{-# LANGUAGE FlexibleContexts, Rank2Types, TemplateHaskell, OverloadedStrings, GADTs, DeriveGeneric #-}
{- | Configuration and settings for the server. All constructor names are
     exported, but notice that they start with an underscore.
     They also have an equivalent lens without the
     underscore. Please prefer to use the lens interface.
-}
module SecondTransfer.Sessions.Config(
                 sessionId
               , defaultSessionsConfig
               , defaultSessionsEnrichedHeaders
               , sessionsCallbacks
               , sessionsEnrichedHeaders

               , reportErrorCallback_SC
               , dataDeliveryCallback_SC
               , newSessionCallback_SC

               , dataFrameSize
               , addUsedProtocol
               , pushEnabled
               , firstPushStream
               , networkChunkSize
               , trayMaxSize

               , SessionComponent                       (..)
               , SessionCoordinates                     (..)
               , SessionsCallbacks                      (..)
               , SessionsEnrichedHeaders                (..)
               , SessionsConfig                         (..)
               , SessionGenericHandle                   (..)

               , ErrorCallback
               , DataFrameDeliveryCallback
               , NewSessionCallback                     (..)
               , HashableSockAddr

               , ActivityMeteredSession                 (..)
               , CleanlyPrunableSession                 (..)

       ) where


-- import           Control.Concurrent.MVar (MVar)
import           Control.Exception                        (SomeException)
import           Control.Lens                             (makeLenses)

--import           GHC.Generics (Generic)
--import           Data.Word                                (Word8)

--import           System.Mem.Weak                          (Weak)
import           System.Clock                             (TimeSpec)

import           SecondTransfer.IOCallbacks.Types         (IOCallbacks)
import           SecondTransfer.Sessions.HashableSockAddr (HashableSockAddr)

-- | Information used to identify a particular session.
newtype SessionCoordinates = SessionCoordinates  Int
    deriving Show

instance Eq SessionCoordinates where
    (SessionCoordinates a) == (SessionCoordinates b) =  a == b

-- | Get/set a numeric Id from a `SessionCoordinates`. For example, to
--   get the session id with this, import `Control.Lens.(^.)` and then do
--
-- @
--      session_id = session_coordinates ^. sessionId
-- @
--
sessionId :: Functor f => (Int -> f Int) -> SessionCoordinates -> f SessionCoordinates
sessionId f (SessionCoordinates session_id) =
    fmap SessionCoordinates (f session_id)


-- | Components at an individual session. Used to report
--   where in the session an error was produced. This interface is likely
--   to change in the future, as we add more metadata to exceptions
data SessionComponent =
    SessionInputThread_HTTP2SessionComponent
    |SessionHeadersOutputThread_HTTP2SessionComponent
    |SessionDataOutputThread_HTTP2SessionComponent
    |SessionClientPollThread_HTTP2SessionComponent
    |Framer_HTTP2SessionComponent
    |Session_HTTP11
    deriving Show


-- Which protocol a session is using... no need for this right now
-- data UsedProtocol =
--      HTTP11_UsP
--     |HTTP2_UsP

-- | Used by this session engine to report an error at some component, in a particular
--   session.
type ErrorCallback = (SessionComponent, SessionCoordinates, SomeException) -> IO ()


-- | Sessions follow this class, so that they can be rescinded on inactivity
class ActivityMeteredSession a where
    sessionLastActivity :: a -> IO TimeSpec

-- | Clean-cut of sessions
class CleanlyPrunableSession a where
    cleanlyCloseSession :: a -> IO ()


-- | Used by the session engine to report delivery of each data frame. Keep this callback very
--   light, it runs in the main sending thread. It is called as
--   f session_id stream_id ordinal when_delivered
type DataFrameDeliveryCallback =  Int -> Int -> Int -> TimeSpec ->  IO ()


-- | An object with information about a new session, wrapped in a weak pointer. At the time the
--   newSessionCallback_SC is invoked, the reference inside the weak pointer is guranteed to be alive.
--   It may die later though.
data SessionGenericHandle where
    Whole_SGH :: (ActivityMeteredSession a, CleanlyPrunableSession a) => a -> SessionGenericHandle
    Partial_SGH :: (ActivityMeteredSession a) => a -> IOCallbacks -> SessionGenericHandle

instance ActivityMeteredSession SessionGenericHandle where
    sessionLastActivity (Whole_SGH a) = sessionLastActivity a
    sessionLastActivity (Partial_SGH a _) = sessionLastActivity a


-- | Callback to be invoked when a  client establishes a new session. The first parameter
--   is the address of the client, and the second parameter is a controller that can be used to
--   reduce the number of connections from time to time, the third parameter is a key on which
--   the second paramter should be made a weak pointer
newtype NewSessionCallback =  NewSessionCallback ( HashableSockAddr -> SessionGenericHandle -> forall a . a -> IO () )

-- | Callbacks that you can provide your sessions to notify you
--   of interesting things happening in the server.
data SessionsCallbacks = SessionsCallbacks {
    -- | Used to report errors during this session
    _reportErrorCallback_SC  :: Maybe ErrorCallback
    -- | Used to report delivery of individual data frames
  ,  _dataDeliveryCallback_SC :: Maybe DataFrameDeliveryCallback
    -- | Used to notify the session manager of new sessions, so
    --   that the session manager registers them (in a weak map)
    --   if need comes
  , _newSessionCallback_SC  :: Maybe NewSessionCallback
  }

makeLenses ''SessionsCallbacks


-- | This is a temporal interface, but an useful one nonetheless.
--   By setting some values here to True, second-transfer will add
--   some headers to inbound requests, and some headers to outbound
--   requests.
--
--   This interface is deprecated in favor of the AwareWorker
--   functionality....
data SessionsEnrichedHeaders = SessionsEnrichedHeaders {
    -- | Adds a second-transfer-eh--used-protocol header
    --   to inbound requests. Default: False
    _addUsedProtocol :: Bool
    }

makeLenses ''SessionsEnrichedHeaders

-- | Don't insert any extra-headers by default.
defaultSessionsEnrichedHeaders :: SessionsEnrichedHeaders
defaultSessionsEnrichedHeaders = SessionsEnrichedHeaders {
    _addUsedProtocol = False
    }


-- | Configuration information you can provide to the session maker.
data SessionsConfig = SessionsConfig {
   -- | Session callbacks
   _sessionsCallbacks         :: SessionsCallbacks
 , _sessionsEnrichedHeaders   :: SessionsEnrichedHeaders
   -- | Size to use when splitting data in data frames, to be sent.
   --   TODO: An equivalent maxRecvSize should be defined here...
 , _dataFrameSize             :: Int
   -- | Should we enable PUSH in sessions? Notice that the client
   --   can still disable PUSH at will. Also users of the library
   --   can decide not to use it. This just puts another layer ...
 , _pushEnabled               :: Bool
   -- | The number to use for the first pushed stream. Should be even
 , _firstPushStream            :: Int
   -- | Max amount of bytes to try to send in one go. The session will
   --   send less data if less is available, otherwise it will send slightly
   --   more than this amount, depending on packet boundaries. This is
   --   used to avoid TCP and TLS fragmentation at the network layer
 , _networkChunkSize          :: Int
   -- | Max number of packets to hold in the output tray. A high number means
   --   that more memory is used by the packets have a higher chance of going
   --   out in a favourable order.
 , _trayMaxSize               :: Int
   }

makeLenses ''SessionsConfig

-- -- | Lens to access sessionsCallbacks in the `SessionsConfig` object.
-- sessionsCallbacks :: Lens' SessionsConfig SessionsCallbacks
-- sessionsCallbacks  f (
--     SessionsConfig {
--         _sessionsCallbacks= s
--     }) = fmap (\ s' -> SessionsConfig {_sessionsCallbacks = s'}) (f s)


-- | Creates a default sessions context. Modify as needed using
--   the lenses interfaces
defaultSessionsConfig :: SessionsConfig
defaultSessionsConfig = SessionsConfig {
     _sessionsCallbacks = SessionsCallbacks {
            _reportErrorCallback_SC = Nothing,
            _dataDeliveryCallback_SC = Nothing,
            _newSessionCallback_SC = Nothing
        }
  , _sessionsEnrichedHeaders = defaultSessionsEnrichedHeaders
  , _dataFrameSize = 16*1024
  , _pushEnabled = True
  , _firstPushStream = 8
  , _networkChunkSize = 18*1024
  -- Max number of packets that can be waiting to exit. A big number here
  -- is desirable, but counts towards the memory consumption when the network is slow...
  -- so for now let's make it a little bit lower. In the future we may want to adjust
  -- this number dynamically.
  -- , _trayMaxSize = 128
  , _trayMaxSize = 16
    }