-----------------------------------------------------------------------------------------
-- A Haskell port of GNU's getopt library
--
-- Sven Panne <Sven.Panne@informatik.uni-muenchen.de> Oct. 1996; last change: Jul. 1998
--
-- Two rather obscure features are missing: The Bash 2.0 non-option hack (if you don't
-- already know it, you probably don't want to hear about it...) and the recognition of
-- long options with a single dash (e.g. '-help' is recognised as '--help', as long as
-- there is no short option 'h').
--
-- Other differences between GNU's getopt and this implementation:
--    * To enforce a coherent description of options and arguments, there are explanation
--      fields in the option/argument descriptor.
--    * Error messages are now more informative, but no longer POSIX compliant... :-(
--
-- And a final Haskell advertisement: The GNU C implementation uses well over 1100 lines,
-- we need only 199 here, including a 46 line example! :-)
-----------------------------------------------------------------------------------------

module FST.GetOpt (
   ArgOrder(..), OptDescr(..), ArgDescr(..), usageInfo, getOpt
   ) where

import Data.List (isPrefixOf)

data ArgOrder a                        -- what to do with options following non-options:
   = RequireOrder                      --    no option processing after first non-option
   | Permute                           --    freely intersperse options and non-options
   | ReturnInOrder (String -> a)       --    wrap non-options into options

data OptDescr a =                      -- description of a single options:
   Option [Char]                       --    list of short option characters
          [String]                     --    list of long option strings (without "--")
          (ArgDescr a)                 --    argument descriptor
          String                       --    explanation of option for user

data ArgDescr a                        -- description of an argument option:
   = NoArg                   a         --    no argument expected
   | ReqArg (String       -> a) String --    option requires argument
   | OptArg (Maybe String -> a) String --    optional argument

data OptKind a                         -- kind of cmd line arg (internal use only):
   = Opt       a                       --    an option
   | NonOpt    String                  --    a non-option
   | EndOfOpts                         --    end-of-options marker (i.e. "--")
   | OptErr    String                  --    something went wrong...

usageInfo :: String                    -- header
          -> [OptDescr a]              -- option descriptors
          -> String                    -- nicely formatted decription of options
usageInfo header optDescr = unlines (header:table)
   where (ss,ls,ds)     = (unzip3 . map fmtOpt) optDescr
         table          = zipWith3 paste (sameLen ss) (sameLen ls) (sameLen ds)
         paste x y z    = "  " ++ x ++ "  " ++ y ++ "  " ++ z
         sameLen xs     = flushLeft ((maximum . map length) xs) xs
         flushLeft n xs = [ take n (x ++ repeat ' ') | x <- xs ]

fmtOpt :: OptDescr a -> (String,String,String)
fmtOpt (Option sos los ad descr) = (sepBy ", " (map (fmtShort ad) sos),
                                    sepBy ", " (map (fmtLong  ad) los),
                                    descr)
   where sepBy _   []     = ""
         sepBy _   [x]    = x
         sepBy sep (x:xs) = x ++ sep ++ sepBy sep xs

fmtShort :: ArgDescr a -> Char -> String
fmtShort (NoArg  _   ) so = "-" ++ [so]
fmtShort (ReqArg _ ad) so = "-" ++ [so] ++ " " ++ ad
fmtShort (OptArg _ ad) so = "-" ++ [so] ++ "[" ++ ad ++ "]"

fmtLong :: ArgDescr a -> String -> String
fmtLong (NoArg  _   ) lo = "--" ++ lo
fmtLong (ReqArg _ ad) lo = "--" ++ lo ++ "=" ++ ad
fmtLong (OptArg _ ad) lo = "--" ++ lo ++ "[=" ++ ad ++ "]"

getOpt :: ArgOrder a                   -- non-option handling
       -> [OptDescr a]                 -- option descriptors
       -> [String]                     -- the commandline arguments
       -> ([a],[String],[String])      -- (options,non-options,error messages)
getOpt _        _        []   =  ([],[],[])
getOpt ordering optDescr args = procNextOpt opt ordering
   where procNextOpt (Opt o)    _                 = (o:os,xs,es)
         procNextOpt (NonOpt x) RequireOrder      = ([],x:rest,[])
         procNextOpt (NonOpt x) Permute           = (os,x:xs,es)
         procNextOpt (NonOpt x) (ReturnInOrder f) = (f x :os, xs,es)
         procNextOpt EndOfOpts  RequireOrder      = ([],rest,[])
         procNextOpt EndOfOpts  Permute           = ([],rest,[])
         procNextOpt EndOfOpts  (ReturnInOrder f) = (map f rest,[],[])
         procNextOpt (OptErr e) _                 = (os,xs,e:es)

         (opt,rest) = getNext args optDescr
         (os,xs,es) = getOpt ordering optDescr rest

-- take a look at the next cmd line arg and decide what to do with it
getNext :: [String] -> [OptDescr a] -> (OptKind a,[String])
getNext (('-':'-':[]):rest) _        = (EndOfOpts,rest)
getNext (('-':'-':xs):rest) optDescr = longOpt xs rest optDescr
getNext (('-':x:xs)  :rest) optDescr = shortOpt x xs rest optDescr
getNext (a           :rest) _        = (NonOpt a,rest)
getNext []                  _        = error "getNext: impossible"

-- handle long option
longOpt :: String -> [String] -> [OptDescr a] -> (OptKind a,[String])
longOpt xs rest optDescr = long ads arg rest
   where (opt,arg) = break (=='=') xs
         options   = [ o  | o@(Option _ ls _ _) <- optDescr, l <- ls, opt `isPrefixOf` l ]
         ads       = [ ad | Option _ _ ad _ <- options ]
         optStr    = ("--"++opt)

         long (_:_:_)      _        rest1     = (errAmbig options optStr,rest1)
         long [NoArg  a  ] []       rest1     = (Opt a,rest1)
         long [NoArg  _  ] ('=':_)  rest1     = (errNoArg optStr,rest1)
         long [ReqArg _ d] []       []        = (errReq d optStr,[])
         long [ReqArg f _] []       (r:rest1) = (Opt (f r),rest1)
         long [ReqArg f _] ('=':ys) rest1     = (Opt (f ys),rest1)
         long [OptArg f _] []       rest1     = (Opt (f Nothing),rest1)
         long [OptArg f _] ('=':ys) rest1     = (Opt (f (Just ys)),rest1)
         long [_]          (_  :_)  _         = error "long: impossible"
         long []           _        rest1     = (errUnrec optStr,rest1)

-- handle short option
shortOpt :: Char -> String -> [String] -> [OptDescr a] -> (OptKind a,[String])
shortOpt x xs rest optDescr = short ads xs rest
  where options = [ o  | o@(Option ss _ _ _) <- optDescr, s <- ss, x == s ]
        ads     = [ ad | Option _ _ ad _ <- options ]
        optStr  = '-':[x]

        short (_:_:_)        _  rest1     = (errAmbig options optStr,rest1)
        short (NoArg  a  :_) [] rest1     = (Opt a,rest1)
        short (NoArg  a  :_) ys rest1     = (Opt a,('-':ys):rest1)
        short (ReqArg _ d:_) [] []        = (errReq d optStr,[])
        short (ReqArg f _:_) [] (r:rest1) = (Opt (f r),rest1)
        short (ReqArg f _:_) ys rest1     = (Opt (f ys),rest1)
        short (OptArg f _:_) [] rest1     = (Opt (f Nothing),rest1)
        short (OptArg f _:_) ys rest1     = (Opt (f (Just ys)),rest1)
        short []             [] rest1     = (errUnrec optStr,rest1)
        short []             ys rest1     = (errUnrec optStr,('-':ys):rest1)

-- miscellaneous error formatting

errAmbig :: [OptDescr a] -> String -> OptKind a
errAmbig ods optStr = OptErr (usageInfo header ods)
   where header = "option `" ++ optStr ++ "' is ambiguous; could be one of:"

errReq :: String -> String -> OptKind a
errReq d optStr = OptErr ("option `" ++ optStr ++ "' requires an argument " ++ d ++ "\n")

errUnrec :: String -> OptKind a
errUnrec optStr = OptErr ("unrecognized option `" ++ optStr ++ "'\n")

errNoArg :: String -> OptKind a
errNoArg optStr = OptErr ("option `" ++ optStr ++ "' doesn't allow an argument\n")