import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;

public class AsteroidGame extends Applet
{
  /*
  This is the program that runs the whole shabang
   */

  //this is the width and height of the veiwing area
  public final static int WIDTH = 400, HEIGHT = 400, DELAY = 50;

  public final static double THRUST = 1.0;

  public final static DPoint
    STARTING_POINT_SHIP    = new DPoint(300.0, 300.0),
    STARTING_POINT_PURSUER = new DPoint( 20.0,  20.0);

  private final static Color PURSUER_COLOR = new Color(204,153,204);

  SpaceShip ship, pursuer;
  AsteroidField field;
  ConfigurationSpace cSpace;
  boolean isInvincible;
  Graphics g, gb;    // main graphics and graphics for buffer
  Image buffer;      // offscreen buffer image
  Thread gameThread; // thread that repetitively moves asteroids and redraws

  public void init() // applet initialization done only at startup
  {
    cSpace = new ConfigurationSpace();
    buffer = createImage(WIDTH,HEIGHT);
    gb = buffer.getGraphics();
    g  = this.getGraphics();
    MovingPolygon.X_LIMIT = new Integer(WIDTH).doubleValue();
    MovingPolygon.Y_LIMIT = new Integer(HEIGHT).doubleValue();
    isInvincible = false;
    reset();
    addKeyListener(new KeyHandler());
  }

  public void reset() // initialization for each new level
  {
    synchronized(gb)
    { // clear the buffer
      gb.setColor(Color.black);
      gb.fillRect(0,0,WIDTH,HEIGHT);
    }

    ship    = new SpaceShip(STARTING_POINT_SHIP);
    pursuer = new SpaceShip(STARTING_POINT_PURSUER);
    field   = new AsteroidField();
    while (field.inCollision(ship))    ship.translate(-4.0, 0.0);
    while (field.inCollision(pursuer)) pursuer.translate(4.0, 0.0);
  }

  public void start() // when starting up the applet...
  {
    if (gameThread == null)
    {
      gameThread = new Thread(new GameRunner());
      gameThread.start();
    }
  }

  public void stop()  // when killing the applet...
  {
    if (gameThread != null) gameThread.stop();
    gameThread = null;
  }


  private void drawScreen()
  {
    // draw the user controlled ship
    synchronized(gb)
    {
      gb.setColor(Color.cyan);
      gb.drawPolygon(ship.toPolygon());
    }

    // draw the pursuer ship
    synchronized(gb)
    {
      gb.setColor(PURSUER_COLOR);
      gb.drawPolygon(pursuer.toPolygon());
    }
    
    for (int k = 0; k < field.numAsteroids; k++)
      synchronized(gb)
      {
        gb.setColor(new Color(204, 102, 0));
        gb.drawPolygon(field.asteroids[k].toPolygon());
      }

    // display the buffer
    g.drawImage(buffer,0,0,this);

    // clear the buffer
    synchronized(gb)
    {
      gb.setColor(Color.black);
      gb.fillRect(0,0,WIDTH,HEIGHT);
    }
  }


  class GameRunner implements Runnable
  {
    public void run()
    {
      // repetetively executes the drawing and calculating of paths for the asteroid game
      // until all of the asteroids disappear or the ship is in collision with something.

      long sleepTime, timer = System.currentTimeMillis();
      requestFocus();

      while ( field.numAsteroids > 0 &&
              ( (!field.inCollision(ship) && !pursuer.inCollision(ship)) ||
                isInvincible ) )
      {
        drawScreen();

        // wait a few milliseconds between screen updates if necessary
        sleepTime = DELAY + timer - System.currentTimeMillis();
        if (sleepTime >= 0) try { Thread.sleep(sleepTime); }
                            catch (InterruptedException e) {}
        timer = System.currentTimeMillis();

        // move everything one time slice and generate new paths, if needed.
        ship.move();
        field.move();
        if (cSpace.pathNearlyCompleted()) cSpace.generatePath(pursuer,ship,field);
        cSpace.followPath(pursuer);
        pursuer.move();

        //checks if pursuer runs into an asteroid
        int c = field.findCollision(pursuer);
        if (c != -1) field.impact(field.asteroids[c]);
      }

      if (field.numAsteroids > 0) // you lose
      {
        gb.setColor(Color.red);
        gb.drawString("YOU LOSE",160,200);
      }
      else // you win
      {
        gb.setColor(Color.yellow);
        gb.drawString("YOU WIN!! Congratulations!",100,200);
      }

      drawScreen();
    }
  }

  class KeyHandler extends KeyAdapter
  {
    // recieves and handles keyboard input

    public void keyPressed(KeyEvent e)
    {
      switch (e.getKeyCode())
      {
      case KeyEvent.VK_I:     isInvincible = !isInvincible; break;
      case KeyEvent.VK_UP:    ship.fireThrusters(THRUST);  break;
      case KeyEvent.VK_DOWN:  ship.fireThrusters(-THRUST); break;
      case KeyEvent.VK_LEFT:  ship.rotateCCW(); break;
      case KeyEvent.VK_RIGHT: ship.rotateCW(); break;
      case KeyEvent.VK_SPACE: 
        DPoint impact = ship.fireAt(field);
        if (impact == null)
          impact = new DPoint(ship.vertices[0].x + new Integer(WIDTH/4).doubleValue()*Math.cos(ship.rotation),
                              ship.vertices[0].y + new Integer(WIDTH/4).doubleValue()*Math.sin(ship.rotation));
        synchronized(gb)
        { // draw the laser beam
          gb.setColor(Color.green);
          gb.drawLine(new Double(impact.x).intValue(),
                      new Double(impact.y).intValue(),
                      new Double(ship.vertices[0].x).intValue(),
                      new Double(ship.vertices[0].y).intValue());
        }
      }
    }
  }

}