from random import *
from turtle import *
from freegames import floor, vector

tiles = {}
neighbors = [
    vector(100, 0),
    vector(-100, 0),
    vector(0, 100),
    vector(0, -100),
]

def load():
    """Load tiles and scramble."""
    count = 1
    for y in range(-200, 200, 100):
        for x in range(-200, 200, 100):
            mark = vector(x, y)
            tiles[mark] = count
            count += 1
    tiles[mark] = None
    for count in range(1000):
        neighbor = choice(neighbors)
        spot = mark + neighbor
        if spot in tiles:
            number = tiles[spot]
            tiles[spot] = None
            tiles[mark] = number
            mark = spot

def square(mark, number):
    """Draw white square with black outline and number."""
    up()
    goto(mark.x, mark.y)
    down()
    color('black', 'white')
    begin_fill()
    for count in range(4):
        forward(99)
        left(90)
    end_fill()
    if number is None:
        return
    elif number < 10:
        forward(20)
        write(number, font=('Arial', 60, 'normal'))

def tap(x, y):
    """Swap tile and empty square."""
    x = floor(x, 100)
    y = floor(y, 100)
    mark = vector(x, y)
    for neighbor in neighbors:
        spot = mark + neighbor
        if spot in tiles and tiles[spot] is None:
            number = tiles[mark]
            tiles[spot] = number
            square(spot, number)
            tiles[mark] = None
            square(mark, None)

def draw():
    """Draw all tiles."""
    for mark in tiles:
        square(mark, tiles[mark])
    update()

setup(420, 420, 370, 0)
hideturtle()
tracer(False)
load()
draw()
onscreenclick(tap)
done()