    {-# LANGUAGE DeriveDataTypeable #-}
    {-# LANGUAGE FlexibleContexts, FlexibleInstances #-}
    {-# LANGUAGE TypeOperators #-}
    {-# LANGUAGE ScopedTypeVariables #-}
    -- | Vty supports a configuration file format and associated 'Config'
    -- data type. The 'Config' can be provided to 'mkVty' to customize the
    -- application's use of Vty.
    --
    -- Lines in config files that fail to parse are ignored. Later entries
    -- take precedence over earlier ones.
    --
    -- = Debug
    --
    -- == @debugLog@
    --
    -- Format:
    --
    -- @
    --  \"debugLog\" string
    -- @
    --
    -- The value of the environment variable @VTY_DEBUG_LOG@ is equivalent
    -- to a debugLog entry at the end of the last config file.
    --
    -- = Input Processing
    --
    -- == @map@
    --
    -- Format:
    --
    -- @
    --  \"map\" term string key modifier_list
    --  where
    --      key := KEsc | KChar Char | KBS ... (same as 'Key')
    --      modifier_list := \"[\" modifier+ \"]\"
    --      modifier := MShift | MCtrl | MMeta | MAlt
    --      term := "_" | string
    -- @
    --
    -- E.g., if the contents are
    --
    -- @
    --  map _       \"\\ESC[B\"    KUp   []
    --  map _       \"\\ESC[1;3B\" KDown [MAlt]
    --  map \"xterm\" \"\\ESC[D\"    KLeft []
    -- @
    --
    -- Then the bytes @\"\\ESC[B\"@ will result in the KUp event on all
    -- terminals. The bytes @\"\\ESC[1;3B\"@ will result in the event KDown
    -- with the MAlt modifier on all terminals. The bytes @\"\\ESC[D\"@ will
    -- result in the KLeft event when @TERM@ is @xterm@.
    --
    -- If a debug log is requested then vty will output the current input
    -- table to the log in the above format. A workflow for using this is
    -- to set @VTY_DEBUG_LOG@. Run the application. Check the debug log for
    -- incorrect mappings. Add corrected mappings to @$HOME/.vty/config@.
    module Graphics.Vty.Config
      ( InputMap
      , Config(..)
      , VtyConfigurationError(..)
      , userConfig
      , overrideEnvConfig
      , standardIOConfig
      , runParseConfig
      , parseConfigFile
      , defaultConfig
      )
    where

    import Prelude

    import Control.Applicative hiding (many)

    import Control.Exception (catch, IOException, Exception(..), throwIO)
    import Control.Monad (liftM, guard, void)

    import qualified Data.ByteString as BS
    import Data.Monoid
    import Data.Typeable (Typeable)

    import Graphics.Vty.Input.Events

    import GHC.Generics

    import System.Directory (getAppUserDataDirectory)
    import System.Posix.Env (getEnv)
    import System.Posix.IO (stdInput, stdOutput)
    import System.Posix.Types (Fd(..))

    import Text.Parsec hiding ((<|>))
    import Text.Parsec.Token ( GenLanguageDef(..) )
    import qualified Text.Parsec.Token as P

    -- | Type of errors that can be thrown when configuring VTY
    data VtyConfigurationError
      = VtyMissingTermEnvVar -- ^ TERM environment variable not set
      deriving (Show, Eq, Typeable)

    instance Exception VtyConfigurationError where
      displayException VtyMissingTermEnvVar = "TERM environment variable not set"

    -- | Mappings from input bytes to event in the order specified. Later
    -- entries take precedence over earlier in the case multiple entries
    -- have the same byte string.
    type InputMap = [(Maybe String, String, Event)]

    -- | A Vty configuration.
    data Config = Config
        {
        -- | The default is 1 character.
          vmin  :: Maybe Int
        -- | The default is 100 milliseconds, 0.1 seconds.
        , vtime :: Maybe Int
        -- | The default is False.
        , mouseMode :: Maybe Bool
        -- | The default is False.
        , bracketedPasteMode :: Maybe Bool
        -- | Debug information is appended to this file if not Nothing.
        , debugLog           :: Maybe FilePath
        -- | The (input byte, output event) pairs extend the internal input
        -- table of VTY and the table from terminfo.
        --
        -- See "Graphics.Vty.Config" module documentation for documentation
        -- of the @map@ directive.
        , inputMap           :: InputMap
        -- | The input file descriptor to use. The default is
        -- 'System.Posix.IO.stdInput'
        , inputFd           :: Maybe Fd
        -- | The output file descriptor to use. The default is
        -- 'System.Posix.IO.stdOutput'
        , outputFd          :: Maybe Fd
        -- | The terminal name used to look up terminfo capabilities.
        -- The default is the value of the TERM environment variable.
        , termName           :: Maybe String
        } deriving (Show, Eq)

    defaultConfig :: Config
    defaultConfig = mempty

    instance Monoid Config where
        mempty = Config
            { vmin         = Nothing
            , vtime        = Nothing
            , mouseMode    = Nothing
            , bracketedPasteMode = Nothing
            , debugLog     = mempty
            , inputMap     = mempty
            , inputFd     = Nothing
            , outputFd    = Nothing
            , termName     = Nothing
            }
        mappend c0 c1 = Config
            -- latter config takes priority for everything but inputMap
            { vmin          = vmin c1     <|> vmin c0
            , vtime         = vtime c1    <|> vtime c0
            , mouseMode     = mouseMode c1
            , bracketedPasteMode = bracketedPasteMode c1
            , debugLog      = debugLog c1 <|> debugLog c0
            , inputMap      = inputMap c0 <>  inputMap c1
            , inputFd      = inputFd c1 <|> inputFd c0
            , outputFd     = outputFd c1 <|> outputFd c0
            , termName      = termName c1 <|> termName c0
            }

    -- | Load a configuration from @'getAppUserDataDirectory'/config@ and
    -- @$VTY_CONFIG_FILE@.
    userConfig :: IO Config
    userConfig = do
        configFile <- (mappend <$> getAppUserDataDirectory "vty" <*> pure "/config") >>= parseConfigFile
        overrideConfig <- maybe (return defaultConfig) parseConfigFile =<< getEnv "VTY_CONFIG_FILE"
        let base = configFile <> overrideConfig
        mappend base <$> overrideEnvConfig

    overrideEnvConfig :: IO Config
    overrideEnvConfig = do
        d <- getEnv "VTY_DEBUG_LOG"
        return $ defaultConfig { debugLog = d }

    -- | Configures VTY using defaults suitable for terminals. This function
    -- can raise 'VtyConfigurationError'.
    standardIOConfig :: IO Config
    standardIOConfig = do
        mb <- getEnv "TERM"
        case mb of
          Nothing -> throwIO VtyMissingTermEnvVar
          Just t ->
            return defaultConfig
              { vmin               = Just 1
              , mouseMode          = Just False
              , bracketedPasteMode = Just False
              , vtime              = Just 100
              , inputFd            = Just stdInput
              , outputFd           = Just stdOutput
              , termName           = Just t
              }

    parseConfigFile :: FilePath -> IO Config
    parseConfigFile path = do
        catch (runParseConfig path <$> BS.readFile path)
              (\(_ :: IOException) -> return defaultConfig)

    runParseConfig :: String -> BS.ByteString -> Config
    runParseConfig name cfgTxt =
      case runParser parseConfig () name cfgTxt of
        Right cfg -> cfg
        Left{}    -> defaultConfig

    ------------------------------------------------------------------------

    type Parser = Parsec BS.ByteString ()

    configLanguage :: Monad m => P.GenLanguageDef BS.ByteString () m
    configLanguage = LanguageDef
        { commentStart    = "{-"
        , commentEnd      = "-}"
        , commentLine     = "--"
        , nestedComments  = True
        , identStart      = letter <|> char '_'
        , identLetter     = alphaNum <|> oneOf "_'"
        , opStart         = opLetter configLanguage
        , opLetter        = oneOf ":!#$%&*+./<=>?@\\^|-~"
        , reservedOpNames = []
        , reservedNames   = []
        , caseSensitive   = True
        }

    configLexer :: Monad m => P.GenTokenParser BS.ByteString () m
    configLexer = P.makeTokenParser configLanguage

    mapDecl :: Parser Config
    mapDecl = do
        "map" <- P.identifier configLexer
        termIdent <- (char '_' >> P.whiteSpace configLexer >> return Nothing)
                 <|> (Just <$> P.stringLiteral configLexer)
        bytes     <- P.stringLiteral configLexer
        key       <- parseValue
        modifiers <- parseValue
        return defaultConfig { inputMap = [(termIdent, bytes, EvKey key modifiers)] }

    debugLogDecl :: Parser Config
    debugLogDecl = do
        "debugLog" <- P.identifier configLexer
        path       <- P.stringLiteral configLexer
        return defaultConfig { debugLog = Just path }

    ignoreLine :: Parser ()
    ignoreLine = void $ manyTill anyChar newline

    parseConfig :: Parser Config
    parseConfig = liftM mconcat $ many $ do
        P.whiteSpace configLexer
        let directives = [try mapDecl, try debugLogDecl]
        choice directives <|> (ignoreLine >> return defaultConfig)

    class    Parse a        where parseValue :: Parser a
    instance Parse Char     where parseValue = P.charLiteral configLexer
    instance Parse Int      where parseValue = fromInteger <$> P.natural configLexer
    instance Parse Key      where parseValue = genericParse
    instance Parse Modifier where parseValue = genericParse
    instance Parse a => Parse [a] where
      parseValue = P.brackets configLexer
                     (parseValue `sepBy` P.symbol configLexer ",")

    ------------------------------------------------------------------------
    -- Derived parser for ADTs via generics
    ------------------------------------------------------------------------

    genericParse :: (Generic a, GParse (Rep a)) => Parser a
    genericParse = to <$> gparse

    class    GParse f                      where gparse :: Parser (f a)
    instance GParse f => GParse (M1 S i f) where gparse = M1 <$> gparse
    instance GParse U1                     where gparse = return U1
    instance Parse a => GParse (K1 i a)    where gparse = K1 <$> parseValue

    instance (GParse f, GParse g) => GParse (f :*: g) where
      gparse = (:*:) <$> gparse <*> gparse

    instance GParseAlts f => GParse (M1 D i f) where
      gparse =
        do con <- P.identifier configLexer
           M1 <$> gparseAlts con

    ------------------------------------------------------------------------

    class GParseAlts f where
      gparseAlts :: String -> Parser (f a)

    instance (Constructor i, GParse f) => GParseAlts (M1 C i f) where
      gparseAlts con =
        do guard (con == conName (M1 Nothing :: C1 i Maybe a))
           M1 <$> gparse

    instance (GParseAlts f, GParseAlts g) => GParseAlts (f :+: g) where
      gparseAlts con = L1 <$> gparseAlts con <|> R1 <$> gparseAlts con

    instance GParseAlts V1 where gparseAlts _ = fail "GParse: V1"