#!/usr/bin/expect --

# This is a script for switching to another user and then
# suspending (`suspend -f`) and resuming (`fg`) his shell

package require cmdline
set opts {
    {s.arg "sudo su -"	"user switching method"}
    {u.arg ""		"username to switch to"}
}
set usage ": \[options]\noptions:"
array set conf [::cmdline::getoptions argv $opts $usage]

log_user 1
match_max 8192
expect_after {
    timeout { send_error "TIMEOUT\n" ; exit 1 }
    eof     { send_error "EXITED\n" ; exit 2 }
}
set timeout 2

# user switching command, by default `sudo su -`
set swcmd $conf(s)
# ending of typical shell prompt (zsh/sh):
set shpmt "(%|#|\\$) \\Z"
catch {set shpmt $env(EXPECT_PROMPT)}
# initial username:
set user0 [exec id -un]
# user we switch to (with $swcmd), by default initial user
if {$conf(u) != ""} {set swuser $conf(u)} else {set swuser $user0}

# 1. start shell
spawn bash
expect -re "$shpmt" {}

# 2. sudo-ing swuser's shell:
send "$swcmd $swuser\r"
expect {
    -re "$swuser.*$shpmt" {}
    -re "assword: ?\\Z" {
	stty -echo
	expect_user -timeout -1 -re "(.*)\n" {set swpwd $expect_out(1,string)}
	stty echo
	send "$swpwd\r"
	expect -re "$swuser.*$shpmt" {}
    }
}

# 3. getting pid and ppid of swuser's shell (needed for 5b):
send "echo \$\$:\$PPID\r"
expect -re "(?n)^(\[\[:digit:\]\]*):(\[\[:digit:\]\]*)\r?\n(.*)$shpmt" {}
set swpid  $expect_out(1,string)
set swppid $expect_out(2,string)

#send_error "$user0:$swpid:$swppid\n"

# 4. suspending swuser's shell (trying to return to parent shell):
send "suspend -f\r"
expect {
    -re "$shpmt" {
	# 5a. got to parent shell -- resuming swuser's shell by `fg`:
	send "fg\r"
	set hung no
    }
    timeout {
	# 5b. `suspend -f` has hung -- resuming swuser's shell by SIGCONT:
	send_error "kill $swppid\n"
	send_error [exec kill -CONT $swppid]
	set hung yes
    }
}
expect -re "$shpmt" {}

# 6. exiting [both] shells
#set swstat [wait -nowait]
#send_error [pid]:[exp_pid]:$swstat\n
send "exit\rexit\r"
expect eof {}
#send_error [wait -nowait]\n
#exec kill -KILL -[exp_pid]
if {$hung} {send_error "BUGGY\n" ; exit 3 }

# vi:set sw=4: