{-# OPTIONS_GHC -fno-warn-unused-imports #-}
{-# LANGUAGE FlexibleContexts #-}
-- |
-- Module      : Graphics.Image.IO
-- Copyright   : (c) Alexey Kuleshevich 2016
-- License     : BSD3
-- Maintainer  : Alexey Kuleshevich <lehins@yandex.ru>
-- Stability   : experimental
-- Portability : non-portable
module Graphics.Image.IO (
  -- * Reading
  readImage, readImageExact,
  -- * Writing
  writeImage, writeImageExact,
  -- * Displaying
  displayImage, setDisplayProgram, 
  -- * Supported Image Formats
  module Graphics.Image.IO.External
  -- $supported
  ) where

import Prelude as P hiding (readFile, writeFile)
import qualified Control.Monad as M (foldM)
import Control.Concurrent (forkIO, ThreadId)
import Data.Char (toLower)
import Data.Maybe (fromMaybe)
import Data.IORef
import Data.ByteString (readFile)
import Graphics.Image.ColorSpace
import Graphics.Image.Interface
import Graphics.Image.IO.Base
import Graphics.Image.IO.External
import qualified Data.ByteString.Lazy as BL (writeFile, hPut)
import System.Exit (ExitCode(ExitSuccess))
import System.FilePath (takeExtension)
import System.IO (Handle, hFlush)
import System.IO.Temp (withSystemTempFile)
import System.Process (waitForProcess, showCommandForUser)

guessFormat :: (ImageFormat f, Enum f) => FilePath -> Maybe f
guessFormat path =
  headMaybe . dropWhile (not . isFormat e) . enumFrom . toEnum $ 0
  where e = P.map toLower . takeExtension $ path
        headMaybe ls = if null ls then Nothing else Just $ head ls

-- | This function will try to guess an image format from file's extension,
-- then it will attempt to read it as such. It will fall back onto the rest of
-- the supported formats and will try to read them regarless of file's
-- extension. Whenever image cannot be decoded, 'Left' containing all errors for
-- each attempted format will be returned, and 'Right' containing an image
-- otherwise. Image will be read into a type signature specified 'ColorSpace'
-- ('Graphics.Image.ColorSpace.Y', 'Graphics.Image.ColorSpace.YA',
-- 'Graphics.Image.ColorSpace.RGB' and 'Graphics.Image.ColorSpace.RGBA' only)
-- with 'Double' precision, while doing all necessary conversions.
readImage :: Readable (Image arr cs Double) InputFormat =>
          -> IO (Either String (Image arr cs Double))
readImage path = do
  imgstr <- readFile path
  let maybeFormat = guessFormat path :: Maybe InputFormat
      formats = enumFrom . toEnum $ 0
      orderedFormats = maybe formats (\f -> f:filter (/=f) formats) maybeFormat
      reader (Left err) format = 
        return $ either (Left . ((err++"\n")++)) Right (decode format imgstr)
      reader img         _     = return img
  M.foldM reader (Left "") orderedFormats

-- | This function allows for reading any supported image in the exact colorspace
-- and precision it is currently encoded in. For instance, frog image can be
-- read into it's 'Graphics.Image.ColorSpace.YCbCr' colorspace with
-- 'Graphics.Image.ColorSpace.Word8' precision and into any supported array
-- representation.
-- >>> readImageExact JPG "images/frog.jpg" :: IO (Either String (Image RP YCbCr Word8))
-- Right <Image RepaParallel YCbCr (Word8): 200x320>
-- The drawback here is that colorspace and precision has to match exactly,
-- otherwise it will return an error:
-- >>> readImageExact JPG "images/frog.jpg" :: IO (Either String (Image RD RGB Word8))
-- Left "JuicyPixel decoding error: Input image is in YCbCr8 (Pixel YCbCr Word8), cannot convert it to RGB8 (Pixel RGB Word8) colorspace."
-- Attempt to read an image in a particular color space that is not supported by
-- the format, will result in a compile error. Refer to 'Readable' class for all
-- images that can be decoded.
readImageExact :: Readable img format =>
                  -- ^ A file format that an image should be read as. See
                   -- <#g:4 Supported Image Formats>
               -> FilePath -- ^ Location of an image.
               -> IO (Either String img)
readImageExact format path = fmap (decode format) (readFile path)

-- | Just like 'readImage', this function will guess an output file format from the
-- extension and write to file any image that is in one of 'Y', 'YA', 'RGB' or
-- 'RGBA' 'ColorSpace's with 'Double' precision. While doing necessary
-- conversions the choice will be given to the most suited color space supported
-- by the format, for instance, in case of a 'PNG' format, an ('Image' @arr@
-- 'RGBA' 'Double') would be written as 'RGBA'16, hence preserving transparency
-- and using highest supported precision 'Word16'. At the same time, writing
-- that image in 'GIF' format would save it in @RGB8@, since 'Word8' is the
-- highest precision 'GIF' supports and it currently cannot be saved with
-- transparency.
writeImage :: (ManifestArray arr cs Double, Writable (Image arr cs Double) OutputFormat) =>
              FilePath            -- ^ Location where an image should be written.
           -> Image arr cs Double -- ^ An image to write. 
           -> IO ()
writeImage path = BL.writeFile path . encode format [] where
  format = fromMaybe (error ("Could not guess output format. Use 'writeImageExact' "++
                         "or supply a filename with supported format."))
           (guessFormat path :: Maybe OutputFormat)

-- | Write an image in a specific format, while supplying any format specific
-- options. Precision and color space that an image will be written is decided
-- from image's type. Attempt to write image file in a format that does not
-- support color space and precision combination will result in a compile error.
writeImageExact :: Writable img format =>
                   -- ^ A file format that an image should be saved in. See
                   -- <#g:4 Supported Image Formats>
                -> [SaveOption format] -- ^ A list of format specific options.
                -> FilePath -- ^ Location where an image should be written.
                -> img -- ^ An image to write. Can be a list of images in case
                       -- of formats supporting animation.
                -> IO ()
writeImageExact format opts path = BL.writeFile path . encode format opts

-- | Sets the program to be use when displaying an image, where 'Bool'
-- specifies if current thread should block until the program is closed when
-- calling 'displayImage' function. GPicView @("gpicview", False)@ is set as a
-- default program with a nonblocking flag. Here are some examples:
-- >>> setDisplayProgram ("gpicview", True) -- use gpicview and block current thread.
-- >>> setDisplayProgram ("gimp", False) -- use gimp and don't block current thread.
-- >>> setDisplayProgram ("xv", False)
-- >>> setDisplayProgram ("display", False)
setDisplayProgram :: (String, Bool) -> IO ()
setDisplayProgram = writeIORef displayProgram 

{- | Makes a call to the current display program, which can be changed using
'setDisplayProgram'. An image is written as a @.tiff@ file into an operating
system's temporary directory and passed as an argument to the display
program. If a blocking flag was set to 'False' using 'setDisplayProgram', then
function will return immediately with ('Just' 'ThreadId'), otherwise it will
block current thread until external program is terminated, in which case
'Nothing' is returned. Temporary file is deleted, after a program displaying an
image is closed.

  >>> frog <- readImageRGB "images/frog.jpg"
  >>> displayImage frog
  Just ThreadId 505
  >>> setDisplayProgram ("gimp", True)
  >>> displayImage frog -- will only return after gimp is closed.

displayImage :: (ManifestArray arr cs e, Writable (Image arr cs e) TIF) =>
                Image arr cs e -- ^ Image to be displayed
             -> IO (Maybe ThreadId)
displayImage img = do
  (program, block) <- readIORef displayProgram
  let displayAction = withSystemTempFile "tmp-img.tiff" (displayUsing img program)
  if block
    then displayAction >> return Nothing
    else Just <$> forkIO displayAction

displayUsing :: (ManifestArray arr cs e, Writable (Image arr cs e) TIF) =>
                Image arr cs e -> String -> FilePath -> Handle -> IO ()
displayUsing img program path h = do
  BL.hPut h $ encode TIF [] img
  hFlush h
  ph <- spawnProcess program [path]
  e <- waitForProcess ph
  let printExit ExitSuccess = return ()
      printExit exitCode = do
        putStrLn $ showCommandForUser program [path]
        print exitCode
  printExit e

{- $supported
Encoding and decoding of images is done using
<http://hackage.haskell.org/package/JuicyPixels JuicyPixels> and
<http://hackage.haskell.org/package/netpbm netpbm> packages.
List of image formats that are currently supported, and their exact
'ColorSpace's and precision for reading and writing:
* 'BMP':

    * __in__: ('Y' 'Word8'), ('RGB'  'Word8'), ('RGBA'  'Word8')
    * __out__: ('Y' 'Word8'), ('RGB'  'Word8'), ('RGBA'  'Word8')

* 'GIF':

    * __in__: ('RGB'  'Word8'), ('RGBA'  'Word8')
    * __out__: ('RGB'  'Word8')
    * Also supports reading and writing animated images, when used as @['GIF']@

* 'HDR':

    * __in__: ('RGB'  'Float')
    * __out__: ('RGB'  'Float')

* 'JPG':

    * __in__: ('Y' 'Word8'), ('YA' 'Word8'), ('RGB'  'Word8'), ('CMYK'  'Word8'),
    ('YCbCr', 'Word8')
    * __out__: ('Y' 'Word8'), ('YA', 'Word8'), ('RGB'  'Word8'), ('CMYK'  'Word8'),
    ('YCbCr', 'Word8')

* 'PNG':

    * __in__: ('Y' 'Word8'), ('Y' 'Word16'), ('YA' 'Word8'), ('YA' 'Word16'),
    ('RGB'  'Word8'), ('RGB'  'Word16'), ('RGBA'  'Word8'), ('RGBA'  'Word16')
    * __out__: ('Y' 'Word8'), ('Y' 'Word16'), ('YA' 'Word8'), ('YA' 'Word16'),
    ('RGB'  'Word8'), ('RGB'  'Word16'), ('RGBA'  'Word8'), ('RGBA'  'Word16')

* 'TGA':

    * __in__: ('Y' 'Word8'), ('RGB'  'Word8'), ('RGBA'  'Word8')
    * __out__: ('Y' 'Word8'), ('RGB'  'Word8'), ('RGBA'  'Word8')

* 'TIF':

    * __in__: ('Y' 'Word8'), ('Y' 'Word16'), ('YA' 'Word8'), ('YA' 'Word16'),
    ('RGB'  'Word8'), ('RGB'  'Word16'), ('RGBA'  'Word8'), ('RGBA'  'Word16'),
    ('CMYK'  'Word8'), ('CMYK'  'Word16')
    * __out__: ('Y' 'Word8'), ('Y' 'Word16'), ('YA' 'Word8'), ('YA' 'Word16'),
    ('RGB'  'Word8'), ('RGB'  'Word16'), ('RGBA'  'Word8'), ('RGBA'  'Word16')
    ('CMYK'  'Word8'), ('CMYK'  'Word16'), ('YCbCr'  'Word8')

* 'PBM':

    * __in__: ('Binary' 'Bit')
    * Also supports sequence of images in one file, when read as @['PBM']@

* 'PGM':

    * __in__: ('Y' 'Word8'), ('Y' 'Word16')
    * Also supports sequence of images in one file, when read as @['PGM']@

* 'PPM':

    * __in__: ('RGB'  'Word8'), ('RGB'  'Word16')
    * Also supports sequence of images in one file, when read as @['PPM']@