{-# LANGUAGE BangPatterns #-}
module Brick.Widgets.Internal
  ( renderFinal
  , cropToContext
  , cropResultToContext
  , renderDynBorder
  )
where

import Lens.Micro ((^.), (&), (%~))
import Control.Monad.Trans.State.Lazy
import Control.Monad.Trans.Reader
import Data.Maybe (catMaybes)
import qualified Graphics.Vty as V

import Brick.Types
import Brick.Types.Internal
import Brick.AttrMap
import Brick.Widgets.Border.Style
import Brick.BorderMap (BorderMap)
import qualified Brick.BorderMap as BM

renderFinal :: AttrMap
            -> [Widget n]
            -> V.DisplayRegion
            -> ([CursorLocation n] -> Maybe (CursorLocation n))
            -> RenderState n
            -> (RenderState n, V.Picture, Maybe (CursorLocation n), [Extent n])
renderFinal aMap layerRenders (w, h) chooseCursor rs =
    (newRS, picWithBg, theCursor, concat layerExtents)
    where
        (layerResults, !newRS) = flip runState rs $ sequence $
            (\p -> runReaderT p ctx) <$>
            (render <$> cropToContext <$> layerRenders)

        ctx = Context { ctxAttrName = mempty
                      , availWidth = w
                      , availHeight = h
                      , windowWidth = w
                      , windowHeight = h
                      , ctxBorderStyle = defaultBorderStyle
                      , ctxAttrMap = aMap
                      , ctxDynBorders = False
                      , ctxVScrollBarOrientation = Nothing
                      , ctxVScrollBarRenderer = Nothing
                      , ctxHScrollBarOrientation = Nothing
                      , ctxHScrollBarRenderer = Nothing
                      , ctxHScrollBarShowHandles = False
                      , ctxVScrollBarShowHandles = False
                      , ctxHScrollBarClickableConstr = Nothing
                      , ctxVScrollBarClickableConstr = Nothing
                      }
        pic = V.picForLayers $ uncurry V.resize (w, h) <$> (^.imageL) <$> layerResults

        -- picWithBg is a workaround for runaway attributes.
        -- See https://github.com/coreyoconnor/vty/issues/95
        picWithBg = pic { V.picBackground = V.Background ' ' V.defAttr }

        layerCursors = (^.cursorsL) <$> layerResults
        layerExtents = reverse $ (^.extentsL) <$> layerResults
        theCursor = chooseCursor $ concat layerCursors

-- | After rendering the specified widget, crop its result image to the
-- dimensions in the rendering context.
cropToContext :: Widget n -> Widget n
cropToContext p =
    Widget (hSize p) (vSize p) (render p >>= cropResultToContext)

cropResultToContext :: Result n -> RenderM n (Result n)
cropResultToContext result = do
    c <- getContext
    return $ result & imageL   %~ cropImage   c
                    & cursorsL %~ cropCursors c
                    & extentsL %~ cropExtents c
                    & bordersL %~ cropBorders c

cropImage :: Context n -> V.Image -> V.Image
cropImage c = V.crop (max 0 $ c^.availWidthL) (max 0 $ c^.availHeightL)

cropCursors :: Context n -> [CursorLocation n] -> [CursorLocation n]
cropCursors ctx cs = catMaybes $ cropCursor <$> cs
    where
        -- A cursor location is removed if it is not within the region
        -- described by the context.
        cropCursor c | outOfContext c = Nothing
                     | otherwise      = Just c
        outOfContext c =
            or [ c^.cursorLocationL.locationRowL    < 0
               , c^.cursorLocationL.locationColumnL < 0
               , c^.cursorLocationL.locationRowL    >= ctx^.availHeightL
               , c^.cursorLocationL.locationColumnL >= ctx^.availWidthL
               ]

cropExtents :: Context n -> [Extent n] -> [Extent n]
cropExtents ctx es = catMaybes $ cropExtent <$> es
    where
        -- An extent is cropped in places where it is not within the
        -- region described by the context.
        --
        -- If its entirety is outside the context region, it is dropped.
        --
        -- Otherwise its size and upper left corner are adjusted so that
        -- they are contained within the context region.
        cropExtent (Extent n (Location (c, r)) (w, h)) =
            -- First, clamp the upper-left corner to at least (0, 0).
            let c' = max c 0
                r' = max r 0
                -- Then, determine the new lower-right corner based on
                -- the clamped corner.
                endCol = c' + w
                endRow = r' + h
                -- Then clamp the lower-right corner based on the
                -- context
                endCol' = min (ctx^.availWidthL) endCol
                endRow' = min (ctx^.availHeightL) endRow
                -- Then compute the new width and height from the
                -- clamped lower-right corner.
                w' = endCol' - c'
                h' = endRow' - r'
                e = Extent n (Location (c', r')) (w', h')
            in if w' < 0 || h' < 0
               then Nothing
               else Just e

cropBorders :: Context n -> BorderMap DynBorder -> BorderMap DynBorder
cropBorders ctx = BM.crop Edges
    { eTop = 0
    , eBottom = availHeight ctx - 1
    , eLeft = 0
    , eRight = availWidth ctx - 1
    }

renderDynBorder :: DynBorder -> V.Image
renderDynBorder db = V.char (dbAttr db) $ getBorderChar $ dbStyle db
    where
        getBorderChar = case bsDraw <$> dbSegments db of
            --    top   bot   left  right
            Edges False False False False -> const ' '
            Edges False False _     _     -> bsHorizontal
            Edges _     _     False False -> bsVertical
            Edges False True  False True  -> bsCornerTL
            Edges False True  True  False -> bsCornerTR
            Edges True  False False True  -> bsCornerBL
            Edges True  False True  False -> bsCornerBR
            Edges False True  True  True  -> bsIntersectT
            Edges True  False True  True  -> bsIntersectB
            Edges True  True  False True  -> bsIntersectL
            Edges True  True  True  False -> bsIntersectR
            Edges True  True  True  True  -> bsIntersectFull