using System;
using System.Collections.Generic;
using System.Data.Common;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Runtime.Versioning;
using System.Security.AccessControl;
using System.Text;
using System.Threading.Tasks;



namespace System
{
    /// <summary>
    /// A handle to an OpenGL object,
    /// must be indexed from a <see cref="glHandleSet"/>.
    /// Direct call will cause <see langword="InvalidOperationException"/>
    /// </summary>
    public unsafe struct glHandle
    {
        internal uint* valuePtr;

        public glHandle()
        {
            throw new InvalidOperationException();
        }

        internal glHandle(uint* val)
        {
            valuePtr = val;
        }

        public uint Value
        {
            get { return *valuePtr; }
        }

    }

    /// <summary>
    /// A handle to an OpenGL object.
    /// </summary>
    public unsafe class glHandleSet
    {
        private readonly uint[] _value;
        internal int length;
        internal uint* handle;

        public glHandle this[int index]
        {
            get
            {
                if (index > length)
                {
                    throw new IndexOutOfRangeException();
                }
                return new glHandle(handle + index);
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void SetValue(int index, uint value)
        {
            _value[index] = value;
        }

        public glHandleSet(int count)
        {
            _value = new uint[count];
            length = count;
            handle = (uint*)GCHandle.Alloc(_value, GCHandleType.Pinned).AddrOfPinnedObject();
        }

        /// <summary>
        /// temporarily release the handle of GLhandle sets.
        /// Please call <see cref="Pin"/> method before indexing.
        /// </summary>
        public void Free()
        {
            if (_value == null)
            {
                return;
            }
            GCHandle h = GCHandle.FromIntPtr((IntPtr)handle);
            h.Free();
        }

        public void Pin()
        {
            if (_value == null)
            {
                return;
            }
            handle = (uint*)GCHandle.Alloc(_value, GCHandleType.Pinned).AddrOfPinnedObject();
        }

        /// <summary>
        /// Realse all resource in this handle. 
        /// This will release all resource in this <see cref="glHandle"/>.
        /// This <see langword="glHandle"/> will be not usable.
        /// </summary>
        public void Release()
        {
            if (_value == null)
            {
                return;
            }
            else
            {
                GCHandle.FromIntPtr((IntPtr)handle).Free();
                handle = (uint*)IntPtr.Zero;
            }
        }

    }
}