;
            Debug.Assert(span.Length >= 2);
            Debug.Assert(span.First() == '#');
            var id = 0u;
            for (var i = 1; i < span.Length; ++i)
            {
                Debug.Assert(span.Ptr[i] >= '0' && span.Ptr[i] <= '9');
                id = id * 10 + span.Ptr[i] - '0';
            }
            return new StepId(id);
        }
    }

    public class StepUnassigned : StepValue
    {
        public static readonly StepUnassigned Default = new();

        public override string ToString()
            => "$";

        public static StepUnassigned Create(StepToken token)
        {
            Debug.Assert(token.Type == StepTokenType.Unassigned);
            var span = token.Span;
            Debug.Assert(span.Length == 1);
            Debug.Assert(span.First() == '$');
            return Default;
        }
    }

    public class StepRedeclared : StepValue
    {
        public static readonly StepRedeclared Default = new();

        public override string ToString()
            => "*";

        public static StepRedeclared Create(StepToken token)
        {
            Debug.Assert(token.Type == StepTokenType.Redeclared);
            var span = token.Span;
            Debug.Assert(span.Length == 1);
            Debug.Assert(span.First() == '*');
            return Default;
        }
    }
}