---

using System.Collections.Generic;
using System.Linq;
using Xbim.Ifc;
using Xbim.Ifc4.Interfaces;

namespace IfcBimEditor
{
    public static class IfcSpatialTreeBuilder
    {
        public static List<IfcSpatialNode> Build(IfcStore model)
        {
            var seen = new HashSet<string>();
            return model.Instances.OfType<IIfcProject>()
                .Select(p => BuildNode(p, seen)).ToList();
        }

        private static IfcSpatialNode BuildNode(
            IIfcObjectDefinition obj, HashSet<string> seen)
        {
            var node = new IfcSpatialNode
            {
                Entity = obj,
                Type = obj.ExpressType.Name,
                Name = obj.Name.ToString(),
                Description = obj.Description.ToString()
            };
            if (!seen.Add(obj.GlobalId.ToString())) return node;

            // IFC decomposition: project/site/building/storey/assemblies.
            foreach (var rel in obj.IsDecomposedBy.OfType<IIfcRelAggregates>())
                foreach (var child in rel.RelatedObjects)
                    if (!seen.Contains(child.GlobalId.ToString()))
                        node.Children.Add(BuildNode(child, seen));

            // IFC spatial containment: elements assigned to a storey or space.
            if (obj is IIfcSpatialStructureElement spatial)
                foreach (var rel in spatial.ContainsElements)
                    foreach (var element in rel.RelatedElements)
                        if (!seen.Contains(element.GlobalId.ToString()))
                            node.Children.Add(BuildNode(element, seen));
            return node;
        }
    }
}