-- |
--   Copyright   :  (c) Sam T. 2013
--   License     :  MIT
--   Maintainer  :  pxqr.sta@gmail.com
--   Stability   :  experimental
--   Portability :  non-portable
--
--
--   This module provides straigthforward Tracker protocol
--   implementation. The tracker is an HTTP/HTTPS service used to
--   discovery peers for a particular existing torrent and keep
--   statistics about the swarm.
--
--   For more convenient high level API see
--   "Network.BitTorrent.Tracker" module.
--
--   For more information see:
--   <https://wiki.theory.org/BitTorrentSpecification#Tracker_HTTP.2FHTTPS_Protocol>
--
{-# OPTIONS -fno-warn-orphans           #-}
{-# LANGUAGE OverloadedStrings          #-}
{-# LANGUAGE RecordWildCards            #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE FlexibleInstances #-}
-- TODO: add "compact" field to TRequest
module Network.BitTorrent.Tracker.Protocol
       ( Event(..), TRequest(..), TResponse(..)
       , askTracker, leaveTracker

         -- * Defaults
       , defaultPorts, defaultNumWant
       )
       where

import Control.Applicative
import Control.Monad
import Data.Char as Char
import Data.Word (Word32)
import Data.Map  as M
import Data.Maybe
import Data.Word
import Data.Monoid
import Data.BEncode
import Data.ByteString as B
import           Data.Text as T
import Data.Serialize hiding (Result)
import Data.URLEncoded as URL
import Data.Torrent

import Network
import Network.Socket
import Network.HTTP
import Network.URI

import Network.BitTorrent.Peer
import Network.BitTorrent.Exchange.Protocol hiding (Request)


-- | Events used to specify which kind of tracker request is performed.
data Event = Started
             -- ^ For the first request: when a peer join the swarm.
           | Stopped
             -- ^ Sent when the peer is shutting down.
           | Completed
             -- ^ To be sent when the peer completes a download.
             deriving (Show, Read, Eq, Ord, Enum, Bounded)


-- | A tracker request is HTTP GET request; used to include metrics
--   from clients that help the tracker keep overall statistics about
--   the torrent. The most important, requests are used by the tracker
--   to keep track lists of active peer for a particular torrent.
--
data TRequest = TRequest { -- TODO peer here -- TODO detach announce
     reqAnnounce   :: !URI
     -- ^ Announce url of the torrent usually obtained from 'Torrent'.

   , reqInfoHash   :: !InfoHash
     -- ^ Hash of info part of the torrent usually obtained from
     -- 'Torrent'.

   , reqPeerId     :: !PeerId
     -- ^ ID of the peer doing request.

   , reqPort       :: !PortNumber
     -- ^ Port to listen to for connections from other
     -- peers. Normally, tracker should respond with this port when
     -- some peer request the tracker with the same info hash.

   , reqUploaded   :: !Integer
     -- ^ Number of bytes that the peer has uploaded in the swarm.

   , reqDownloaded :: !Integer
     -- ^ Number of bytes downloaded in the swarm by the peer.

   , reqLeft       :: !Integer
     -- ^ Number of bytes needed in order to complete download.

   , reqIP         :: Maybe HostAddress
     -- ^ The peer IP. Needed only when client communicated with
     -- tracker throught a proxy.

   , reqNumWant    :: Maybe Int
     -- ^ Number of peers that the peers wants to receive from. See
     -- note for 'defaultNumWant'.

   , reqEvent      :: Maybe Event
      -- ^ If not specified, the request is regular periodic request.
   } deriving Show


-- | The tracker response includes a peer list that helps the client
--   participate in the torrent. The most important is 'respPeer' list
--   used to join the swarm.
--
data TResponse =
     Failure Text -- ^ Failure reason in human readable form.
   | OK { -- TODO rename to anounce
       respWarning     ::  Maybe Text
       -- ^ Human readable warning.

     , respInterval    :: !Int
       -- ^ Recommended interval to wait between requests.

     , respMinInterval ::  Maybe Int
       -- ^ Minimal amount of time between requests. A peer /should/
       -- make timeout with at least 'respMinInterval' value,
       -- otherwise tracker might not respond. If not specified the
       -- same applies to 'respInterval'.

     , respComplete    ::  Maybe Int
       -- ^ Number of peers completed the torrent. (seeders)

     , respIncomplete  ::  Maybe Int
       -- ^ Number of peers downloading the torrent. (leechers)

     , respPeers       :: ![PeerAddr]
       -- ^ Peers that must be contacted.
     } deriving Show


instance BEncodable TResponse where
  toBEncode (Failure t)  = fromAssocs ["failure reason" --> t]
  toBEncode resp@(OK {}) = fromAssocs
    [ "interval"     -->  respInterval resp
    , "min interval" -->? respMinInterval resp
    , "complete"     -->? respComplete resp
    , "incomplete"   -->? respIncomplete resp
    , "peers"        -->  respPeers resp
    ]

  fromBEncode (BDict d)
    | Just t <- M.lookup "failure reason" d = Failure <$> fromBEncode t
    | otherwise = OK <$> d >--? "warning message"
                     <*> d >--  "interval"
                     <*> d >--? "min interval"
                     <*> d >--? "complete"
                     <*> d >--? "incomplete"
                     <*> getPeers (M.lookup "peers" d)

      where
        getPeers :: Maybe BEncode -> Result [PeerAddr]
        getPeers (Just (BList l))     = fromBEncode (BList l)
        getPeers (Just (BString s))   = runGet getCompactPeerList s
        getPeers  _                   = decodingError "Peers"

  fromBEncode _ = decodingError "TResponse"

instance URLShow PortNumber where
  urlShow = urlShow . fromEnum

instance URLShow Word32 where
  urlShow = show

instance URLShow Event where
  urlShow e = urlShow (Char.toLower x : xs)
    where
      -- INVARIANT: this is always nonempty list
      (x : xs) = show e

instance URLEncode TRequest where
  urlEncode req = mconcat
      [ s "peer_id"    %=  reqPeerId req
      , s "port"       %=  reqPort req
      , s "uploaded"   %=  reqUploaded req
      , s "downloaded" %=  reqDownloaded req
      , s "left"       %=  reqLeft req
      , s "ip"         %=? reqIP req
      , s "numwant"    %=? reqNumWant req
      , s "event"      %=? reqEvent req
      ]
    where s :: String -> String;  s = id; {-# INLINE s #-}

encodeRequest :: TRequest -> URI
encodeRequest req = URL.urlEncode req
                    `addToURI`      reqAnnounce req
                    `addHashToURI`  reqInfoHash req


-- | Ports typically reserved for bittorrent P2P communication.
defaultPorts :: [PortNumber]
defaultPorts =  [6881..6889]

-- | Above 25, new peers are highly unlikely to increase download
--   speed.  Even 30 peers is /plenty/, the official client version 3
--   in fact only actively forms new connections if it has less than
--   30 peers and will refuse connections if it has 55.
--
--   So the default value is set to 50 because usually 30-50% of peers
--   are not responding.
--
defaultNumWant :: Int
defaultNumWant = 50

mkHTTPRequest :: URI -> Request ByteString
mkHTTPRequest uri = Request uri GET [] ""

-- | Send request and receive response from the tracker specified in
-- announce list. This function throws 'IOException' if it couldn't
-- send request or receive response or decode response.
--
askTracker :: TRequest -> IO TResponse
askTracker req = do
    let r = mkHTTPRequest (encodeRequest req)

    rawResp  <- simpleHTTP r
    respBody <- getResponseBody rawResp
    checkResult $ decoded respBody
  where

    checkResult (Left err)
      = ioError $ userError $ err ++ " in tracker response"
    checkResult (Right (Failure err))
      = ioError $ userError $ show err ++ " in tracker response"
    checkResult (Right resp)          = return resp

-- | The same as the 'askTracker' but ignore response. Used in
-- conjunction with 'Stopped'.
leaveTracker :: TRequest -> IO ()
leaveTracker req = do
  let r = mkHTTPRequest (encodeRequest req)

  rawResp  <- simpleHTTP r
  _ <- getResponseBody rawResp
  return ()