{-# language DataKinds #-}
{-# language DeriveAnyClass #-}
{-# language DerivingStrategies #-}
{-# language GADTs #-}
{-# language KindSignatures #-}
{-# language StandaloneDeriving #-}
module Socket.Datagram
  ( Socket(..)
  , SendException(..)
  , ReceiveException(..)
  , SocketException(..)
  ) where

import Socket (Interruptibility(..),Connectedness,Family)
import Socket.IPv4 (SocketException(..))
import System.Posix.Types (Fd)

import Data.Kind (Type)
import Data.Typeable (Typeable)
import Control.Exception (Exception)

data SendException :: Interruptibility -> Type where
  -- | The datagram did not fit in the buffer. The field is the
  --   number of bytes that were successfully copied into the
  --   send buffer. The datagram does still get sent when this
  --   happens.
  --   TODO: Can this actually happen? SendMessageSize might be
  --   what actually happens in this case.
  SendTruncated :: !Int -> SendException i
  -- | Attempted to send to a broadcast address.
  SendBroadcasted :: SendException i
  -- | A previous attempt to send to the peer failed, and
  --   the failure is asynchronously reported via ICMP on a later
  --   attempt to send to the peer. It is likely that the
  --   peer is not listening on the requested port or that the
  --   datagram could not be routed to the peer. (This is a
  --   confusing way to notify the user of a send failure, but
  --   it is how Linux does it.) This does not happen reliably.
  --   Certain network environment block the ICMP traffic needed
  --   for the sender to learn that its messages have not been
  --   delivered. This happens with UNIX-domain sockets nothing
  --   is bound to the peer address. In that context, this exception
  --   happens reliably. (@ECONNREFUSED@ or @ENOTCONN@)
  SendConnectionRefused :: SendException i
  -- | The size of the message made it impossible for the message
  -- to be delivered atomically. (@EMSGSIZE@)
  SendMessageSize :: SendException i
  -- | STM-style interrupt (much safer than C-style interrupt)
  SendInterrupted :: SendException 'Interruptible

deriving stock instance Show (SendException i)
deriving stock instance Eq (SendException i)
deriving anyclass instance (Typeable i) => Exception (SendException i)

-- | Exceptions that can happen while attempting to receive
--   a datagram. 
data ReceiveException :: Interruptibility -> Type where
  -- | The datagram did not fit in the buffer. The field is the
  --   original size of the datagram that was truncated. If
  --   this happens, the process probably needs to start using
  --   a larger receive buffer.
  ReceiveTruncated :: !Int -> ReceiveException i
  -- | A previous attempt to send to the peer failed, and
  --   the failure is asynchronously reported via ICMP on a later
  --   attempt to receive from the peer. It is likely that the
  --   peer is not listening on the requested port or that the
  --   datagram could not be routed to the peer. Even if the user
  --   has not sent anything, then this exception can result from
  --   a previous socket bound to the same port. In this case,
  --   it can be safely ignored. However, if the user has sent
  --   something over the socket, this exception means that it
  --   likely did not arrive. (This is a confusing way to notify
  --   the user of a send failure, but it is how Linux does it.)
  ReceiveConnectionRefused :: ReceiveException i
  -- | STM-style interrupt (much safer than C-style interrupt)
  ReceiveInterrupted :: ReceiveException 'Interruptible

deriving stock instance Show (ReceiveException i)
deriving stock instance Eq (ReceiveException i)
deriving anyclass instance (Typeable i) => Exception (ReceiveException i)

-- | A datagram socket. The 'Connectedness' refers to whether or
-- not POSIX @connect@ has been applied to the socket. A connected
-- socket socket uses POSIX @send@/@recv@ to communicate with a
-- single peer. An unconnected socket uses POSIX @sendto@/@recvfrom@
-- to communicate with many peers. The 'Family' refers to whether this
-- socket uses IPv4, IPv6, or Unix (local).
newtype Socket :: Connectedness -> Family -> Type where
  Socket :: Fd -> Socket c a
  deriving (Eq,Ord,Show)