{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE Rank2Types #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE AllowAmbiguousTypes #-}

module Data.ZRE (
    zreVer
  , newZRE
  , parseZRE
  , encodeZRE
  , zreBeacon
  , parseBeacon
  , Name
  , Headers
  , Content
  , Group
  , mkGroup
  , unGroup
  , Groups
  , Seq
  , GroupSeq
  , ZREMsg(..)
  , ZRECmd(..)
  , SymbolicGroup
  , KnownGroup
  , knownToGroup
  ) where

import Prelude hiding (putStrLn, take)
import Data.ByteString (ByteString)

import qualified Data.ByteString.Char8 as B
import qualified Data.ByteString.Lazy as BL

import GHC.Word

import Data.Map (Map)
import Data.Set (Set)

import qualified Data.Set

import Data.UUID
import Data.Time.Clock

import System.ZMQ4.Endpoint
import Data.ZMQParse

import GHC.TypeLits
import Data.Proxy

zreVer :: Int
zreVer = 2
zreSig :: Word16
zreSig = 0xAAA1

type Seq = Int
type GroupSeq = Int

type SymbolicGroup = Symbol
type KnownGroup = KnownSymbol

-- | Convert from symbolic "KnownGroup" to "Group".
knownToGroup :: forall n. KnownGroup n => Group
knownToGroup  = Group $ B.pack $ symbolVal @n Proxy

newtype Group = Group ByteString
  deriving (Show, Eq, Ord)

-- | Constructor for "Group"
mkGroup :: ByteString -> Group
mkGroup = Group

unGroup :: Group -> ByteString
unGroup (Group a) = a

type Groups = Set Group

type Name = ByteString
type Headers = Map ByteString ByteString
type Content = [ByteString]

data ZREMsg = ZREMsg {
    msgFrom :: Maybe UUID
  , msgSeq :: Seq
  , msgTime :: Maybe UTCTime
  , msgCmd :: ZRECmd
  } deriving (Show, Eq, Ord)

data ZRECmd =
    Hello Endpoint Groups GroupSeq Name Headers
  | Whisper Content
  | Shout Group Content
  | Join Group GroupSeq
  | Leave Group GroupSeq
  | Ping
  | PingOk
  deriving (Show, Eq, Ord)

zreBeacon :: ByteString -> Port -> ByteString
zreBeacon uuid port = runPut $ do
  putByteString "ZRE"
  -- XXX: for compatibility with zyre implementation
  -- this should use 0x01 instead, but why when
  -- we can stick zre version there and use it for filtering?
  -- for now leave in compat mode as we don't
  -- assert this but zyre does
  putInt8 $ fromIntegral (0x01 :: Int) -- compat
  --putInt8 $ fromIntegral zreVer -- non-compat
  putByteString uuid
  putInt16be $ fromIntegral port

parseUUID :: Get UUID
parseUUID =  do
  muuid <- fromByteString . BL.fromStrict <$> getByteString 16
  case muuid of
    Just uuid -> return uuid
    Nothing -> fail "Unable to parse UUID"

parseBeacon :: ByteString
            -> (Either String (ByteString, Integer, UUID, Integer))
parseBeacon = runGet $ do
  lead <- getByteString 3
  ver <- getInt8
  uuid <- parseUUID
  port <- getInt16
  return (lead, ver, uuid, port)

cmdCode :: ZRECmd -> Word8
cmdCode (Hello _ _ _ _ _) = 0x01
cmdCode (Whisper _)       = 0x02
cmdCode (Shout _ _)       = 0x03
cmdCode (Join _ _)        = 0x04
cmdCode (Leave _ _)       = 0x05
cmdCode Ping              = 0x06
cmdCode PingOk            = 0x07

getContent :: ZRECmd -> Content
getContent (Whisper c) = c
getContent (Shout _ c) = c
getContent _ = []

newZRE :: Seq -> ZRECmd -> ZREMsg
newZRE seqNum cmd = ZREMsg Nothing seqNum Nothing cmd

encodeZRE :: ZREMsg -> [ByteString]
encodeZRE ZREMsg{..} = msg:(getContent msgCmd)
  where
    msg = runPut $ do
      putWord16be zreSig
      putWord8 $ cmdCode msgCmd
      putInt8 $ fromIntegral zreVer
      putInt16be $ fromIntegral msgSeq
      encodeCmd msgCmd

encodeCmd :: ZRECmd -> PutM ()
encodeCmd (Hello endpoint groups statusSeq name headers) = do
  putByteStringLen (pEndpoint endpoint)
  putByteStrings $ (Data.Set.map (\(Group g) -> g)) groups
  putInt8 $ fromIntegral statusSeq
  putByteStringLen name
  putMap headers
encodeCmd (Shout group _content) = putGroup group
encodeCmd (Join group statusSeq) = do
  putGroup group
  putInt8 $ fromIntegral statusSeq
encodeCmd (Leave group statusSeq) = do
  putGroup group
  putInt8 $ fromIntegral statusSeq
encodeCmd _ = return ()

putGroup :: Group -> PutM ()
putGroup (Group g) = putByteStringLen g

parseHello :: Get ZRECmd
parseHello = Hello
  <$> parseEndpoint'
  <*> (Data.Set.fromList . map Group <$> parseStrings)
  <*> getInt8
  <*> parseString
  <*> parseMap
  where
    parseEndpoint' = do
      s <- parseString
      case parseAttoEndpoint s of
        (Left err) -> fail $ "Unable to parse endpoint: " ++ err
        (Right endpoint) -> return endpoint

parseGroup :: Get Group
parseGroup = Group <$> parseString

parseShout :: Content -> Get ZRECmd
parseShout frames = Shout <$> parseGroup <*> pure frames

parseJoin :: Get ZRECmd
parseJoin = Join <$> parseGroup <*> getInt8

parseLeave :: Get ZRECmd
parseLeave = Leave <$> parseGroup <*> getInt8

parseCmd :: ByteString -> Content -> Get ZREMsg
parseCmd from frames = do
    cmd <- (getInt8 :: Get Int)
    ver <- getInt8
    sqn <- getInt16

    case runGet parseUUID from of
      (Left err) -> fail $ "No UUID: " ++ err
      (Right uuid)-> do
        if ver /= zreVer
          then fail "Protocol version mismatch"
          else do

            zcmd <- case cmd of
              0x01 -> parseHello
              0x02 -> pure $ Whisper frames -- parseWhisper
              0x03 -> parseShout frames
              0x04 -> parseJoin
              0x05 -> parseLeave
              0x06 -> pure Ping
              0x07 -> pure PingOk
              _    -> fail "Unknown command"

            return $ ZREMsg (Just uuid) sqn Nothing zcmd

parseZRE :: [ByteString] -> Either String ZREMsg
parseZRE (from:msg:rest) = parseZre from msg rest
parseZRE _ = Left "empty message"

parseZre :: ByteString -> ByteString -> Content -> Either String ZREMsg
parseZre from msg frames = flip runGet msg $ do
  sig <- getInt16
  if sig /= zreSig
    then fail "Signature mismatch"
    else do
      -- we need to drop 1st byte of from string which is '1':UUID (17 bytes)
      res <- parseCmd (B.tail from) frames
      return res