{-# LANGUAGE OverloadedStrings, CPP #-}
module Network.HTTP.Types.URI
(
  -- * Query string
  QueryItem
, Query
, SimpleQueryItem
, SimpleQuery
, simpleQueryToQuery
, renderQuery
, renderQueryBuilder
, renderSimpleQuery
, parseQuery
, parseSimpleQuery
  -- ** Text query string (UTF8 encoded)
, QueryText
, queryTextToQuery
, queryToQueryText
, renderQueryText
, parseQueryText
  -- * Path segments
, encodePathSegments
, decodePathSegments
, encodePathSegmentsRelative
  -- * Path (segments + query string)
, extractPath
, encodePath
, decodePath
  -- * URL encoding / decoding
, urlEncodeBuilder
, urlEncode
, urlDecode
)
where

import           Control.Arrow
import           Data.Bits
import           Data.Char
import           Data.List
import           Data.Maybe
#if __GLASGOW_HASKELL__ < 710
import           Data.Monoid
#endif
import           Data.Text                      (Text)
import           Data.Text.Encoding             (encodeUtf8, decodeUtf8With)
import           Data.Text.Encoding.Error       (lenientDecode)
import           Data.Word
import qualified Blaze.ByteString.Builder       as Blaze
import qualified Data.ByteString                as B
import           Data.ByteString.Char8          () {-IsString-}

-- | Query item
type QueryItem = (B.ByteString, Maybe B.ByteString)

-- | Query.
-- 
-- General form: a=b&c=d, but if the value is Nothing, it becomes
-- a&c=d.
type Query = [QueryItem]

-- | Like Query, but with 'Text' instead of 'B.ByteString' (UTF8-encoded).
type QueryText = [(Text, Maybe Text)]

-- | Convert 'QueryText' to 'Query'.
queryTextToQuery :: QueryText -> Query
queryTextToQuery = map $ encodeUtf8 *** fmap encodeUtf8

-- | Convert 'QueryText' to a 'Blaze.Builder'.
renderQueryText :: Bool -- ^ prepend a question mark?
                -> QueryText
                -> Blaze.Builder
renderQueryText b = renderQueryBuilder b . queryTextToQuery

-- | Convert 'Query' to 'QueryText' (leniently decoding the UTF-8).
queryToQueryText :: Query -> QueryText
queryToQueryText =
    map $ go *** fmap go
  where
    go = decodeUtf8With lenientDecode

-- | Parse 'QueryText' from a 'B.ByteString'. See 'parseQuery' for details.
parseQueryText :: B.ByteString -> QueryText
parseQueryText = queryToQueryText . parseQuery

-- | Simplified Query item type without support for parameter-less items.
type SimpleQueryItem = (B.ByteString, B.ByteString)

-- | Simplified Query type without support for parameter-less items.
type SimpleQuery = [SimpleQueryItem]

-- | Convert 'SimpleQuery' to 'Query'.
simpleQueryToQuery :: SimpleQuery -> Query
simpleQueryToQuery = map (\(a, b) -> (a, Just b))

-- | Convert 'Query' to a 'Builder'.
renderQueryBuilder :: Bool -- ^ prepend a question mark?
                   -> Query
                   -> Blaze.Builder
renderQueryBuilder _ [] = mempty
-- FIXME replace mconcat + map with foldr
renderQueryBuilder qmark' (p:ps) = mconcat
    $ go (if qmark' then qmark else mempty) p
    : map (go amp) ps
  where
    qmark = Blaze.copyByteString "?"
    amp = Blaze.copyByteString "&"
    equal = Blaze.copyByteString "="
    go sep (k, mv) = mconcat [
                      sep
                     , urlEncodeBuilder True k
                     , case mv of
                         Nothing -> mempty
                         Just v -> equal `mappend` urlEncodeBuilder True v
                     ]

-- | Convert 'Query' to 'ByteString'.
renderQuery :: Bool -- ^ prepend question mark?
            -> Query -> B.ByteString
renderQuery qm = Blaze.toByteString . renderQueryBuilder qm

-- | Convert 'SimpleQuery' to 'ByteString'.
renderSimpleQuery :: Bool -- ^ prepend question mark?
                  -> SimpleQuery -> B.ByteString
renderSimpleQuery useQuestionMark = renderQuery useQuestionMark . simpleQueryToQuery

-- | Split out the query string into a list of keys and values. A few
-- importants points:
-- 
-- * The result returned is still bytestrings, since we perform no character
-- decoding here. Most likely, you will want to use UTF-8 decoding, but this is
-- left to the user of the library.
-- 
-- * Percent decoding errors are ignored. In particular, "%Q" will be output as
-- "%Q".
parseQuery :: B.ByteString -> Query
parseQuery = parseQueryString' . dropQuestion
  where
    dropQuestion q =
        case B.uncons q of
            Just (63, q') -> q'
            _ -> q
    parseQueryString' q | B.null q = []
    parseQueryString' q =
        let (x, xs) = breakDiscard queryStringSeparators q
         in parsePair x : parseQueryString' xs
      where
        parsePair x =
            let (k, v) = B.breakByte 61 x -- equal sign
                v'' =
                    case B.uncons v of
                        Just (_, v') -> Just $ urlDecode True v'
                        _ -> Nothing
             in (urlDecode True k, v'')

queryStringSeparators :: B.ByteString
queryStringSeparators = B.pack [38,59] -- ampersand, semicolon

-- | Break the second bytestring at the first occurence of any bytes from
-- the first bytestring, discarding that byte.
breakDiscard :: B.ByteString -> B.ByteString -> (B.ByteString, B.ByteString)
breakDiscard seps s =
    let (x, y) = B.break (`B.elem` seps) s
     in (x, B.drop 1 y)

-- | Parse 'SimpleQuery' from a 'ByteString'.
parseSimpleQuery :: B.ByteString -> SimpleQuery
parseSimpleQuery = map (second $ fromMaybe B.empty) . parseQuery

ord8 :: Char -> Word8
ord8 = fromIntegral . ord

unreservedQS, unreservedPI :: [Word8]
unreservedQS = map ord8 "-_.~"
unreservedPI = map ord8 "-_.~:@&=+$,"

-- | Percent-encoding for URLs.
urlEncodeBuilder' :: [Word8] -> B.ByteString -> Blaze.Builder
urlEncodeBuilder' extraUnreserved = mconcat . map encodeChar . B.unpack
    where
      encodeChar ch | unreserved ch = Blaze.fromWord8 ch
                    | otherwise     = h2 ch
      
      unreserved ch | ch >= 65 && ch <= 90  = True -- A-Z
                    | ch >= 97 && ch <= 122 = True -- a-z
                    | ch >= 48 && ch <= 57  = True -- 0-9
      unreserved c = c `elem` extraUnreserved
      
      h2 v = let (a, b) = v `divMod` 16 in Blaze.fromWord8s [37, h a, h b] -- percent (%)
      h i | i < 10    = 48 + i -- zero (0)
          | otherwise = 65 + i - 10 -- 65: A

-- | Percent-encoding for URLs (using 'Blaze.Builder').
urlEncodeBuilder
    :: Bool -- ^ Whether input is in query string. True: Query string, False: Path element
    -> B.ByteString
    -> Blaze.Builder
urlEncodeBuilder True  = urlEncodeBuilder' unreservedQS
urlEncodeBuilder False = urlEncodeBuilder' unreservedPI

-- | Percent-encoding for URLs.
urlEncode :: Bool -- ^ Whether to decode '+' to ' '
          -> B.ByteString -- ^ The ByteString to encode as URL
          -> B.ByteString -- ^ The encoded URL
urlEncode q = Blaze.toByteString . urlEncodeBuilder q

-- | Percent-decoding.
urlDecode :: Bool -- ^ Whether to decode '+' to ' '
          -> B.ByteString -> B.ByteString
urlDecode replacePlus z = fst $ B.unfoldrN (B.length z) go z
  where
    go bs =
        case B.uncons bs of
            Nothing -> Nothing
            Just (43, ws) | replacePlus -> Just (32, ws) -- plus to space
            Just (37, ws) -> Just $ fromMaybe (37, ws) $ do -- percent
                (x, xs) <- B.uncons ws
                x' <- hexVal x
                (y, ys) <- B.uncons xs
                y' <- hexVal y
                Just (combine x' y', ys)
            Just (w, ws) -> Just (w, ws)
    hexVal w
        | 48 <= w && w <= 57  = Just $ w - 48 -- 0 - 9
        | 65 <= w && w <= 70  = Just $ w - 55 -- A - F
        | 97 <= w && w <= 102 = Just $ w - 87 -- a - f
        | otherwise = Nothing
    combine :: Word8 -> Word8 -> Word8
    combine a b = shiftL a 4 .|. b

-- | Encodes a list of path segments into a valid URL fragment.
-- 
-- This function takes the following three steps:
-- 
-- * UTF-8 encodes the characters.
-- 
-- * Performs percent encoding on all unreserved characters, as well as \:\@\=\+\$,
-- 
-- * Prepends each segment with a slash.
-- 
-- For example:
-- 
-- > encodePathSegments [\"foo\", \"bar\", \"baz\"]
-- 
-- \"\/foo\/bar\/baz\"
-- 
-- > encodePathSegments [\"foo bar\", \"baz\/bin\"]
-- 
-- \"\/foo\%20bar\/baz\%2Fbin\"
-- 
-- > encodePathSegments [\"שלום\"]
-- 
-- \"\/%D7%A9%D7%9C%D7%95%D7%9D\"
-- 
-- Huge thanks to Jeremy Shaw who created the original implementation of this
-- function in web-routes and did such thorough research to determine all
-- correct escaping procedures.
encodePathSegments :: [Text] -> Blaze.Builder
encodePathSegments [] = mempty
encodePathSegments (x:xs) =
    Blaze.copyByteString "/"
    `mappend` encodePathSegment x
    `mappend` encodePathSegments xs

-- | Like encodePathSegments, but without the initial slash.
encodePathSegmentsRelative :: [Text] -> Blaze.Builder
encodePathSegmentsRelative xs = mconcat $ intersperse (Blaze.copyByteString "/") (map encodePathSegment xs)

encodePathSegment :: Text -> Blaze.Builder
encodePathSegment = urlEncodeBuilder False . encodeUtf8

-- | Parse a list of path segments from a valid URL fragment.
decodePathSegments :: B.ByteString -> [Text]
decodePathSegments "" = []
decodePathSegments "/" = []
decodePathSegments a =
    go $ drop1Slash a
  where
    drop1Slash bs =
        case B.uncons bs of
            Just (47, bs') -> bs' -- 47 == /
            _ -> bs
    go bs =
        let (x, y) = B.breakByte 47 bs
         in decodePathSegment x :
            if B.null y
                then []
                else go $ B.drop 1 y

decodePathSegment :: B.ByteString -> Text
decodePathSegment = decodeUtf8With lenientDecode . urlDecode False

-- | Extract whole path (path segments + query) from a
-- <http://tools.ietf.org/html/rfc2616#section-5.1.2 RFC 2616 Request-URI>.
--
-- >>> extractPath "/path"
-- "/path"
--
-- >>> extractPath "http://example.com:8080/path"
-- "/path"
--
-- >>> extractPath "http://example.com"
-- "/"
--
-- >>> extractPath ""
-- "/"
extractPath :: B.ByteString -> B.ByteString
extractPath = ensureNonEmpty . extract
  where
    extract path
      | "http://"  `B.isPrefixOf` path = (snd . breakOnSlash . B.drop 7) path
      | "https://" `B.isPrefixOf` path = (snd . breakOnSlash . B.drop 8) path
      | otherwise                      = path
    breakOnSlash = B.breakByte 47
    ensureNonEmpty "" = "/"
    ensureNonEmpty p  = p

-- | Encode a whole path (path segments + query).
encodePath :: [Text] -> Query -> Blaze.Builder
encodePath x [] = encodePathSegments x
encodePath x y = encodePathSegments x `mappend` renderQueryBuilder True y

-- | Decode a whole path (path segments + query).
decodePath :: B.ByteString -> ([Text], Query)
decodePath b =
    let (x, y) = B.breakByte 63 b -- question mark
    in (decodePathSegments x, parseQuery y)
