using System;
using System.Diagnostics;
using System.Windows.Forms;
using Amphora;
using Blacklight.Core;
using Blacklight.Core.Cameras;

namespace Konis.Testbed
{
    public partial class Testbed : Form
    {
        // Windows runs its own message loop while a window is being dragged or resized, so Application.Idle stops
        // firing and the next frame would otherwise get the whole drag as one step.
        private static readonly TimeSpan LongestFrame = TimeSpan.FromMilliseconds(100);

        private readonly Stopwatch clock = Stopwatch.StartNew();
        private readonly ParticleDemo demo;
        private TimeSpan? lastFrame = null;
        private double speed = 1.0;

        public Testbed()
        {
            InitializeComponent();

            demo = new ParticleDemo(viewport.DrawableSurface, viewport.Camera, new Rand((ulong)DateTime.UtcNow.Ticks));

            // The left button spawns, so the camera drags with the middle one.
            viewport.Controller.Options.DragNavigateButton = PointerButtons.Middle;
            viewport.InputRouter.AddLowestPriority(viewport.Controller);
            viewport.InputRouter.AddHighestPriority(
                new ClickSpawner(demo, viewport.DrawableSurface, viewport.Camera));
        }

        /// <summary>
        /// Gets or sets whether the form closes itself once it has drawn a frame.
        /// </summary>
        public bool ExitAfterFirstFrame { get; set; } = false;

        /// <summary>
        /// Whether the pump has nothing waiting, so the loop can run another frame rather than yield to it.
        /// </summary>
        private static bool IsApplicationIdle()
        {
            return !NativeMethods.PeekMessage(
                out NativeMethods.QueuedMessage _,
                window: IntPtr.Zero, // Messages from any window on this thread.
                filterMin: 0, filterMax: 0, // Every message.
                remove: NativeMethods.PM_NOREMOVE);
        }

        private void Frame()
        {
            TimeSpan now = clock.Elapsed;
            TimeSpan elapsed = now - (lastFrame ?? now);
            lastFrame = now;

            if (elapsed > LongestFrame)
            {
                elapsed = LongestFrame;
            }

            Duration real = Duration.FromSeconds(elapsed.TotalSeconds);
            demo.World.Update(new FxTime(real, real * speed, speed));
            demo.Draw();

            if (ExitAfterFirstFrame)
            {
                Application.Idle -= ApplicationIdle;
                Close();
            }
        }

        // The loop runs flat out and lets the vsync inside the frame's submit pace it, so the pump only gets a turn
        // once something is actually waiting on it.
        private void ApplicationIdle(object sender, EventArgs e)
        {
            try
            {
                while (IsApplicationIdle())
                {
                    Frame();
                }
            }
            catch (GraphicsDeviceFailedException exception)
            {
                // The device can't draw again, so there's nothing to resume.
                Application.Idle -= ApplicationIdle;
                MessageBox.Show(this,
                    exception.Message + "\n\nThis is a problem with the graphics driver or hardware, not the testbed.",
                    "Graphics driver failure", MessageBoxButtons.OK, MessageBoxIcon.Error);
                Close();
            }
        }

        protected override void OnLoad(EventArgs e)
        {
            base.OnLoad(e);

            // A run that closes after one frame spawns every effect first, so that frame draws particles.
            if (ExitAfterFirstFrame)
            {
                for (int i = 0; i < Effects.All.Length; i++)
                {
                    demo.EffectIndex = i;
                    demo.Spawn(new Azimuth.Vector3(0, 0, 0), preWarmSeconds: 1f);
                }

                demo.EffectIndex = 0;
            }

            Application.Idle += ApplicationIdle;
        }

        protected override void OnFormClosing(FormClosingEventArgs e)
        {
            Application.Idle -= ApplicationIdle;

            base.OnFormClosing(e);
        }
    }
}