{-# LANGUAGE ScopedTypeVariables #-}

module World where
import Cell
import Graphics.Gloss.Interface.Pure.Game
import Graphics.Gloss.Data.Extent
import Graphics.Gloss.Data.QuadTree
import Graphics.Gloss.Algorithms.RayCast


-- | The game world.
data World
        = World
        { worldWidth            :: Int
        , worldHeight           :: Int
        , worldTree             :: QuadTree Cell
        , worldCellSize         :: Int
        , worldCellSpace        :: Int }
        deriving Show


-- | Get the extent covering the entire world.
worldExtent :: World -> Extent
worldExtent world
        = makeExtent (worldWidth world) 0 (worldHeight world) 0


-- | Load a world from a file.
loadWorld :: FilePath -> IO World
loadWorld fileName
 = do   str     <- readFile fileName
        return  $ readWorld str


-- | Read a world from a string.
readWorld :: String -> World
readWorld str
 = let  ("WORLD" : strWidthHeight : skip : cellLines)
                        = lines str

        [width, height] = map read $ words strWidthHeight
        rows    = take height $ cellLines

        cells   = concat
                $ map (readLine width)
                $ reverse rows

        extent  = makeExtent height 0 width 0

   in   World   { worldWidth            = width
                , worldHeight           = height
                , worldTree             = makeWorldTree extent cells
                , worldCellSize         = 20
                , worldCellSpace        = 0 }

readLine :: Int -> String -> [Cell]
readLine width (s:str)
        = map readCell
        $ take width str



-- | Get the size of the window needed to display a world.
windowSizeOfWorld :: World -> (Int, Int)
windowSizeOfWorld world
 = let  cellSize        = worldCellSize world
        cellSpace       = worldCellSpace world
        cellPad         = cellSize + cellSpace
        height          = cellPad * (worldHeight world) + cellSpace
        width           = cellPad * (worldWidth  world) + cellSpace
   in   (width, height)


-- | Create the tree representing the world from a list of all its cells.
makeWorldTree :: Extent -> [Cell] -> QuadTree Cell
makeWorldTree extent cells
 = foldr insert' emptyTree nonEmptyPosCells
 where
        insert' (pos, cell) tree
         = case insertByCoord extent pos cell tree of
                Nothing         -> tree
                Just tree'      -> tree'

        (width, height)
                = sizeOfExtent extent

        posCells
                = zip   [(x, y) | y <- [0 .. height - 1]
                                , x <- [0 .. width - 1]]
                        cells

        nonEmptyPosCells
                = filter (\x -> snd x /= CellEmpty) posCells


-- | Get the world position coresponding to a point in the window.
worldPosOfWindowPos :: World -> Point -> Point
worldPosOfWindowPos world (x, y)
 = let  (windowSizeX, windowSizeY)
                = windowSizeOfWorld world

        offsetX = fromIntegral $ windowSizeX `div` 2
        offsetY = fromIntegral $ windowSizeY `div` 2

        scale   = fromIntegral $ worldCellSize world

        x'      = (x + offsetX) / scale
        y'      = (y + offsetY) / scale

  in    (x', y')


-- | Check if a the cell at a given coordinate is visible from a point.
cellAtCoordIsVisibleFromCoord :: World -> Coord -> Coord -> Bool
cellAtCoordIsVisibleFromCoord world cFrom cTo
 = let  (cx, cy)        = cFrom
        pFrom           = (fromIntegral cx + 0.5 , fromIntegral cy + 0.5)
   in   cellAtCoordIsVisibleFromPoint world pFrom cTo


-- | Check if a cell at a given coordinate is visible from a point.
--      We say it's visible if the center of any of its faces is visible.
cellAtCoordIsVisibleFromPoint :: World -> Point -> Coord -> Bool
cellAtCoordIsVisibleFromPoint world pFrom (x', y')
 = or $ map (cellAtPointIsVisibleFromPoint world pFrom) [pa, pb, pc, pd]
 where  x :: Float      = fromIntegral x' + 0.5
        y :: Float      = fromIntegral y' + 0.5
        pa      = (x - 0.4999, y)
        pb      = (x + 0.4999, y)
        pc      = (x, y - 0.4999)
        pd      = (x, y + 0.4999)


-- | Check if a point on some cell (P2) is visible from some other point (P1).
cellAtPointIsVisibleFromPoint :: World -> Point -> Point -> Bool
cellAtPointIsVisibleFromPoint world p1 p2
 = let  mOccluder       = castSegIntoWorld world p1 p2
   in   case mOccluder of
         Nothing                        -> False
         Just (pos, extent, cell)       -> pointInExtent extent p2


-- | Given a line segment (P1-P2) get the cell closest to P1 that intersects the segment.
castSegIntoWorld :: World -> Point -> Point -> Maybe (Point, Extent, Cell)
castSegIntoWorld world p1 p2
        = castSegIntoCellularQuadTree p1 p2 (worldExtent world) (worldTree world)


-- | Given a line segment (P1-P2) get the cell closest to P1 that intersects the segment.
traceSegIntoWorld :: World -> Point -> Point -> [(Point, Extent, Cell)]
traceSegIntoWorld world p1 p2
        = traceSegIntoCellularQuadTree p1 p2 (worldExtent world) (worldTree world)