{-# LANGUAGE DeriveFunctor #-}
{-# LANGUAGE LambdaCase    #-}
module Connection where

import Control.Applicative
import Control.Arrow
import Control.Concurrent.STM
import qualified Data.Map as Map
         ;import Data.Map (Map)

import PingMachine

-- | This type indicates the current status of a connection.  The type
-- parameter indicates protocol-specific status information.  To present
-- information as a user-comprehensible string, use 'showStatus'.
data Status status
    = Dormant
    | InProgress status
    | Established
 deriving (Show,Eq,Ord,Functor)

-- | A policy indicates a desired connection status.
data Policy
    = RefusingToConnect -- ^ We desire no connection.
    | OpenToConnect     -- ^ We will cooperate if a remote side initiates.
    | TryingToConnect   -- ^ We desire to be connected.
 deriving (Eq,Ord,Show)

-- | Information obtained via the 'connectionStatus' interface to
-- 'Manager'.
data Connection status = Connection
    { connStatus    :: Status status
    , connPolicy    :: Policy
    }
 deriving Functor

-- | This is an interface to make or query status information about connections
-- of a specific kind.
--
-- Type parameters:
--
--    /k/ names a connection.  It should implement Ord, and can be parsed and
--    displayed using 'stringToKey' and 'showKey'.
--
--    /status/ indicates the progress of a connection.  It is intended as a
--    parameter to the 'InProgress' constructor of 'Status'.
--
data Manager status k = Manager
    { -- | Connect or disconnect a connection.
      setPolicy    :: k -> Policy -> IO ()
      -- | Lookup a connection status.
    , status       :: k -> STM (Connection status)
      -- | Obtain a list of all known connections.
    , connections  :: STM [k]
      -- | Parse a connection key out of a string.  Inverse of 'showKey'.
    , stringToKey  :: String -> Maybe k
      -- | Convert a progress value to a string.
    , showProgress :: status -> String
      -- | Show a connection key as a string.
    , showKey      :: k -> String
    }

-- | Present status information (visible in a UI) for a connection.
showStatus :: Manager status k -> Status status -> String
showStatus mgr Dormant        = "dormant"
showStatus mgr Established    = "established"
showStatus mgr (InProgress s) = "in progress ("++showProgress mgr s++")"


-- | Combine two different species of 'Manager' into a single interface using
-- 'Either' to combine key and status types.
addManagers :: (Ord kA, Ord kB) =>
            Manager statusA kA
            -> Manager statusB kB
            -> Manager (Either statusA statusB) (Either kA kB)
addManagers mgrA mgrB = Manager
    { setPolicy = either (setPolicy mgrA) (setPolicy mgrB)
    , status = \case
        Left  k -> fmap Left  <$> status mgrA k
        Right k -> fmap Right <$> status mgrB k
    , connections = do
        as <- connections mgrA
        bs <- connections mgrB
        return $ map Left as ++ map Right bs
    , stringToKey = \str ->  Left <$> stringToKey mgrA str
                        <|> Right <$> stringToKey mgrB str
    , showProgress = either (showProgress mgrA) (showProgress mgrB)
    , showKey = either (showKey mgrA) (showKey mgrB)
    }