import pygame


def initialize():
    """
    This function sets some global constants (i.e., the values of these global
    variables never change).
    """
    pygame.init()

    # set up the display window
    global width, height, screen
    width = 640
    height = 480
    screen = pygame.display.set_mode((width,height))

    # load the picture
    global guy
    guy = pygame.image.load("WalkingSquare1.gif")


def move_and_bounce_rect(dt, x, y, speed_x, speed_y, obj_width, obj_height):
    """
    This function calculates an object's new position based on its
    old position, the time that has passed since the last update,
    and its speed. It also makes sure that the object bounces
    off the edge of the screen.
    """

    x = x + dt * speed_x
    if (x < 0):
        x = 0
        speed_x = - speed_x
    elif (x > width - obj_width):
        x = width - obj_width
        speed_x = - speed_x
        
    y = y + dt * speed_y
    if (y < 0):
        y = 0
        speed_y = - speed_y
    elif (y > height - obj_height):
        y = height - obj_height
        speed_y = - speed_y

    return x, y, speed_x, speed_y


def run_game():

    # initialize the guy's position and speed
    g_x = 100
    g_y = 100
    g_speed_x = 0
    g_speed_y = 0

    # start clock
    clock = pygame.time.Clock()
    
    keepGoing = True

    while (keepGoing):

        dt = clock.tick()

        # go through all events that happened and ...
        for event in pygame.event.get():
            
            # ... check whether the event was a quit event
            if event.type == pygame.QUIT:
                keepGoing = False

            # ... check whether the event was of type pygame.KEYDOWN and
            # if so, check which key was pressed and change the speed of the character accordingly

            # ... check whether the event was of type pygame.KEYUP
            # if so, check which key was released and set the correspondind speed to 0


        g_x, g_y, g_speed_x, g_speed_y = move_and_bounce_rect(dt, g_x, g_y, g_speed_x, g_speed_y,
                                                              guy.get_width(), guy.get_height())


        # set background color
        screen.fill(pygame.color.Color("green"))

        # draw image
        screen.blit(guy,(g_x,g_y))

        # update display
        pygame.display.update()


def done():
    
    pygame.quit()
    


def main():

    initialize()

    run_game()

    done()



main()