'''Program demonstrating a recursive image using turtles.'''

import turtle

# initial side length of the triangle
SIDE_LEN = 250

# draw a fractal of this order
FRACTAL_ORDER = 4

def draw_side(size, order):
    '''Draw a koch fractal with the given side length and 
    fractal order.'''
    if order == 0:
        # base case: an order 0 fractal is a straight line
        turtle.forward(size)
    else:
        # recursive case:
        # draw four different (order - 1) fractals
        next_size = size / 3
        next_order = order - 1
        draw_side(next_size, next_order)
        turtle.left(60)
        draw_side(next_size, next_order)
        turtle.right(120)
        draw_side(next_size, next_order)
        turtle.left(60)
        draw_side(next_size, next_order)
        

def main():
    '''Draw an order FRACTAL_ORDER koch fractal.'''
    turtle.speed('fastest')
    turtle.up()
    turtle.goto(-SIDE_LEN/2, SIDE_LEN/2)    # center the triangle
    turtle.down()
    
    for i in range(3):  # draw three sides of the triangle
        draw_side(SIDE_LEN, FRACTAL_ORDER)
        turtle.right(120)

main()