add validation and guards

src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs

@@ -6,7 +6,7 @@ namespace SharpGLTF.Schema2
 {
     public partial class MeshExtInstanceFeatures
     {
-        private Node  _node;
+        private Node _node;
         internal MeshExtInstanceFeatures(Node node)
         {
             _node = node;
@@ -48,16 +48,80 @@ public MeshExtInstanceFeatureID(int featureCount, int? attribute = null, int? pr
             _propertyTable = propertyTable;
             _nullFeatureId = nullFeatureId;
         }
+
+        /// <summary>
+        /// The number of unique features in the attribute
+        /// </summary>
+        public int FeatureCount { get => _featureCount; }
+
+        /// <summary>
+        /// An attribute containing feature IDs. When this is omitted, then the feature IDs are assigned to the GPU instances by their index.
+        /// </summary>
+        public int? Attribute { get => _attribute; }
+
+        /// <summary>
+        /// A label assigned to this feature ID set
+        /// </summary>
+        public string Label { get => _label; }
+
+        /// <summary>
+        /// The index of the property table containing per-feature property values. Only applicable when using the `EXT_structural_metadata` extension.
+        /// </summary>
+        public int? PropertyTable { get => _propertyTable; }
+
+        /// <summary>
+        /// A value that indicates that no feature is associated with this instance
+        /// </summary>
+        public int? NullFeatureId { get => _nullFeatureId; }
     }
 
     public static class ExtInstanceFeatures
     {
-        public static void SetFeatureIds(this Node node, List<MeshExtInstanceFeatureID> list)
+        /// <summary>
+        /// Set the instance feature ids for this node.
+        /// </summary>
+        /// <param name="node"></param>
+        /// <param name="instanceFeatureIds"></param>
+        public static void SetFeatureIds(this Node node, List<MeshExtInstanceFeatureID> instanceFeatureIds)
         {
-            if (list == null) { node.RemoveExtensions<MeshExtInstanceFeatures>(); return; }
+            if (instanceFeatureIds == null) { node.RemoveExtensions<MeshExtInstanceFeatures>(); return; }
+
+            Guard.NotNullOrEmpty(instanceFeatureIds, nameof(instanceFeatureIds));
+
+            foreach (var instanceFeatureId in instanceFeatureIds)
+            {
+                ValidateInstanceFeatureId(node, instanceFeatureId);
+            };
 
             var ext = node.UseExtension<MeshExtInstanceFeatures>();
-            ext.FeatureIds = list;
+            ext.FeatureIds = instanceFeatureIds;
+        }
+
+        private static void ValidateInstanceFeatureId(Node node, MeshExtInstanceFeatureID item)
+        {
+            Guard.MustBeGreaterThanOrEqualTo((int)item.FeatureCount, 1, nameof(item.FeatureCount));
+
+            if (item.NullFeatureId.HasValue)
+            {
+                Guard.MustBeGreaterThanOrEqualTo((int)item.NullFeatureId, 0, nameof(item.NullFeatureId));
+            }
+            if (item.Label != null)
+            {
+                var regex = "^[a-zA-Z_][a-zA-Z0-9_]*$";
+                Guard.IsTrue(System.Text.RegularExpressions.Regex.IsMatch(item.Label, regex), nameof(item.Label));
+            }
+            if (item.Attribute.HasValue)
+            {
+                Guard.MustBeGreaterThanOrEqualTo((int)item.Attribute, 0, nameof(item.Attribute));
+                // todo: check attribute
+                // Guard that the custom vertex attribute (_FEATURE_ID_{attribute}) exists when FeatureID has attribute set
+                // var expectedVertexAttribute = $"_FEATURE_ID_{item.Attribute}";
+                // Guard.NotNull(primitive.GetVertexAccessor(expectedVertexAttribute), expectedVertexAttribute);
+            }
+            if (item.PropertyTable.HasValue)
+            {
+                Guard.MustBeGreaterThanOrEqualTo((int)item.PropertyTable, 0, nameof(item.PropertyTable));
+            }
         }
     }
 }