import pygame
import math

cell_size = 18

grid_x_count = 19
grid_y_count = 14

def update():
    global selected_x
    global selected_y

    mouse_x, mouse_y = pygame.mouse.get_pos()
    selected_x = math.floor(mouse_x / cell_size)
    selected_y = math.floor(mouse_y / cell_size)

    if selected_x > grid_x_count - 1:
        selected_x = grid_x_count - 1
    if selected_y > grid_y_count - 1:
        selected_y = grid_y_count - 1

def draw():
    screen.fill((0, 0, 0))

    for y in range(grid_y_count):
        for x in range(grid_x_count):
            if x == selected_x and y == selected_y:
                image = 'covered_highlighted'
            else:
                image = 'covered'
            screen.blit(image, (x * cell_size, y * cell_size))