module Resource.Image.Atlas
  ( Atlas(..)
  , fromTileSize
  , fromImageSize
  ) where

import RIO

import Geomancy (UVec2, Vec2, uvec2, withUVec2, vec2)

-- | Regular grid atlas
data Atlas = Atlas
  { sizeTiles  :: UVec2
  , sizePx     :: UVec2
  , tileSizePx :: UVec2
  , marginPx   :: UVec2
  , uvScale    :: Vec2
  }
  deriving (Eq, Show, Generic)

fromTileSize :: UVec2 -> UVec2 -> UVec2 -> Atlas
fromTileSize sizeTiles tileSizePx marginPx = Atlas{..}
  where
    sizePx = sizeTiles * tileSizePx + (sizeTiles - 1) * marginPx
    uvScale = fromU tileSizePx / fromU sizePx

fromImageSize :: UVec2 -> UVec2 -> UVec2 -> Either UVec2 Atlas
fromImageSize sizePx tileSizePx marginPx =
  if leftovers == totalMargins then
    Right Atlas{..}
  else
    Left leftovers
  where
    totalMargins = (sizeTiles - 1) * marginPx

    (sizeTiles, leftovers) =
      withUVec2 sizePx \aw ah ->
      withUVec2 tileSizePx \tw th ->
        let
          (w, wRem) = aw `divMod` tw
          (h, hRem) = ah `divMod` th
        in
          ( uvec2 w h
          , uvec2 wRem hRem
          )

    uvScale = fromU tileSizePx / fromU sizePx

fromU :: UVec2 -> Vec2
fromU u =
  withUVec2 u \x y ->
    vec2 (fromIntegral x) (fromIntegral y)