#region --- License ---
/* Copyright (c) 2006, 2007 Stefanos Apostolopoulos
 * Contributions from Erik Ylvisaker
 * See license.txt for license info
 */
#endregion

#region --- Using Directives ---

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Diagnostics;

using OpenTK.Graphics;
using OpenTK.Graphics.OpenGL;

#endregion

namespace OpenTK.Platform.Windows
{
    /// \internal
    /// <summary>
    /// Provides methods to create and control an opengl context on the Windows platform.
    /// This class supports OpenTK, and is not intended for use by OpenTK programs.
    /// </summary>
    internal sealed class WinGLContext : DesktopGraphicsContext
    {
        static readonly object LoadLock = new object();
        static readonly object SyncRoot = new object();

        static IntPtr opengl32Handle;
        const string opengl32Name = "OPENGL32.DLL";

        bool vsync_supported;

        readonly WinGraphicsMode ModeSelector;

        #region --- Contructors ---

        static WinGLContext()
        {
            lock (LoadLock)
            {
                // Dynamically load opengl32.dll in order to use the extension loading capabilities of Wgl.
                if (opengl32Handle == IntPtr.Zero)
                {
                    opengl32Handle = Functions.LoadLibrary(opengl32Name);
                    if (opengl32Handle == IntPtr.Zero)
                        throw new ApplicationException(String.Format("LoadLibrary(\"{0}\") call failed with code {1}",
                                                                     opengl32Name, Marshal.GetLastWin32Error()));
                    Debug.WriteLine(String.Format("Loaded opengl32.dll: {0}", opengl32Handle));
                }

                // We need to create a temp context in order to load
                // wgl extensions (e.g. for multisampling or GL3).
                // We cannot rely on OpenTK.Platform.Wgl until we
                // create the context and call Wgl.LoadAll().
                Debug.Print("Creating temporary context for wgl extensions.");
                using (INativeWindow native = new NativeWindow())
                {
                    // Create temporary context and load WGL entry points
                    // First, set a compatible pixel format to the device context
                    // of the temp window
                    WinWindowInfo window = native.WindowInfo as WinWindowInfo;
                    WinGraphicsMode selector = new WinGraphicsMode(window.DeviceContext);
                    SetGraphicsModePFD(selector, GraphicsMode.Default, window);

                    // Then, construct a temporary context and load all wgl extensions
                    ContextHandle temp_context = new ContextHandle(Wgl.Imports.CreateContext(window.DeviceContext));
                    if (temp_context != ContextHandle.Zero)
                    {
						// Make the context current.
						// Note: on some video cards and on some virtual machines, wglMakeCurrent
						// may fail with an errorcode of 6 (INVALID_HANDLE). The suggested workaround
						// is to call wglMakeCurrent in a loop until it succeeds.
						// See https://www.opengl.org/discussion_boards/showthread.php/171058-nVidia-wglMakeCurrent()-multiple-threads
						// Sigh...
						for (int retry = 0; retry < 5; retry++)
						{
							bool success = Wgl.Imports.MakeCurrent(window.DeviceContext, temp_context.Handle);
							if (!success)
							{
								Debug.Print("wglMakeCurrent failed with error: {0}. Retrying", Marshal.GetLastWin32Error());
								System.Threading.Thread.Sleep(10);
							}
							else
							{
								// wglMakeCurrent succeeded, we are done here!
								break;
							}
						}

						// Load wgl extensions and destroy temporary context
						Wgl.LoadAll();
                        Wgl.Imports.MakeCurrent(IntPtr.Zero, IntPtr.Zero);
                        Wgl.Imports.DeleteContext(temp_context.Handle);
                    }
                    else
                    {
                        Debug.Print("wglCreateContext failed with error: {0}", Marshal.GetLastWin32Error());
                    }
                }
            }
        }

        public WinGLContext(GraphicsMode format, WinWindowInfo window, IGraphicsContext sharedContext,
            int major, int minor, GraphicsContextFlags flags)
        {
            // There are many ways this code can break when accessed by multiple threads. The biggest offender is
            // the sharedContext stuff, which will only become valid *after* this constructor returns.
            // The easiest solution is to serialize all context construction - hence the big lock, below.
            lock (SyncRoot)
            {
                if (window == null)
                    throw new ArgumentNullException("window", "Must point to a valid window.");
                if (window.Handle == IntPtr.Zero)
                    throw new ArgumentException("window", "Must be a valid window.");

                Debug.Print("OpenGL will be bound to window:{0} on thread:{1}", window.Handle,
                    System.Threading.Thread.CurrentThread.ManagedThreadId);

                lock (LoadLock)
                {
                    ModeSelector = new WinGraphicsMode(window.DeviceContext);
                    Mode = SetGraphicsModePFD(ModeSelector, format, (WinWindowInfo)window);

                    if (Wgl.Delegates.wglCreateContextAttribsARB != null)
                    {
                        try
                        {
                            Debug.Write("Using WGL_ARB_create_context... ");

                            List<int> attributes = new List<int>();
                            attributes.Add((int)ArbCreateContext.MajorVersion);
                            attributes.Add(major);
                            attributes.Add((int)ArbCreateContext.MinorVersion);
                            attributes.Add(minor);
                            if (flags != 0)
                            {
                                attributes.Add((int)ArbCreateContext.ContextFlags);
                                attributes.Add((int)GetARBContextFlags(flags));
                                attributes.Add((int)ArbCreateContext.ProfileMask);
                                attributes.Add((int)GetARBContextProfile(flags));
                            }
                            // According to the docs, " <attribList> specifies a list of attributes for the context.
                            // The list consists of a sequence of <name,value> pairs terminated by the
                            // value 0. [...]"
                            // Is this a single 0, or a <0, 0> pair? (Defensive coding: add two zeroes just in case).
                            attributes.Add(0);
                            attributes.Add(0);

                            Handle = new ContextHandle(
                                Wgl.Arb.CreateContextAttribs(
                                    window.DeviceContext,
                                    sharedContext != null ? (sharedContext as IGraphicsContextInternal).Context.Handle : IntPtr.Zero,
                                    attributes.ToArray()));
                            if (Handle == ContextHandle.Zero)
                                Debug.Print("failed. (Error: {0})", Marshal.GetLastWin32Error());
                        }
                        catch (EntryPointNotFoundException e) { Debug.Print(e.ToString()); }
                        catch (NullReferenceException e) { Debug.Print(e.ToString()); }
                    }
                }

                if (Handle == ContextHandle.Zero)
                {
                    // Failed to create GL3-level context, fall back to GL2.
                    Debug.Write("Falling back to GL2... ");
                    Handle = new ContextHandle(Wgl.Imports.CreateContext(window.DeviceContext));
                    if (Handle == ContextHandle.Zero)
                        Handle = new ContextHandle(Wgl.Imports.CreateContext(window.DeviceContext));
                    if (Handle == ContextHandle.Zero)
                        throw new GraphicsContextException(
                            String.Format("Context creation failed. Wgl.CreateContext() error: {0}.",
                                Marshal.GetLastWin32Error()));
                }

                Debug.WriteLine(String.Format("success! (id: {0})", Handle));

                // Todo: is this comment still true?
                // On intel drivers, wgl entry points appear to change
                // when creating multiple contexts. As a workaround,
                // we reload Wgl entry points every time we create a
                // new context - this solves the issue without any apparent
                // side-effects (i.e. the old contexts can still be handled
                // using the new entry points.)
                // Sigh...
                Wgl.LoadAll();

                if (sharedContext != null)
                {
                    Marshal.GetLastWin32Error();
                    Debug.Write(String.Format("Sharing state with context {0}: ", sharedContext));
                    bool result = Wgl.Imports.ShareLists((sharedContext as IGraphicsContextInternal).Context.Handle, Handle.Handle);
                    Debug.WriteLine(result ? "success!" : "failed with win32 error " + Marshal.GetLastWin32Error());
                }
            }
        }

        static ArbCreateContext GetARBContextFlags(GraphicsContextFlags flags)
        {
            ArbCreateContext result = 0;
            result |= (flags & GraphicsContextFlags.ForwardCompatible) != 0 ?
                ArbCreateContext.CoreProfileBit : ArbCreateContext.CompatibilityProfileBit;
            return result;
        }

        static ArbCreateContext GetARBContextProfile(GraphicsContextFlags flags)
        {
            ArbCreateContext result = 0;
            result |= (flags & GraphicsContextFlags.Debug) != 0 ? ArbCreateContext.DebugBit : 0;
            return result;
        }

        public WinGLContext(ContextHandle handle, WinWindowInfo window, IGraphicsContext sharedContext,
            int major, int minor, GraphicsContextFlags flags)
        {
            if (handle == ContextHandle.Zero)
                throw new ArgumentException("handle");
            if (window == null)
                throw new ArgumentNullException("window");

            Handle = handle;
        }

        #endregion

        #region IGraphicsContext Members

        #region SwapBuffers

        public override void SwapBuffers()
        {
            if (!Functions.SwapBuffers(DeviceContext))
                throw new GraphicsContextException(String.Format(
                    "Failed to swap buffers for context {0} current. Error: {1}", this, Marshal.GetLastWin32Error()));
        }

        #endregion

        #region MakeCurrent

        public override void MakeCurrent(IWindowInfo window)
        {
            lock (SyncRoot)
            lock (LoadLock)
            {
                bool success;

                WinWindowInfo wnd = window as WinWindowInfo;
                if (wnd != null)
                {
                    if (wnd.Handle == IntPtr.Zero)
                        throw new ArgumentException("window", "Must point to a valid window.");

                    success = Wgl.Imports.MakeCurrent(wnd.DeviceContext, Handle.Handle);
                }
                else
                {
                    success = Wgl.Imports.MakeCurrent(IntPtr.Zero, IntPtr.Zero);
                }

                if (!success)
                    throw new GraphicsContextException(String.Format(
                        "Failed to make context {0} current. Error: {1}", this, Marshal.GetLastWin32Error()));
            }
        }

        #endregion

        #region IsCurrent

        public override bool IsCurrent
        {
            get { return Wgl.Imports.GetCurrentContext() == Handle.Handle; }
        }

        #endregion

        #region SwapInterval

        public override int SwapInterval
        {
            get
            {
                lock (LoadLock)
                {
                    if (vsync_supported)
                        return Wgl.Ext.GetSwapInterval();
                    else
                        return 0;
                }
            }
            set
            {
                lock (LoadLock)
                {
                    if (vsync_supported)
                        Wgl.Ext.SwapInterval(value);
                }
            }
        }

        #endregion

        #region void LoadAll()

        public override void LoadAll()
        {
            lock (LoadLock)
            {
                Wgl.LoadAll();
                vsync_supported = Wgl.Arb.SupportsExtension(this, "WGL_EXT_swap_control") &&
                    Wgl.Load("wglGetSwapIntervalEXT") && Wgl.Load("wglSwapIntervalEXT");
            }

            base.LoadAll();
        }

        #endregion

        #endregion

        #region IGLContextInternal Members

        #region IWindowInfo IGLContextInternal.Info
        /*
        IWindowInfo IGraphicsContextInternal.Info
        {
            get { return (IWindowInfo)windowInfo; }
        }
        */
        #endregion

        #region GetAddress

        public override IntPtr GetAddress(string function_string)
        {
            return Wgl.Imports.GetProcAddress(function_string);
        }

        #endregion

        #endregion

        #region Internal Methods

        #region SetGraphicsModePFD

        // Note: there is no relevant ARB function.
        internal static GraphicsMode SetGraphicsModePFD(WinGraphicsMode mode_selector,
            GraphicsMode mode, WinWindowInfo window)
        {
            Debug.Write("Setting pixel format... ");
            if (window == null)
                throw new ArgumentNullException("window", "Must point to a valid window.");

            if (!mode.Index.HasValue)
            {
                mode = mode_selector.SelectGraphicsMode(
                    mode.ColorFormat, mode.Depth, mode.Stencil,
                    mode.Samples, mode.AccumulatorFormat,
                    mode.Buffers, mode.Stereo);
            }

            PixelFormatDescriptor pfd = new PixelFormatDescriptor();
            Functions.DescribePixelFormat(
                window.DeviceContext, (int)mode.Index.Value,
                API.PixelFormatDescriptorSize, ref pfd);
            
            Debug.WriteLine(mode.Index.ToString());
            
            if (!Functions.SetPixelFormat(window.DeviceContext, (int)mode.Index.Value, ref pfd))
            {
                throw new GraphicsContextException(String.Format(
                    "Requested GraphicsMode not available. SetPixelFormat error: {0}",
                    Marshal.GetLastWin32Error()));
            }

            return mode;
        }

        #endregion

        #region internal IntPtr DeviceContext

        internal IntPtr DeviceContext
        {
            get
            {
                return Wgl.Imports.GetCurrentDC();
            }
        }


        #endregion

        #endregion

        #region Overrides

        /// <summary>Returns a System.String describing this OpenGL context.</summary>
        /// <returns>A System.String describing this OpenGL context.</returns>
        public override string ToString()
        {
            return (this as IGraphicsContextInternal).Context.ToString();
        }

        #endregion

        #region IDisposable Members

        public override void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        private void Dispose(bool calledManually)
        {
            if (!IsDisposed)
            {
                if (calledManually)
                {
                    DestroyContext();
                }
                else
                {
                    Debug.Print("[Warning] OpenGL context {0} leaked. Did you forget to call IGraphicsContext.Dispose()?",
                        Handle.Handle);
                }
                IsDisposed = true;
            }
        }

        ~WinGLContext()
        {
            Dispose(false);
        }

        #region private void DestroyContext()

        private void DestroyContext()
        {
            if (Handle != ContextHandle.Zero)
            {
                try
                {
                    // This will fail if the user calls Dispose() on thread X when the context is current on thread Y.
                    if (!Wgl.Imports.DeleteContext(Handle.Handle))
                        Debug.Print("Failed to destroy OpenGL context {0}. Error: {1}",
                            Handle.ToString(), Marshal.GetLastWin32Error());
                }
                catch (AccessViolationException e)
                {
                    Debug.WriteLine("An access violation occured while destroying the OpenGL context. Please report at http://www.opentk.com.");
                    Debug.Indent();
                    Debug.Print("Marshal.GetLastWin32Error(): {0}", Marshal.GetLastWin32Error().ToString());
                    Debug.WriteLine(e.ToString());
                    Debug.Unindent();
                }
                Handle = ContextHandle.Zero;
            }
        }

        #endregion

        #endregion
    }
}