gaemstone/src/gaemstone.SourceGen/Structure/TypeEntityInfo.cs

using System.Collections.Generic;
using Microsoft.CodeAnalysis;

namespace gaemstone.SourceGen.Structure;

public class TypeEntityInfo : BaseEntityInfo
{
	public new INamedTypeSymbol Symbol => (INamedTypeSymbol)base.Symbol;

	public List<BaseEntityInfo> Children { get; } = new();
	protected override IEnumerable<BaseInfo> GetChildren() => Children;

	public bool IsModule { get; }
	private bool IsEntity { get; }
	public bool IsTag { get; }
	public bool IsComponent { get; private set; }
	public bool IsSingleton { get; }
	public bool IsRelation { get; }

	// Built-in entities error if they don't exist.
	// When a module is built-in, most attributes become descriptive,
	// and don't change or affect the entity they're attached to.
	public bool IsBuiltIn { get; protected set; }

	public bool IsValueType     => Symbol.IsValueType;
	public bool IsReferenceType => Symbol.IsReferenceType;
	// TODO: Make sure that component has (instance) fields, non-component entity does not have fields.

	public TypeEntityInfo(ISymbol symbol)
		: base(symbol)
	{
		IsModule    = Has("Module");
		IsEntity    = Has("Entity");
		IsTag       = Has("Tag");
		IsComponent = Has("Component");
		IsSingleton = Has("Singleton");
		IsRelation  = Has("Relation");

		IsBuiltIn = !IsModule && !IsEntity && !IsTag
				 && !IsComponent && !IsSingleton && !IsRelation
				 && (EntityPath != null);
	}

	protected override IEnumerable<Diagnostic> ValidateSelf()
	{
		foreach (var diag in base.ValidateSelf()) yield return diag;

		if (Symbol.IsStatic) yield return Diagnostic.Create(
			Descriptors.TypeMustNotBeStatic, Location);
		if (Symbol.IsAbstract) yield return Diagnostic.Create(
			Descriptors.TypeMustNotBeAbstract, Location);

		var attributeList = new List<string>();
		if (IsModule)    attributeList.Add("Module");
		if (IsEntity)    attributeList.Add("Entity");
		if (IsRelation)  attributeList.Add("Relation");
		if (IsTag)       attributeList.Add("Tag");
		if (IsComponent) attributeList.Add("Component");
		if (IsSingleton) attributeList.Add("Singleton");

		switch (attributeList)
		{
			// No attributes are only valid if [Path] is set.
			case [  ]:
				if (!IsBuiltIn) yield return Diagnostic.Create(
					Descriptors.AttributesRequireTypeOrPath, Location,
					$"[{string.Join(", ", attributeList)}]");
				break;
			// A single attribute is valid.
			case [ _ ]:
			// The following are valid attribute combinations.
			case [ "Module", "Singleton" ]:
			case [ "Relation", "Tag" ]:
			case [ "Relation", "Component" ]:
				break;
			default:
				yield return Diagnostic.Create(
					Descriptors.InvalidAttributeCombination, Location,
					$"[{string.Join(", ", attributeList)}]");
				if (IsModule) yield return Diagnostic.Create(
					Descriptors.ValidModuleAttributesHint, Location);
				if (IsRelation) yield return Diagnostic.Create(
					Descriptors.ValidRelationAttributesHint, Location);
				if (IsSingleton && IsComponent) yield return Diagnostic.Create(
					Descriptors.SingletonImpliesComponentHint, Location);
				break;
		}

		// In in a built-in module, this entity is built-in, too.
		if (Parent is ModuleEntityInfo { IsBuiltIn: true })
			IsBuiltIn = true;

		// Singletons are special kinds of components.
		if (IsSingleton) IsComponent = true;
	}
}