-- |
--   Copyright   :  (c) Sam Truzjan 2013
--   License     :  BSD3
--   Maintainer  :  pxqr.sta@gmail.com
--   Stability   :  experimental
--   Portability :  portable
--
--   BitTorrent uses a \"distributed sloppy hash table\" (DHT) for
--   storing peer contact information for \"trackerless\" torrents. In
--   effect, each peer becomes a tracker.
--
--   Normally you don't need to import other DHT modules.
--
--   For more info see:
--   <http://www.bittorrent.org/beps/bep_0005.html>
--
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE TemplateHaskell   #-}
{-# LANGUAGE TypeOperators     #-}
{-# LANGUAGE ScopedTypeVariables #-}
module Network.BitTorrent.DHT
       ( -- * Distributed Hash Table
         DHT
       , Options (..)
       , fullLogging
       , dht

         -- * Bootstrapping
         -- $bootstrapping-terms
       , tNodes
       , defaultBootstrapNodes
       , resolveHostName
       , bootstrap
       , isBootstrapped

         -- * Initialization
       , snapshot

         -- * Operations
       , Network.BitTorrent.DHT.lookup
       , Network.BitTorrent.DHT.insert
       , Network.BitTorrent.DHT.delete

         -- * Embedding
         -- ** Session
       , LogFun
       , Node
       , defaultHandlers
       , newNode
       , closeNode

         -- ** Monad
       , MonadDHT (..)
       , runDHT
       ) where

import Control.Monad.Logger
import Control.Monad.Reader
import Control.Exception
import qualified Data.ByteString as BS
import Data.Conduit as C
import qualified Data.Conduit.List as C
import Data.Serialize
import Network.Socket
import Text.PrettyPrint.HughesPJClass as PP (pPrint,render)

import Data.Torrent
import Network.BitTorrent.Address
import Network.BitTorrent.DHT.Query
import Network.BitTorrent.DHT.Session
import Network.BitTorrent.DHT.Routing as T hiding (null)
import qualified Data.Text as Text
import Data.Monoid
import Network.DatagramServer.Mainline (KMessageOf)


{-----------------------------------------------------------------------
--  DHT types
-----------------------------------------------------------------------}

class MonadDHT m where
  liftDHT :: DHT IPv4 a -> m a

instance MonadDHT (DHT IPv4) where
  liftDHT = id

-- | Convenience method.  Pass this to 'dht' to enable full logging.
fullLogging :: LogSource -> LogLevel -> Bool
fullLogging _ _ = True

-- | Run DHT on specified port. <add note about resources>
dht :: (Ord ip, Address ip)
    => Options     -- ^ normally you need to use 'Data.Default.def';
    -> NodeAddr ip -- ^ address to bind this node;
    -> (LogSource -> LogLevel -> Bool) -- ^ use 'fullLogging' as a noisy default
    -> DHT ip a    -- ^ actions to run: 'bootstrap', 'lookup', etc;
    -> IO a        -- ^ result.
dht opts addr logfilter action = do
  runStderrLoggingT $ filterLogger logfilter $ LoggingT $ \ logger -> do
    bracket (newNode defaultHandlers opts addr logger Nothing) closeNode $
      \ node -> runDHT node action
{-# INLINE dht #-}

{-----------------------------------------------------------------------
--  Bootstrapping
-----------------------------------------------------------------------}
-- $bootstrapping-terms
--
--  [@Bootstrapping@] DHT @bootstrapping@ is the process of filling
--  routing 'Table' by /good/ nodes.
--
--  [@Bootstrapping time@] Bootstrapping process can take up to 5
--  minutes. Bootstrapping should only happen at first application
--  startup, if possible you should use 'snapshot' & 'restore'
--  mechanism which must work faster.
--
--  [@Bootstrap nodes@] DHT @bootstrap node@ is either:
--
--    * a specialized high performance node maintained by bittorrent
--    software authors\/maintainers, like those listed in
--    'defaultBootstrapNodes'. /Specialized/ means that those nodes
--    may not support 'insert' queries and is running for the sake of
--    bootstrapping only.
--
--    * an ordinary bittorrent client running DHT node. The list of
--    such bootstrapping nodes usually obtained from
--    'Data.Torrent.tNodes' field or
--    'Network.BitTorrent.Exchange.Message.Port' messages.

-- Do not include the following hosts in the default bootstrap nodes list:
--
--   * "dht.aelitis.com" and "dht6.azureusplatform.com" - since
--   Azureus client have a different (and probably incompatible) DHT
--   protocol implementation.
--
--   * "router.utorrent.com" since it is just an alias to
--   "router.bittorrent.com".
--      XXX: ignoring this advise as it resolves to a different
--      ip address for me.

-- | List of bootstrap nodes maintained by different bittorrent
-- software authors.
defaultBootstrapNodes :: [NodeAddr HostName]
defaultBootstrapNodes =
  [ NodeAddr "router.bittorrent.com"  6881 -- by BitTorrent Inc.

    -- doesn't work at the moment (use git blame)  of commit
  , NodeAddr "dht.transmissionbt.com" 6881 -- by Transmission project

  , NodeAddr "router.utorrent.com"  6881
  ]

-- TODO Multihomed hosts

-- | Resolve either a numeric network address or a hostname to a
-- numeric IP address of the node.  Usually used to resolve
-- 'defaultBootstrapNodes' or 'Data.Torrent.tNodes' lists.
resolveHostName :: NodeAddr HostName -> IO (NodeAddr IPv4)
resolveHostName NodeAddr {..} = do
  let hints = defaultHints { addrFamily = AF_INET, addrSocketType = Datagram }
  -- getAddrInfo throws exception on empty list, so the pattern matching never fail
  info : _ <- getAddrInfo (Just hints) (Just nodeHost) (Just (show nodePort))
  case fromSockAddr (addrAddress info) of
    Nothing   -> error "resolveNodeAddr: impossible"
    Just addr -> return addr

-- | One good node may be sufficient.
--
--   This operation do block, use
--   'Control.Concurrent.Async.Lifted.async' if needed.
bootstrap :: forall ip. Address ip => Maybe BS.ByteString -> [NodeAddr ip] -> DHT ip ()
bootstrap mbs startNodes = do
  restored <-
    case decode <$> mbs of
        Just (Right tbl) -> return (T.toList tbl)
        Just (Left e)    -> do $(logWarnS) "restore" (Text.pack e)
                               return []
        Nothing          -> return []

  $(logInfoS) "bootstrap" "Start node bootstrapping"
  let searchAll aliveNodes = do
        nid <- myNodeIdAccordingTo (error "FIXME")
        nss <- C.sourceList [aliveNodes] $= search nid (findNodeQ nid) $$ C.consume
        return ( nss :: [[NodeInfo KMessageOf ip ()]] )
  input_nodes <- (restored ++) . T.toList <$> getTable
  -- Step 1: Use iterative searches to flesh out the table..
  do let knowns = map (map $ nodeAddr . fst) input_nodes
     -- Below, we reverse the nodes since the table serialization puts the
     -- nearest nodes last and we want to choose a similar node id to bootstrap
     -- faster.
     (alive_knowns,_) <- unzip <$> queryParallel (pingQ <$> reverse (concat knowns))
     b <- isBootstrapped
     -- If our cached nodes are alive and our IP address did not change, it's possible
     -- we are already bootsrapped, so no need to do any searches.
     when (not b) $ do
         nss <- searchAll $ take 2 alive_knowns
         -- We only use the supplied bootstrap nodes when we don't know of any
         -- others to try.
         when (null nss) $ do
            -- TODO filter duplicated in startNodes list
            -- TODO retransmissions for startNodes
            (aliveNodes,_) <- unzip <$> queryParallel (pingQ <$> startNodes)
            _ <- searchAll $ take 2 aliveNodes
            return ()
  -- Step 2: Repeatedly refresh incomplete buckets until the table is full.
  maxbuckets <- asks $ optBucketCount . options
  flip fix 0 $ \loop icnt -> do
      tbl <- getTable
      let unfull = filter ((/=defaultBucketSize) . snd)
          us = zip
                -- is_last = True for the last bucket
                (True:repeat False)
                -- Only non-full buckets unless it is the last one and the
                -- maximum number of buckets has not been reached.
                $ case reverse $ zip [0..] $ T.shape tbl of
                    p@(n,_):ps | n+1==maxbuckets -> unfull (p:ps)
                    p:ps                         -> p:unfull ps
                    []                           -> []
      forM_ us $ \(is_last,(index,_)) -> do
        nid <- myNodeIdAccordingTo (error "FIXME")
        sample <- liftIO $ genBucketSample nid (bucketRange index is_last)
        $(logDebugS) "bootstrapping"
            $ "BOOTSTRAP sample"
              <> Text.pack (show (is_last,index,T.shape tbl))
              <> " " <> Text.pack (render $ pPrint sample)
        refreshNodes sample
      $(logDebugS) "bootstrapping"
        $ "BOOTSTRAP finished iteration "
          <> Text.pack (show (icnt,T.shape tbl,us,defaultBucketSize))
      when (not (null us) && icnt < div (3*maxbuckets) 2)
        $ loop (succ icnt)
  $(logInfoS) "bootstrap" "Node bootstrapping finished"

-- | Check if this node is already bootstrapped.
--   @bootstrap [good_node] >> isBootstrapped@@ should always return 'True'.
--
--   This operation do not block.
--
isBootstrapped :: Eq ip => DHT ip Bool
isBootstrapped = T.full <$> getTable

{-----------------------------------------------------------------------
-- Initialization
-----------------------------------------------------------------------}

-- | Serialize current DHT session to byte string.
--
--   This is blocking operation, use
-- 'Control.Concurrent.Async.Lifted.async' if needed.
snapshot :: Address ip => DHT ip BS.ByteString
snapshot = do
    tbl <- getTable
    return $ encode tbl

{-----------------------------------------------------------------------
--  Operations
-----------------------------------------------------------------------}

-- | Get list of peers which downloading this torrent.
--
--   This operation is incremental and do block.
--
lookup :: Address ip => InfoHash -> DHT ip `C.Source` [PeerAddr ip]
lookup topic = do      -- TODO retry getClosest if bucket is empty
  closest <- lift $ getClosest topic
  C.sourceList [closest] $= search topic (getPeersQ topic)

-- TODO do not republish if the topic is already in announceSet

-- | Announce that /this/ peer may have some pieces of the specified
-- torrent. DHT will reannounce this data periodically using
-- 'optReannounce' interval.
--
--   This operation is synchronous and do block, use
--   'Control.Concurrent.Async.Lifted.async' if needed.
--
insert :: Address ip => InfoHash -> PortNumber -> DHT ip ()
insert ih p = do
  publish ih p
  insertTopic ih p

-- | Stop announcing /this/ peer for the specified torrent.
--
--   This operation is atomic and may block for a while.
--
delete :: InfoHash -> PortNumber -> DHT ip ()
delete = deleteTopic
{-# INLINE delete #-}