{-# LANGUAGE DeriveDataTypeable        #-}
{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE FlexibleContexts          #-}
{-# LANGUAGE FlexibleInstances         #-}
{-# LANGUAGE GADTs                     #-}
{-# LANGUAGE MultiParamTypeClasses     #-}
{-# LANGUAGE TypeFamilies              #-}
{-# LANGUAGE TypeSynonymInstances      #-}
{-# LANGUAGE ViewPatterns              #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  Diagrams.Backend.Cairo.Internal
-- Copyright   :  (c) 2011 Diagrams-cairo team (see LICENSE)
-- License     :  BSD-style (see LICENSE)
-- Maintainer  :  diagrams-discuss@googlegroups.com
--
-- This module contains the internal implementation guts of the
-- diagrams cairo backend.  If you want to see how the cairo backend
-- works under the hood, you are in the right place (try clicking on
-- the \"Source\" links).  (Guts under the hood, what an awful mixed
-- metaphor.)  If you know what you are doing and really want access
-- to the internals of the implementation, you are also in the right
-- place.  Otherwise, you should have no need of this module; import
-- "Diagrams.Backend.Cairo.CmdLine" or "Diagrams.Backend.Cairo"
-- instead.
--
-- The one exception is that this module may have to be imported
-- sometimes to work around an apparent bug in certain versions of
-- GHC, which results in a \"not in scope\" error for 'CairoOptions'.
--
-- The types of all the @fromX@ functions look funny in the Haddock
-- output, which displays them like @Type -> Type@.  In fact they are
-- all of the form @Type -> Graphics.Rendering.Cairo.Type@, /i.e./
-- they convert from a diagrams type to a cairo type of the same name.
-----------------------------------------------------------------------------
module Diagrams.Backend.Cairo.Internal where

import           Diagrams.Core.Transform

import           Diagrams.Located                (viewLoc)
import           Diagrams.Prelude
import           Diagrams.Trail
import           Diagrams.TwoD.Adjust            (adjustDia2D,
                                                  setDefault2DAttributes)
import           Diagrams.TwoD.Image
import           Diagrams.TwoD.Path              (Clip (..), getFillRule)
import           Diagrams.TwoD.Size              (requiredScaleT)
import           Diagrams.TwoD.Text

import qualified Graphics.Rendering.Cairo        as C
import qualified Graphics.Rendering.Cairo.Matrix as CM

import           Control.Monad.State
import           Data.List                       (isSuffixOf)
import           Data.Maybe                      (catMaybes, fromMaybe)

import           Control.Exception               (try)

import qualified Data.Foldable                   as F

import           Data.Typeable

-- | This data declaration is simply used as a token to distinguish
--   the cairo backend: (1) when calling functions where the type
--   inference engine would otherwise have no way to know which
--   backend you wanted to use, and (2) as an argument to the
--   'Backend' and 'Renderable' type classes.
data Cairo = Cairo
  deriving (Eq,Ord,Read,Show,Typeable)

-- | Output types supported by cairo, including four different file
--   types (PNG, PS, PDF, SVG).  If you want to output directly to GTK
--   windows, see the @diagrams-gtk@ package.
data OutputType =
    PNG         -- ^ Portable Network Graphics output.
  | PS          -- ^ PostScript output
  | PDF         -- ^ Portable Document Format output.
  | SVG         -- ^ Scalable Vector Graphics output.
  | RenderOnly  -- ^ Don't output any file; the returned @IO ()@
                --   action will do nothing, but the @Render ()@
                --   action can be used (/e.g./ to draw to a Gtk
                --   window; see the @diagrams-gtk@ package).
  deriving (Eq, Ord, Read, Show, Bounded, Enum, Typeable)

instance Monoid (Render Cairo R2) where
  mempty  = C $ return ()
  (C rd1) `mappend` (C rd2) = C (rd1 >> rd2)

-- | The custom monad in which intermediate drawing options take
--   place; 'Graphics.Rendering.Cairo.Render' is cairo's own rendering
--   monad.  Right now we simply maintain a Bool state to track
--   whether or not we saw any lines in the most recent path (as
--   opposed to loops).  If we did, we should ignore any fill
--   attribute.  diagrams-lib separates lines and loops into separate
--   path primitives so we don't have to worry about seeing them
--   together in the same path.
type RenderM a = StateT Bool C.Render a  -- no state for now

-- Simple, stupid implementations of save and restore for now.  If
-- need be we could switch to a more sophisticated implementation
-- using an "undoable state" monad which lets you save (push state
-- onto a stack) and restore (pop from the stack).

-- | Push the current context onto a stack.
save :: RenderM ()
save = lift C.save

-- | Restore the context from a stack.
restore :: RenderM ()
restore = lift C.restore

instance Backend Cairo R2 where
  data Render  Cairo R2 = C (RenderM ())
  type Result  Cairo R2 = (IO (), C.Render ())
  data Options Cairo R2 = CairoOptions
          { cairoFileName   :: String     -- ^ The name of the file you want generated
          , cairoSizeSpec   :: SizeSpec2D -- ^ The requested size of the output
          , cairoOutputType :: OutputType -- ^ the output format and associated options
          , cairoBypassAdjust  :: Bool    -- ^ Should the 'adjustDia' step be bypassed during rendering?
          }
    deriving Show

  withStyle _ s t (C r) = C $ do
    save
    cairoMiscStyle s
    put False
    r
    ignoreFill <- get
    lift $ do
      cairoTransf t
      cairoStrokeStyle ignoreFill s
      C.stroke
    restore

  doRender _ (CairoOptions file size out _) (C r) = (renderIO, r')
    where r' = evalStateT r False
          renderIO = do
            let surfaceF s = C.renderWith s r'

                -- Everything except Dims is arbitrary. The backend
                -- should have first run 'adjustDia' to update the
                -- final size of the diagram with explicit dimensions,
                -- so normally we would only expect to get Dims anyway.
                (w,h) = case size of
                          Width w'   -> (w',w')
                          Height h'  -> (h',h')
                          Dims w' h' -> (w',h')
                          Absolute   -> (100,100)

            case out of
              PNG ->
                C.withImageSurface C.FormatARGB32 (round w) (round h) $ \surface -> do
                  surfaceF surface
                  C.surfaceWriteToPNG surface file
              PS  -> C.withPSSurface  file w h surfaceF
              PDF -> C.withPDFSurface file w h surfaceF
              SVG -> C.withSVGSurface file w h surfaceF
              RenderOnly -> return ()

  adjustDia c opts d = if cairoBypassAdjust opts
                         then (opts, d # setDefault2DAttributes)
                         else adjustDia2D cairoSizeSpec
                                          setCairoSizeSpec
                                          c opts (d # reflectY)
    where setCairoSizeSpec sz o = o { cairoSizeSpec = sz }

-- | Render an object that the cairo backend knows how to render.
renderC :: (Renderable a Cairo, V a ~ R2) => a -> RenderM ()
renderC a = case (render Cairo a) of C r -> r

-- | Handle \"miscellaneous\" style attributes (clip, font stuff, fill
--   color and fill rule).
cairoMiscStyle :: Style v -> RenderM ()
cairoMiscStyle s =
  sequence_
  . catMaybes $ [ handle clip
                , handle fSize
                , handleFontFace
                , handle fColor
                , handle lFillRule
                ]
  where handle :: AttributeClass a => (a -> RenderM ()) -> Maybe (RenderM ())
        handle f = f `fmap` getAttr s
        clip     = mapM_ (\p -> renderC p >> lift C.clip) . getClip
        fSize    = lift . C.setFontSize . getFontSize
        fFace    = fromMaybe "" $ getFont <$> getAttr s
        fSlant   = fromFontSlant  . fromMaybe FontSlantNormal
                 $ getFontSlant  <$> getAttr s
        fWeight  = fromFontWeight . fromMaybe FontWeightNormal
                 $ getFontWeight <$> getAttr s
        handleFontFace = Just . lift $ C.selectFontFace fFace fSlant fWeight
        fColor c = lift $ setSource (getFillColor c) s
        lFillRule = lift . C.setFillRule . fromFillRule . getFillRule

fromFontSlant :: FontSlant -> C.FontSlant
fromFontSlant FontSlantNormal   = C.FontSlantNormal
fromFontSlant FontSlantItalic   = C.FontSlantItalic
fromFontSlant FontSlantOblique  = C.FontSlantOblique

fromFontWeight :: FontWeight -> C.FontWeight
fromFontWeight FontWeightNormal = C.FontWeightNormal
fromFontWeight FontWeightBold   = C.FontWeightBold

-- | Handle style attributes having to do with stroke.
cairoStrokeStyle :: Bool -> Style v -> C.Render ()
cairoStrokeStyle ignoreFill s =
  sequence_
  . catMaybes $ [ if ignoreFill then Nothing else handle fColor
                , handle lColor  -- see Note [color order]
                , handle lWidth
                , handle lCap
                , handle lJoin
                , handle lDashing
                ]
  where handle :: (AttributeClass a) => (a -> C.Render ()) -> Maybe (C.Render ())
        handle f = f `fmap` getAttr s
        fColor c = setSource (getFillColor c) s >> C.fillPreserve
        lColor c = setSource (getLineColor c) s
        lWidth   = C.setLineWidth . getLineWidth
        lCap     = C.setLineCap . fromLineCap . getLineCap
        lJoin    = C.setLineJoin . fromLineJoin . getLineJoin
        lDashing (getDashing -> Dashing ds offs) =
          C.setDash ds offs

-- | Set the source color.
setSource :: Color c => c -> Style v -> C.Render ()
setSource c s = C.setSourceRGBA r g b a'
  where (r,g,b,a) = colorToSRGBA c
        a'        = case getOpacity <$> getAttr s of
                      Nothing -> a
                      Just d  -> a * d


-- | Multiply the current transformation matrix by the given 2D
--   transformation.
cairoTransf :: T2 -> C.Render ()
cairoTransf t = C.transform m
  where m = CM.Matrix a1 a2 b1 b2 c1 c2
        (unr2 -> (a1,a2)) = apply t unitX
        (unr2 -> (b1,b2)) = apply t unitY
        (unr2 -> (c1,c2)) = transl t

{- ~~~~ Note [color order]

   It's important for the line and fill colors to be handled in the
   given order (fill color first, then line color) because of the way
   Cairo handles them (both are taken from the sourceRGBA).
-}

fromLineCap :: LineCap -> C.LineCap
fromLineCap LineCapButt   = C.LineCapButt
fromLineCap LineCapRound  = C.LineCapRound
fromLineCap LineCapSquare = C.LineCapSquare

fromLineJoin :: LineJoin -> C.LineJoin
fromLineJoin LineJoinMiter = C.LineJoinMiter
fromLineJoin LineJoinRound = C.LineJoinRound
fromLineJoin LineJoinBevel = C.LineJoinBevel

fromFillRule :: FillRule -> C.FillRule
fromFillRule Winding = C.FillRuleWinding
fromFillRule EvenOdd = C.FillRuleEvenOdd

instance Renderable (Segment Closed R2) Cairo where
  render _ (Linear (OffsetClosed v)) = C . lift $ uncurry C.relLineTo (unr2 v)
  render _ (Cubic (unr2 -> (x1,y1))
                  (unr2 -> (x2,y2))
                  (OffsetClosed (unr2 -> (x3,y3))))
    = C . lift $ C.relCurveTo x1 y1 x2 y2 x3 y3

instance Renderable (Trail R2) Cairo where
  render _ t = flip withLine t $ renderT . lineSegments
    where
      renderT segs =
        C $ do
          mapM_ renderC segs
          lift $ when (isLoop t) C.closePath

          when (isLine t) (put True)
            -- remember that we saw a Line, so we will ignore fill attribute

instance Renderable (Path R2) Cairo where
  render _ (Path trs) = C $ lift C.newPath >> F.mapM_ renderTrail trs
    where renderTrail (viewLoc -> (unp2 -> p, tr)) = do
            lift $ uncurry C.moveTo p
            renderC tr


-- Can only do PNG files at the moment...
instance Renderable Image Cairo where
  render _ (Image file sz tr) = C . lift $ do
    if ".png" `isSuffixOf` file
      then do
        C.save
        cairoTransf (tr <> reflectionY)
        pngSurfChk <- liftIO (try $ C.imageSurfaceCreateFromPNG file
                              :: IO (Either IOError C.Surface))
        case pngSurfChk of
          Right pngSurf -> do
            w <- C.imageSurfaceGetWidth pngSurf
            h <- C.imageSurfaceGetHeight pngSurf
            cairoTransf $ requiredScaleT sz (fromIntegral w, fromIntegral h)
            C.setSourceSurface pngSurf (-fromIntegral w / 2)
                                       (-fromIntegral h / 2)
          Left _ ->
            liftIO . putStrLn $
              "Warning: can't read image file <" ++ file ++ ">"
        C.paint
        C.restore
      else
        liftIO . putStr . unlines $
          [ "Warning: Cairo backend can currently only render embedded"
          , "  images in .png format.  Ignoring <" ++ file ++ ">."
          ]

-- see http://www.cairographics.org/tutorial/#L1understandingtext
instance Renderable Text Cairo where
  render _ (Text tr al str) = C $ do
    lift $ do
      C.save
      -- XXX should use reflection font matrix here instead?
      cairoTransf (tr <> reflectionY)
      (refX, refY) <- case al of
        BoxAlignedText xt yt -> do
          tExt <- C.textExtents str
          fExt <- C.fontExtents
          let l = C.textExtentsXbearing tExt
              r = C.textExtentsXadvance tExt
              b = C.fontExtentsDescent  fExt
              t = C.fontExtentsAscent   fExt
          return (lerp l r xt, lerp (-b) t yt)
        BaselineText -> return (0, 0)
      cairoTransf (moveOriginBy (r2 (refX, -refY)) mempty)
      C.showText str
      C.restore