public JsonSchemaNode AddSchema(JsonSchemaNode existingNode, JsonSchema schema)
        {
            string newId;

            if (existingNode != null)
            {
                if (existingNode.Schemas.Contains(schema))
                {
                    return(existingNode);
                }

                newId = JsonSchemaNode.GetId(existingNode.Schemas.Union(new[] { schema }));
            }
            else
            {
                newId = JsonSchemaNode.GetId(new[] { schema });
            }

            if (_nodes.Contains(newId))
            {
                return(_nodes[newId]);
            }

            JsonSchemaNode currentNode = (existingNode != null)
        ? existingNode.Combine(schema)
        : new JsonSchemaNode(schema);

            _nodes.Add(currentNode);

            AddProperties(schema.Properties, currentNode.Properties);

            AddProperties(schema.PatternProperties, currentNode.PatternProperties);

            if (schema.Items != null)
            {
                for (int i = 0; i < schema.Items.Count; i++)
                {
                    AddItem(currentNode, i, schema.Items[i]);
                }
            }

            if (schema.AdditionalProperties != null)
            {
                AddAdditionalProperties(currentNode, schema.AdditionalProperties);
            }

            if (schema.Extends != null)
            {
                currentNode = AddSchema(currentNode, schema.Extends);
            }

            return(currentNode);
        }