{-  Vivant: Haskell OpenGL game.
    Copyright (C) 2020 Yann Herklotz

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
-}

module Main where

import Control.Monad
import Foreign.C.Types
import Foreign.Ptr
import Foreign.Storable (sizeOf)
import SDL.Vect
import System.Exit (exitFailure)
import System.IO
import SDL (($=))
import SDL.Time (ticks)
import SDL.Raw.Video as SDL (glSetAttribute)
import SDL.Raw.Enum as SDL
import Data.Word (Word32)
import Linear

import qualified Graphics.Rendering.OpenGL as GL
import qualified Data.ByteString as BS
import qualified Data.Vector.Storable as V
import qualified SDL

import Paths_vivant (getDataDir)
import Vivant.Shader (createProgram)

screenWidth, screenHeight :: CInt
(screenWidth, screenHeight) = (640, 480)

data Camera = Camera
  { cameraPos   :: V3 Float
  , cameraUp    :: V3 Float
  , cameraFront :: V3 Float
  , cameraSpeed :: Float
  , cameraPitch :: Float
  , cameraYaw   :: Float
  } deriving (Show)

initialCamera :: Camera
initialCamera = Camera
  { cameraPos   = V3 0 0 3
  , cameraUp    = V3 0 1 0
  , cameraFront = V3 0 0 (-1)
  , cameraSpeed = 0.05
  , cameraPitch = 0
  , cameraYaw   = (-90)
  }

data Game = Game
  { gameProgram     :: Maybe (GL.Program)
  , gameVao         :: Maybe (GL.VertexArrayObject)
  , gameModelP      :: Ptr (M44 Float)
  , gameViewP       :: Ptr (M44 Float)
  , gameProjectionP :: Ptr (M44 Float)
  , gameCamera      :: Camera
  } deriving (Show)

initialGameState :: Game
initialGameState = Game
  { gameProgram     = Nothing
  , gameVao         = Nothing
  , gameModelP      = nullPtr
  , gameViewP       = nullPtr
  , gameProjectionP = nullPtr
  , gameCamera      = initialCamera
  }

main :: IO ()
main = do
    SDL.initialize [SDL.InitVideo]
    SDL.HintRenderScaleQuality $= SDL.ScaleLinear
    do renderQuality <- SDL.get SDL.HintRenderScaleQuality
       when (renderQuality /= SDL.ScaleLinear) $
         putStrLn "Warning: Linear texture filtering not enabled!"

    window <-
      SDL.createWindow
        "SDL / OpenGL Example"
        SDL.defaultWindow {SDL.windowInitialSize = V2 screenWidth screenHeight,
                           SDL.windowGraphicsContext = SDL.OpenGLContext SDL.defaultOpenGL}

    SDL.glSetAttribute SDL_GL_CONTEXT_PROFILE_MASK SDL_GL_CONTEXT_PROFILE_CORE
    SDL.glSetAttribute SDL_GL_CONTEXT_MAJOR_VERSION 3
    SDL.glSetAttribute SDL_GL_CONTEXT_MINOR_VERSION 2

    SDL.glSetAttribute SDL_GL_DOUBLEBUFFER 1
    SDL.glSetAttribute SDL_GL_DEPTH_SIZE 24

    SDL.showWindow window

    _ <- SDL.glCreateContext window

    GL.viewport $= (GL.Position 0 0, GL.Size (fromIntegral screenWidth) (fromIntegral screenHeight))

    game <- initResources

    let loop = do
          events <- SDL.pollEvents
          let quit = elem SDL.QuitEvent $ map SDL.eventPayload events

          draw game
          SDL.glSwapWindow window

          unless quit loop

    loop

    SDL.destroyWindow window
    SDL.quit

setVertexAttribute :: GL.Program -> String -> Int -> Int -> Int -> IO ()
setVertexAttribute program name vertices stride offset = do
    let floatSize = sizeOf (1.0 :: Float)
    attrib <- GL.get $ GL.attribLocation program name
    GL.vertexAttribPointer attrib $= (GL.ToFloat, GL.VertexArrayDescriptor 2 GL.Float
                                       (fromIntegral $ stride * floatSize)
                                       (plusPtr nullPtr (offset * floatSize)))
    GL.vertexAttribArray attrib $= GL.Enabled

initResources :: IO Game
initResources = do
    vao <- GL.genObjectName
    GL.bindVertexArrayObject $= Just vao

    vbo <- GL.genObjectName
    GL.bindBuffer GL.ArrayBuffer $= Just vbo
    V.unsafeWith vertices $ \ptr ->
        GL.bufferData GL.ArrayBuffer $= (vectorSize vertices, castPtr ptr, GL.StaticDraw)

    prog <- createProgram

    setVertexAttribute prog "position" 2 0 0

    return $ initialGameState { gameProgram = Just prog, gameVao = Just vao }

draw :: Game -> IO ()
draw game@(Game {gameProgram = Just p, gameVao = Just v}) = do
    GL.clearColor $= GL.Color4 1 1 1 1
    GL.clear [GL.ColorBuffer, GL.DepthBuffer]

    GL.currentProgram $= gameProgram game
    GL.bindVertexArrayObject $= gameVao game

    ourColorLoc <- GL.uniformLocation p "ourColour"
    tick <- ticks
    GL.uniform ourColorLoc $= (GL.Vector4 (1::Float) (sin (fromIntegral tick / 500) / 2 + 0.5) 1 1)

    GL.drawArrays GL.Triangles 0 6

    GL.bindVertexArrayObject $= Nothing
    return ()

vectorSize array = fromIntegral $ V.length array * sizeOf (1.0 :: Float)

vertices :: V.Vector Float
vertices = V.fromList [  0.5, -0.5
                      , -0.5, -0.5
                      ,  0.5,  0.5
                      , -0.5,  0.5
                      , -0.5, -0.5
                      ,  0.5,  0.5
                      ]

texCoords :: V.Vector Float
texCoords = V.fromList [   0, 0
                       ,   1, 0
                       , 0.5, 1
                       ]