Connected.Framework/Connected.Interop/Merging/JsonMerger.cs

using System.Collections;
using System.Reflection;
using System.Text.Json.Nodes;
using System.Text.Json.Serialization;

namespace Connected.Interop.Merging
{
	internal sealed class JsonMerger : Merger
	{
		public void Merge(object destination, JsonNode? source)
		{
			if (source is null || destination is null)
				return;

			foreach (var property in Properties.GetImplementedProperties(destination))
				MergeProperty(destination, source, property);
		}

		private void MergeProperty(object destination, JsonNode source, PropertyInfo property)
		{
			if (property.FindAttribute<JsonIgnoreAttribute>() is not null)
				return;

			if (property.PropertyType.IsTypePrimitive())
			{
				if (!property.CanWrite || source is not JsonObject jo || ResolveJsonProperty(property, jo) is not JsonValue jprop)
					return;

				if (!TypeConversion.TryConvert(jprop.ToString(), out object? convertedValue, property.PropertyType))
					return;

				property.SetValue(destination, convertedValue);
			}
			else if (IsArray(property))
				MergeEnumerable(destination, source, property);
			else
				MergeObject(destination, source, property);
		}

		private static JsonValue? ResolveJsonProperty(PropertyInfo property, JsonObject json)
		{
			foreach (var prop in json)
			{
				if (string.Equals(prop.Key, property.Name, StringComparison.OrdinalIgnoreCase))
					return prop.Value as JsonValue;
			}

			return null;
		}

		private void MergeEnumerable(object destination, JsonNode source, PropertyInfo property)
		{
			if (source is not JsonObject jobject)
				return;

			if (!jobject.ContainsKey(property.Name) || jobject[property.Name] is not JsonArray array || !array.Any())
				return;

			var value = property.GetValue(destination);

			if (value is null && !property.CanWrite)
				return;

			var addMethod = property.PropertyType.GetMethod(nameof(IList.Add), BindingFlags.Public | BindingFlags.Instance | BindingFlags.NonPublic);
			var instance = addMethod is not null ? Activator.CreateInstance(property.PropertyType) : Array.CreateInstance(property.PropertyType, array.Count);
			var elementType = property.PropertyType.GenericTypeArguments[0];

			for (var i = 0; i < array.Count; i++)
			{
				var json = array[i];
				var item = Activator.CreateInstance(elementType);

				Merge(item, json);

				if (addMethod is not null)
					addMethod.Invoke(instance, new object[] { item });
				else
					((Array)instance).SetValue(item, i);
			}

			property.SetValue(destination, instance);
		}

		private void MergeObject(object destination, JsonNode source, PropertyInfo property)
		{
			var value = property.GetValue(destination);

			if (value is null && property.CanWrite)
				property.SetValue(destination, property.PropertyType.CreateInstance());

			value = property.GetValue(destination);

			if (value is null)
				return;

			foreach (var instanceProperty in Properties.GetImplementedProperties(value))
				MergeProperty(value, source, instanceProperty);
		}
	}
}