using System.Collections.Generic;
using Microsoft.Xna.Framework.Graphics;

namespace Kav
{
    public class InstanceData<T> where T : struct, IVertexType
    {
        public T[] InstanceDataArray { get; }
        public DynamicVertexBuffer VertexBuffer { get; }
        public int InstanceCount { get; private set; }

        public InstanceData(GraphicsDevice graphicsDevice, int size)
        {
            InstanceDataArray = new T[size];

            VertexBuffer = new DynamicVertexBuffer(
                graphicsDevice,
                typeof(T),
                size,
                BufferUsage.WriteOnly
            );

            InstanceCount = 0;
        }

        public void AddAndSetData(IEnumerable<T> data)
        {
            InstanceCount = 0;
            foreach (var datum in data)
            {
                AddData(datum);
            }

            if (InstanceCount == 0) { throw new System.Exception(); }

            SetData();
        }

        public void AddData(T datum)
        {
            InstanceDataArray[InstanceCount] = datum;
            InstanceCount += 1;
        }

        public void SetData()
        {
            if (InstanceCount > 0)
            {
                VertexBuffer.SetData(
                    InstanceDataArray,
                    0,
                    InstanceCount,
                    SetDataOptions.NoOverwrite
                );
            }
        }

        public void Clear()
        {
            InstanceCount = 0;
        }
    }
}