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use "signals"
use "files"
use @pony_os_errno[I32]()
use @ponyint_wnohang[I32]() if posix
use @ponyint_win_process_create[USize](appname: Pointer[U8] tag,
  cmdline: Pointer[U8] tag, environ: Pointer[U8] tag, wdir: Pointer[U8] tag,
  stdin_fd: U32, stdout_fd: U32, stderr_fd: U32,
  error_code: Pointer[U32], error_msg: Pointer[Pointer[U8]] tag)
use @ponyint_win_process_wait[I32](hProc: USize, code: Pointer[I32])
use @ponyint_win_process_kill[I32](hProc: USize)
use @execve[I32](path: Pointer[U8] tag, argp: Pointer[Pointer[U8] tag] tag,
  envp: Pointer[Pointer[U8] tag] tag)
use @fork[I32]()
use @chdir[I32](path: Pointer[U8] tag)
use @dup2[I32](fildes: U32, fildes2: U32)
use @write[ISize](fd: U32, buf: Pointer[U8] tag, size: USize)
use @kill[I32](pid_t: I32, sig: U32)
use @waitpid[I32](pid: I32, stat_loc: Pointer[I32] tag, opts: I32)
use @_exit[None](status: I32)

// for Windows System Error Codes see: https://docs.microsoft.com/de-de/windows/desktop/Debug/system-error-codes
primitive _ERRORBADEXEFORMAT
  fun apply(): U32 =>
    """
    ERROR_BAD_EXE_FORMAT
    %1 is not a valid Win32 application.
    """
    193 // 0xC1

primitive _ERRORDIRECTORY
  fun apply(): U32 =>
    """
    The directory name is invalid.
    """
    267 // 0x10B

primitive _STDINFILENO
  fun apply(): U32 => 0

primitive _STDOUTFILENO
  fun apply(): U32 => 1

primitive _STDERRFILENO
  fun apply(): U32 => 2

// Operation not permitted
primitive _EPERM
  fun apply(): I32 => 1

// No such process
primitive _ESRCH
  fun apply(): I32 => 3

// Interrupted function
primitive _EINTR
  fun apply(): I32 => 4

// Try again
primitive _EAGAIN
  fun apply(): I32 =>
    ifdef bsd or osx then 35
    elseif linux then 11
    elseif windows then 22
    else compile_error "no EAGAIN" end

// Invalid argument
primitive _EINVAL
  fun apply(): I32 => 22

primitive _EXOSERR
  fun apply(): I32 => 71

// For handling errors between @fork and @execve
primitive _StepChdir
  fun apply(): U8 => 1

primitive _StepExecve
  fun apply(): U8 => 2

primitive _WNOHANG
  fun apply(): I32 =>
    ifdef posix then
      @ponyint_wnohang()
    else
      compile_error "no clue what WNOHANG is on this platform."
    end

class val Exited is (Stringable & Equatable[ProcessExitStatus])
  """
  Process exit status: Process exited with an exit code.
  """
  let _exit_code: I32

  new val create(code: I32) =>
    _exit_code = code

  fun exit_code(): I32 =>
    """
    Retrieve the exit code of the exited process.
    """
    _exit_code

  fun string(): String iso^ =>
    recover iso
      String(10)
        .>append("Exited(")
        .>append(_exit_code.string())
        .>append(")")
    end

  fun eq(other: ProcessExitStatus): Bool =>
    match other
    | let e: Exited =>
      e._exit_code == _exit_code
    else
      false
    end

class val Signaled is (Stringable & Equatable[ProcessExitStatus])
  """
  Process exit status: Process was terminated by a signal.
  """
  let _signal: U32

  new val create(sig: U32) =>
    _signal = sig

  fun signal(): U32 =>
    """
    Retrieve the signal number that exited the process.
    """
    _signal

  fun string(): String iso^ =>
    recover iso
      String(12)
        .>append("Signaled(")
        .>append(_signal.string())
        .>append(")")
    end

  fun eq(other: ProcessExitStatus): Bool =>
    match other
    | let s: Signaled =>
      s._signal == _signal
    else
      false
    end


type ProcessExitStatus is (Exited | Signaled)
  """
  Representing possible exit states of processes.
  A process either exited with an exit code or, only on posix systems,
  has been terminated by a signal.
  """

primitive _StillRunning

type _WaitResult is (ProcessExitStatus | WaitpidError | _StillRunning)


interface _Process
  fun kill()
  fun ref wait(): _WaitResult
    """
    Only polls, does not actually wait for the process to finish,
    in order to not block a scheduler thread.
    """


class _ProcessNone is _Process
  fun kill() => None
  fun ref wait(): _WaitResult => Exited(255)

class _ProcessPosix is _Process
  let pid: I32

  new create(
    path: String,
    args: Array[String] val,
    vars: Array[String] val,
    wdir: (FilePath | None),
    err: _Pipe,
    stdin: _Pipe,
    stdout: _Pipe,
    stderr: _Pipe) ?
  =>
    // Prepare argp and envp ahead of fork() as it's not safe to allocate in
    // the child after fork() is called.
    let argp = _make_argv(args)
    let envp = _make_argv(vars)
    // Fork the child process, handling errors and the child fork case.
    pid = @fork()
    match pid
    | -1 => error
    | 0 => _child_fork(path, argp, envp, wdir, err, stdin, stdout, stderr)
    end

  fun tag _make_argv(args: Array[String] box): Array[Pointer[U8] tag] =>
    """
    Convert an array of String parameters into an array of
    C pointers to same strings.
    """
    let argv = Array[Pointer[U8] tag](args.size() + 1)
    for s in args.values() do
      argv.push(s.cstring())
    end
    argv.push(Pointer[U8]) // nullpointer to terminate list of args
    argv

  fun _child_fork(
    path: String,
    argp: Array[Pointer[U8] tag],
    envp: Array[Pointer[U8] tag],
    wdir: (FilePath | None),
    err: _Pipe, stdin: _Pipe, stdout: _Pipe, stderr: _Pipe)
  =>
    """
    We are now in the child process. We redirect STDIN, STDOUT and STDERR
    to their pipes and execute the command. The command is executed via
    execve which does not return on success, and the text, data, bss, and
    stack of the calling process are overwritten by that of the program
    loaded. We've set the FD_CLOEXEC flag on all file descriptors to ensure
    that they are all closed automatically once @execve gets called.
    """
    _dup2(stdin.far_fd, _STDINFILENO())   // redirect stdin
    _dup2(stdout.far_fd, _STDOUTFILENO()) // redirect stdout
    _dup2(stderr.far_fd, _STDERRFILENO()) // redirect stderr

    var step: U8 = _StepChdir()

    match wdir
    | let d: FilePath =>
      let dir: Pointer[U8] tag = d.path.cstring()
      if 0 > @chdir(dir) then
        @write(err.far_fd, addressof step, USize(1))
        @_exit(_EXOSERR())
      end
    | None => None
    end

    step = _StepExecve()
    if 0 > @execve(path.cstring(), argp.cpointer(),
      envp.cpointer())
    then
      @write(err.far_fd, addressof step, USize(1))
      @_exit(_EXOSERR())
    end

  fun tag _dup2(oldfd: U32, newfd: U32) =>
    """
    Creates a copy of the file descriptor oldfd using the file
    descriptor number specified in newfd. If the file descriptor newfd
    was previously open, it is silently closed before being reused.
    If dup2() fails because of EINTR we retry.
    """
    while (@dup2(oldfd, newfd) < 0) do
      if @pony_os_errno() == _EINTR() then
        continue
      else
        @_exit(I32(-1))
      end
    end

  fun kill() =>
    """
    Terminate the process, first trying SIGTERM and if that fails, try SIGKILL.
    """
    if pid > 0 then
      // Try a graceful termination
      if @kill(pid, Sig.term()) < 0 then
        match @pony_os_errno()
        | _EINVAL() => None // Invalid argument, shouldn't happen but
                            // tryinng SIGKILL isn't likely to help.
        | _ESRCH() => None  // No such process, child has terminated
        else
          // Couldn't SIGTERM, as a last resort SIGKILL
          @kill(pid, Sig.kill())
        end
      end
    end

  fun ref wait(): _WaitResult =>
    """Only polls, does not block."""
    if pid > 0 then
      var wstatus: I32 = 0
      let options: I32 = 0 or _WNOHANG()
      // poll, do not block
      match @waitpid(pid, addressof wstatus, options)
      | let err: I32 if err < 0 =>
        // one could possibly do at some point:
        //let wpe = WaitPidError(@pony_os_errno())
        WaitpidError
      | let exited_pid: I32 if exited_pid == pid => // our process changed state
        if _WaitPidStatus.exited(wstatus) then
          Exited(_WaitPidStatus.exit_code(wstatus))
        elseif _WaitPidStatus.signaled(wstatus) then
          Signaled(_WaitPidStatus.termsig(wstatus).u32())
        elseif _WaitPidStatus.stopped(wstatus) then
          Signaled(_WaitPidStatus.stopsig(wstatus).u32())
        elseif _WaitPidStatus.continued(wstatus) then
          _StillRunning
        else
          // *shrug*
          WaitpidError
        end
      | 0 => _StillRunning
      else
        WaitpidError
      end
    else
      WaitpidError
    end

primitive _WaitPidStatus
  """
  Pure Pony implementaton of C macros for investigating
  the status returned by `waitpid()`.
  """

  fun exited(wstatus: I32): Bool =>
    termsig(wstatus) == 0

  fun exit_code(wstatus: I32): I32 =>
    (wstatus and 0xff00) >> 8

  fun signaled(wstatus: I32): Bool =>
    ((termsig(wstatus) + 1) >> 1).i8() > 0

  fun termsig(wstatus: I32): I32 =>
    (wstatus and 0x7f)

  fun stopped(wstatus: I32): Bool =>
    (wstatus and 0xff) == 0x7f

  fun stopsig(wstatus: I32): I32 =>
    exit_code(wstatus)

  fun coredumped(wstatus: I32): Bool =>
    (wstatus and 0x80) != 0

  fun continued(wstatus: I32): Bool =>
    wstatus == 0xffff


class _ProcessWindows is _Process
  let h_process: USize
  let process_error: (ProcessError | None)
  var final_wait_result: (_WaitResult | None) = None

  new create(
    path: String,
    args: Array[String] val,
    vars: Array[String] val,
    wdir: (FilePath | None),
    stdin: _Pipe,
    stdout: _Pipe,
    stderr: _Pipe)
  =>
    ifdef windows then
      let wdir_ptr =
        match wdir
        | let wdir_fp: FilePath => wdir_fp.path.cstring()
        | None => Pointer[U8] // NULL -> use parent directory
        end
      var error_code: U32 = 0
      var error_message = Pointer[U8]
      h_process = @ponyint_win_process_create(
          path.cstring(),
          _make_cmdline(args).cstring(),
          _make_environ(vars).cpointer(),
          wdir_ptr,
          stdin.far_fd, stdout.far_fd, stderr.far_fd,
          addressof error_code, addressof error_message)
      process_error =
        if h_process == 0 then
          match error_code
          | _ERRORBADEXEFORMAT() => ProcessError(ExecveError)
          | _ERRORDIRECTORY() =>
            let wdirpath =
              match wdir
              | let wdir_fp: FilePath => wdir_fp.path
              | None => "?"
              end
            ProcessError(ChdirError, "Failed to change directory to "
              + wdirpath)
          else
            let message = String.from_cstring(error_message)
            ProcessError(ForkError, recover message.clone() end)
          end
        end
    else
      compile_error "unsupported platform"
    end

  fun tag _make_cmdline(args: Array[String] val): String =>
    var cmdline: String = ""
    for arg in args.values() do
      // quote args with spaces on Windows
      var next = arg
      ifdef windows then
        try
          if arg.contains(" ") and (not arg(0)? == '"') then
            next = "\"" + arg + "\""
          end
        end
      end
      cmdline = cmdline + next + " "
    end
    cmdline

  fun tag _make_environ(vars: Array[String] val): Array[U8] =>
    var size: USize = 0
    for varr in vars.values() do
      size = size + varr.size() + 1 // name=value\0
    end
    size = size + 1 // last \0
    var environ = Array[U8](size)
    for varr in vars.values() do
      environ.append(varr)
      environ.push(0)
    end
    environ.push(0)
    environ

  fun kill() =>
    if h_process != 0 then
      @ponyint_win_process_kill(h_process)
    end

  fun ref wait(): _WaitResult =>
    match final_wait_result
    | let wr: _WaitResult =>
      wr
    else
      var wr: _WaitResult = WaitpidError
      if h_process != 0 then
        var exit_code: I32 = 0
        match @ponyint_win_process_wait(h_process, addressof exit_code)
        | 0 =>
          wr = Exited(exit_code)
          final_wait_result = wr
          wr
        | 1 => _StillRunning
        | let code: I32 =>
          // we might want to propagate that code to the user, but should it do
          // for other errors too
          final_wait_result = wr
          wr
        end
      else
        final_wait_result = wr
        wr
      end
    end