using System;
using System.Diagnostics;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;

namespace TimingTest
{
    public class Game1 : Microsoft.Xna.Framework.Game
    {
        bool vsync = false;

        GraphicsDeviceManager graphics;
        SpriteBatch spriteBatch;
        Texture2D spinner;

        double theta = 0;
        double spinSpeed = 0.005f;

        float screenWidth = 1280;
        float screenHeight = 768;

        const double MILLISECONDS = 1000.0;
        const double TARGET_SPEED = 60.0; //Logic tick rate in hertz

        const double dt = MILLISECONDS / TARGET_SPEED;

        double currentTime;
        double accumulator = 0.0;
        Stopwatch logicTimer = new Stopwatch();


        public Game1()
        {
            graphics = new GraphicsDeviceManager(this);
            Content.RootDirectory = "Content";

            graphics.PreferredBackBufferWidth = (int)screenWidth;
            graphics.PreferredBackBufferHeight = (int)screenHeight;
            graphics.SynchronizeWithVerticalRetrace = vsync;

            logicTimer.Start();
            currentTime = logicTimer.ElapsedMilliseconds;

            this.IsFixedTimeStep = false;
            //Setting IsFixedTimeStep to false makes Update and Draw run in lockstep as fast as your
            //system can do go. This allows me to control the update timing using the accumulator loop.
            //Using IsFixedTimeStep=true caps the framerate and introduces some other behaviors I'd like
            //to avoid.
        }

        protected override void LoadContent()
        {
            spriteBatch = new SpriteBatch(GraphicsDevice);
            spinner = Content.Load<Texture2D>("Spinner"); //I'm using this image: http://i.imgur.com/5qkVH1d.png
        }

        protected override void Update(GameTime gameTime)
        {
            if (Keyboard.GetState().IsKeyDown(Keys.Escape))
                this.Exit();

            double newTime = logicTimer.ElapsedMilliseconds;
            double frameTime = newTime - currentTime;

            currentTime = newTime;
            accumulator += frameTime;

            while (accumulator >= dt)
            {
                theta = (theta + spinSpeed * dt) % (Math.PI * 2.0);
                accumulator -= dt;
            }
        }

        protected override void Draw(GameTime gameTime)
        {
            GraphicsDevice.Clear(Color.CornflowerBlue);

            spriteBatch.Begin();
            spriteBatch.Draw(spinner, new Vector2(screenWidth / 2, screenHeight / 2), null, Color.White, (float)theta, new Vector2(spinner.Width / 2, spinner.Height / 2), Vector2.One, SpriteEffects.None, 0f);
            spriteBatch.End();
        }
    }
}