import System.IO
import Data.Char
import Debug.Trace

w = 192 * 4
h = 108 * 4

type Color = (Int, Int, Int)    -- red green blue
darkness  = (0, 0, 50)
starlight = (250, 250, 180)

colormix :: Double -> Color -> Color -> Color
colormix amount c1 c2 = (round $ p*fromIntegral r1 + (1-p)*fromIntegral r2,
                    round $ p*fromIntegral g1 + (1-p)*fromIntegral g2,
                    round $ p*fromIntegral b1 + (1-p)*fromIntegral b2)
                    where   (r1, g1, b1) = c1
                            (r2, g2, b2) = c2
                            p = max 0 $ min 1 amount

imgheader = "P3 " ++ (show w) ++ " " ++ (show h) ++ " 255\n"

cartProd xs ys = [(x,y) | y <- ys, x <- xs]

pixels = cartProd (take w [0,1..]) (take h [0,1..])

star_luminosity crit (x, y) = fromIntegral
                        (min 4 $
                            ( ((x^2 + y^3 + (x+y+2)^3) `mod` (256)) `div` (256 `div` crit) )
                        ) / 4

stardist :: (Int, Int) -> (Int, Int) -> Double
stardist p1 p2 = sqrt $ fromIntegral ( (x1-x2)^2 + (y1-y2)^2)
                    where   (x1, y1) = p1
                            (x2, y2) = p2

roughness = 5
nearest_potential_star_centre :: (Int, Int) -> (Int, Int)
nearest_potential_star_centre (x, y) = ((x `div` roughness) * roughness + (roughness `div` 2),
                                        (y `div` roughness) * roughness + (roughness `div` 2))

star_color crit (x, y) = colormix (lum * (stardist (x,y) nearest) / 2 ) darkness starlight
                where   nearest = nearest_potential_star_centre (x,y)
                        lum     = star_luminosity crit nearest

pixel_to_ppm :: Color -> String
pixel_to_ppm (r,g,b) = show r ++ " " ++ show g ++ " " ++ show b ++ "\n"

image :: Int -> String
image crit = imgheader ++ (foldr (++) "" (map (pixel_to_ppm . star_color crit) pixels))

write_sky :: Int -> IO ()
write_sky crit = trace ("Rendering " ++ show crit)
                 writeFile ("skyimg/sky" ++ show crit ++ ".ppm") (image crit)

main = mapM write_sky [2, 20,30,40,50]