{-# LANGUAGE FlexibleContexts      #-}
{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedStrings     #-}
{-# LANGUAGE RecordWildCards       #-}
{-# LANGUAGE ScopedTypeVariables   #-}

-- |
-- Module:      Network.Distributed.Process
-- Copyright:   (c) 2018 Sean McGroarty
-- License:     BSD3
-- Maintainer:  Sean McGroarty <mcgroas@tcd.ie.com>
-- Stability:   experimental
--
module Network.Distributed.Process
  ( runRequestNode
  , runRequestNode'
  , joinNetwork
  , joinNetwork'
  , findPids
  , gatherDeps
  , receiveF
  , withTransfer
  ) where

import           Network.Distributed.Transfer
import           Network.Distributed.Types
import           Network.Distributed.Utils

import           Control.Applicative
import           Control.Monad
import           Control.Monad.Catch
import           Prelude                                            hiding
                                                                     (FilePath,
                                                                     log)

import           Control.Distributed.Process.Backend.SimpleLocalnet
import           Control.Distributed.Process.Lifted                 hiding
                                                                     (bracket,
                                                                     catch)
import           Control.Distributed.Process.Lifted.Class
import qualified Control.Distributed.Process.Node.Lifted            as PN

import           Data.Maybe                                         (catMaybes)

import           Filesystem
import           Filesystem.Path                                    (directory)
import           Filesystem.Path.CurrentOS                          (decode)

import           Control.Monad.Reader

----------------------------------------------------------------------------
-- | Logs that the Node is joining the network and returns a Backend
mkBackend :: NetworkConfig -> IO Backend
mkBackend nc@NetworkConfig {..} = do
  log ("Node joining network on: " ++ show nc)
  initializeBackend hostNetworkConfig portNetworkConfig PN.initRemoteTable

-- | Runs a Process that is a master node
runRequestNode ::
     Int
  -- ^ Number of slave nodes the master should wait for
  -> NetworkConfig
  -> IO ()
runRequestNode waitN nc = do
  backend <- mkBackend nc
  let cfg = AppConfig waitN backend
  flip PN.runProcess (runApp cfg runRequestNode') =<< newLocalNode backend
  runStackBuildT

-- | Internal for master node
runRequestNode' :: App ()
runRequestNode' = do
  log "Searching the Network..."
  pids <- findPids
  logSucc ("Found Nodes: " ++ show pids)
  pDeps <- gatherDeps pids
  log "Finding most compatable node..."
  myDeps <- listDeps
  withTransfer pDeps myDeps retryReq $ \pid (sPort, rPort) -> do
    log $ "Node: " ++ show pid ++ " Is the best match."
    send pid (TransferReq sPort)
    log "Working..."
    receiveF rPort
    logSucc "Transmission complete. All files received. Ready to build."
  mapM_ (`send` Terminate) pids
  where
    retryReq :: SomeException -> App ()
    retryReq _ = logWarn "Slave died. Retrying..." >> runRequestNode'

-- | Creates the Backend and runs a Process that is a Slave node
joinNetwork :: NetworkConfig -> IO ()
joinNetwork = mkBackend >=> newLocalNode >=> flip PN.runProcess joinNetwork'

-- | Internal for slave node
joinNetwork' :: Process ()
joinNetwork' = do
  me <- getSelfPid
  register "slaveNodeS" me
  loop me
  where
    loop me = receiveWait [match $ \req -> receiveReq me req]
    receiveReq :: ProcessId -> Request -> Process ()
    receiveReq me (Ping pid) = do
      log "Received a Ping!"
      deps <- listDeps
      send pid (PD (deps, me))
      loop me
    receiveReq me (TransferReq sPort) = do
      log "Received request to transmit files... Beginning transmission"
      pipeFiles (sendChan sPort) *> sendChan sPort TransferDone
      logSucc "Transmission complete"
      loop me
    receiveReq _ Terminate = log "Received a request to terminate. Bye."

-- | Faciliaties a safe Transfer bewteen nodes
withTransfer ::
     (Exception e, MonadProcess m, MonadCatch m)
  => [ProcessDeps]
  -- ^ Slaves process dependencies
  -> Deps
  -- ^ Masters dependencies
  -> (e -> m ())
  -- ^ Recovery function
  -> (ProcessId -> (SendPort Transfer, ReceivePort Transfer) -> m ())
  -- ^ Action to execute with the linked process and typed-channel
  -> m ()
withTransfer pDeps myDeps retry action =
  case getBestPid pDeps myDeps (Nothing, 0) of
    Just n  -> runAction n `catch` retry
    Nothing -> logWarn "No Nodes share dependencies, aborting."
  where
    runAction n = do
      link n
      chan <- newChan
      linkPort (fst chan)
      action n chan
      unlinkPort (fst chan)
      unlink n

-- | Internal function used to gather ProcessId's
findPids ::
     (MonadMask m, MonadProcess m, MonadReader AppConfig m) => m [ProcessId]
findPids = loop =<< asks nodes
  where
    loop nc = do
      backend <- asks backend
      nids <- liftIO $ findPeers backend 1000000
      pids <-
        bracket (mapM monitorNode nids) (mapM unmonitor) $ \_ -> do
          mapM_ (`whereisRemoteAsync` "slaveNodeS") nids
          catMaybes <$>
            replicateM
              (length nids)
              (receiveWait
                 [ match (\(WhereIsReply "slaveNodeS" mPid) -> pure mPid)
                 , match (\NodeMonitorNotification {} -> pure Nothing)
                 ])
      if length pids == nc
        then pure pids
        else loop nc

-- | Internal function used to get all slaves dependencies
gatherDeps :: (MonadProcess m, MonadMask m) => Network -> m [ProcessDeps]
gatherDeps pids = do
  ping <- Ping <$> getSelfPid
  mapM_ (`send` ping) pids
  bracket (mapM monitor pids) (mapM unmonitor) $ \_ ->
    catMaybes <$>
    replicateM
      (length pids)
      (receiveWait
         [ match $ \(PD pd) -> pure $ Just pd
         , match $ \NodeMonitorNotification {} -> pure Nothing
         ])

-- | Internal function used to reveive the Transfer
receiveF :: MonadProcess m => ReceivePort Transfer -> m ()
receiveF rPort = work =<< receiveChan rPort
  where
    work (TransferInProg (path, file)) = do
      liftIO $ do
        let path' = decode path
        createTree (directory path')
        Filesystem.writeFile path' file
      receiveF rPort
    work TransferDone = pure ()