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{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE OverloadedStrings          #-}
{-# LANGUAGE RecordWildCards            #-}
module Patat.Main
    ( main
    ) where


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import           Control.Applicative          ((<$>), (<*>))
import           Control.Concurrent           (forkIO, killThread, threadDelay)
import           Control.Concurrent.Chan      (Chan)
import qualified Control.Concurrent.Chan      as Chan
import           Control.Exception            (bracket)
import           Control.Monad                (forever, unless, when)
import qualified Data.Aeson.Extended          as A
import           Data.Monoid                  (mempty, (<>))
import           Data.Time                    (UTCTime)
import           Data.Version                 (showVersion)
import qualified Options.Applicative          as OA
import           Patat.AutoAdvance
import qualified Patat.Images                 as Images
import           Patat.Presentation
import qualified Paths_patat
import           Prelude
import qualified System.Console.ANSI          as Ansi
import           System.Directory             (doesFileExist,
                                               getModificationTime)
import           System.Exit                  (exitFailure, exitSuccess)
import qualified System.IO                    as IO
import qualified Text.Pandoc                  as Pandoc
import qualified Text.PrettyPrint.ANSI.Leijen as PP


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data Options = Options
    { oFilePath :: !(Maybe FilePath)
    , oForce    :: !Bool
    , oDump     :: !Bool
    , oWatch    :: !Bool
    , oVersion  :: !Bool
    } deriving (Show)


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parseOptions :: OA.Parser Options
parseOptions = Options
    <$> (OA.optional $ OA.strArgument $
            OA.metavar "FILENAME" <>
            OA.help    "Input file")
    <*> (OA.switch $
            OA.long    "force" <>
            OA.short   'f' <>
            OA.help    "Force ANSI terminal" <>
            OA.hidden)
    <*> (OA.switch $
            OA.long    "dump" <>
            OA.short   'd' <>
            OA.help    "Just dump all slides and exit" <>
            OA.hidden)
    <*> (OA.switch $
            OA.long    "watch" <>
            OA.short   'w' <>
            OA.help    "Watch file for changes")
    <*> (OA.switch $
            OA.long    "version" <>
            OA.help    "Display version info and exit" <>
            OA.hidden)


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parserInfo :: OA.ParserInfo Options
parserInfo = OA.info (OA.helper <*> parseOptions) $
    OA.fullDesc <>
    OA.header ("patat v" <> showVersion Paths_patat.version) <>
    OA.progDescDoc (Just desc)
  where
    desc = PP.vcat
        [ "Terminal-based presentations using Pandoc"
        , ""
        , "Controls:"
        , "- Next slide:             space, enter, l, right, pagedown"
        , "- Previous slide:         backspace, h, left, pageup"
        , "- Go forward 10 slides:   j, down"
        , "- Go backward 10 slides:  k, up"
        , "- First slide:            0"
        , "- Last slide:             G"
        , "- Reload file:            r"
        , "- Quit:                   q"
        ]


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parserPrefs :: OA.ParserPrefs
parserPrefs = OA.prefs OA.showHelpOnError


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errorAndExit :: [String] -> IO a
errorAndExit msg = do
    mapM_ (IO.hPutStrLn IO.stderr) msg
    exitFailure


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assertAnsiFeatures :: IO ()
assertAnsiFeatures = do
    supports <- Ansi.hSupportsANSI IO.stdout
    unless supports $ errorAndExit
        [ "It looks like your terminal does not support ANSI codes."
        , "If you still want to run the presentation, use `--force`."
        ]


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main :: IO ()
main = do
    options <- OA.customExecParser parserPrefs parserInfo

    when (oVersion options) $ do
        putStrLn (showVersion Paths_patat.version)
        putStrLn $ "Using pandoc: " ++ Pandoc.pandocVersion
        exitSuccess

    filePath <- case oFilePath options of
        Just fp -> return fp
        Nothing -> OA.handleParseResult $ OA.Failure $
            OA.parserFailure parserPrefs parserInfo OA.ShowHelpText mempty

    errOrPres <- readPresentation filePath
    pres      <- either (errorAndExit . return) return errOrPres

    unless (oForce options) assertAnsiFeatures

    -- (Maybe) initialize images backend.
    images <- traverse Images.new (psImages $ pSettings pres)

    if oDump options
        then dumpPresentation pres
        else interactiveLoop options images pres
  where
    interactiveLoop :: Options -> Maybe Images.Handle -> Presentation -> IO ()
    interactiveLoop options images pres0 =
        interactively readPresentationCommand $ \commandChan0 -> do

        -- If an auto delay is set, use 'autoAdvance' to create a new one.
        commandChan <- case psAutoAdvanceDelay (pSettings pres0) of
            Nothing                    -> return commandChan0
            Just (A.FlexibleNum delay) -> autoAdvance delay commandChan0

        -- Spawn a thread that adds 'Reload' commands based on the file time.
        mtime0 <- getModificationTime (pFilePath pres0)
        when (oWatch options) $ do
            _ <- forkIO $ watcher commandChan (pFilePath pres0) mtime0
            return ()

        let loop :: Presentation -> Maybe String -> IO ()
            loop pres mbError = do
                cleanup <- case mbError of
                    Nothing  -> displayPresentation images pres
                    Just err -> displayPresentationError pres err

                c      <- Chan.readChan commandChan
                update <- updatePresentation c pres
                cleanup
                case update of
                    ExitedPresentation        -> return ()
                    UpdatedPresentation pres' -> loop pres' Nothing
                    ErroredPresentation err   -> loop pres (Just err)

        loop pres0 Nothing


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-- | Utility for dealing with pecularities of stdin & interactive applications
-- on the terminal.  Tries to restore the original state of the terminal as much
-- as possible.
interactively
    -- | Reads a command from stdin (or from some other IO).  This will be
    -- interrupted by 'killThread' when the application finishes.
    :: (IO.Handle -> IO a)
    -- | Application to run.
    -> (Chan a -> IO ())
    -- | Returns when application finishes.
    -> IO ()
interactively reader app = bracket setup teardown $ \(_, _, _, chan) -> app chan
  where
    setup = do
        chan <- Chan.newChan
        echo <- IO.hGetEcho      IO.stdin
        buff <- IO.hGetBuffering IO.stdin
        IO.hSetEcho      IO.stdin False
        IO.hSetBuffering IO.stdin IO.NoBuffering
        Ansi.hideCursor
        readerThreadId <- forkIO $ forever $
            reader IO.stdin >>= Chan.writeChan chan
        return (echo, buff, readerThreadId, chan)

    teardown (echo, buff, readerThreadId, _chan) = do
        Ansi.showCursor
        Ansi.clearScreen
        Ansi.setCursorPosition 0 0
        killThread readerThreadId
        IO.hSetEcho      IO.stdin echo
        IO.hSetBuffering IO.stdin buff


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watcher :: Chan.Chan PresentationCommand -> FilePath -> UTCTime -> IO a
watcher chan filePath mtime0 = do
    -- The extra exists check helps because some editors temporarily make the
    -- file disappear while writing.
    exists <- doesFileExist filePath
    mtime1 <- if exists then getModificationTime filePath else return mtime0

    when (mtime1 > mtime0) $ Chan.writeChan chan Reload
    threadDelay (200 * 1000)
    watcher chan filePath mtime1