import org.lwjgl.LWJGLException;
import org.lwjgl.opengl.Display;
import org.lwjgl.opengl.DisplayMode;
import org.lwjgl.opengl.GL11;
import org.lwjgl.opengl.PixelFormat;

import static org.lwjgl.opengl.GL11.*;

public class GameWindow
{
   //Player class
   class player
   {
      //vars
      double x;
      double y;
      double prevX;
      double prevY;
      double viewX;
      double viewY;
      double size;

      //constructor
      player()
      {
         x = 25;
         y = 150;
         prevX = x;
         prevY = y;
         viewX = x;
         viewY = y;
         size = 64;
      }
   }

   //Create a player 
   player p = new player();

   //Main
   public static void main(String[] argv)
   {
      GameWindow gWin = new GameWindow();
      gWin.run();
   }

   //Run function
   public void run()
   {
      //Attempt to create the window
      try
      {
         //Set the size and create it
         Display.setDisplayMode(new DisplayMode(800, 600));
         Display.setVSyncEnabled(true);
         Display.create();
      }
      catch(LWJGLException e)
      {
         int j = GL11.glGetError();
         System.out.println("ERROR : " + j);

         //e.printStackTrace();
         System.exit(0);
      }

      //Init openGL
      glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
      glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
      //glDisable(GL_DEPTH_BUFFER_BIT);

      glMatrixMode(GL_PROJECTION);
      glLoadIdentity();

      glOrtho(0, 800, 600, 0, -1, 1);

      glMatrixMode(GL_MODELVIEW);
      glLoadIdentity();

      int err = GL11.glGetError();
      if(err != GL_NO_ERROR)
      {
         System.out.println("err");
         System.exit(0);
      }

      //set up the need vars and timers
      long updateTime = 1000 * 1000 * 1000 / 25;
      int loops = 0;
      int MaxLoops = 10;
      int frames = 0;

      long gameClock = System.nanoTime();
      long lastFrame = gameClock;


      //The GAME LOOP! T.T
      while(!Display.isCloseRequested())
      {
         //For FPS count
         frames++;

         loops = 0;
         while((System.nanoTime() >= gameClock) && (loops < MaxLoops))
         {
            //Store the player's previous position
            p.prevX = p.x;

            //Move the player
            //If the go "out of bound" reset their position to the left side of the screen
            if(p.x > 800)
            {
               p.x = 0 - p.size;
               p.prevX = 0 - p.size;
            }
            else
               p.x += 7;

            //Update the loop count and game clock
            gameClock += updateTime;
            loops++;
         }

         //Calculate for the interpolation value
         double alpha = (double)(System.nanoTime() - gameClock + updateTime) / updateTime;
         System.out.println(alpha);

         //Account for the interpolation
         p.viewX = p.prevX + alpha * (p.x - p.prevX);
         p.viewY = p.prevY + alpha * (p.y - p.prevY);

         //Get the current FPS
         if(System.currentTimeMillis() - lastFrame > 1000)
         {
            Display.setTitle("FPS : "+ frames);
            frames = 0;
            lastFrame += 1000;
         }

         //Draw
         draw();

         //UPdate the display
         Display.update();
      }

      Display.destroy();
   }

   //Draw function
   void draw()
   {
      glClear(GL_COLOR_BUFFER_BIT);

      glBegin(GL_QUADS);

      glColor3f(1, 1, 1);
      glVertex2d(0, 0);
      glVertex2d(800, 0);
      glVertex2d(800, 600);
      glVertex2d(0, 600);

      glEnd();

      glBegin(GL_QUADS);

      glColor3f(0, 0, 0);
      glVertex2d(p.viewX, p.viewY);
      glVertex2d(p.viewX + p.size, p.viewY);
      glVertex2d(p.viewX + p.size, p.viewY + p.size);
      glVertex2d(p.viewX, p.viewY + p.size);

      glEnd();
   }

}