using StgSharp.Math;
using System;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Text;

namespace StgSharp.Graphics
{
    public partial class Form
    {
        /// <summary>
        /// Create a set of <see cref="ElementBuffer"/>.
        /// </summary>
        /// <param name="count">Amount of EBO to be created.</param>
        /// <returns></returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        protected ElementBuffer CreateElementBuffer(uint count)
        {
            return new ElementBuffer(count, this.gl);
        }
    }

    /// <summary>
    /// A collecion of handle to Element Buffer Object in OpenGL.
    /// Each <see cref="uint"/> value indexed from instance of this class this 
    /// is the only handle to one Element Buffer Object.
    /// </summary>
    public unsafe class ElementBuffer : IBufferObject
    {
        internal ElementBuffer(uint n, IglFunc gl)
        {
            _bufferID = new uint[n];
            GL = gl;
            fixed (uint* id = _bufferID)
            {
                GL.GenBuffers(n, id);
            }
        }

        public uint this[int n]
        {
            get { return _bufferID[n]; }
        }

        public override void Bind(int index)
        {
            GL.BindBuffer(BufferType.ELEMENT_ARRAY_BUFFER, _bufferID[index]);
        }

        public void SetValue<T>(int index, T[] bufferArray, BufferUsage usage)
            where T : struct, IConvertible
        {
            GL.BindBuffer(BufferType.ELEMENT_ARRAY_BUFFER, _bufferID[index]);
            GL.SetBufferData(BufferType.ELEMENT_ARRAY_BUFFER, bufferArray, usage);
        }

        protected sealed override void Dispose(bool disposing)
        {
            if (disposing)
            {
                GL.DeleteBuffers((uint)_bufferID.Length, _bufferID);
            }
        }
    }
}