{- This file is part of Vervis.
 -
 - Written in 2016, 2019, 2022 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 Control.Applicative ((<|>), optional)
import Control.Monad (when)
import Control.Monad.IO.Class (liftIO)
import Control.Monad.Logger
import Control.Monad.Trans.Class (lift)
import Control.Monad.Trans.Maybe (MaybeT (MaybeT, runMaybeT))
import Control.Monad.Trans.Reader (ReaderT (runReaderT), ask)
import Data.Attoparsec.Text
import Data.ByteString (ByteString)
import Data.ByteString.Lazy (fromStrict)
import Data.Foldable (find)
import Data.Git.Storage (isRepo)
import Data.Maybe (isJust)
import Data.Monoid ((<>))
import Data.String (fromString)
import Data.Text (Text)
import Database.Persist
import Database.Persist.Sql
import Formatting ((%))
import Network.SSH
import Network.SSH.Channel
import Network.SSH.Crypto
import Network.SSH.Session
import System.Directory (doesFileExist, doesDirectoryExist)
import System.Environment
import System.FilePath ((</>))
import System.Process (CreateProcess (..), StdStream (..), createProcess, proc)
import Web.Hashids
import Yesod.Core.Dispatch

import qualified Data.Text as T
import qualified Formatting as F

import Yesod.Hashids

import Vervis.Access
import Vervis.Model
import Vervis.Model.Ident
import Vervis.Model.Role
import Vervis.Path
import Vervis.Settings

-------------------------------------------------------------------------------
-- Types
-------------------------------------------------------------------------------

type ChannelBase = LoggingT (ReaderT ConnectionPool IO)
type SessionBase = LoggingT (ReaderT ConnectionPool IO)
type UserAuthId = PersonId

type Channel = ChannelT UserAuthId ChannelBase
type Session = SessionT SessionBase UserAuthId ChannelBase
type SshChanDB = SqlPersistT Channel
type SshSessDB = SqlPersistT Session

data Action
    = DarcsTransferMode (KeyHashid Repo)
    | DarcsApply (KeyHashid Repo)
    | GitUploadPack (KeyHashid Repo)
    | GitReceivePack (KeyHashid Repo)
    deriving Show

-- | Result of running an action on the server side as a response to an SSH
-- channel request.
data ActionResult
    = ARDone Text -- ^ Action finished successfully with message
    | ARProcess   -- ^ Action executed process, the rest depends on the process
    | ARFail Text -- ^ Action failed with message

-------------------------------------------------------------------------------
-- Utils
-------------------------------------------------------------------------------

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

-------------------------------------------------------------------------------
-- Auth
-------------------------------------------------------------------------------

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

-------------------------------------------------------------------------------
-- Actions
-------------------------------------------------------------------------------

toKeyHashid t =
    case fromPathPiece t of
        Nothing -> fail "Can't parse keyhashid"
        Just kh -> return kh

--TOD TODO TODO check paths for safety... no /./ or /../ and so on

darcsRepoSpecP :: Parser (KeyHashid Repo)
darcsRepoSpecP = toKeyHashid =<< (part <* optional (char '/'))
    where
    part = takeWhile1 $ \ c -> c /= '/' && c /= '\''

gitRepoSpecP :: Parser (KeyHashid Repo)
gitRepoSpecP = toKeyHashid =<< (msh *> part)
    where
    part = takeWhile1 $ \ c -> c /= '/' && c /= '\''
    msh  = optional $ satisfy $ \ c -> c == '/' || c == '~'

actionP :: Parser Action
actionP =   DarcsTransferMode <$>
            ("darcs transfer-mode --repodir " *> darcsRepoSpecP)
        <|> DarcsApply <$>
            ("darcs apply --all  --repodir '" *> darcsRepoSpecP <* char '\'')
        <|> GitUploadPack <$>
            ("git-upload-pack '"  *> gitRepoSpecP <* char '\'')
        <|> GitReceivePack <$>
            ("git-receive-pack '" *> gitRepoSpecP <* char '\'')

parseExec :: Text -> Either String Action
parseExec input = parseOnly (actionP <* endOfInput) input

detectAction :: ChannelRequest -> Either Text Action
detectAction (Execute s) =
    case parseExec $ T.pack s of
        Left _       -> Left "Unsupported command"
        Right action -> Right action
detectAction _           = Left "Unsupported channel request"

execute :: FilePath -> [String] -> Channel ()
execute cmd args = do
    lift $ $logDebugS src $
        F.sformat ("Executing " % F.string % " " % F.shown) cmd args
    let config = (proc cmd args)
            { std_in  = CreatePipe
            , std_out = CreatePipe
            , std_err = CreatePipe
            }
        verifyPipe Nothing  = error "createProcess didn't create all the pipes"
        verifyPipe (Just h) = h
        verifyPipes (mIn, mOut, mErr, ph) =
            (verifyPipe mIn, verifyPipe mOut, verifyPipe mErr, ph)
    spawnProcess $ verifyPipes <$> createProcess config

whenRepoExists
    :: Text
    -> (FilePath -> IO Bool)
    -> Bool
    -> FilePath
    -> Channel ActionResult
    -> Channel ActionResult
whenRepoExists vcs checkFS checkedDB repoPath action = do
    looksGood <- liftIO $ checkFS repoPath
    if looksGood
        then action
        else do
            when checkedDB $ lift $ $logErrorS src $
                T.concat [vcs, " repo not found! ", T.pack repoPath]
            return $ ARFail $ T.concat ["No such ", vcs, " repository"]

whenDarcsRepoExists
    :: Bool -> FilePath -> Channel ActionResult -> Channel ActionResult
whenDarcsRepoExists =
    whenRepoExists "Darcs" $ doesDirectoryExist . (</> "_darcs")

whenGitRepoExists
    :: Bool -> FilePath -> Channel ActionResult -> Channel ActionResult
whenGitRepoExists = whenRepoExists "Git" $ isRepo . fromString

canPushTo :: RepoId -> Channel Bool
canPushTo repoID = do
    pid <- authId <$> askAuthDetails
    oas <- runChanDB $ checkRepoAccess' (Just pid) ProjOpPush repoID
    return $
        case oas of
            ObjectAccessAllowed -> True
            _                   -> False

runAction
    :: (KeyHashid Repo -> Maybe RepoId)
    -> FilePath
    -> Bool
    -> Action
    -> Channel ActionResult
runAction decodeRepoHash root _wantReply action =
    case action of
        DarcsTransferMode repoHash -> do
            let repoPath = repoDir root repoHash
            whenDarcsRepoExists False repoPath $ do
                execute "darcs" ["transfer-mode", "--repodir", repoPath]
                return ARProcess
        DarcsApply repoHash -> do
            let repoPath = repoDir root repoHash
            can <-
                case decodeRepoHash repoHash of
                    Nothing -> return False
                    Just repoID -> canPushTo repoID
            if can
                then whenDarcsRepoExists True repoPath $ do
                    pid <- authId <$> askAuthDetails
                    liftIO $ setEnv "VERVIS_SSH_USER" (show $ fromSqlKey pid)
                    execute "darcs" ["apply", "--all", "--repodir", repoPath]
                    return ARProcess
                else return $ ARFail "You can't push to this repository"
        GitUploadPack repoHash -> do
            let repoPath = repoDir root repoHash
            whenGitRepoExists False repoPath $ do
                execute "git-upload-pack" [repoPath]
                return ARProcess
        GitReceivePack repoHash -> do
            let repoPath = repoDir root repoHash
            can <-
                case decodeRepoHash repoHash of
                    Nothing -> return False
                    Just repoID -> canPushTo repoID
            if can
                then whenGitRepoExists True repoPath $ do
                    pid <- authId <$> askAuthDetails
                    liftIO $ setEnv "VERVIS_SSH_USER" (show $ fromSqlKey pid)
                    execute "git-receive-pack" [repoPath]
                    return ARProcess
                else return $ ARFail "You can't push to this repository"

handle
    :: (KeyHashid Repo -> Maybe RepoId)
    -> FilePath
    -> Bool
    -> ChannelRequest
    -> Channel ()
handle decodeRepoHash repoDir wantReply request = do
    lift $ $logDebugS src $ T.pack $ show request
    case detectAction request of
        Left e    -> do
            lift $ $logDebugS src $ "Invalid action: " <> e
            channelError $ T.unpack e
            when wantReply channelFail
        Right act -> do
            lift $ $logDebugS src $ T.pack $ show act
            res <- runAction decodeRepoHash repoDir wantReply act
            case res of
                ARDone msg -> do
                    lift $ $logDebugS src $ "Action done: " <> msg
                    channelMessage $ T.unpack msg
                    when wantReply channelSuccess
                    channelDone
                ARProcess  -> do
                    lift $ $logDebugS src "Action ran process"
                    when wantReply channelSuccess
                ARFail msg -> do
                    lift $ $logDebugS src $ "Action failed: " <> msg
                    channelError $ T.unpack msg
                    when wantReply channelSuccess
                    channelDone

-------------------------------------------------------------------------------
-- Config and running
-------------------------------------------------------------------------------

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

mkConfig
    :: AppSettings
    -> HashidsContext
    -> ConnectionPool
    -> LogFunc
    -> IO (Config SessionBase ChannelBase UserAuthId)
mkConfig settings ctx 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 (decodeKeyHashidPure ctx) (appRepoDir settings)
            , ccRunBaseMonad   =
                flip runReaderT pool . flip runLoggingT logFunc
            }
        , cPort        = fromIntegral $ appSshPort settings
        , cReadyAction = ready logFunc
        }

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