{-# OPTIONS_GHC -Wwarn #-}
{-# LANGUAGE DeriveFunctor #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  Haddock.Interface.ParseModuleHeader
-- Copyright   :  (c) Simon Marlow 2006, Isaac Dupree 2009
-- License     :  BSD-like
--
-- Maintainer  :  haddock@projects.haskell.org
-- Stability   :  experimental
-- Portability :  portable
-----------------------------------------------------------------------------
module Haddock.Interface.ParseModuleHeader (parseModuleHeader) where

import Control.Applicative (Alternative (..))
import Control.Monad (ap)
import Data.Char
import GHC.Driver.Session
import Haddock.Parser
import Haddock.Types

-- -----------------------------------------------------------------------------
-- Parsing module headers

-- NB.  The headers must be given in the order Module, Description,
-- Copyright, License, Maintainer, Stability, Portability, except that
-- any or all may be omitted.
parseModuleHeader :: DynFlags -> Maybe Package -> String -> (HaddockModInfo NsRdrName, MDoc NsRdrName)
parseModuleHeader dflags pkgName str0 =
   let
      kvs :: [(String, String)]
      str1 :: String

      (kvs, str1) = maybe ([], str0) id $ runP fields str0

      -- trim whitespaces
      trim :: String -> String
      trim = dropWhile isSpace . reverse . dropWhile isSpace . reverse

      getKey :: String -> Maybe String
      getKey key = fmap trim (lookup key kvs)

      descriptionOpt = getKey "Description"
      copyrightOpt   = getKey "Copyright"
      licenseOpt     = getKey "License"
      licenceOpt     = getKey "Licence"
      spdxLicenceOpt = getKey "SPDX-License-Identifier"
      maintainerOpt  = getKey "Maintainer"
      stabilityOpt   = getKey "Stability"
      portabilityOpt = getKey "Portability"

   in (HaddockModInfo {
          hmi_description = parseString dflags <$> descriptionOpt,
          hmi_copyright = copyrightOpt,
          hmi_license = spdxLicenceOpt <|> licenseOpt <|> licenceOpt,
          hmi_maintainer = maintainerOpt,
          hmi_stability = stabilityOpt,
          hmi_portability = portabilityOpt,
          hmi_safety = Nothing,
          hmi_language = Nothing, -- set in LexParseRn
          hmi_extensions = [] -- also set in LexParseRn
          }, parseParas dflags pkgName str1)

-------------------------------------------------------------------------------
-- Small parser to parse module header.
-------------------------------------------------------------------------------

-- | The below is a small parser framework how we read keys.
--
-- all fields in the header are optional and have the form
--
-- [spaces1][field name][spaces] ":"
--    [text]"\n" ([spaces2][space][text]"\n" | [spaces]"\n")*
-- where each [spaces2] should have [spaces1] as a prefix.
--
-- Thus for the key "Description",
--
-- > Description : this is a
-- >    rather long
-- >
-- >    description
-- >
-- > The module comment starts here
--
-- the value will be "this is a .. description" and the rest will begin
-- at "The module comment".

-- | 'C' is a 'Char' carrying its column.
--
-- This let us make an indentation-aware parser, as we know current indentation.
-- by looking at the next character in the stream ('curInd').
--
-- Thus we can munch all spaces but only not-spaces which are indented.
--
data C = C {-# UNPACK #-} !Int Char

newtype P a = P { unP :: [C] -> Maybe ([C], a) }
  deriving Functor

instance Applicative P where
    pure x = P $ \s -> Just (s, x)
    (<*>)  = ap

instance Monad P where
    return = pure
    m >>= k = P $ \s0 -> do
        (s1, x) <- unP m s0
        unP (k x) s1

instance Alternative P where
    empty   = P $ \_ -> Nothing
    a <|> b = P $ \s -> unP a s <|> unP b s

runP :: P a -> String -> Maybe a
runP p input = fmap snd (unP p input')
  where
    input' = concat
        [ zipWith C [0..] l ++ [C (length l) '\n']
        | l <- lines input
        ]

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

curInd :: P Int
curInd = P $ \s -> Just . (,) s $ case s of
    []        -> 0
    C i _ : _ -> i

rest :: P String
rest = P $ \cs -> Just ([], [ c | C _ c <- cs ])

munch :: (Int -> Char -> Bool) -> P String
munch p = P $ \cs ->
    let (xs,ys) = takeWhileMaybe p' cs in Just (ys, xs)
  where
    p' (C i c)
        | p i c  = Just c
        | otherwise = Nothing

munch1 :: (Int -> Char -> Bool) -> P String
munch1 p = P $ \s -> case s of
    [] -> Nothing
    (c:cs) | Just c' <- p' c -> let (xs,ys) = takeWhileMaybe p' cs in Just (ys, c' : xs)
           | otherwise -> Nothing
  where
    p' (C i c)
        | p i c  = Just c
        | otherwise = Nothing

char :: Char -> P Char
char c = P $ \s -> case s of
    []                        -> Nothing
    (C _ c' : cs) | c == c'   -> Just (cs, c)
                  | otherwise -> Nothing

skipSpaces :: P ()
skipSpaces = P $ \cs -> Just (dropWhile (\(C _ c) -> isSpace c) cs, ())

takeWhileMaybe :: (a -> Maybe b) -> [a] -> ([b], [a])
takeWhileMaybe f = go where
    go xs0@[] = ([], xs0)
    go xs0@(x:xs) = case f x of
        Just y  -> let (ys, zs) = go xs in (y : ys, zs)
        Nothing -> ([], xs0)

-------------------------------------------------------------------------------
-- Fields
-------------------------------------------------------------------------------

field :: Int -> P (String, String)
field i = do
    fn <- munch1 $ \_ c -> isAlpha c || c == '-'
    skipSpaces
    _ <- char ':'
    skipSpaces
    val <- munch $ \j c -> isSpace c || j > i
    return (fn, val)

fields :: P ([(String, String)], String)
fields = do
    skipSpaces
    i  <- curInd
    fs <- many (field i)
    r  <- rest
    return (fs, r)

