{-# language CPP                        #-}
{-# language GeneralizedNewtypeDeriving #-}
{-# language LambdaCase                 #-}
{-# language ScopedTypeVariables        #-}
{-# language TypeFamilies               #-}

module Termbox.Banana
  ( -- $intro

    TermboxEvent
  , main
  , Scene(..)
  , Cells
  , set
  , Cursor(..)
    -- * Re-exports
  , Termbox.black
  , Termbox.red
  , Termbox.green
  , Termbox.yellow
  , Termbox.blue
  , Termbox.magenta
  , Termbox.cyan
  , Termbox.white
  , Termbox.bold
  , Termbox.underline
  , Termbox.reverse
  , Termbox.Attr
  , Termbox.Cell(..)
  , Termbox.Event(..)
  , Termbox.InitError(..)
  , Termbox.InputMode(..)
  , Termbox.Key(..)
  , Termbox.Mouse(..)
  , Termbox.MouseMode(..)
  , Termbox.OutputMode(..)
  ) where

import Control.Concurrent.MVar
import Data.Function (fix)
import Reactive.Banana
import Reactive.Banana.Frameworks

import qualified Termbox

-- $intro
-- This module is intended to be imported qualified.
--
-- @
-- import qualified Termbox.Banana as Termbox
-- @

-- | A @termbox@ event. This type alias exists only for Haddock readability;
-- in code, you are encouraged to use
--
-- * @Event@ for @reactive-banana@ events
-- * @Termbox.Event@ for @termbox@ events
--
-- @since 0.1.0
type TermboxEvent
  = Termbox.Event

-- | A scene to render; a grid of cells and a cursor.
--
-- @since 0.1.0
data Scene
  = Scene !Cells !Cursor

-- | A grid of cells.
--
-- Create a 'Cells' with 'set' or 'mempty' and combine them with ('<>').
--
-- @since 0.1.0
newtype Cells
  = Cells (IO ())
#if MIN_VERSION_base(4,10,0)
  deriving (Monoid, Semigroup)
#else
instance Monoid Cells where
  mempty = Cells (pure ())
  mappend = (<>)
instance Semigroup Cells where
  Cells x <> Cells y = Cells (x >> y)
#endif

-- | A cursor.
--
-- @since 0.1.0
data Cursor
  = Cursor !Int !Int -- ^ Column, then row
  | NoCursor

-- | Set a single cell's value (column, then row).
--
-- @since 0.1.0
set :: Int -> Int -> Termbox.Cell -> Cells
set x y z =
  Cells (Termbox.set x y z)

type EventSource a
  = (AddHandler a, a -> IO ())

-- | Run a @termbox@ program with the specified input and output modes.
--
-- Given
--
-- * the terminal event stream
-- * the time-varying terminal size (width, then height)
--
-- return
--
-- * a time-varying scene to render
-- * an event stream of arbitrary values, only the first of which is relevant,
--   which ends the @termbox@ program and returns from the @main@ action.
--
-- @since 0.1.0
main
  :: Termbox.InputMode -- ^
  -> Termbox.OutputMode -- ^
  -> (  Event TermboxEvent
     -> Behavior (Int, Int)
     -> MomentIO (Behavior Scene, Event a))
  -> IO a
main imode omode run =
  Termbox.main $ do
    Termbox.setInputMode imode
    Termbox.setOutputMode omode

    doneVar :: MVar a <-
      newEmptyMVar

    (eventAddHandler, fireEvent) :: EventSource TermboxEvent <-
      newAddHandler

    network :: EventNetwork <-
      compile $ do
        eEvent :: Event TermboxEvent <-
          fromAddHandler eventAddHandler

        let
          eResize :: Event (Int, Int)
          eResize =
            filterJust
              ((\case
                Termbox.EventResize w h -> Just (w, h)
                _ -> Nothing)
              <$> eEvent)

        bSize :: Behavior (Int, Int) <- do
          flip stepper eResize =<<
            liftIO Termbox.size

        moment run eEvent bSize (putMVar doneVar)

    actuate network

    fix $ \loop -> do
      Termbox.poll >>= fireEvent
      tryReadMVar doneVar >>=
        maybe loop pure

moment
  :: (  Event TermboxEvent
     -> Behavior (Int, Int)
     -> MomentIO (Behavior Scene, Event a))
  -> Event TermboxEvent
  -> Behavior (Int, Int)
  -> (a -> IO ())
  -> MomentIO ()
moment run eEvent bSize abort = do
  (bScene, eDone) :: (Behavior Scene, Event a) <-
    run eEvent bSize

  eScene :: Event (Future Scene) <-
    changes bScene

  let
    render :: Scene -> IO ()
    render (Scene (Cells cells) cursor) = do
      Termbox.clear mempty mempty
      cells
      case cursor of
        Cursor c r -> Termbox.setCursor c r
        NoCursor -> Termbox.hideCursor
      Termbox.flush

  liftIO . render =<< valueB bScene
  reactimate (abort <$> eDone)
  reactimate' ((fmap.fmap) render eScene)