module Main where

import qualified Data.Set as S
import Graphics.Gloss

type Cell = (Int, Int)
type Plane = S.Set Cell

main :: IO ()
main = simulate (InWindow "Game of Life" (500, 500) (0, 0)) white 10 seed (draw) (step)
  where step view delta alive = live alive
        draw alive = pictures $ map (drawCell) (S.toList alive)
          where drawCell (x, y) = translate (fromIntegral x * 5 :: Float) (fromIntegral y * 5 :: Float) $ rectangleSolid 5 5

-- Returns a set of cells surrounding a cell
offset :: Cell -> Plane
offset (x, y) = S.fromList [(x + dx, y + dy) | dx <- [-1..1], dy <- [-1..1], not (dx == 0 && dy == 0)]

-- Returns the amount of cells surrounding a cell
neighbors :: Plane -> Cell -> Int
neighbors alive cell = S.size $ S.filter (`S.member` alive) (offset cell)

-- Takes a generation and produces the next
live :: Plane -> Plane
live alive = S.filter (willlive alive) (more alive)
  where more alive = S.union alive $ S.unions [offset cell | cell <- S.toList alive]
        willlive alive cell
          | S.member cell alive = neighbors alive cell `elem` [2, 3]
          | otherwise = neighbors alive cell == 3

-- Gospers Glider Gun
seed :: Plane
seed = S.fromList [(5, 1), (5, 2), (6, 1), (6, 2), (5, 11), (6, 11), (7, 11), (4, 12), (3, 13), (3, 14), (8, 12), (9, 13), (9, 14), (6, 15), (4, 16), (5, 17), (6, 17), (7, 17), (6, 18), (8, 16), (3, 21), (4, 21), (5, 21), (3, 22), (4, 22), (5, 22), (2, 23), (6, 23), (1, 25), (2, 25), (6, 25), (7, 25), (3, 35), (4, 35), (3, 36), (4, 36)]