using OpenTK.Mathematics;

namespace Dashboard.Drawing.OpenGL
{
    /// <summary>
    /// The current stack of transformations.
    /// </summary>
    public class TransformStack
    {
        private Matrix4 _top = Matrix4.Identity;
        private readonly Stack<Matrix4> _stack = new Stack<Matrix4>();

        /// <summary>
        /// The top-most transform matrix.
        /// </summary>
        public ref readonly Matrix4 Top => ref _top;

        /// <summary>
        /// The number of matrices in the stack.
        /// </summary>
        public int Count => _stack.Count;

        /// <summary>
        /// Push a transform.
        /// </summary>
        /// <param name="transform">The transform to push.</param>
        public void Push(in Matrix4 transform)
        {
            _stack.Push(_top);
            _top = transform * _top;
        }

        /// <summary>
        /// Pop a transform.
        /// </summary>
        public void Pop()
        {
            if (!_stack.TryPop(out _top))
                _top = Matrix4.Identity;
        }

        /// <summary>
        /// Clear the stack of transformations.
        /// </summary>
        public void Clear()
        {
            _stack.Clear();
            _top = Matrix4.Identity;
        }
    }
}