import pygame as pg
import random

WHITE = (255,)*3

def snap(x, scale):
	return int(x//scale)*scale


class Starfield:

    def __init__(self,
                 screen,
                 inv_density=10,
                 grid_step=31,
                 paralax = 2,
                 star_color=WHITE,
                 star_size = 1):
        self.rng = random.Random()
        self.screen = screen
        self.inv_density = inv_density
        self.paralax = paralax
        self.grid_step = grid_step
        self.star_color = star_color
        self.star_size = star_size

    def draw(self,  screen, map_pos):
        sky_pos = pg.math.Vector2((map_pos.x, map_pos.y))/self.paralax
        xstart = snap(sky_pos.x, self.grid_step)
        ystart = snap(sky_pos.y, self.grid_step)
        xstop  = xstart + screen.get_rect().width
        ystop  = ystart + screen.get_rect().width
        for x in range(xstart, xstop, self.grid_step):
            for y in range(ystart, ystop, self.grid_step):
                self.rng.seed(hash((x,y)))
                if self.rng.randint(0, self.inv_density) == 0:
                    xoff = self.rng.randint(0, self.grid_step)
                    yoff = self.rng.randint(0, self.grid_step)
                    cx = x + xoff - sky_pos.x
                    cy = y + yoff - sky_pos.y
                    pg.draw.circle(screen, self.star_color, (cx,cy), self.star_size)