{-# LANGUAGE
    DeriveGeneric
  , GeneralizedNewtypeDeriving
  , OverloadedStrings
  , RecordWildCards
  #-}

module Web.Dependencies.Sparrow.Types where

import Web.Dependencies.Sparrow.Session (SessionID)

import Data.Hashable (Hashable)
import Data.Text (Text, intercalate)
import qualified Data.Text.Lazy.Encoding as LT
import qualified Data.ByteString.Lazy as LBS
import Data.Aeson (ToJSON (..), FromJSON (..), Value (String, Object), (.=), object, (.:))
import Data.Aeson.Types (typeMismatch)
import Data.Aeson.Attoparsec (attoAeson)
import Data.Attoparsec.Text (Parser, takeWhile1, char, sepBy)
import Control.Applicative ((<|>))
import Control.DeepSeq (NFData)
import GHC.Generics (Generic)


-- * Conceptual

-- ** Server

data ServerArgs m deltaOut = ServerArgs
  { serverDeltaReject :: m ()
  , serverSendCurrent :: deltaOut -> m ()
  }

data ServerReturn m initOut deltaIn deltaOut = ServerReturn
  { serverInitOut   :: initOut
  , serverOnOpen    :: ServerArgs m deltaOut
                    -> m ()
    -- ^ only after initOut is provided can we send deltas - invoked once, and should
    -- return a totally 'Control.Concurrent.Async.link'ed thread (if spawned)
    -- to kill with the subscription dies
  , serverOnReceive :: ServerArgs m deltaOut
                    -> deltaIn -> m () -- ^ invoked for each receive
  }

data ServerContinue m initOut deltaIn deltaOut = ServerContinue
  { serverContinue      :: Broadcast m -> m (ServerReturn m initOut deltaIn deltaOut)
  , serverOnUnsubscribe :: m ()
  }

type Server m initIn initOut deltaIn deltaOut =
  initIn -> m (Maybe (ServerContinue m initOut deltaIn deltaOut))



-- ** Client

data ClientReturn m initOut deltaIn = ClientReturn
  { clientSendCurrent   :: deltaIn -> m () -- was vs. can't be successful?
  , clientInitOut       :: initOut
  , clientUnsubscribe   :: m ()
  }

data ClientArgs m initIn initOut deltaIn deltaOut = ClientArgs
  { clientReceive  :: ClientReturn m initOut deltaIn -> deltaOut -> m ()
  , clientInitIn   :: initIn
  , clientOnReject :: m () -- ^ From a delta rejection, not init one
  }

type Client m initIn initOut deltaIn deltaOut =
  ( ClientArgs m initIn initOut deltaIn deltaOut
    -> m (Maybe (ClientReturn m initOut deltaIn))
    ) -> m ()


-- ** Topic

newtype Topic = Topic {getTopic :: [Text]}
  deriving (Eq, Ord, Generic, Hashable, Show, NFData)

instance FromJSON Topic where
  parseJSON = attoAeson (Topic <$> breaker)
    where
      breaker :: Parser [Text]
      breaker = takeWhile1 (/= '/') `sepBy` char '/'

instance ToJSON Topic where
  toJSON (Topic xs) = String (intercalate "/" xs)


-- ** Broadcast

type Broadcast m = Topic -> m (Maybe (Value -> Maybe (m ())))


-- * JSON Encodings



data WithSessionID a = WithSessionID
  { withSessionIDSessionID :: {-# UNPACK #-} !SessionID
  , withSessionIDContent   :: a
  } deriving (Eq, Show, Generic)

instance NFData a => NFData (WithSessionID a)

instance ToJSON a => ToJSON (WithSessionID a) where
  toJSON WithSessionID{..} = object
    [ "sessionID" .= withSessionIDSessionID
    , "content" .= withSessionIDContent
    ]

instance FromJSON a => FromJSON (WithSessionID a) where
  parseJSON (Object o) = WithSessionID <$> (o .: "sessionID") <*> (o .: "content")
  parseJSON x = typeMismatch "WithSessionID" x

data WithTopic a = WithTopic
  { withTopicTopic   :: !Topic
  , withTopicContent :: a
  } deriving (Eq, Show, Generic)

instance NFData a => NFData (WithTopic a)

instance ToJSON a => ToJSON (WithTopic a) where
  toJSON WithTopic{..} = object
    [ "topic" .= withTopicTopic
    , "content" .= withTopicContent
    ]

instance FromJSON a => FromJSON (WithTopic a) where
  parseJSON (Object o) = WithTopic <$> (o .: "topic") <*> (o .: "content")
  parseJSON x = typeMismatch "WithTopic" x


data InitResponse a
  = InitBadEncoding !LBS.ByteString
  | InitDecodingError !String -- when manually decoding the content, casted
  | InitRejected
  | InitResponse a
  deriving (Eq, Show, Generic)

instance NFData a => NFData (InitResponse a)

instance ToJSON a => ToJSON (InitResponse a) where
  toJSON x = case x of
    InitBadEncoding y -> object ["error" .= object ["badRequest" .= LT.decodeUtf8 y]]
    InitDecodingError y -> object ["error" .= object ["decoding" .= y]]
    InitRejected -> object ["error" .= String "rejected"]
    InitResponse y -> object ["content" .= y]

instance FromJSON a => FromJSON (InitResponse a) where
  parseJSON json = case json of
    Object o -> do
      let error' = do
            json' <- o .: "error"
            case json' of
              String x
                | x == "rejected" -> pure InitRejected
                | otherwise -> fail'
              Object o' -> do
                let badEncoding = (InitBadEncoding . LT.encodeUtf8) <$> o' .: "badRequest"
                    decodingError = InitDecodingError <$> o' .: "decoding"
                badEncoding <|> decodingError
              _ -> fail'
          response = InitResponse <$> o .: "content"
      error' <|> response
    _ -> fail'
    where
      fail' = typeMismatch "InitResponse" json


data WSHTTPResponse
  = NoSessionID
  deriving (Eq, Show, Generic)

instance NFData WSHTTPResponse

instance ToJSON WSHTTPResponse where
  toJSON x = case x of
    NoSessionID -> object ["error" .= String "no sessionID query parameter"]

instance FromJSON WSHTTPResponse where
  parseJSON json = case json of
    Object o -> do
      json' <- o .: "error"
      case json' of
        String x
          | x == "no sessionID query parameter" -> pure NoSessionID
          | otherwise -> fail'
        _ -> fail'
    _ -> fail'
    where
      fail' = typeMismatch "WSHTTPResponse" json


data WSIncoming a
  = WSUnsubscribe
    { wsUnsubscribeTopic :: !Topic
    }
  | WSIncoming a
  deriving (Eq, Show, Generic)

instance NFData a => NFData (WSIncoming a)

instance ToJSON a => ToJSON (WSIncoming a) where
  toJSON x = case x of
    WSUnsubscribe topic -> object ["unsubscribe" .= topic]
    WSIncoming y -> object ["content" .= y]

instance FromJSON a => FromJSON (WSIncoming a) where
  parseJSON (Object o) = do
    let unsubscribe = WSUnsubscribe <$> o .: "unsubscribe"
        incoming = WSIncoming <$> o .: "content"
    unsubscribe <|> incoming
  parseJSON x = typeMismatch "WSIncoming" x

data WSOutgoing a
  = WSTopicsSubscribed [Topic]
  | WSTopicAdded !Topic
  | WSTopicRemoved !Topic
  | WSTopicRejected !Topic
  | WSDecodingError !String
  | WSOutgoing a
  deriving (Eq, Show, Generic)

instance NFData a => NFData (WSOutgoing a)

instance ToJSON a => ToJSON (WSOutgoing a) where
  toJSON x = case x of
    WSDecodingError e -> object ["error" .= object ["decoding" .= e]]
    WSTopicsSubscribed subs -> object ["subs" .= object ["init" .= subs]]
    WSTopicAdded sub -> object ["subs" .= object ["add" .= sub]]
    WSTopicRemoved sub -> object ["subs" .= object ["del" .= sub]]
    WSTopicRejected sub -> object ["subs" .= object ["reject" .= sub]]
    WSOutgoing y -> object ["content" .= y]

instance FromJSON a => FromJSON (WSOutgoing a) where
  parseJSON json = case json of
    Object o -> do
      let content = WSOutgoing <$> o .: "content"
          error' = do
            json' <- o .: "error"
            case json' of
              Object o' -> do
                let decodingError = WSDecodingError <$> o' .: "decoding"
                decodingError
              _ -> fail'
          subs = do
            json' <- o .: "subs"
            case json' of
              Object o' -> do
                let subsInit = WSTopicsSubscribed <$> o' .: "init"
                    subAdd = WSTopicAdded <$> o' .: "add"
                    subDel = WSTopicRemoved <$> o' .: "del"
                    subReject = WSTopicRejected <$> o' .: "reject"
                subsInit <|> subAdd <|> subDel <|> subReject
              _ -> fail'
      content <|> error' <|> subs
    _ -> fail'
    where
      fail' = typeMismatch "WSOutgoing" json