using System;
using gaemstone.ECS;
using Silk.NET.Maths;
using Silk.NET.OpenGL;
using ModelRoot = SharpGLTF.Schema2.ModelRoot;

namespace gaemstone.Client;

public static class MeshManager
{
	const uint PositionAttribIndex = 0;
	const uint NormalAttribIndex   = 1;
	const uint UvAttribIndex       = 2;

	public static Mesh Load(Universe universe, string name)
	{
		ModelRoot root;
		using (var stream = Resources.GetStream(name))
			root = ModelRoot.ReadGLB(stream, new());
		var primitive = root.LogicalMeshes[0].Primitives[0];

		var indices  = primitive.IndexAccessor;
		var vertices = primitive.VertexAccessors["POSITION"];
		var normals  = primitive.VertexAccessors["NORMAL"];

		var GL  = universe.Lookup<Game>().Get<Windowing.Canvas>().GL;
		var vao = GL.GenVertexArray();
		GL.BindVertexArray(vao);

		GL.CreateBufferFromData(indices.SourceBufferView.Content,
								BufferTargetARB.ElementArrayBuffer);

		GL.CreateBufferFromData(vertices.SourceBufferView.Content);
		GL.EnableVertexAttribArray(PositionAttribIndex);
		unsafe { GL.VertexAttribPointer(PositionAttribIndex, 3,
			(VertexAttribPointerType)vertices.Encoding, vertices.Normalized,
			(uint)vertices.SourceBufferView.ByteStride, (void*)vertices.ByteOffset); }

		GL.CreateBufferFromData(normals.SourceBufferView.Content);
		GL.EnableVertexAttribArray(NormalAttribIndex);
		unsafe { GL.VertexAttribPointer(NormalAttribIndex, 3,
			(VertexAttribPointerType)vertices.Encoding, vertices.Normalized,
			(uint)vertices.SourceBufferView.ByteStride, (void*)vertices.ByteOffset); }

		var numVertices = primitive.IndexAccessor.Count;
		return new(vao, numVertices);
	}

	public static Mesh Create(Universe universe,
		ReadOnlySpan<ushort> indices, ReadOnlySpan<Vector3D<float>> vertices,
		ReadOnlySpan<Vector3D<float>> normals, ReadOnlySpan<Vector2D<float>> uvs)
	{
		var GL  = universe.Lookup<Game>().Get<Windowing.Canvas>().GL;
		var vao = GL.GenVertexArray();
		GL.BindVertexArray(vao);

		GL.CreateBufferFromData(indices, BufferTargetARB.ElementArrayBuffer);
		GL.CreateBufferFromData(vertices);
		GL.EnableVertexAttribArray(PositionAttribIndex);
		unsafe { GL.VertexAttribPointer(PositionAttribIndex, 3,
			VertexAttribPointerType.Float, false, 0, (void*)0); }
		if (!normals.IsEmpty) {
			GL.CreateBufferFromData(normals);
			GL.EnableVertexAttribArray(NormalAttribIndex);
			unsafe { GL.VertexAttribPointer(NormalAttribIndex, 3,
				VertexAttribPointerType.Float, false, 0, (void*)0); }
		}
		if (!uvs.IsEmpty) {
			GL.CreateBufferFromData(uvs);
			GL.EnableVertexAttribArray(UvAttribIndex);
			unsafe { GL.VertexAttribPointer(UvAttribIndex, 2,
				VertexAttribPointerType.Float, false, 0, (void*)0); }
		}

		return new(vao, indices.Length);
	}

	public static Mesh Create(Universe universe, ReadOnlySpan<Vector3D<float>> vertices,
		ReadOnlySpan<Vector3D<float>> normals, ReadOnlySpan<Vector2D<float>> uvs)
	{
		var GL  = universe.Lookup<Game>().Get<Windowing.Canvas>().GL;
		var vao = GL.GenVertexArray();
		GL.BindVertexArray(vao);

		GL.CreateBufferFromData(vertices);
		GL.EnableVertexAttribArray(PositionAttribIndex);
		unsafe { GL.VertexAttribPointer(PositionAttribIndex, 3,
			VertexAttribPointerType.Float, false, 0, (void*)0); }
		if (!normals.IsEmpty) {
			GL.CreateBufferFromData(normals);
			GL.EnableVertexAttribArray(NormalAttribIndex);
			unsafe { GL.VertexAttribPointer(NormalAttribIndex, 3,
				VertexAttribPointerType.Float, false, 0, (void*)0); }
		}
		if (!uvs.IsEmpty) {
			GL.CreateBufferFromData(uvs);
			GL.EnableVertexAttribArray(UvAttribIndex);
			unsafe { GL.VertexAttribPointer(UvAttribIndex, 2,
				VertexAttribPointerType.Float, false, 0, (void*)0); }
		}

		return new(vao, vertices.Length, false);
	}
}