{- This file is part of Vervis.
 -
 - Written in 2016 by fr33domlover <fr33domlover@riseup.net>.
 -
 - ♡ Copying is an act of love. Please copy, reuse and share.
 -
 - The author(s) have dedicated all copyright and related and neighboring
 - rights to this software to the public domain worldwide. This software is
 - distributed without any warranty.
 -
 - You should have received a copy of the CC0 Public Domain Dedication along
 - with this software. If not, see
 - <http://creativecommons.org/publicdomain/zero/1.0/>.
 -}

module Vervis.Ssh
    ( runSsh
    )
where

import Prelude

import Control.Monad (when)
import Control.Monad.IO.Class (liftIO)
import Control.Monad.Logger
import Control.Monad.Trans.Class (lift)
import Control.Monad.Trans.Reader (ReaderT (runReaderT), ask)
import Data.ByteString.Char8 (ByteString, unpack)
import Data.ByteString.Lazy (fromStrict)
import Data.Foldable (find)
import Data.Text (Text, pack)
import Database.Persist
import Database.Persist.Sql (SqlBackend, ConnectionPool, runSqlPool)
import Network.SSH
import Network.SSH.Channel
import Network.SSH.Crypto
import Network.SSH.Session
import Yesod.Default.Main (LogFunc)

import Vervis.Model
import Vervis.Settings

-- TODO:
-- [x] Implement serious logging (info, warning, error, etc.) with
--     monad-logger, maybe see how loggin works in the scaffolding
-- [ ] See which git commands darcsden SSH supports and see if I can implement
--     them with Hit (i think it was git upload-pack)

type ChannelB = LoggingT (ReaderT ConnectionPool IO)
type SessionB = LoggingT (ReaderT ConnectionPool IO)
type Backend = SqlBackend

type Channel = ChannelT ChannelB
type Session = SessionT SessionB ChannelB
type SshChanDB = ReaderT Backend Channel
type SshSessDB = ReaderT Backend Session

src :: Text
src = "SSH"

runChanDB :: SshChanDB a -> Channel a
runChanDB action = do
    pool <- lift . lift $ ask
    runSqlPool action pool

runSessDB :: SshSessDB a -> Session a
runSessDB action = do
    pool <- lift . lift $ ask
    runSqlPool action pool

chanFail :: Bool -> ByteString -> Channel ()
chanFail wantReply msg = do
    channelError $ unpack msg
    when wantReply channelFail

authorize :: Authorize -> Session Bool
authorize (Password  _    _)   = return False
authorize (PublicKey name key) = do
    mkeys <- runSessDB $ do
        mp <- getBy $ UniquePersonLogin $ pack name
        case mp of
            Nothing              -> return Nothing
            Just (Entity pid _p) ->
                fmap Just $ selectList [SshKeyPerson ==. pid] []
    case mkeys of
        Nothing -> do
            $logInfoS src "Auth failed: Invalid user"
            return False
        Just keys -> do
            let eValue (Entity _ v) = v
                matches =
                    (== key) . blobToKey . fromStrict . sshKeyContent . eValue
            case find matches keys of
                Nothing -> do
                    $logInfoS src "Auth failed: No matching key found"
                    return False
                Just match -> do
                    $logInfoS src "Auth succeeded"
                    return True

handle :: Bool -> ChannelRequest -> Channel ()
handle wantReply request = do
    liftIO $ print request
    chanFail wantReply "I don't execute any commands yet, come back later"

ready :: LogFunc -> IO ()
ready = runLoggingT $ $logInfoS src "SSH server component starting"

mkConfig
    :: AppSettings
    -> ConnectionPool
    -> LogFunc
    -> IO (Config SessionB ChannelB)
mkConfig settings pool logFunc = do
    keyPair <- keyPairFromFile $ appSshKeyFile settings
    return $ Config
        { cSession     = SessionConfig
            { scAuthMethods  = ["publickey"]
            , scAuthorize    = authorize
            , scKeyPair      = keyPair
            , scRunBaseMonad =
                flip runReaderT pool . flip runLoggingT logFunc
            }
        , cChannel     = ChannelConfig
            { ccRequestHandler = handle
            , ccRunBaseMonad   =
                flip runReaderT pool . flip runLoggingT logFunc
            }
        , cPort        = fromIntegral $ appSshPort settings
        , cReadyAction = ready logFunc
        }

runSsh :: AppSettings -> ConnectionPool -> LogFunc -> IO ()
runSsh settings pool logFunc = do
    config <- mkConfig settings pool logFunc
    startConfig config