import pygame
import sys
import random

pygame.display.init()
# modes = pygame.display.list_modes()
# print modes
# size_x = modes[0][0]
# size_y = modes[0][1]

size_x = 640
size_y = 480

window = pygame.display.set_mode((size_x,size_y))
screen = pygame.display.get_surface()

def input(events): 
    for event in events: 
        if event.type == pygame.QUIT: 
            sys.exit(0) 
        elif event.type == pygame.KEYDOWN and event.key == pygame.K_ESCAPE:
            sys.exit(0)

snow = []
filledSnow = [0 for i in range(size_x)]

def addSnow(filledSnow,x):
    left = 9999
    if x > 0:
        left = filledSnow[x-1]
    mid = filledSnow[x]
    right = 9999
    if x < len(filledSnow)-1:
        right = filledSnow[x+1]

    delta = 1
    if left < mid + 1:
        filledSnow[x-1] = filledSnow[x-1] + delta
    elif right < mid + 1:
        filledSnow[x+1] = filledSnow[x+1] + delta
    else:
        filledSnow[x] = filledSnow[x] + delta
            
class Snow:
    def __init__(self):
        self.x = random.randrange(size_x)
        self.y = - random.randrange(100)
        self.dx = random.random() - random.random()
        self.dy = random.randrange(1,30) + random.random()
        self.size = random.randrange(1,4)
        c = random.randrange(256)
        self.color = [c,c,c]
        #self.color = [random.randrange(256),random.randrange(256),random.randrange(256)]

    def draw(self,screen):
        pygame.draw.circle(screen,self.color,(self.x,self.y),self.size)
        self.x += self.dx
        self.y += self.dy
        if self.x < 0 or self.x > size_x:
            self.x = random.randrange(size_x)
            self.y = 0
            self.dy = random.randrange(1,30) + random.random()
            
        if (self.y > size_y - filledSnow[int(self.x)]):
            addSnow(filledSnow,int(self.x))
            self.x = random.randrange(size_x)
            self.y = 0
            self.dy = random.randrange(1,30) + random.random()

for i in range(600):
    snow.append(Snow())
    
while True:
    screen.fill([0,0,0])
    
    for s in snow:
        s.draw(screen)
        
    for x,y in enumerate(filledSnow):
        screen.fill([255,255,255],[x,size_y - y,1,y])
        
    input(pygame.event.get())
    pygame.display.flip()