"""
 pong.py

 An implementation of pong[1]
 using Zelle's graphics library[2].

 [1] https://en.wikipedia.org/wiki/Pong
 [2] https://mcsp.wartburg.edu/zelle/python/

 Jim Mahoney | cs.marlboro.college | MIT License | Nov 2019
"""
from graphics import GraphWin, Rectangle, Circle, Point
from time import sleep

# global constants (using the CONSTANTS_IN_CAPITALS convention)

# Sizes and positions are in pixels.
# Coords have x=0 at left, y=0 at top.
WIDTH = 1000
HEIGHT = 800
BORDER = 100                 
BALL_RADIUS = 50
BALL_BORDER_WIDTH = 5
BALL_X_INIT = WIDTH // 2
BALL_Y_INIT = HEIGHT // 2
BALL_COLOR = 'blue'
BALL_BORDER_COLOR = 'black'
TICK = 0.01                  # time per event loop, in seconds
BALL_V_X_INIT = 4.0          # initial velocity in pixels per tick
BALL_V_Y_INIT = 3.0

class Ball:
    """ A ball is a circle in a window """
    
    def __init__(self, window):
        self.window = window
        self.v_x = BALL_V_X_INIT
        self.v_y = BALL_V_Y_INIT
        # -- ball --
        self.circle = Circle(Point(WIDTH//2, HEIGHT//2), BALL_RADIUS)
        self.circle.setFill(BALL_COLOR)
        self.circle.setWidth(BALL_BORDER_WIDTH)
        self.circle.setOutline(BALL_BORDER_COLOR)
        # -- display --
        self.draw()
        
    def draw(self):
        """ Draw the ball in its window """
        self.circle.draw(self.window)
        
    def bounce_walls(self):
        """ Reverse the x or y velocity if the ball hits a wall """
        # circle bounds - not quite in Zelle's API;
        # found by using dir() to look at circle object
        left = self.circle.p1.x
        top = self.circle.p1.y
        right = self.circle.p2.x
        bottom = self.circle.p2.y
        # collision with top or bottom?
        if top <= BORDER or bottom >= HEIGHT - BORDER:
            self.v_y = - self.v_y
        # collision with left or right?
        if left <= BORDER or right >= WIDTH - BORDER:
            self.v_x = - self.v_x

    def update(self):
        """ Change ball's velocity if it hits something
            and move it forward one time tick 
        """
        self.bounce_walls()
        self.circle.move(int(self.v_x), int(self.v_y))
    
class Paddle:
    pass

class Screen:
    """ The pong game screen and its components """
    
    def __init__(self):
        self.window = GraphWin('Pong!', WIDTH, HEIGHT)
        self.box = Rectangle(Point(BORDER, BORDER),
                             Point(WIDTH - BORDER, HEIGHT - BORDER))
        self.box.setFill('grey')
        self.box.draw(self.window)
        self.ball = Ball(self.window)
        
    def run(self):
        """ The pong event loop """
        while True:
            sleep(TICK)
            self.ball.update()

def main():
    Screen().run()

if __name__ == '__main__':
    import doctest
    doctest.testmod()
    main()