{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TupleSections #-}
module Stack.FileWatch
    ( fileWatch
    , fileWatchPoll
    , printExceptionStderr
    ) where

import Blaze.ByteString.Builder (toLazyByteString, copyByteString)
import Blaze.ByteString.Builder.Char.Utf8 (fromShow)
import Control.Concurrent.Async (race_)
import Control.Concurrent.STM
import Control.Exception (Exception, fromException)
import Control.Exception.Safe (tryAny)
import Control.Monad (forever, unless, when)
import qualified Data.ByteString.Lazy as L
import qualified Data.Map.Strict as Map
import Data.Monoid ((<>))
import Data.Set (Set)
import qualified Data.Set as Set
import Data.String (fromString)
import Data.Traversable (forM)
import GHC.IO.Handle (hIsTerminalDevice)
import Path
import System.Console.ANSI
import System.Exit
import System.FSNotify
import System.IO (Handle, stdout, stderr, hPutStrLn)

-- | Print an exception to stderr
printExceptionStderr :: Exception e => e -> IO ()
printExceptionStderr e =
    L.hPut stderr $ toLazyByteString $ fromShow e <> copyByteString "\n"

fileWatch :: Handle
          -> ((Set (Path Abs File) -> IO ()) -> IO ())
          -> IO ()
fileWatch = fileWatchConf defaultConfig

fileWatchPoll :: Handle
              -> ((Set (Path Abs File) -> IO ()) -> IO ())
              -> IO ()
fileWatchPoll = fileWatchConf $ defaultConfig { confUsePolling = True }

-- | Run an action, watching for file changes
--
-- The action provided takes a callback that is used to set the files to be
-- watched. When any of those files are changed, we rerun the action again.
fileWatchConf :: WatchConfig
              -> Handle
              -> ((Set (Path Abs File) -> IO ()) -> IO ())
              -> IO ()
fileWatchConf cfg out inner = withManagerConf cfg $ \manager -> do
    let putLn = hPutStrLn out
    let withColor color action = do
            outputIsTerminal <- hIsTerminalDevice stdout
            if outputIsTerminal
            then do
                setSGR [SetColor Foreground Dull color]
                action
                setSGR [Reset]
            else action

    allFiles <- newTVarIO Set.empty
    dirtyVar <- newTVarIO True
    watchVar <- newTVarIO Map.empty

    let onChange event = atomically $ do
            files <- readTVar allFiles
            when (eventPath event `Set.member` files) (writeTVar dirtyVar True)

        setWatched :: Set (Path Abs File) -> IO ()
        setWatched files = do
            atomically $ writeTVar allFiles $ Set.map toFilePath files
            watch0 <- readTVarIO watchVar
            let actions = Map.mergeWithKey
                    keepListening
                    stopListening
                    startListening
                    watch0
                    newDirs
            watch1 <- forM (Map.toList actions) $ \(k, mmv) -> do
                mv <- mmv
                return $
                    case mv of
                        Nothing -> Map.empty
                        Just v -> Map.singleton k v
            atomically $ writeTVar watchVar $ Map.unions watch1
          where
            newDirs = Map.fromList $ map (, ())
                    $ Set.toList
                    $ Set.map parent files

            keepListening _dir listen () = Just $ return $ Just listen
            stopListening = Map.map $ \f -> do
                () <- f
                return Nothing
            startListening = Map.mapWithKey $ \dir () -> do
                let dir' = fromString $ toFilePath dir
                listen <- watchDir manager dir' (const True) onChange
                return $ Just listen


    let watchInput = do
            line <- getLine
            unless (line == "quit") $ do
                case line of
                    "help" -> do
                        putLn ""
                        putLn "help: display this help"
                        putLn "quit: exit"
                        putLn "build: force a rebuild"
                        putLn "watched: display watched files"
                    "build" -> atomically $ writeTVar dirtyVar True
                    "watched" -> do
                        watch <- readTVarIO allFiles
                        mapM_ putLn (Set.toList watch)
                    "" -> atomically $ writeTVar dirtyVar True
                    _ -> putLn $ concat
                        [ "Unknown command: "
                        , show line
                        , ". Try 'help'"
                        ]

                watchInput

    race_ watchInput $ forever $ do
        atomically $ do
            dirty <- readTVar dirtyVar
            check dirty

        eres <- tryAny $ inner setWatched

        -- Clear dirtiness flag after the build to avoid an infinite
        -- loop caused by the build itself triggering dirtiness. This
        -- could be viewed as a bug, since files changed during the
        -- build will not trigger an extra rebuild, but overall seems
        -- like better behavior. See
        -- https://github.com/commercialhaskell/stack/issues/822
        atomically $ writeTVar dirtyVar False

        case eres of
            Left e -> do
                let color = case fromException e of
                        Just ExitSuccess -> Green
                        _ -> Red
                withColor color $ printExceptionStderr e
            _ -> withColor Green $
                putLn "Success! Waiting for next file change."

        putLn "Type help for available commands. Press enter to force a rebuild."
