using System.Runtime.CompilerServices;
using Dashboard.Drawing;
using OpenTK.Graphics.OpenGL;

namespace Dashboard.OpenGL
{
    public class GLBuffer(GLDeviceContext dc, BufferAccessPattern pattern, int handle, long size, long offset) : IBuffer
    {
        // TODO: At the moment, this class does no pooling. Convert it to a pool for better API usage.

        public BufferAccessPattern AccessPattern { get; } = pattern;
        public long Size { get; private set; } = size;
        public long Offset { get; private set; } = offset;
        public int Handle { get; private set; }

        public void Reallocate(long newSize)
        {
            GL.CreateBuffer(out int handle);
            GL.BindBuffer(BufferTarget.ArrayBuffer, handle);
            GL.BufferData(BufferTarget.ArrayBuffer, (nint)newSize, (nint)0, AccessPattern switch
            {
                BufferAccessPattern.Stream => BufferUsage.StreamDraw,
                BufferAccessPattern.Static => BufferUsage.StaticDraw,
                BufferAccessPattern.Download => BufferUsage.DynamicCopy,
                BufferAccessPattern.Upload => BufferUsage.DynamicCopy,
                _ => BufferUsage.DynamicDraw,
            });

            if (Handle != -1)
                GL.DeleteBuffer(Handle);

            Handle = handle;
            Size = newSize;
            Offset = 0;
        }

        public unsafe Span<T> Map<T>(long offset, int count = -1)
            where T : unmanaged
        {
            ArgumentOutOfRangeException.ThrowIfNegative(offset);

            if (count < 0)
                count = (int)(Size / Unsafe.SizeOf<T>());

            long absOffset = Offset + offset;
            long absCount = count * Unsafe.SizeOf<T>();
            ArgumentOutOfRangeException.ThrowIfGreaterThan(offset + absCount, Size);

            GL.BindBuffer(BufferTarget.ArrayBuffer, Handle);
            nint ptr = (nint)GL.MapBuffer(BufferTarget.ArrayBuffer, BufferAccess.ReadWrite);

            return new Span<T>((T*)(ptr + absOffset), count);
        }

        public void Unmap()
        {
            GL.BindBuffer(BufferTarget.ArrayBuffer, Handle);
            GL.UnmapBuffer(BufferTarget.ArrayBuffer);
        }

        public void Read<T>(long offset, Span<T> span) where T : unmanaged
        {
            long absCount = span.Length * Unsafe.SizeOf<T>();
            ArgumentOutOfRangeException.ThrowIfGreaterThan(offset + absCount, Size);

            GL.BindBuffer(BufferTarget.ArrayBuffer, Handle);
            GL.GetBufferSubData(BufferTarget.ArrayBuffer, (nint)(Offset + offset), (nint)absCount, span);
        }

        public void Write<T>(long offset, ReadOnlySpan<T> span) where T : unmanaged
        {
            long absCount = span.Length * Unsafe.SizeOf<T>();
            ArgumentOutOfRangeException.ThrowIfGreaterThan(offset + absCount, Size);

            GL.BindBuffer(BufferTarget.ArrayBuffer, Handle);
            GL.BufferSubData(BufferTarget.ArrayBuffer, (nint)(Offset + offset), (nint)absCount, span);
        }

        public void Dispose()
        {
            if (Handle == -1)
                return;

            dc.Collector.DeleteBufffer(Handle);
            Handle = -1;

            GC.SuppressFinalize(this);
        }

        public static GLBuffer Create(GLDeviceContext dc, BufferAccessPattern pattern, long size)
        {
            GLBuffer buffer = new GLBuffer(dc, pattern, -1, 0, 0);
            buffer.Reallocate(size);

            return buffer;
        }
    }
}