(define-module (language python module _posixsubprocess)
  #:use-module (language python for)
  #:use-module (language python try)
  #:use-module (language python module python)
  #:use-module (language python bool)
  #:use-module (language python module os)
  #:use-module (language python module errno)
  #:use-module (language python list)
  #:use-module (language python exceptions)
  #:export (fork_exec))

(define (child_exec exec_array argv envp cwd
                    p2cread p2cwrite
                    c2pread c2pwrite
                    errread errwrite
                    errpipe_read errpipe_write
                    closed_fds restore_signals
                    call_setsid
                    fds_to_keep preexec_fn)

  (define errwrite #f)
  (define execmsg  #f)
  (close p2cwrite)
  (close c2pread)
  (close errread)
  (close errpipe_read)

  (if (= c2pwrite 0)
      (set! c2pwrite (dup c2pwrite)))

  (let lp ()
    (when (or (= errwrite 0) (= errwrite 1))
      (set! errwrite (dup errwrite))
      (lp)))
  
  (if (> p2cread 0)
      (dup2 p2cread 0))

  (if (> c2pwrite 1)
      (dup2 c2pwrite 1))

  (if (> errwrite 2)
      (dup2 errwrite 2))

  (if (> p2cread 2)
      (close p2cread))

  (if (and (> c2pwrite 2) (not (= c2pwrite p2cread)))
      (close c2pwrite))
  (if (and (> errwrite 2) (not (= errwrite p2cread))
           (not (= errwrite c2pwrite)))
      (close errwrite))

  (if (bool cwd)
      (chdir cwd))

  (if (bool call_setsid)
      (setsid))
  
  (if (bool preexec_fn)
      (try
       preexec_fn
       (#:except #t (set! msg "Exception occured in preexec_fn"))))

  (if (bool closed_fd)
      (for ((fd : fds_to_close)) ()
           (close fd)))

  (let ((argv (to-list argv))
        (envp (if (bool envp) (to-list envp) envp)))
    (for ((e : exec_array)) ((ep #f))
         (try
          (lambda ()
            (if (bool envp)
                (execve e argv envp)
                (execv  e argv)))
          (#:except #t =>
             (lambda x
               (if (not execmsg)
                   (set! execmsg ""))
               (set! execmsg
                 (+ execmsg + (format #f " exec error: ~a~%" x))))))
         (let ((er (errno)))
           (if (and (not (= er ENOENT)) (not (=  er ENOTDIR)) (not ep))
               er
               ep))
         #:final
         (if ep (set_errno ep) (set_errno 0))))

  (if errwrite
      (write errpipe_write errwrite))

  (if execmsg
      (write errpipe_write execmsg))
  
  (if (errno)
      (write errpipe_write (format #f "exec failed with errno ~a" (errno)))))
  
  

(define (fork_exec process_args executable_list
                   close_fds fds_to_keep
                   cwd env_list
                   p2cread p2cwrite c2pread c2pwrite
                   errread errwrite
                   errpipe_read errpipe_write
                   restore_signals start_new_session preexec_fn)

  (if (and (bool close_fds) (< errpipe_read 3))
      (raise (ValueError "errpipe_write must be >= 3")))

  (for ((fd : fds_to_keep)) ()
       (if (not (isinstance fd int))
           (raise (ValueError "bad values(s) in fds_to_keep"))))

  (let ((pid (fork)))
    (if (= pid 0)
        (begin
          ;; Child process
          (child_exec executable_list
                      process_args
                      env_list
                      cwd
                      p2cread
                      p2cwrite
                      c2pread
                      c2pwrite
                      errread
                      errwrite
                      errpipe_read
                      errpipe_write
                      close_fds
                      restore_signals
                      call_setsid
                      fds_to_keep
                      preexec_fn)))))