using System;
using System.Runtime.Versioning;
using System.Threading;
using System.Threading.Tasks;
using Blacklight.Core;
using Blacklight.Core.Cameras;
using Blacklight.WebGL2;

// [JSImport]/[JSExport] require the assembly to be marked browser-targeted, or they won't compile.
[assembly: SupportedOSPlatform("browser")]

namespace Glass.Testbed
{
    internal static class Program
    {
        // A backgrounded tab stops getting frames and delivers the whole gap on the first one after, so the same
        // cap the desktop needs for a window drag applies here.
        private static readonly TimeSpan LongestTick = TimeSpan.FromMilliseconds(100);

        private static World world = null!;
        private static double? lastTimestampInMilliseconds = null;

        private static void OnFrame(double timestampInMilliseconds)
        {
            TimeSpan elapsed = TimeSpan.FromMilliseconds(
                timestampInMilliseconds - (lastTimestampInMilliseconds ?? timestampInMilliseconds));
            lastTimestampInMilliseconds = timestampInMilliseconds;

            world.Tick(elapsed < LongestTick ? elapsed : LongestTick);
        }

        private static async Task Main()
        {
            await GL.EnsureLoadedAsync();

            WindowHandle window = WebGL2Backend.CreateWindowHandle();

            var inputRouter = new InputRouter();
            inputRouter.AddLowestPriority(new MicroscopeController { Handle = window });

            world = new World(
                window,
                inputRouter,
                new MicroscopeCamera(window),
                cursorSurface: new WebGL2CursorSurface(),
                pointerSource: new WebGL2Input(WebGL2Backend.DefaultCanvasElementId, inputRouter),
                // requestAnimationFrame is paced off the display and the driver decides when, which is what
                // Driver means; the browser offers nothing to turn it off with.
                verticalSync: VerticalSyncMode.Driver);

            GL.StartRenderLoop(OnFrame);

            // Don't let Main return.  The browser drives frames, but the runtime must stay resident.
            await Task.Delay(Timeout.Infinite);
        }
    }
}