{-# LANGUAGE OverloadedStrings #-}

module Network.HTTP.Date.Parser (parseHTTPDate) where

import Control.Applicative
import Control.Monad
import Data.Attoparsec.ByteString
import Data.Attoparsec.ByteString.Char8
import Data.ByteString
import Data.Char
import Network.HTTP.Date.Types

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

-- |
-- Parsing HTTP Date. Currently only RFC1123 style is supported.
--
-- >>> parseHTTPDate "Tue, 15 Nov 1994 08:12:31 GMT"
-- Just (HTTPDate {hdYear = 1994, hdMonth = 11, hdDay = 15, hdHour = 8, hdMinute = 12, hdSecond = 31, hdWkday = 2})

parseHTTPDate :: ByteString -> Maybe HTTPDate
parseHTTPDate :: ByteString -> Maybe HTTPDate
parseHTTPDate ByteString
bs = case Parser HTTPDate -> ByteString -> Either String HTTPDate
forall a. Parser a -> ByteString -> Either String a
parseOnly Parser HTTPDate
rfc1123Date ByteString
bs of
    Right HTTPDate
ut -> HTTPDate -> Maybe HTTPDate
forall a. a -> Maybe a
Just HTTPDate
ut
    Either String HTTPDate
_        -> Maybe HTTPDate
forall a. Maybe a
Nothing

rfc1123Date :: Parser HTTPDate
rfc1123Date :: Parser HTTPDate
rfc1123Date = do
    w <- Parser Int
wkday
    void $ string ", "
    (y,m,d) <- date1
    sp
    (h,n,s) <- time
    sp
    -- RFC 2616 defines GMT only but there are actually ill-formed ones such 
    -- as "+0000" and "UTC" in the wild.
    void $ string "GMT" <|> string "+0000" <|> string "UTC"
    return $ defaultHTTPDate {
        hdYear   = y
      , hdMonth  = m
      , hdDay    = d
      , hdHour   = h
      , hdMinute = n
      , hdSecond = s
      , hdWkday  = w
      }

wkday :: Parser Int
wkday :: Parser Int
wkday = Int
1 Int -> Parser ByteString ByteString -> Parser Int
forall a b. a -> Parser ByteString b -> Parser ByteString a
forall (f :: * -> *) a b. Functor f => a -> f b -> f a
<$ ByteString -> Parser ByteString ByteString
string ByteString
"Mon"
    Parser Int -> Parser Int -> Parser Int
forall a.
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<|> Int
2 Int -> Parser ByteString ByteString -> Parser Int
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<$ ByteString -> Parser ByteString ByteString
string ByteString
"Tue"
    Parser Int -> Parser Int -> Parser Int
forall a.
Parser ByteString a -> Parser ByteString a -> Parser ByteString a
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<|> Int
3 Int -> Parser ByteString ByteString -> Parser Int
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string ByteString
"Wed"
    Parser Int -> Parser Int -> Parser Int
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<|> Int
4 Int -> Parser ByteString ByteString -> Parser Int
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string ByteString
"Thu"
    Parser Int -> Parser Int -> Parser Int
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5 Int -> Parser ByteString ByteString -> Parser Int
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string ByteString
"Fri"
    Parser Int -> Parser Int -> Parser Int
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6 Int -> Parser ByteString ByteString -> Parser Int
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string ByteString
"Sat"
    Parser Int -> Parser Int -> Parser Int
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Parser ByteString a -> Parser ByteString a -> Parser ByteString a
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<|> Int
7 Int -> Parser ByteString ByteString -> Parser Int
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forall (f :: * -> *) a b. Functor f => a -> f b -> f a
<$ ByteString -> Parser ByteString ByteString
string ByteString
"Sun"

date1 :: Parser (Int,Int,Int)
date1 :: Parser (Int, Int, Int)
date1 = do
    d <- Parser Int
day
    sp
    m <- month
    sp
    y <- year
    return (y,m,d)
 where
   day :: Parser Int
day = Parser Int
digit2
   year :: Parser Int
year = Parser Int
digit4

sp :: Parser ()
sp :: Parser ByteString ()
sp = () () -> Parser ByteString Char -> Parser ByteString ()
forall a b. a -> Parser ByteString b -> Parser ByteString a
forall (f :: * -> *) a b. Functor f => a -> f b -> f a
<$ Char -> Parser ByteString Char
char Char
' '

time :: Parser (Int,Int,Int)
time :: Parser (Int, Int, Int)
time = do
    h <- Parser Int
digit2
    void $ char ':'
    m <- digit2
    void $ char ':'
    s <- digit2
    return (h,m,s)

month :: Parser Int
month :: Parser Int
month =  Int
1 Int -> Parser ByteString ByteString -> Parser Int
forall a b. a -> Parser ByteString b -> Parser ByteString a
forall (f :: * -> *) a b. Functor f => a -> f b -> f a
<$ ByteString -> Parser ByteString ByteString
string ByteString
"Jan"
    Parser Int -> Parser Int -> Parser Int
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<|>  Int
2 Int -> Parser ByteString ByteString -> Parser Int
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string ByteString
"Feb"
    Parser Int -> Parser Int -> Parser Int
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3 Int -> Parser ByteString ByteString -> Parser Int
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string ByteString
"Mar"
    Parser Int -> Parser Int -> Parser Int
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4 Int -> Parser ByteString ByteString -> Parser Int
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string ByteString
"Apr"
    Parser Int -> Parser Int -> Parser Int
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5 Int -> Parser ByteString ByteString -> Parser Int
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"May"
    Parser Int -> Parser Int -> Parser Int
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6 Int -> Parser ByteString ByteString -> Parser Int
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"Jun"
    Parser Int -> Parser Int -> Parser Int
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"Jul"
    Parser Int -> Parser Int -> Parser Int
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"Aug"
    Parser Int -> Parser Int -> Parser Int
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string ByteString
"Sep"
    Parser Int -> Parser Int -> Parser Int
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<|> Int
10 Int -> Parser ByteString ByteString -> Parser Int
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"Oct"
    Parser Int -> Parser Int -> Parser Int
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11 Int -> Parser ByteString ByteString -> Parser Int
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string ByteString
"Nov"
    Parser Int -> Parser Int -> Parser Int
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Parser ByteString a -> Parser ByteString a -> Parser ByteString a
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<|> Int
12 Int -> Parser ByteString ByteString -> Parser Int
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<$ ByteString -> Parser ByteString ByteString
string ByteString
"Dec"

digit2 :: Parser Int
digit2 :: Parser Int
digit2 = do
    x1 <- Char -> Int
toInt (Char -> Int) -> Parser ByteString Char -> Parser Int
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> Parser ByteString Char
digit
    x2 <- toInt <$> digit
    return $ x1 * 10 + x2

digit4 :: Parser Int
digit4 :: Parser Int
digit4 = do
    x1 <- Char -> Int
toInt (Char -> Int) -> Parser ByteString Char -> Parser Int
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> Parser ByteString Char
digit
    x2 <- toInt <$> digit
    x3 <- toInt <$> digit
    x4 <- toInt <$> digit
    return $ x1 * 1000 + x2 * 100 + x3 * 10 + x4

toInt :: Char -> Int
toInt :: Char -> Int
toInt Char
c = Char -> Int
ord Char
c Int -> Int -> Int
forall a. Num a => a -> a -> a
- Char -> Int
ord Char
'0'