{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE GADTSyntax #-}

-- | Class of errors used in the Api.
--
module Bcc.Api.Error
  ( Error(..)
  , throwErrorAsException
  , ErrorAsException(..)
  , FileError(..)
  ) where

import           Prelude

import           Control.Exception (Exception(..), IOException, throwIO)
import           System.IO (Handle)


class Show e => Error e where

    displayError :: e -> String

instance Error () where
    displayError :: () -> String
displayError () = String
""


-- | The preferred approach is to use 'Except' or 'ExceptT', but you can if
-- necessary use IO exceptions.
--
throwErrorAsException :: Error e => e -> IO a
throwErrorAsException :: e -> IO a
throwErrorAsException e
e = ErrorAsException -> IO a
forall e a. Exception e => e -> IO a
throwIO (e -> ErrorAsException
forall e. Error e => e -> ErrorAsException
ErrorAsException e
e)

data ErrorAsException where
     ErrorAsException :: Error e => e -> ErrorAsException

instance Show ErrorAsException where
    show :: ErrorAsException -> String
show (ErrorAsException e
e) = e -> String
forall a. Show a => a -> String
show e
e

instance Exception ErrorAsException where
    displayException :: ErrorAsException -> String
displayException (ErrorAsException e
e) = e -> String
forall e. Error e => e -> String
displayError e
e


data FileError e = FileError   FilePath e
                 | FileErrorTempFile
                     FilePath
                     -- ^ Target path
                     FilePath
                     -- ^ Temporary path
                     Handle
                 | FileIOError FilePath IOException
  deriving Int -> FileError e -> ShowS
[FileError e] -> ShowS
FileError e -> String
(Int -> FileError e -> ShowS)
-> (FileError e -> String)
-> ([FileError e] -> ShowS)
-> Show (FileError e)
forall e. Show e => Int -> FileError e -> ShowS
forall e. Show e => [FileError e] -> ShowS
forall e. Show e => FileError e -> String
forall a.
(Int -> a -> ShowS) -> (a -> String) -> ([a] -> ShowS) -> Show a
showList :: [FileError e] -> ShowS
$cshowList :: forall e. Show e => [FileError e] -> ShowS
show :: FileError e -> String
$cshow :: forall e. Show e => FileError e -> String
showsPrec :: Int -> FileError e -> ShowS
$cshowsPrec :: forall e. Show e => Int -> FileError e -> ShowS
Show

instance Error e => Error (FileError e) where
  displayError :: FileError e -> String
displayError (FileErrorTempFile String
targetPath String
tempPath Handle
h)=
    String
"Error creating temporary file at: " String -> ShowS
forall a. [a] -> [a] -> [a]
++ String
tempPath String -> ShowS
forall a. [a] -> [a] -> [a]
++
    String
"/n" String -> ShowS
forall a. [a] -> [a] -> [a]
++ String
"Target path: " String -> ShowS
forall a. [a] -> [a] -> [a]
++ String
targetPath String -> ShowS
forall a. [a] -> [a] -> [a]
++
    String
"/n" String -> ShowS
forall a. [a] -> [a] -> [a]
++ String
"Handle: " String -> ShowS
forall a. [a] -> [a] -> [a]
++ Handle -> String
forall a. Show a => a -> String
show Handle
h
  displayError (FileIOError String
path IOException
ioe) =
    String
path String -> ShowS
forall a. [a] -> [a] -> [a]
++ String
": " String -> ShowS
forall a. [a] -> [a] -> [a]
++ IOException -> String
forall e. Exception e => e -> String
displayException IOException
ioe
  displayError (FileError String
path e
e) =
    String
path String -> ShowS
forall a. [a] -> [a] -> [a]
++ String
": " String -> ShowS
forall a. [a] -> [a] -> [a]
++ e -> String
forall e. Error e => e -> String
displayError e
e