{-# LANGUAGE
    BangPatterns
  , OverloadedStrings
  , UnicodeSyntax
  #-}
-- |This is an auxiliary parser utilities for parsing things related
-- on HTTP protocol.
--
-- In general you don't have to use this module directly.
module Network.HTTP.Lucu.Parser.Http
    ( isCtl
    , isText
    , isSeparator
    , isChar
    , isToken
    , isSPHT

    , listOf

    , crlf
    , sp
    , lws

    , token
    , separators
    , quotedStr
    , qvalue

    , atMost
    )
    where
import Control.Applicative
import Control.Applicative.Unicode
import Control.Monad.Unicode
import Data.Ascii (Ascii)
import qualified Data.Ascii as A
import Data.Attoparsec.Char8 as P
import qualified Data.Attoparsec.FastSet as FS
import qualified Data.ByteString.Char8 as BS
import Prelude.Unicode

-- |@'isCtl' c@ is 'Prelude.False' iff @0x20 <= c < 0x7F@.
isCtl ∷ Char → Bool
{-# INLINE isCtl #-}
isCtl c
    | c ≤ '\x1f' = True
    | c > '\x7f' = True
    | otherwise  = False

-- |@'isText'@ is equivalent to @'not' '.' 'isCtl'@
isText ∷ Char → Bool
{-# INLINE isText #-}
isText = (¬) ∘ isCtl

-- |@'isSeparator' c@ is 'Prelude.True' iff c is one of HTTP
-- separators.
isSeparator ∷ Char → Bool
{-# INLINE isSeparator #-}
isSeparator = flip FS.memberChar set
    where
      {-# NOINLINE set #-}
      set = FS.charClass "()<>@,;:\\\"/[]?={}\x20\x09"

-- |@'isChar' c@ is 'Prelude.True' iff @c <= 0x7f@.
isChar ∷ Char → Bool
{-# INLINE isChar #-}
isChar = (≤ '\x7F')

-- |@'isToken' c@ is equivalent to @not ('isCtl' c || 'isSeparator'
-- c)@
isToken ∷ Char → Bool
{-# INLINE isToken #-}
isToken !c
    = (¬) (isCtl c ∨ isSeparator c)

-- |@'listOf' p@ is similar to @'sepBy' p ('char' \',\')@ but it
-- allows any occurrences of 'lws' before and after each tokens.
listOf ∷ Parser a → Parser [a]
{-# INLINEABLE listOf #-}
listOf p
    = try $
      do skipMany lws
         sepBy p $ do skipMany lws
                      _ <- char ','
                      skipMany lws

-- |'token' is similar to @'takeWhile1' 'isToken'@
token ∷ Parser Ascii
{-# INLINE token #-}
token = A.unsafeFromByteString <$> takeWhile1 isToken

-- |The CRLF: 0x0D 0x0A.
crlf ∷ Parser ()
{-# INLINE crlf #-}
crlf = string "\x0D\x0A" ≫ return ()

-- |The SP: 0x20.
sp ∷ Parser ()
{-# INLINE sp #-}
sp = char '\x20' ≫ return ()

-- |HTTP LWS: crlf? (sp | ht)+
lws ∷ Parser ()
{-# INLINEABLE lws #-}
lws = try $
      do option () crlf
         _ ← satisfy isSPHT
         skipWhile isSPHT

-- |Returns 'True' for SP and HT.
isSPHT ∷ Char → Bool
{-# INLINE isSPHT #-}
isSPHT '\x20' = True
isSPHT '\x09' = True
isSPHT _      = False

-- |@'separators'@ is similar to @'takeWhile1' 'isSeparator'@.
separators ∷ Parser Ascii
{-# INLINE separators #-}
separators = A.unsafeFromByteString <$> takeWhile1 isSeparator

-- |'quotedStr' accepts a string surrounded by double quotation
-- marks. Quotes can be escaped by backslashes.
quotedStr ∷ Parser Ascii
{-# INLINEABLE quotedStr #-}
quotedStr = try $
            do _  ← char '"'
               xs ← P.many (qdtext <|> quotedPair)
               _  ← char '"'
               return $ A.unsafeFromByteString $ BS.pack xs
    where
      qdtext ∷ Parser Char
      {-# INLINE qdtext #-}
      qdtext = satisfy (\c → c ≢ '"' ∧ (¬) (isCtl c))

      quotedPair ∷ Parser Char
      {-# INLINE quotedPair #-}
      quotedPair = char '\\' ≫ satisfy isChar

-- |'qvalue' accepts a so-called qvalue.
qvalue ∷ Parser Double
{-# INLINEABLE qvalue #-}
qvalue = do x  ← char '0'
            xs ← option "" $
                 do y  ← char '.'
                    ys ← atMost 3 digit
                    return (y:ys)
            return $ read (x:xs)
         <|>
         do x  ← char '1'
            xs ← option "" $
                 do y  ← char '.'
                    ys ← atMost 3 (char '0')
                    return (y:ys)
            return $ read (x:xs)

-- |@'atMost' n v@ is like @'P.many' v@ but applies the given action
-- at most @n@ times.
atMost ∷ Alternative f ⇒ Int → f a → f [a]
{-# INLINE atMost #-}
atMost 0 _ = pure []
atMost n v = ( (:) <$> v ⊛ atMost (n-1) v )
             <|>
             pure []