    {-# LANGUAGE CPP #-}
    module Mueval.ArgsParse (Options(..), interpreterOpts, getOptions) where

    import Control.Monad (liftM)
    import System.Console.GetOpt

    import Mueval.Context (defaultModules, defaultPackages)

    -- | See the results of --help for information on what each option means.
    data Options = Options
     { timeLimit :: Int
       , modules :: Maybe [String]
       , expression :: String
       , loadFile :: String
       , user :: String
       , printType :: Bool
       , typeOnly :: Bool
       , extensions :: Bool
       , namedExtensions :: [String]
       , noImports :: Bool
       , rLimits :: Bool
       , packageTrust :: Bool
       , trustedPackages :: [String]
       , help :: Bool
     } deriving Show

    defaultOptions :: Options
    defaultOptions = Options { expression = ""
                               , modules = Just defaultModules
                               , timeLimit = 5
                               , user = ""
                               , loadFile = ""
                               , printType = False
                               , typeOnly = False
                               , extensions = False
                               , namedExtensions = []
                               , noImports = False
                               , rLimits = False
                               , packageTrust = False
                               , trustedPackages = defaultPackages
                               , help = False }

    options :: [OptDescr (Options -> Options)]
    options = [Option "p"     ["password"]
                          (ReqArg (\u opts -> opts {user = u}) "PASSWORD")
                          "The password for the mubot account. If this is set, mueval will attempt to setuid to the mubot user. This is optional, as it requires the mubot user to be set up properly. (Currently a null-op.)",
               Option "t"     ["time-limit"]
                          (ReqArg (\t opts -> opts { timeLimit = read t :: Int }) "TIME")
                          "Time limit for compilation and evaluation",

               Option "l"     ["load-file"]
                          (ReqArg (\e opts -> opts { loadFile = e}) "FILE")
                          "A local file for Mueval to load, providing definitions. Contents are trusted! Do not put anything dubious in it!",

               Option "m"     ["module"]
                          (ReqArg (\m opts -> opts { modules = liftM (m:) (modules opts)}) "MODULE")
                          "A module we should import functions from for evaluation. (Can be given multiple times.)",
               Option "n"     ["no-imports"]
                          (NoArg (\opts -> opts { noImports = True}))
                          "Whether to import any default modules, such as Prelude; this is useful if you are loading a file which, say, redefines Prelude operators. This can be subverted by using --load-file.",
               Option "E"     ["Extensions"]
                          (NoArg (\opts -> opts { extensions = True}))
                          "Whether to enable the Glasgow extensions to Haskell '98. Defaults to false, but enabling is useful for QuickCheck.",
               Option "X"     ["extension"]
                          (ReqArg (\e opts -> opts { namedExtensions = e : namedExtensions opts }) "EXTENSION")
                          "Pass additional flags enabling extensions just like you would to ghc. Example: -XViewPatterns",
               Option "e"     ["expression"]
                          (ReqArg (\e opts -> opts { expression = e}) "EXPRESSION")
                          "The expression to be evaluated.",
               Option "i"     ["inferred-type"]
                          (NoArg (\opts -> opts { printType = True}))
                          "Whether to enable printing of inferred type and the expression (as Mueval sees it). Defaults to false.",
               Option "T"     ["type-only"]
                          (NoArg (\opts -> opts { typeOnly = True}))
                          "Only print the expression and type, don't evaluate the expression. Defaults to false.",
               Option "r"     ["resource-limits"]
                          (NoArg (\opts -> opts { rLimits = True}))
                          "Enable resource limits (using POSIX rlimits). Mueval does not by default since rlimits are broken on many systems.",
               Option "S"     ["package-trust"]
                          (NoArg (\opts -> opts {packageTrust = True, namedExtensions = "Safe" : namedExtensions opts}))
                          "Enable Safe-Haskell package trust system",
               Option "s"     ["trust"]
                          (ReqArg (\e opts -> opts {trustedPackages = e : trustedPackages opts}) "PACKAGE")
                          "Specify a package to be trusted by Safe Haskell (ignored unless -S also present)",
               Option "h" ["help"]
                           (NoArg (\opts -> opts { help = True}))
                           "Prints out usage info."
              ]

    interpreterOpts :: [String] -> Either (Bool, String) Options
    interpreterOpts argv
        | help opts = Left (True,msg)
        | not (null ers) = Left (False, concat ers ++ msg)
        | otherwise = Right opts
      where (o,_,ers) = getOpt Permute options argv
            msg = usageInfo header options
            opts = foldl (flip id) defaultOptions o

    header :: String
    header = "Usage: mueval [OPTION...] --expression EXPRESSION..."

    -- | Just give us the end result options; this parsing for
    --   us. Bonus points for handling UTF.
    getOptions :: [String] -> Either (Bool, String) Options
    getOptions = interpreterOpts . map decodeString

    decodeString :: String -> String
    #if __GLASGOW_HASKELL__ >= 702
    decodeString = id
    #else
    decodeString = Codec.decodeString
    #endif