import pygame

BLOCKSIZE = 20
width = 800
height = 600
SIZE = (width, height)
BLACK = (0, 0, 0)
YELLOW = (255, 255, 0)
RED = (255, 0, 0)

class Block:
    def __init__(self, grid_pos, visibility):
        self.grid_pos = grid_pos
        self.visibility = visibility
    def set_visible(self):
        self.visibility = True
    def unset_visible(self):
        self.visibility = False
    def draw(self,screen):
        block_shape = (self.grid_pos[0], self.grid_pos[1], BLOCKSIZE, BLOCKSIZE)
        pygame.draw.rect(screen, YELLOW, block_shape)
        pygame.draw.rect(screen, RED, block_shape, 1)

def main():
    global blocks
    blocks = {}
    screen = init_game()
    create_grid(screen)
    game_loop(screen)
    exit_game()

def init_game():
    pygame.init()
    screen = pygame.display.set_mode(SIZE)
    return screen

def game_loop(screen):
    while True:
        if not event_handling():
            break
        if not update_game():
            break
        event = event_handling()
        update_game()
        draw_game(screen)

def event_handling():
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            return False
        if event.type == pygame.MOUSEBUTTONUP:
            pos = pygame.mouse.get_pos()
            x = pos[0] // BLOCKSIZE * BLOCKSIZE
            y = pos[1] // BLOCKSIZE * BLOCKSIZE
            blocks[(x,y)].set_visible()
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LSHIFT:
                pos = pygame.mouse.get_pos()
                x = pos[0] // BLOCKSIZE * BLOCKSIZE
                y = pos[1] // BLOCKSIZE * BLOCKSIZE
                blocks[(x,y)].unset_visible()
    return True


def update_game():
    return True

def draw_game(screen):
    screen.fill(BLACK)
    for x,y in blocks:
        if blocks[(x,y)].visibility:
            blocks[(x,y)].draw(screen)
    pygame.display.flip()

def create_grid(screen):
    y = 0
    for _ in range(SIZE[1]//BLOCKSIZE*BLOCKSIZE):
        x = 0
        for _ in range(SIZE[0]//BLOCKSIZE*BLOCKSIZE):
            blocks[(x,y)]= (Block ((x, y), False))
            x += BLOCKSIZE
        y += BLOCKSIZE

def exit_game():
    pygame.quit()

main()