import pygame
import random

def run_game():
    
    ## Initialize the pygame submodules and set up the display window.

    pygame.init()

    width = 640
    height = 480
    my_win = pygame.display.set_mode((width,height))

    # We will use the same radius for all balls.
    radius = 20

    # starting position and speed for the ball
    x = random.randint(0+radius, width-radius)
    y = random.randint(0+radius,height-radius)
    xspeed = float(random.randint(-10,10))/10
    yspeed = float(random.randint(-10,10))/10

    ball = [x, y, xspeed, yspeed]


    ## The game loop starts here.
    
    keepGoing = True    
    while (keepGoing):

        ## Handle events.

        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                keepGoing = False

        # update circle position
        ball[0] = ball[0] + ball[2]
        ball[1] = ball[1] + ball[3]

        if (ball[0] < radius):
            ball[2] = -1 * ball[2]
        if (ball[0] > width-radius):
            ball[2] = -1 * ball[2]
        if (ball[1] < radius):
            ball[3] = -1 * ball[3]
        if (ball[1] > height-radius):
            ball[3] = -1 * ball[3]
        

        ## Draw picture and update display

        my_win.fill(pygame.color.Color("lightblue"))

        pygame.draw.circle(my_win, pygame.color.Color('darkmagenta'), (int(ball[0]),int(ball[1])),radius)

        pygame.display.update()

    ## The game loop ends here.

    pygame.quit()


## Call the function run_game.

run_game()