module Graphics.Glyph.Shaders where

import Control.Monad
import qualified Data.ByteString as BS
import Data.Maybe
import Graphics.Rendering.OpenGL

loadShader :: ShaderType -> FilePath -> IO (String, Maybe Shader)
loadShader typ path = do
  shader <- createShader typ
  (shaderSourceBS shader $=) =<< BS.readFile path
  compileShader shader

  ok <- get (compileStatus shader)
  infoLog <- get (shaderInfoLog shader)

  unless ok $
    deleteObjectNames [shader]

  return (infoLog, if not ok then Nothing else Just shader)

loadShaders :: [(ShaderType, FilePath)] -> IO [(String, Maybe Shader)]
loadShaders = mapM (uncurry loadShader)

workingShaders :: [(a, Maybe Shader)] -> [Shader]
workingShaders lst = map (fromJust . snd) (filter (isJust . snd) lst)

createShaderProgram :: [Shader] -> IO (String, Maybe Program)
createShaderProgram shaders = do
  p <- createProgram
  mapM_ (attachShader p) shaders
  linkProgram p

  ok <- get $ linkStatus p
  info <- get $ programInfoLog p

  unless ok $
    deleteObjectNames [p]

  return (info, if not ok then Nothing else Just p)

getUniform :: Uniform a => String -> IO (Maybe (StateVar a))
getUniform name =
  get currentProgram
    >>= ( \pr -> case pr of
            Just p -> liftM (Just . uniform) (get $ uniformLocation p name)
            Nothing -> return Nothing
        )

getUniformForProgram :: Uniform a => String -> Program -> IO (StateVar a)
getUniformForProgram name prog =
  liftM uniform (get $ uniformLocation prog name)

getUniformLocation :: String -> IO (Maybe UniformLocation)
getUniformLocation name =
  get currentProgram
    >>= maybe
      (return Nothing)
      ( \prog ->
          liftM Just (get $ uniformLocation prog name)
      )