{-# LANGUAGE BangPatterns, TypeSynonymInstances, FlexibleInstances, TupleSections #-}
{-# OPTIONS_GHC -O2 #-}
{- Building this module with -O0 causes streams not to fuse and too much
 - memory to be used. -}

-- | 
-- Copyright: 2015 Joey Hess <id@joeyh.name>
-- License: BSD-2-clause
-- 
-- Concurrent output handling, internals.
--
-- May change at any time.

module System.Console.Concurrent.Internal where

import System.IO
import System.Directory
import System.Exit
import Control.Monad
import Control.Monad.IO.Class (liftIO, MonadIO)
import System.IO.Unsafe (unsafePerformIO)
import Control.Concurrent
import Control.Concurrent.STM
import Control.Concurrent.Async
import Data.Maybe
import Data.List
import Data.Monoid
import qualified System.Process as P
import qualified Data.Text as T
import qualified Data.Text.IO as T
import qualified Data.Text.Lazy as L
import Control.Applicative
import Prelude

import Utility.Monad
import Utility.Exception

data OutputHandle = OutputHandle
        { outputLock :: TMVar Lock
        , outputBuffer :: TMVar OutputBuffer
        , errorBuffer :: TMVar OutputBuffer
        , outputThreads :: TMVar Integer
        }

data Lock = Locked

-- | A shared global variable for the OutputHandle.
{-# NOINLINE globalOutputHandle #-}
globalOutputHandle :: OutputHandle
globalOutputHandle = unsafePerformIO $ OutputHandle
        <$> newEmptyTMVarIO
        <*> newTMVarIO (OutputBuffer [])
        <*> newTMVarIO (OutputBuffer [])
        <*> newTMVarIO 0

-- | Holds a lock while performing an action. This allows the action to
-- perform its own output to the console, without using functions from this
-- module.
--
-- While this is running, other threads that try to lockOutput will block.
-- Any calls to `outputConcurrent` and `createProcessConcurrent` will not
-- block, but the output will be buffered and displayed only once the
-- action is done.
lockOutput :: (MonadIO m, MonadMask m) => m a -> m a
lockOutput = bracket_ (liftIO takeOutputLock) (liftIO dropOutputLock)

-- | Blocks until we have the output lock.
takeOutputLock :: IO ()
takeOutputLock = void $ takeOutputLock' True

-- | Tries to take the output lock, without blocking.
tryTakeOutputLock :: IO Bool
tryTakeOutputLock = takeOutputLock' False

withLock :: (TMVar Lock -> STM a) -> IO a
withLock a = atomically $ a (outputLock globalOutputHandle)

takeOutputLock' :: Bool -> IO Bool
takeOutputLock' block = do
        locked <- withLock $ \l -> do
                v <- tryTakeTMVar l
                case v of
                        Just Locked
                                | block -> retry
                                | otherwise -> do
                                        -- Restore value we took.
                                        putTMVar l Locked
                                        return False
                        Nothing -> do
                                putTMVar l Locked
                                return True
        when locked $ do
                (outbuf, errbuf) <- atomically $ (,)
                        <$> swapTMVar (outputBuffer globalOutputHandle) (OutputBuffer [])
                        <*> swapTMVar (errorBuffer globalOutputHandle) (OutputBuffer [])
                emitOutputBuffer StdOut outbuf
                emitOutputBuffer StdErr errbuf
        return locked

-- | Only safe to call after taking the output lock.
dropOutputLock :: IO ()
dropOutputLock = withLock $ void . takeTMVar

-- | Use this around any actions that use `outputConcurrent`
-- or `createProcessConcurrent`
--
-- This is necessary to ensure that buffered concurrent output actually
-- gets displayed before the program exits.
withConcurrentOutput :: (MonadIO m, MonadMask m) => m a -> m a
withConcurrentOutput a = a `finally` liftIO flushConcurrentOutput

-- | Blocks until any processes started by `createProcessConcurrent` have
-- finished, and any buffered output is displayed. Also blocks while
-- `lockOutput` is is use.
--
-- `withConcurrentOutput` calls this at the end, so you do not normally
-- need to use this.
flushConcurrentOutput :: IO ()
flushConcurrentOutput = do
        atomically $ do
                r <- takeTMVar (outputThreads globalOutputHandle)
                if r <= 0
                        then putTMVar (outputThreads globalOutputHandle) r
                        else retry
        -- Take output lock to wait for anything else that might be
        -- currently generating output.
        lockOutput $ return ()

-- | Values that can be output.
class Outputable v where
        toOutput :: v -> T.Text

instance Outputable T.Text where
        toOutput = id

-- | Note that using a lazy Text as an Outputable value 
-- will buffer it all in memory.
instance Outputable L.Text where
        toOutput = toOutput . L.toStrict

instance Outputable String where
        toOutput = toOutput . T.pack

-- | Displays a value to stdout.
--
-- Uses locking to ensure that the whole output occurs atomically
-- even when other threads are concurrently generating output.
--
-- No newline is appended to the value, so if you want a newline, be sure
-- to include it yourself.
--
-- When something else is writing to the console at the same time, this does
-- not block. It buffers the value, so it will be displayed once the other
-- writer is done.
--
-- When outputConcurrent is used within a call to
-- `System.Console.Regions.displayConsoleRegions`, the output is displayed
-- above the currently open console regions. Only lines ending in a newline
-- are displayed in this case (it uses `waitCompleteLines`).
outputConcurrent :: Outputable v => v -> IO ()
outputConcurrent = outputConcurrent' StdOut

-- | Like `outputConcurrent`, but displays to stderr.
--
-- (Does not throw an exception.)
errorConcurrent :: Outputable v => v -> IO ()
errorConcurrent = outputConcurrent' StdErr

outputConcurrent' :: Outputable v => StdHandle -> v -> IO ()
outputConcurrent' stdh v = bracket setup cleanup go
  where
        setup = tryTakeOutputLock
        cleanup False = return ()
        cleanup True = dropOutputLock
        go True = do
                T.hPutStr h (toOutput v)
                hFlush h
        go False = do
                oldbuf <- atomically $ takeTMVar bv
                newbuf <- addOutputBuffer (Output (toOutput v)) oldbuf
                atomically $ putTMVar bv newbuf
        h = toHandle stdh
        bv = bufferFor stdh

-- | This alias is provided to avoid breaking backwards compatibility.
type ConcurrentProcessHandle = P.ProcessHandle

-- | Same as `P.waitForProcess`; provided to avoid breaking backwards
-- compatibility.
waitForProcessConcurrent :: ConcurrentProcessHandle -> IO ExitCode
waitForProcessConcurrent = P.waitForProcess

-- | Wrapper around `System.Process.createProcess` that prevents 
-- multiple processes that are running concurrently from writing
-- to stdout/stderr at the same time.
--
-- If the process does not output to stdout or stderr, it's run
-- by createProcess entirely as usual. Only processes that can generate
-- output are handled specially:
--
-- A process is allowed to write to stdout and stderr in the usual
-- way, assuming it can successfully take the output lock.
--
-- When the output lock is held (ie, by another concurrent process,
-- or because `outputConcurrent` is being called at the same time),
-- the process is instead run with its stdout and stderr
-- redirected to a buffer. The buffered output will be displayed as soon
-- as the output lock becomes free.
--
-- Note that the the process is waited for by a background thread,
-- so unlike createProcess, neglecting to call waitForProcess will not
-- result in zombie processess.
createProcessConcurrent :: P.CreateProcess -> IO (Maybe Handle, Maybe Handle, Maybe Handle, P.ProcessHandle)
createProcessConcurrent p
        | willOutput (P.std_out p) || willOutput (P.std_err p) =
                ifM tryTakeOutputLock
                        ( fgProcess p
                        , bgProcess p
                        )
        | otherwise = do
                r@(_, _, _, h) <- P.createProcess p
                _ <- async $ void $ tryIO $ P.waitForProcess h
                return r

-- | Wrapper around `System.Process.createProcess` that makes sure a process
-- is run in the foreground, with direct access to stdout and stderr.
-- Useful when eg, running an interactive process.
--
-- Note that the the process is waited for by a background thread,
-- so unlike createProcess, neglecting to call waitForProcess will not
-- result in zombie processess.
createProcessForeground :: P.CreateProcess -> IO (Maybe Handle, Maybe Handle, Maybe Handle, P.ProcessHandle)
createProcessForeground p = do
        takeOutputLock
        fgProcess p

fgProcess :: P.CreateProcess -> IO (Maybe Handle, Maybe Handle, Maybe Handle, P.ProcessHandle)
fgProcess p = do
        r@(_, _, _, h) <- P.createProcess p
                `onException` dropOutputLock
        registerOutputThread
        -- Wait for the process to exit and drop the lock.
        _ <- async $ do
                void $ tryIO $ P.waitForProcess h
                unregisterOutputThread
                dropOutputLock
        return r

bgProcess :: P.CreateProcess -> IO (Maybe Handle, Maybe Handle, Maybe Handle, P.ProcessHandle)
bgProcess p = do
        let p' = p
                { P.std_out = rediroutput (P.std_out p)
                , P.std_err = rediroutput (P.std_err p)
                }
        registerOutputThread
        (stdin_h, stdout_h, stderr_h, h) <- P.createProcess p'
                `onException` unregisterOutputThread
        let r =
                ( stdin_h
                , mungeret (P.std_out p) stdout_h
                , mungeret (P.std_err p) stderr_h
                , h
                )
        -- Wait for the process for symmetry with fgProcess,
        -- which does the same.
        _ <- async $ void $ tryIO $ P.waitForProcess h
        outbuf <- setupOutputBuffer StdOut stdout_h
        errbuf <- setupOutputBuffer StdErr stderr_h
        void $ async $ bufferWriter [outbuf, errbuf]
        return r
  where
        rediroutput ss
                | willOutput ss = P.CreatePipe
                | otherwise = ss
        mungeret ss mh
                | willOutput ss = Nothing
                | otherwise = mh

willOutput :: P.StdStream -> Bool
willOutput P.Inherit = True
willOutput _ = False

-- | Buffered output.
data OutputBuffer = OutputBuffer [OutputBufferedActivity]
        deriving (Eq)

data StdHandle = StdOut | StdErr

toHandle :: StdHandle -> Handle
toHandle StdOut = stdout
toHandle StdErr = stderr

bufferFor :: StdHandle -> TMVar OutputBuffer
bufferFor StdOut = outputBuffer globalOutputHandle
bufferFor StdErr = errorBuffer globalOutputHandle

data OutputBufferedActivity
        = Output T.Text
        | InTempFile
                { tempFile :: FilePath
                , endsInNewLine :: Bool
                }
        deriving (Eq)

data AtEnd = AtEnd
        deriving Eq

data BufSig = BufSig

setupOutputBuffer :: StdHandle -> Maybe Handle -> IO (StdHandle, MVar OutputBuffer, TMVar BufSig, TMVar AtEnd)
setupOutputBuffer h fromh = do
        buf <- newMVar (OutputBuffer [])
        bufsig <- atomically newEmptyTMVar
        bufend <- atomically newEmptyTMVar
        void $ async $ outputDrainer fromh buf bufsig bufend
        return (h, buf, bufsig, bufend)

-- Drain output from the handle, and buffer it.
outputDrainer :: Maybe Handle -> MVar OutputBuffer -> TMVar BufSig -> TMVar AtEnd -> IO ()
outputDrainer mfromh buf bufsig bufend = case mfromh of
        Nothing -> atend
        Just fromh -> go fromh
  where
        go fromh = do
                t <- T.hGetChunk fromh
                if T.null t
                        then do
                                atend
                                hClose fromh
                        else do
                                modifyMVar_ buf $ addOutputBuffer (Output t)
                                changed
                                go fromh
        atend = atomically $ putTMVar bufend AtEnd
        changed = atomically $ do
                void $ tryTakeTMVar bufsig
                putTMVar bufsig BufSig

registerOutputThread :: IO ()
registerOutputThread = do
        let v = outputThreads globalOutputHandle
        atomically $ putTMVar v . succ =<< takeTMVar v

unregisterOutputThread :: IO ()
unregisterOutputThread = do
        let v = outputThreads globalOutputHandle
        atomically $ putTMVar v . pred =<< takeTMVar v

-- Wait to lock output, and once we can, display everything 
-- that's put into the buffers, until the end.
--
-- If end is reached before lock is taken, instead add the command's
-- buffers to the global outputBuffer and errorBuffer.
bufferWriter :: [(StdHandle, MVar OutputBuffer, TMVar BufSig, TMVar AtEnd)] -> IO ()
bufferWriter ts = do
        activitysig <- atomically newEmptyTMVar
        worker1 <- async $ lockOutput $
                ifM (atomically $ tryPutTMVar activitysig ())
                        ( void $ mapConcurrently displaybuf ts
                        , noop -- buffers already moved to global
                        )
        worker2 <- async $ void $ globalbuf activitysig worker1
        void $ async $ do
                void $ waitCatch worker1
                void $ waitCatch worker2
                unregisterOutputThread
  where
        displaybuf v@(outh, buf, bufsig, bufend) = do
                change <- atomically $
                        (Right <$> takeTMVar bufsig)
                                `orElse`
                        (Left <$> takeTMVar bufend)
                l <- takeMVar buf
                putMVar buf (OutputBuffer [])
                emitOutputBuffer outh l
                case change of
                        Right BufSig -> displaybuf v
                        Left AtEnd -> return ()
        globalbuf activitysig worker1 = do
                ok <- atomically $ do
                        -- signal we're going to handle it
                        -- (returns false if the displaybuf already did)
                        ok <- tryPutTMVar activitysig ()
                        -- wait for end of all buffers
                        when ok $
                                mapM_ (\(_outh, _buf, _bufsig, bufend) -> takeTMVar bufend) ts
                        return ok
                when ok $ do
                        -- add all of the command's buffered output to the
                        -- global output buffer, atomically
                        bs <- forM ts $ \(outh, buf, _bufsig, _bufend) ->
                                (outh,) <$> takeMVar buf
                        atomically $
                                forM_ bs $ \(outh, b) ->
                                        bufferOutputSTM' outh b
                        -- worker1 might be blocked waiting for the output
                        -- lock, and we've already done its job, so cancel it
                        cancel worker1

-- Adds a value to the OutputBuffer. When adding Output to a Handle,
-- it's cheaper to combine it with any already buffered Output to that
-- same Handle.
--
-- When the total buffered Output exceeds 1 mb in size, it's moved out of
-- memory, to a temp file. This should only happen rarely, but is done to
-- avoid some verbose process unexpectedly causing excessive memory use.
addOutputBuffer :: OutputBufferedActivity -> OutputBuffer -> IO OutputBuffer
addOutputBuffer (Output t) (OutputBuffer buf)
        | T.length t' <= 1048576 = return $ OutputBuffer (Output t' : other)
        | otherwise = do
                tmpdir <- getTemporaryDirectory
                (tmp, h) <- openTempFile tmpdir "output.tmp"
                let !endnl = endsNewLine t'
                let i = InTempFile
                        { tempFile = tmp
                        , endsInNewLine = endnl
                        }
                T.hPutStr h t'
                hClose h
                return $ OutputBuffer (i : other)
  where
        !t' = T.concat (mapMaybe getOutput this) <> t
        !(this, other) = partition isOutput buf
        isOutput v = case v of
                Output _ -> True
                _ -> False
        getOutput v = case v of
                Output t'' -> Just t''
                _ -> Nothing
addOutputBuffer v (OutputBuffer buf) = return $ OutputBuffer (v:buf)

-- | Adds a value to the output buffer for later display.
--
-- Note that buffering large quantities of data this way will keep it
-- resident in memory until it can be displayed. While `outputConcurrent`
-- uses temp files if the buffer gets too big, this STM function cannot do
-- so.
bufferOutputSTM :: Outputable v => StdHandle -> v -> STM ()
bufferOutputSTM h v = bufferOutputSTM' h (OutputBuffer [Output (toOutput v)])

bufferOutputSTM' :: StdHandle -> OutputBuffer -> STM ()
bufferOutputSTM' h (OutputBuffer newbuf) = do
        (OutputBuffer buf) <- takeTMVar bv
        putTMVar bv (OutputBuffer (newbuf ++ buf))
  where
        bv = bufferFor h

-- | A STM action that waits for some buffered output to become
-- available, and returns it.
--
-- The function can select a subset of output when only some is desired;
-- the fst part is returned and the snd is left in the buffer.
--
-- This will prevent it from being displayed in the usual way, so you'll
-- need to use `emitOutputBuffer` to display it yourself.
outputBufferWaiterSTM :: (OutputBuffer -> (OutputBuffer, OutputBuffer)) -> STM (StdHandle, OutputBuffer)
outputBufferWaiterSTM selector = waitgetbuf StdOut `orElse` waitgetbuf StdErr
  where
        waitgetbuf h = do
                let bv = bufferFor h
                (selected, rest) <- selector <$> takeTMVar bv
                when (selected == OutputBuffer [])
                        retry
                putTMVar bv rest
                return (h, selected)

waitAnyBuffer :: OutputBuffer -> (OutputBuffer, OutputBuffer)
waitAnyBuffer b = (b, OutputBuffer [])

-- | Use with `outputBufferWaiterSTM` to make it only return buffered
-- output that ends with a newline. Anything buffered without a newline
-- is left in the buffer.
waitCompleteLines :: OutputBuffer -> (OutputBuffer, OutputBuffer)
waitCompleteLines (OutputBuffer l) =
        let (selected, rest) = span completeline l
        in (OutputBuffer selected, OutputBuffer rest)
  where
        completeline (v@(InTempFile {})) = endsInNewLine v
        completeline (Output b) = endsNewLine b

endsNewLine :: T.Text -> Bool
endsNewLine t = not (T.null t) && T.last t == '\n'

-- | Emits the content of the OutputBuffer to the Handle
--
-- If you use this, you should use `lockOutput` to ensure you're the only
-- thread writing to the console.
emitOutputBuffer :: StdHandle -> OutputBuffer -> IO ()
emitOutputBuffer stdh (OutputBuffer l) =
        forM_ (reverse l) $ \ba -> case ba of
                Output t -> emit t
                InTempFile tmp _ -> do
                        emit =<< T.readFile tmp
                        void $ tryWhenExists $ removeFile tmp
  where
        outh = toHandle stdh
        emit t = void $ tryIO $ do
                T.hPutStr outh t
                hFlush outh