Error.hs

{-# LANGUAGE  ScopedTypeVariables #-}

-- | Error used by API

module Pdf.Toolbox.Core.Error
(
  PdfError(..),
  PdfE,
  annotateError,
  annotatingError,
  tryPdfIO,
  module Control.Error
)
where

import Control.Error
import Control.Exception
import Control.Monad
import Control.Monad.IO.Class

-- | Errors
data PdfError =
  -- | Parser error
  ParseError [String] String |
  IOError IOError |
  AnnotatedError String PdfError |
  -- | Something unexpected
  UnexpectedError String
  deriving Show

-- | API uses this for error handling
type PdfE m = EitherT PdfError m

-- | Wrap any 'PdfError' into 'AnnotatedError'
--
-- Usefull when you want to add high-level description to
-- error, returned by low-level function
annotateError :: Monad m => String -> PdfE m a -> PdfE m a
annotateError ann = fmapLT (AnnotatedError ann')
  where
  ann' = if length ann <= 50 then ann else take 47 ann ++ "..."

-- | 'annotateError' with fliped arguments
annotatingError :: Monad m => PdfE m a -> String -> PdfE m a
annotatingError = flip annotateError

-- | Catch exception if any and convert to 'IOError'
tryPdfIO :: MonadIO m => IO a -> PdfE m a
tryPdfIO action = do
  res <- liftIO $ Right `liftM` action
      `catch` (\(e :: IOError) -> return $ Left $ IOError e)
  case res of
    Right a -> return a
    Left e -> left e