import pygame
import math
from itertools import cycle

# some simple vector helper functions, stolen from http://stackoverflow.com/a/4114962/142637
def magnitude(v):
    return math.sqrt(sum(v[i]*v[i] for i in range(len(v))))

def add(u, v):
    return [ u[i]+v[i] for i in range(len(u)) ]

def sub(u, v):
    return [ u[i]-v[i] for i in range(len(u)) ]

def dot(u, v):
    return sum(u[i]*v[i] for i in range(len(u)))

def normalize(v):
    vmag = magnitude(v)
    return [ v[i]/vmag  for i in range(len(v)) ]

screen = pygame.display.set_mode((300, 300))
clock = pygame.time.Clock()

class Ball(object):
    def __init__(self, path):
        self.x, self.y = (0, 0)
        self.speed = 2.5
        self.color = (200, 200, 200)
        self.path = cycle(path)
        self.set_target(next(self.path))

    @property
    def pos(self):
        return self.x, self.y

    # for drawing, we need the position as tuple of ints
    # so lets create a helper property
    @property
    def int_pos(self):
        return map(int, self.pos)

    @property
    def target(self):
        return self.t_x, self.t_y

    @property
    def int_target(self):
        return map(int, self.target)

    def next_target(self):
        self.set_target(self.pos)
        self.set_target(next(self.path))

    def set_target(self, pos):
        self.t_x, self.t_y = pos

    def update(self):
        # if we won't move, don't calculate new vectors
        if self.int_pos == self.int_target:
            return self.next_target()

        target_vector = sub(self.target, self.pos)

        # a threshold to stop moving if the distance is to small.
        # it prevents a 'flickering' between two points
        if magnitude(target_vector) < 2:
            return self.next_target()

        # apply the balls's speed to the vector
        move_vector = [c * self.speed for c in normalize(target_vector)]

        # update position
        self.x, self.y = add(self.pos, move_vector)

    def draw(self):
        pygame.draw.circle(screen, self.color, self.int_pos, 4)

pygame.init()
quit = False

path = [(26, 43),
        (105, 110),
        (45, 225),
        (145, 295),
        (266, 211),
        (178, 134),
        (250, 56),
        (147, 12)]

path2 = [(26, 43),
         (105, 10),
         (45, 125),
         (150, 134),
         (150, 26),
         (107, 12)]

ball = Ball(path)
ball.speed = 1.9

ball2 = Ball(path2)
ball2.color = (200, 200, 0)

balls = [ball, ball2]

while not quit:
    quit = pygame.event.get(pygame.QUIT)
    pygame.event.poll()

    map(Ball.update, balls)

    screen.fill((0, 0, 0))

    map(Ball.draw, balls)

    pygame.display.flip()
    clock.tick(60)