using System.Runtime.InteropServices;
using UnityEngine;
using UnityEngine.Rendering;

namespace FidelityFX
{
	/// <summary>
	/// Convenience class for handling a constants buffer containing a single struct item.
	/// This wraps the compute buffer and the value array, as well as providing easy access to both.
	/// </summary>
	public class ConstantsBuffer<TConst>
		where TConst: struct
	{
		private ComputeBuffer _computeBuffer;
            
		private readonly TConst[] _constArray = { new TConst() };
		public ref TConst Value => ref _constArray[0];

		public static ConstantsBuffer<TConst> Create()
		{
			ConstantsBuffer<TConst> buffer = new();
			buffer.Init();
			return buffer;
		}
		
		public void Init()
		{
			_computeBuffer = new ComputeBuffer(1, Marshal.SizeOf<TConst>(), ComputeBufferType.Constant);
		}

		public void UpdateBufferData(CommandBuffer commandBuffer)
		{
			commandBuffer.SetBufferData(_computeBuffer, _constArray);
		}
            
		public void Destroy()
		{
			if (_computeBuffer == null)
				return;
                
			_computeBuffer.Release();
			_computeBuffer = null;
		}

		public static implicit operator ComputeBuffer(ConstantsBuffer<TConst> constants)
		{
			return constants._computeBuffer;
		}
	}
}