/*  
    This file is part of sImlac.

    sImlac is free software: you can redistribute it and/or modify
    it under the terms of the GNU Affero General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    sImlac is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Affero General Public License for more details.

    You should have received a copy of the GNU Affero General Public License
    along with sImlac.  If not, see <http://www.gnu.org/licenses/>.
*/

using System;
using System.Runtime.InteropServices;
using System.ComponentModel;
using System.Threading;

namespace imlac
{
	/// <summary>
	/// HighResTimer gives us access to NT's very-high-resolution PerformanceCounters.
	/// This gives us the precision we need to sync emulation to any speed we desire.
	/// </summary>
    public sealed class HighResTimer
	{
		[DllImport("Kernel32.dll")]
		private static extern bool QueryPerformanceCounter(
			out long lpPerformanceCount);

		[DllImport("Kernel32.dll")]
		private static extern bool QueryPerformanceFrequency(
			out long lpFrequency);		

		public HighResTimer()
		{
			//What's the frequency, Kenneth?
			if (QueryPerformanceFrequency(out _frequency) == false)
			{
				// high-performance counter not supported
				throw new Win32Exception();
			}
		}

		/// <summary>
		/// Returns the current time in seconds.
		/// </summary>
		/// <returns></returns>
		public double GetCurrentTime()
		{
			long currentTime;
			QueryPerformanceCounter(out currentTime);

			return (double)(currentTime) / (double)_frequency;
		}

        private long	_frequency;
	}

    public sealed class FrameTimer
    {
        [DllImport("winmm.dll", EntryPoint = "timeGetDevCaps", SetLastError = true)]
        static extern UInt32 TimeGetDevCaps(ref TimeCaps timeCaps, UInt32 sizeTimeCaps);
        
        [DllImport("winmm.dll", EntryPoint = "timeBeginPeriod")]
        static extern UInt32 TimeBeginPeriod(UInt32 uPeriod);

        [DllImport("winmm.dll", EntryPoint = "timeEndPeriod")]
        public static extern uint TimeEndPeriod(uint uMilliseconds);

        [DllImport("kernel32.dll", EntryPoint = "CreateTimerQueue")]
        public static extern IntPtr CreateTimerQueue();

        [DllImport("kernel32.dll", EntryPoint = "DeleteTimerQueueEx")]
        public static extern bool DeleteTimerQueue(IntPtr hTimerQueue, IntPtr hCompletionEvent);

        [DllImport("kernel32.dll", EntryPoint = "CreateTimerQueueTimer")]
        public static extern bool CreateTimerQueueTimer(out IntPtr phNewTimer, IntPtr hTimerQueue, IntPtr Callback, IntPtr Parameter, UInt32 DueTime, UInt32 Period, uint Flags);

        [DllImport("kernel32.dll", EntryPoint = "ChangeTimerQueueTimer")]
        public static extern bool ChangeTimerQueueTimer(IntPtr hTimerQueue, IntPtr hTimer, UInt32 DueTime, UInt32 Period);


        [DllImport("kernel32.dll", EntryPoint = "DeleteTimerQueueTimer")]
        public static extern bool DeleteTimerQueueTimer(IntPtr hTimerQueue, IntPtr hTimer, IntPtr hCompletionEvent);

        [StructLayout(LayoutKind.Sequential)]
        public struct TimeCaps
        {
            public UInt32 wPeriodMin;
            public UInt32 wPeriodMax;
        };

        [UnmanagedFunctionPointer(CallingConvention.Winapi)]      
        public delegate void UnmanagedTimerCallback(IntPtr param, bool timerOrWait);

        /// <summary>
        /// FrameTimer provides a simple method to synchronize execution to a given framerate.
        /// Calling WaitForFrame() blocks until the start of the next frame.
        /// 
        /// NOTE: This code uses the Win32 TimerQueue APIs instead of the System.Threading.Timer
        /// APIs because the .NET APIs do not allow execution of the callback on the timer's thread --
        /// it queues up a new worker thread.  This lowers the accuracy of the timer, and since we
        /// need all the precision we can get they're not suitable here.
        /// </summary>
        /// <param name="framesPerSecond">The frame rate to sync to.</param>
        public FrameTimer(double framesPerSecond)
        {          
            //
            // Set the timer to the minimum value (1ms).  This should be supported on any modern x86 system.
            // If not, too bad...
            //
            UInt32 res = TimeBeginPeriod(1);

            if (res != 0)
            {
                throw new InvalidOperationException("Unable to set timer period.");
            }

            //
            // Create a new timer queue
            // 
            _hTimerQueue = CreateTimerQueue();

            if (_hTimerQueue == IntPtr.Zero)
            {
                throw new InvalidOperationException("Unable to create timer queue.");
            }

            //
            // Since we only have a resolution of 1ms, we have to do some hackery to get a slightly more accurate framerate.
            // (60fps NTSC requires 16 2/3s ms frame delay.)
            // We alternate between two rates at varying intervals and this gets us fairly close to the desired frame rate  
            // (~60.25 fps for NTSC), which is almost impercetible.
            //
            _callback = new UnmanagedTimerCallback(TimerCallbackFn);

            _highPeriod = (uint)Math.Ceiling(1000.0 * (1.0 / framesPerSecond));
            _lowPeriod = (uint)Math.Floor(1000.0 * (1.0 / framesPerSecond));
            _periodTenths = _periodSwitch = (uint)((1000.0 * (1.0 / framesPerSecond) - Math.Floor(1000.0 * (1.0 / framesPerSecond))) * 10.0);

            if (!CreateTimerQueueTimer(out _hTimer, _hTimerQueue, Marshal.GetFunctionPointerForDelegate(_callback), IntPtr.Zero, _lowPeriod, _lowPeriod, 0x00000020 /* execute in timer thread */))
            {
                throw new InvalidOperationException("Unable to create timer queue timer.");
            }                       

            _event = new AutoResetEvent(false);

            _lowTimer = 0;
        }

        ~FrameTimer()
        {
            try
            {
                //
                // Clean stuff up
                //
                DeleteTimerQueueTimer(_hTimerQueue, _hTimer, IntPtr.Zero);
                DeleteTimerQueue(_hTimerQueue, IntPtr.Zero);

                //
                // Fire off a final event to release any call that's waiting...
                //
                _event.Set();
            }
            catch
            {
                // Nothing.  If the above fails it's due to the Win32 APIs not being present.
                // Just fail quietly.
            }
        }

        /// <summary>
        /// Waits for the timer to fire.
        /// </summary>
        public void WaitForFrame()
        {            
            _event.WaitOne();
        }

        /// <summary>
        /// Callback from timer queue.  Work done here is executed on the timer's thread, so must be quick.
        /// </summary>
        /// <param name="lpParameter"></param>
        /// <param name="TimerOrWaitFired"></param>         
        private void TimerCallbackFn(IntPtr lpParameter, bool TimerOrWaitFired)
        {            
            _event.Set();
            _lowTimer++;            

            if (_lowTimer >= _periodSwitch)
            {
                _lowTimer = 0;
                _period = !_period;
                ChangeTimerQueueTimer(_hTimerQueue, _hTimer, _period ? _lowPeriod : _highPeriod, _period ? _lowPeriod : _highPeriod);

                _periodSwitch = !_period ? _periodTenths : 10 - _periodTenths;
            }
        }       
        
        private IntPtr _hTimerQueue;        
        private IntPtr _hTimer;        
        private AutoResetEvent _event;
        private UnmanagedTimerCallback _callback;
        private uint _lowPeriod;
        private uint _highPeriod;
        private uint _periodSwitch;
        private uint _periodTenths;
        private int _lowTimer;
        private bool _period;
    }
}