# main game loop
def move():
    global pong_dx, pong_dy, AIplayerspeed, seconds, score

# move pong ball
x, y = pong.position()
x += pong_dx
y += pong_dy
pong.setposition(x, y)

if isCollision(pong, player): # collision pong and player
    pong_dx *= -1
    # Update the score
    score += 10
    score_pen.undo()
    score_pen.write("Score: {}".format(score), align="left", font=FONT)
elif isCollision(pong, AIplayer):  # collision pong and AIplayer
    pong_dx *= -1
elif y < -299.5 or y > 299.5:  # check for bounce and redirect it
    pong_dy *= -1
elif x > 300:
    pong_dx *= -1
elif x < -300:
    print("Game Over")
    screen.bye()
    return

# move AI paddle (might speed up pong movement)
AIplayer.forward(AIplayerspeed)

y = AIplayer.ycor()

if y < -250 or y > 250:
    AIplayerspeed *= -1

# display timer
seconds += 0.05
time_pen.undo()
time_pen.write("Time: {}".format(int(seconds)), False, align="Left", font=FONT)
screen.ontimer(move, 50)

screen.update()

screen.tracer(False)
move()
screen.mainloop()