"""Pseudo terminal utilities."""

# Bugs: No signal handling. Doesn't set slave termios and window size.
# Only tested on Linux.
# See: W. Richard Stevens. 1992. Advanced Programming in the
# UNIX Environment. Chapter 19.
# Author: Steen Lumholt -- with additions by Guido.

from select import select
import os
import tty

__all__ = ["openpty","fork","spawn"]

STDIN_FILENO = 0
STDOUT_FILENO = 1
STDERR_FILENO = 2

CHILD = 0

def openpty():
 """openpty() -> (master_fd, slave_fd)
 Open a pty master/slave pair, using os.openpty() if possible."""

 try:
 return os.openpty()
 except (AttributeError, OSError):
 pass
 master_fd, slave_name = _open_terminal()
 slave_fd = slave_open(slave_name)
 return master_fd, slave_fd

def master_open():
 """master_open() -> (master_fd, slave_name)
 Open a pty master and return the fd, and the filename of the slave end.
 Deprecated, use openpty() instead."""

 try:
 master_fd, slave_fd = os.openpty()
 except (AttributeError, OSError):
 pass
 else:
 slave_name = os.ttyname(slave_fd)
 os.close(slave_fd)
 return master_fd, slave_name

 return _open_terminal()

def _open_terminal():
 """Open pty master and return (master_fd, tty_name)."""
 for x in 'pqrstuvwxyzPQRST':
 for y in '0123456789abcdef':
 pty_name = '/dev/pty' + x + y
 try:
 fd = os.open(pty_name, os.O_RDWR)
 except OSError:
 continue
 return (fd, '/dev/tty' + x + y)
 raise OSError('out of pty devices')

def slave_open(tty_name):
 """slave_open(tty_name) -> slave_fd
 Open the pty slave and acquire the controlling terminal, returning
 opened filedescriptor.
 Deprecated, use openpty() instead."""

 result = os.open(tty_name, os.O_RDWR)
 try:
 from fcntl import ioctl, I_PUSH
 except ImportError:
 return result
 try:
 ioctl(result, I_PUSH, "ptem")
 ioctl(result, I_PUSH, "ldterm")
 except OSError:
 pass
 return result

def fork():
 """fork() -> (pid, master_fd)
 Fork and make the child a session leader with a controlling terminal."""

 try:
 pid, fd = os.forkpty()
 except (AttributeError, OSError):
 pass
 else:
 if pid == CHILD:
 try:
 os.setsid()
 except OSError:
 # os.forkpty() already set us session leader
 pass
 return pid, fd

 master_fd, slave_fd = openpty()
 pid = os.fork()
 if pid == CHILD:
 # Establish a new session.
 os.setsid()
 os.close(master_fd)

 # Slave becomes stdin/stdout/stderr of child.
 os.dup2(slave_fd, STDIN_FILENO)
 os.dup2(slave_fd, STDOUT_FILENO)
 os.dup2(slave_fd, STDERR_FILENO)
 if (slave_fd > STDERR_FILENO):
 os.close (slave_fd)

 # Explicitly open the tty to make it become a controlling tty.
 tmp_fd = os.open(os.ttyname(STDOUT_FILENO), os.O_RDWR)
 os.close(tmp_fd)
 else:
 os.close(slave_fd)

 # Parent and child process.
 return pid, master_fd

def _writen(fd, data):
 """Write all the data to a descriptor."""
 while data:
 n = os.write(fd, data)
 data = data[n:]

def _read(fd):
 """Default read function."""
 return os.read(fd, 1024)

def _copy(master_fd, master_read=_read, stdin_read=_read):
 """Parent copy loop.
 Copies
 pty master -> standard output (master_read)
 standard input -> pty master (stdin_read)"""
 fds = [master_fd, STDIN_FILENO]
 while True:
 rfds, wfds, xfds = select(fds, [], [])
 if master_fd in rfds:
 data = master_read(master_fd)
 if not data: # Reached EOF.
 fds.remove(master_fd)
 else:
 os.write(STDOUT_FILENO, data)
 if STDIN_FILENO in rfds:
 data = stdin_read(STDIN_FILENO)
 if not data:
 fds.remove(STDIN_FILENO)
 else:
 _writen(master_fd, data)

def spawn(argv, master_read=_read, stdin_read=_read):
 """Create a spawned process."""
 if type(argv) == type(''):
 argv = (argv,)
 pid, master_fd = fork()
 if pid == CHILD:
 os.execlp(argv[0], *argv)
 try:
 mode = tty.tcgetattr(STDIN_FILENO)
 tty.setraw(STDIN_FILENO)
 restore = 1
 except tty.error: # This is the same as termios.error
 restore = 0
 try:
 _copy(master_fd, master_read, stdin_read)
 except OSError:
 if restore:
 tty.tcsetattr(STDIN_FILENO, tty.TCSAFLUSH, mode)

 os.close(master_fd)
 return os.waitpid(pid, 0)[1]