using System.Reflection;
using System.Runtime.InteropServices;
using OpenTK.Graphics.OpenGL;

namespace Engine.Renderer.Buffer.Vertex;

public interface IVertex
{
    public static IOrderedEnumerable<FieldInfo> GetFields<T>() => GetFields(typeof(T));

    public static IOrderedEnumerable<FieldInfo> GetFields(Type type) =>
        type.GetFields(BindingFlags.Public | BindingFlags.Instance).OrderBy(f => f.MetadataToken);

    public static bool IsValid(Type type)
    {
        if (!type.IsValueType || !type.IsAssignableTo(typeof(IVertex)))
            return false;

        var fields = GetFields(type);
        var totalSize = 0;
        foreach (var field in fields)
        {
            if (!field.FieldType.IsValueType)
                return false;

            var attribute = field.GetCustomAttribute<VertexAttribute>();
            if (attribute == null)
                return false;

            var size = AttributeSize(attribute.Type) * attribute.ComponentCount * attribute.RepeatCount;
            if (size != Marshal.SizeOf(field.FieldType))
                return false;

            totalSize += size;
        }

        return totalSize == Marshal.SizeOf(type);
    }

    public static int AttributeSize(VertexAttribType type) => type switch
    {
        VertexAttribType.Byte or VertexAttribType.UnsignedByte => sizeof(byte),
        VertexAttribType.Short or VertexAttribType.UnsignedShort => sizeof(short),
        VertexAttribType.Int or VertexAttribType.UnsignedInt => sizeof(int),
        VertexAttribType.HalfFloat => Marshal.SizeOf<Half>(),
        VertexAttribType.Float => sizeof(float),
        VertexAttribType.Double => sizeof(double),
        _ => 0
    };
}