    {-# LANGUAGE NoImplicitPrelude #-}
    {-# LANGUAGE DeriveDataTypeable #-}
    {-# LANGUAGE DeriveGeneric      #-}
    {-
    Copyright (C) 2006-2018 John MacFarlane <jgm@berkeley.edu>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    -}
    {- |
       Module      : Text.Pandoc.Error
       Copyright   : Copyright (C) 2006-2018 John MacFarlane
       License     : GNU GPL, version 2 or above

       Maintainer  : John MacFarlane <jgm@berkeley.edu>
       Stability   : alpha
       Portability : portable

    This module provides a standard way to deal with possible errors encounted
    during parsing.

    -}
    module Text.Pandoc.Error (
      PandocError(..),
      handleError) where

    import Prelude
    import Control.Exception (Exception)
    import Data.Typeable (Typeable)
    import GHC.Generics (Generic)
    import Network.HTTP.Client (HttpException)
    import System.Exit (ExitCode (..), exitWith)
    import System.IO (stderr)
    import qualified Text.Pandoc.UTF8 as UTF8
    import Text.Parsec.Error
    import Text.Parsec.Pos hiding (Line)

    type Input = String

    data PandocError = PandocIOError String IOError
                     | PandocHttpError String HttpException
                     | PandocShouldNeverHappenError String
                     | PandocSomeError String
                     | PandocParseError String
                     | PandocParsecError Input ParseError
                     | PandocMakePDFError String
                     | PandocOptionError String
                     | PandocSyntaxMapError String
                     | PandocFailOnWarningError
                     | PandocPDFProgramNotFoundError String
                     | PandocPDFError String
                     | PandocFilterError String String
                     | PandocCouldNotFindDataFileError String
                     | PandocResourceNotFound String
                     | PandocTemplateError String
                     | PandocAppError String
                     | PandocEpubSubdirectoryError String
                     | PandocMacroLoop String
                     deriving (Show, Typeable, Generic)

    instance Exception PandocError

    -- | Handle PandocError by exiting with an error message.
    handleError :: Either PandocError a -> IO a
    handleError (Right r) = return r
    handleError (Left e) =
      case e of
        PandocIOError _ err' -> ioError err'
        PandocHttpError u err' -> err 61 $
          "Could not fetch " ++ u ++ "\n" ++ show err'
        PandocShouldNeverHappenError s -> err 62 s
        PandocSomeError s -> err 63 s
        PandocParseError s -> err 64 s
        PandocParsecError input err' ->
            let errPos = errorPos err'
                errLine = sourceLine errPos
                errColumn = sourceColumn errPos
                ls = lines input ++ [""]
                errorInFile = if length ls > errLine - 1
                                then concat ["\n", ls !! (errLine - 1)
                                            ,"\n", replicate (errColumn - 1) ' '
                                            ,"^"]
                            else ""
            in  err 65 $ "\nError at " ++ show  err' ++
                         -- if error comes from a chunk or included file,
                         -- then we won't get the right text this way:
                         if sourceName errPos == "source"
                            then errorInFile
                            else ""
        PandocMakePDFError s -> err 65 s
        PandocOptionError s -> err 2 s
        PandocSyntaxMapError s -> err 67 s
        PandocFailOnWarningError -> err 3 "Failing because there were warnings."
        PandocPDFProgramNotFoundError pdfprog -> err 47 $
            pdfprog ++ " not found. Please select a different --pdf-engine or install " ++ pdfprog ++ " -- see also /usr/share/doc/pandoc/README.Debian"
        PandocPDFError logmsg -> err 43 $ "Error producing PDF.\n" ++ logmsg
        PandocFilterError filtername msg -> err 83 $ "Error running filter " ++
            filtername ++ ":\n" ++ msg
        PandocCouldNotFindDataFileError fn -> err 97 $
            "Could not find data file " ++ fn
        PandocResourceNotFound fn -> err 99 $
            "File " ++ fn ++ " not found in resource path"
        PandocTemplateError s -> err 5 s
        PandocAppError s -> err 1 s
        PandocEpubSubdirectoryError s -> err 31 $
          "EPUB subdirectory name '" ++ s ++ "' contains illegal characters"
        PandocMacroLoop s -> err 91 $
          "Loop encountered in expanding macro " ++ s

    err :: Int -> String -> IO a
    err exitCode msg = do
      UTF8.hPutStrLn stderr msg
      exitWith $ ExitFailure exitCode
      return undefined