    {- System.Process enhancements, including additional ways of running
     - processes, and logging.
     -
     - Copyright 2012-2015 Joey Hess <id@joeyh.name>
     -
     - License: BSD-2-clause
     -}

    {-# LANGUAGE CPP, Rank2Types #-}
    {-# OPTIONS_GHC -fno-warn-tabs #-}

    module Utility.Process (
            module X,
            CreateProcess(..),
            StdHandle(..),
            readProcess,
            readProcess',
            readProcessEnv,
            writeReadProcessEnv,
            forceSuccessProcess,
            forceSuccessProcess',
            checkSuccessProcess,
            ignoreFailureProcess,
            createProcessSuccess,
            createProcessChecked,
            createBackgroundProcess,
            withHandle,
            withIOHandles,
            withOEHandles,
            withNullHandle,
            withQuietOutput,
            feedWithQuietOutput,
            createProcess,
            waitForProcess,
            startInteractiveProcess,
            stdinHandle,
            stdoutHandle,
            stderrHandle,
            ioHandles,
            processHandle,
            devNull,
    ) where

    import qualified Utility.Process.Shim
    import qualified Utility.Process.Shim as X hiding (CreateProcess(..), createProcess, runInteractiveProcess, readProcess, readProcessWithExitCode, system, rawSystem, runInteractiveCommand, runProcess)
    import Utility.Process.Shim hiding (createProcess, readProcess, waitForProcess)
    import Utility.Misc
    import Utility.Exception

    import System.Exit
    import System.IO
    import System.Log.Logger
    import Control.Concurrent
    import qualified Control.Exception as E
    import Control.Monad

    type CreateProcessRunner = forall a. CreateProcess -> ((Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle) -> IO a) -> IO a

    data StdHandle = StdinHandle | StdoutHandle | StderrHandle
            deriving (Eq)

    -- | Normally, when reading from a process, it does not need to be fed any
    -- standard input.
    readProcess :: FilePath -> [String] -> IO String
    readProcess cmd args = readProcessEnv cmd args Nothing

    readProcessEnv :: FilePath -> [String] -> Maybe [(String, String)] -> IO String
    readProcessEnv cmd args environ = readProcess' p
      where
            p = (proc cmd args)
                    { std_out = CreatePipe
                    , env = environ
                    }

    readProcess' :: CreateProcess -> IO String
    readProcess' p = withHandle StdoutHandle createProcessSuccess p $ \h -> do
            output  <- hGetContentsStrict h
            hClose h
            return output

    -- | Runs an action to write to a process on its stdin,
    -- returns its output, and also allows specifying the environment.
    writeReadProcessEnv
            :: FilePath
            -> [String]
            -> Maybe [(String, String)]
            -> (Maybe (Handle -> IO ()))
            -> (Maybe (Handle -> IO ()))
            -> IO String
    writeReadProcessEnv cmd args environ writestdin adjusthandle = do
            (Just inh, Just outh, _, pid) <- createProcess p

            maybe (return ()) (\a -> a inh) adjusthandle
            maybe (return ()) (\a -> a outh) adjusthandle

            -- fork off a thread to start consuming the output
            output  <- hGetContents outh
            outMVar <- newEmptyMVar
            _ <- forkIO $ E.evaluate (length output) >> putMVar outMVar ()

            -- now write and flush any input
            maybe (return ()) (\a -> a inh >> hFlush inh) writestdin
            hClose inh -- done with stdin

            -- wait on the output
            takeMVar outMVar
            hClose outh

            -- wait on the process
            forceSuccessProcess p pid

            return output

      where
            p = (proc cmd args)
                    { std_in = CreatePipe
                    , std_out = CreatePipe
                    , std_err = Inherit
                    , env = environ
                    }

    -- | Waits for a ProcessHandle, and throws an IOError if the process
    -- did not exit successfully.
    forceSuccessProcess :: CreateProcess -> ProcessHandle -> IO ()
    forceSuccessProcess p pid = waitForProcess pid >>= forceSuccessProcess' p

    forceSuccessProcess' :: CreateProcess -> ExitCode -> IO ()
    forceSuccessProcess' _ ExitSuccess = return ()
    forceSuccessProcess' p (ExitFailure n) = fail $
            showCmd p ++ " exited " ++ show n

    -- | Waits for a ProcessHandle and returns True if it exited successfully.
    -- Note that using this with createProcessChecked will throw away
    -- the Bool, and is only useful to ignore the exit code of a process,
    -- while still waiting for it. -}
    checkSuccessProcess :: ProcessHandle -> IO Bool
    checkSuccessProcess pid = do
            code <- waitForProcess pid
            return $ code == ExitSuccess

    ignoreFailureProcess :: ProcessHandle -> IO Bool
    ignoreFailureProcess pid = do
            void $ waitForProcess pid
            return True

    -- | Runs createProcess, then an action on its handles, and then
    -- forceSuccessProcess.
    createProcessSuccess :: CreateProcessRunner
    createProcessSuccess p a = createProcessChecked (forceSuccessProcess p) p a

    -- | Runs createProcess, then an action on its handles, and then
    -- a checker action on its exit code, which must wait for the process.
    createProcessChecked :: (ProcessHandle -> IO b) -> CreateProcessRunner
    createProcessChecked checker p a = do
            t@(_, _, _, pid) <- createProcess p
            r <- tryNonAsync $ a t
            _ <- checker pid
            either E.throw return r

    -- | Leaves the process running, suitable for lazy streaming.
    -- Note: Zombies will result, and must be waited on.
    createBackgroundProcess :: CreateProcessRunner
    createBackgroundProcess p a = a =<< createProcess p

    -- | Runs a CreateProcessRunner, on a CreateProcess structure, that
    -- is adjusted to pipe only from/to a single StdHandle, and passes
    -- the resulting Handle to an action.
    withHandle
            :: StdHandle
            -> CreateProcessRunner
            -> CreateProcess
            -> (Handle -> IO a)
            -> IO a
    withHandle h creator p a = creator p' $ a . select
      where
            base = p
                    { std_in = Inherit
                    , std_out = Inherit
                    , std_err = Inherit
                    }
            (select, p') = case h of
                    StdinHandle -> (stdinHandle, base { std_in = CreatePipe })
                    StdoutHandle -> (stdoutHandle, base { std_out = CreatePipe })
                    StderrHandle -> (stderrHandle, base { std_err = CreatePipe })

    -- | Like withHandle, but passes (stdin, stdout) handles to the action.
    withIOHandles
            :: CreateProcessRunner
            -> CreateProcess
            -> ((Handle, Handle) -> IO a)
            -> IO a
    withIOHandles creator p a = creator p' $ a . ioHandles
      where
            p' = p
                    { std_in = CreatePipe
                    , std_out = CreatePipe
                    , std_err = Inherit
                    }

    -- | Like withHandle, but passes (stdout, stderr) handles to the action.
    withOEHandles
            :: CreateProcessRunner
            -> CreateProcess
            -> ((Handle, Handle) -> IO a)
            -> IO a
    withOEHandles creator p a = creator p' $ a . oeHandles
      where
            p' = p
                    { std_in = Inherit
                    , std_out = CreatePipe
                    , std_err = CreatePipe
                    }

    withNullHandle :: (Handle -> IO a) -> IO a
    withNullHandle = withFile devNull WriteMode

    -- | Forces the CreateProcessRunner to run quietly;
    -- both stdout and stderr are discarded.
    withQuietOutput
            :: CreateProcessRunner
            -> CreateProcess
            -> IO ()
    withQuietOutput creator p = withNullHandle $ \nullh -> do
            let p' = p
                    { std_out = UseHandle nullh
                    , std_err = UseHandle nullh
                    }
            creator p' $ const $ return ()

    -- | Stdout and stderr are discarded, while the process is fed stdin
    -- from the handle.
    feedWithQuietOutput
            :: CreateProcessRunner
            -> CreateProcess
            -> (Handle -> IO a)
            -> IO a
    feedWithQuietOutput creator p a = withFile devNull WriteMode $ \nullh -> do
            let p' = p
                    { std_in = CreatePipe
                    , std_out = UseHandle nullh
                    , std_err = UseHandle nullh
                    }
            creator p' $ a . stdinHandle

    devNull :: FilePath
    #ifndef mingw32_HOST_OS
    devNull = "/dev/null"
    #else
    -- Use device namespace to prevent GHC from rewriting path
    devNull = "\\\\.\\NUL"
    #endif

    -- | Extract a desired handle from createProcess's tuple.
    -- These partial functions are safe as long as createProcess is run
    -- with appropriate parameters to set up the desired handle.
    -- Get it wrong and the runtime crash will always happen, so should be
    -- easily noticed.
    type HandleExtractor = (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle) -> Handle
    stdinHandle :: HandleExtractor
    stdinHandle (Just h, _, _, _) = h
    stdinHandle _ = error "expected stdinHandle"
    stdoutHandle :: HandleExtractor
    stdoutHandle (_, Just h, _, _) = h
    stdoutHandle _ = error "expected stdoutHandle"
    stderrHandle :: HandleExtractor
    stderrHandle (_, _, Just h, _) = h
    stderrHandle _ = error "expected stderrHandle"
    ioHandles :: (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle) -> (Handle, Handle)
    ioHandles (Just hin, Just hout, _, _) = (hin, hout)
    ioHandles _ = error "expected ioHandles"
    oeHandles :: (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle) -> (Handle, Handle)
    oeHandles (_, Just hout, Just herr, _) = (hout, herr)
    oeHandles _ = error "expected oeHandles"

    processHandle :: (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle) -> ProcessHandle
    processHandle (_, _, _, pid) = pid

    -- | Shows the command that a CreateProcess will run.
    showCmd :: CreateProcess -> String
    showCmd = go . cmdspec
      where
            go (ShellCommand s) = s
            go (RawCommand c ps) = c ++ " " ++ show ps

    -- | Starts an interactive process. Unlike runInteractiveProcess in
    -- System.Process, stderr is inherited.
    startInteractiveProcess
            :: FilePath
            -> [String]
            -> Maybe [(String, String)]
            -> IO (ProcessHandle, Handle, Handle)
    startInteractiveProcess cmd args environ = do
            let p = (proc cmd args)
                    { std_in = CreatePipe
                    , std_out = CreatePipe
                    , std_err = Inherit
                    , env = environ
                    }
            (Just from, Just to, _, pid) <- createProcess p
            return (pid, to, from)

    -- | Wrapper around 'System.Process.createProcess' that does debug logging.
    createProcess :: CreateProcess -> IO (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle)
    createProcess p = do
            debugProcess p
            Utility.Process.Shim.createProcess p

    -- | Debugging trace for a CreateProcess.
    debugProcess :: CreateProcess -> IO ()
    debugProcess p = debugM "Utility.Process" $ unwords
            [ action ++ ":"
            , showCmd p
            ]
      where
            action
                    | piped (std_in p) && piped (std_out p) = "chat"
                    | piped (std_in p)                      = "feed"
                    | piped (std_out p)                     = "read"
                    | otherwise                             = "call"
            piped Inherit = False
            piped _ = True

    -- | Wrapper around 'System.Process.waitForProcess' that does debug logging.
    waitForProcess ::  ProcessHandle -> IO ExitCode
    waitForProcess h = do
            r <- Utility.Process.Shim.waitForProcess h
            debugM "Utility.Process" ("process done " ++ show r)
            return r