{-# LANGUAGE ExistentialQuantification  #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE LambdaCase                 #-}
{-# LANGUAGE NondecreasingIndentation   #-}
module Announcer
    ( Announcer
    , AnnounceKey
    , packAnnounceKey
    , unpackAnnounceKey
    , AnnounceMethod(..)
    , forkAnnouncer
    , stopAnnouncer
    , schedule
    , cancel
    ) where

import Data.Wrapper.PSQ as PSQ
import Network.Kademlia.Search
import Ticker

import Control.Concurrent.Lifted.Instrument
import Control.Concurrent.STM
import Control.Monad
import Data.ByteString                      (ByteString)
import qualified Data.ByteString.Char8      as Char8
import Data.Function
import Data.Hashable
import Data.Maybe
import Data.Time.Clock.POSIX

newtype AnnounceKey = AnnounceKey ByteString
 deriving (Hashable,Ord,Eq)

packAnnounceKey :: Announcer -> String -> STM AnnounceKey
packAnnounceKey _ = return . AnnounceKey . Char8.pack

unpackAnnounceKey :: AnnounceKey -> AnnounceKey -> STM String
unpackAnnounceKey _ (AnnounceKey bs) = return $ Char8.unpack bs

data ScheduledItem
    = forall r. ScheduledItem (AnnounceMethod r)
    | StopAnnouncer

data Announcer = Announcer
    { scheduled :: TVar (PSQ' AnnounceKey POSIXTime ScheduledItem)
    , announcerActive :: TVar Bool
    , lastTick :: TVar POSIXTime
    , announceTicker :: Ticker
    }

scheduleImmediately :: Announcer -> ScheduledItem -> STM ()
scheduleImmediately announcer item
    = modifyTVar' (scheduled announcer) (PSQ.insert' (AnnounceKey "") item 0)

stopAnnouncer :: Announcer -> IO ()
stopAnnouncer announcer = do
    atomically $ scheduleImmediately announcer StopAnnouncer
    atomically $ readTVar (announcerActive announcer) >>= check . not

data AnnounceMethod r = forall nid ni addr r tok a. AnnounceMethod
    { aSearch  :: Search nid addr tok ni r
    , aPublish :: r -> tok -> Maybe ni -> IO (Maybe a)
    }

schedule :: Announcer -> AnnounceKey -> AnnounceMethod r -> r -> IO ()
schedule _ _ _ _ = do
    -- fork the search
    -- add it to the priority queue of announce methods.
    -- update ticker
    return ()

cancel :: Announcer -> AnnounceKey -> AnnounceMethod r -> r -> IO ()
cancel _ _ _ _ = return ()


forkAnnouncer :: IO Announcer
forkAnnouncer = do
    tickvar <- atomically $ newTVar 0
    ticker <- forkTicker $ writeTVar tickvar
    announcer <- atomically $ Announcer <$> newTVar PSQ.empty
                                        <*> newTVar True
                                        <*> pure tickvar
                                        <*> pure ticker
    fork $ announceThread announcer
    return announcer


announceThread :: Announcer -> IO ()
announceThread announcer = do
    myThreadId >>= flip labelThread "announcer"
    fix $ \loop -> do
    action <- atomically $ do
        now <- readTVar $ lastTick announcer
        (item,q) <- readTVar (scheduled announcer)
                    >>= maybe retry return . PSQ.minView
        when (prio item > now) retry        -- Is it time to do something?
        writeTVar (scheduled announcer) q   -- Remove the event from the queue.
        performScheduledItem announcer item -- Go for it!
    mapM_ (>> loop) action
    atomically $ writeTVar (announcerActive announcer) False

performScheduledItem :: Announcer -> Binding' AnnounceKey POSIXTime ScheduledItem -> STM (Maybe (IO ()))
performScheduledItem announcer = \case

    (Binding _ StopAnnouncer _) ->  return Nothing

    -- announcement added:

    -- wait for time to announce or for search to finish.
    --
    -- time for periodic announce:
    --   (re-)announce to the current known set of storing-nodes.
    --   If the search is finished, restart the search.
    --
    -- search finished:
    --   if any of the current storing-nodes set have not been
    --   announced to, announce to them.
    --
    --
    -- announcement removed:
    --