/**
 * Utility methods for working with Poses Points and Vectors in Asteroids.
 * 
 * @author Nathan Sprague
 * @version V1.0, 10/15
 *
 */
public class GameUtils
{

  /**
   * Update the provided velocity according to the indicated thrust value and heading. The thrust
   * will be applied so as to push the velocity value in the direction of the provided heading.
   * 
   * @param velocity
   *          Velocity vector to update
   * @param heading
   *          Direction to push the velocity
   * @param thrust
   *          Magnitude of the thrust in pixels / update^2
   */
  public static void applyThrust(Vector2D velocity, double heading, double thrust)
  {
    Vector2D thrustVector = new Vector2D(heading, thrust);
    velocity.setX(velocity.getX() + thrustVector.getX());
    velocity.setY(velocity.getY() + thrustVector.getY());
  }

  /**
   * Draw an isosceles triangle at the location and heading of the provided Pose. The triangle will
   * be centered at the x,y position of the Pose object.
   *
   * @param pose
   *          - location and heading for the triangle
   * @param width
   *          - the width of the base of the triangle
   * @param height
   *          - the height of the triangle
   */
  public static void drawPoseAsTriangle(Pose pose, double width, double height)
  {

    Point llPoint = transformPoseToScreen(pose, new Point(-.5 * height, -.5 * width));
    Point lrPoint = transformPoseToScreen(pose, new Point(-.5 * height, .5 * width));
    Point endPoint = transformPoseToScreen(pose, new Point(.5 * height, 0));

    double[] xs = new double[3];
    double[] ys = new double[3];

    xs[0] = llPoint.getX();
    xs[1] = endPoint.getX();
    xs[2] = lrPoint.getX();
    ys[0] = llPoint.getY();
    ys[1] = endPoint.getY();
    ys[2] = lrPoint.getY();

    StdDraw.polygon(xs, ys);

  }

  // -------------------------------------------------
  // HELPER METHOD BELOW THIS POINT
  // -------------------------------------------------

  /**
   * Perform a transform from the coordinate frame defined by a Pose object to screen coordinates.
   * 
   * @param pose
   *          - the coordinate frame to transform from
   * @param point
   *          - the point to transform (in pose coordinates)
   * @return - the transformed point (in screen coordinates)
   */
  private static Point transformPoseToScreen(Pose pose, Point point)

  {
    double newX;
    double newY;
    newX = point.getX() * Math.cos(pose.getHeading()) - point.getY() * Math.sin(pose.getHeading())
        + pose.getX();
    newY = point.getX() * Math.sin(pose.getHeading()) + point.getY() * Math.cos(pose.getHeading())
        + pose.getY();
    return new Point(newX, newY);
  }

}