#!/usr/bin/perl
#
# NAME
#     vacation - Reply to mail automatically.
# 
# SYNOPSIS
#     vacation [username]
# 
# DESCRIPTION
#     Vacation automatically replies to incoming mail.
#
#     It is enabled by calling vacation without arguments. The 
#     program creates a .vacation.msg file in your home directory, 
#     which contains the message that is automatically sent to all 
#     senders when vacation is enabled, and starts an editor for 
#     you to modify the message. 
#
#     If no .forward file exists in your home directory, it is 
#     created and will contain a line of the form:
#
#          \username, "|/usr/local/bin/vacation username"
#
#     This sends one copy of an incoming message to username while
#     another copy is piped into vacation.
#
#     If a .forward file is present in your home directory and 
#     it does not contain a line refering to the vacation program,
#     a line is appended of the form:
#
#          "|/usr/local/bin/vacation username"
#
#     This pipes a copy of an incoming message into the
#     the vacation program, in addition to the copies
#     to users or programs which were already specified in the 
#     .forward file.
#
#     If a .forward file is present in your home directory which
#     already contains a line refering to the vacation program, 
#     you are asked whether you want to disable the vacation
#     program. If you answer yes, the line refering to the
#     vacation program is removed from the .forward file. If the
#     .forward file is empty after removing this line, it is
#     removed completely.
#
#     Vacation will not respond to automatically generated mails
#     (like mails generated by vacation). Vacation will also not 
#     respond to mail from either postmaster or mailer-daemon. 
#
# FILES
#     ~/.forward           Contains e-mail adresses or programs
#                          to which mail must be forwarded.
#
#     ~/.vacation.msg      The reply message.
#
# AUTHOR
#     Frits Wiarda
#
# AUTHORS ORIGINAL VERSION
#     Tom Christiansen
#     Larry Wall
#
# NOTES
#     This script has been tested with Fedora Core 6 Linux. Note that
#     for other systems it can be necessary to modify line 1, containing
#     a reference to the perl interpreter.
#
#     Be sure .forward files are processed on your system. Note that some
#     systems refuse to process .forward files that are group writable,
#     while the systems default umask makes files group writable.
#

$CMDNAME = "vacation";
$VERSION = "1.8";

######################################################################
#
# Help text.
#
######################################################################

$HELP = "Reply to mail automatically.\n\nUsage: vacation [username]\n\nWithout parameters vacation prompts the user for instructions.\n";
$USAGE = "Usage: vacation [username]\n";

######################################################################
#
# Print help message when the option "-?" or "--help" is specified.
#
######################################################################

if($ARGV[0] eq "-?" or $ARGV[0] eq "--help") 
{
	print "$CMDNAME $VERSION\n\n$HELP";
	exit 0;
}

######################################################################
# 
# Locate various executables.
#
######################################################################

$ed = "/bin/ed";
unless (-x $ed) { $ed = "/usr/bin/ed"; }
unless (-x $ed) { die "$CMDNAME: Can't locate ed\n"; }

$editor = $ENV{"VISUAL"} || $ENV{"EDITOR"};
unless ($editor) 
{
	$editor = "/bin/vi";
	unless (-x $editor) { $editor = "/usr/bin/vi"; }
	unless (-x $editor) { die "$CMDNAME: Can't locate editor\n"; }
}

$pager = $ENV{"PAGER"};
unless ($pager) 
{
	$pager = "/bin/more";
	unless (-x $pager) { $pager = "/usr/bin/more"; }
	unless (-x $pager) { $pager = "/bin/pg"; }
	unless (-x $pager) { $pager = "/usr/bin/pg"; }
	unless (-x $pager) { die "$CMDNAME: Can't locate pager\n"; }
}

$sendmail = "/bin/sendmail";
unless (-x $sendmail) { $sendmail = "/sbin/sendmail"; }
unless (-x $sendmail) { $sendmail = "/usr/sbin/sendmail"; }
unless (-x $sendmail) { $sendmail = "/usr/bin/sendmail"; }
unless (-x $sendmail) { die "$CMDNAME: Can't locate sendmail\n"; }

$vacation = $0;
unless (-x $vacation) { die "$CMDNAME: Can't locate own executable\n"; }

######################################################################
#
# Determine the user.
#
######################################################################

$user = $ENV{"USER"} || $ENV{"LOGNAME"} || getlogin || (getpwuid($>))[0];

######################################################################
#
# Without command line arguments we are interactive. With
# an option as command line argument or more then one command
# line argument we print an error message. With a user name as
# the only command line argument we answer mail.
#
######################################################################

if (!@ARGV) 
{
	&interactive();
}
else 
{
	$_ = shift;
	if ( /^-/ || @ARGV ) 
	{
		die "$USAGE";
	}
	else 
	{
		$user = $_;
		&answer;
        }
}

######################################################################
#
# Both the interactive and answer subroutines call exit directly. So
# this point is unreachable.
#
######################################################################

die "$CMDNAME: Panic\n";


######################################################################
#
# Answer mode. The vacation program reads mail from the standard
# inut, and uses sendmail to reply to it.
#
######################################################################

sub answer 
{
	# Get the users home directory from the password file.
	$home = (getpwnam($user))[7];
	die "$CMDNAME: No home directory for user $user\n" unless $home;

	# Change to the users home directory.
	chdir $home || die "$CMDNAME: Can't chdir to $home\n";

	# Set input record seperator to an empty line.
	$/ = '';                       

	# Read message into header.
	$header = <STDIN>;     

	# Concatenate headers spread over multiple lines.
	$header =~ s/\n\s+/ /gm;    

	# Do not reply to automatically generated mail.
	if ( $header =~ /^Auto-Submitted:/im ) 
	{
		exit unless ($header =~ /^Auto-Submitted: no/im );
	}
	exit if $header =~ /^Precedence: junk/im;
	exit if $header =~ /^Precedence: bulk/im;

	# Do not reply to mail from mailer-daemon or postmaster.
	exit if $header =~ /^From.*mailer-daemon/im;
	exit if $header =~ /^From.*postmaster/im;

	# Get the sender of the mail.
	($replyto) = ($header =~ /^Reply-To:(.*)/im);
	$replyto =~ s/^\s*//;
	$replyto =~ s/\s*$//;
	($replyto) = ($header =~ /^From:(.*)/im) if $replyto eq "";
	$replyto =~ s/^\s*//;
	$replyto =~ s/\s*$//;
	die "$CMDNAME: No \"From:\" or \"Reply-To:\" header\n" 
		if $replyto eq "";

	# Get the subject of the mail.
	($subject) = ($header =~ /^Subject:(.*)/im);
	$subject =~ s/^\s*//;
	$subject =~ s/\s*$//;
	$subject = "(No subject)" unless $subject;

	# Get reply text. If no .vacation.msg file is present exit,
	# without sending anything and without generating an error 
	# message. (So deleting the message file effectively means 
	# disabling the vacation program.)
	if (open(MSG,".vacation.msg")) 
	{
		undef $/;
		$msg = <MSG>;
		close MSG;
	} 
	else 
	{
		exit;
	} 

	# Replace $SUBJECT with real subject text.
	$msg =~ s/\$SUBJECT/$subject/gm;
    
	# Send reply using sendmail.
	open(MAIL, "|$sendmail -oi -t -f $user") ||
		die "$CMDNAME: Can't run sendmail\n";
	print MAIL <<EOF;
To: $replyto
Auto-Submitted: auto-replied
Precedence: junk
EOF
	print MAIL $msg;
	close MAIL;

	# Ready.
	exit;

}


######################################################################
#
# Internactive mode. The vacation program prompts the user
# for input (whether it should be enabled or disabled, etc.).
#
######################################################################

sub interactive 
{

	# Get the users home directory from the password file.
	$home = (getpwnam($user))[7];
	die "$CMDNAME: No home directory for user $user\n" unless $home;

	# Change to the users home directory.
	chdir $home || die "$CMDNAME: Can't chdir to $home\n";

	# Check whether vacation has been enabled.
	$enabled = 0;
	if (-f ".forward")
	{
		open(FOR, "<.forward") || die "$CMDNAME: Can't open .forward\n";
		while($line = <FOR>)
		{
			if ( $line =~ m|$vacation| )
			{
				$enabled = 1;
			}
		}
		close FOR;
	} 

	# Ask whether the vacation feature must be disabled. After that
	# we are ready and exit.
	if ($enabled) 
	{
		print "The vacation feature is enabled.\n";
		print "\n";
		if (&yorn("Would you like to disable the vacation feature? ")) 
		{
			&disable; 
		}
		else 
		{
			print "Ok, vacation feature NOT disabled.\n";
		}
		exit;
	}

	# Vacation feature is disabled. Start dialog to enable it.
	# After that we are ready and exit.
	print <<EOF;
This program can be used to answer your mail automatically
when you go away on vacation.

EOF
	for (;;) 
	{
		if (-f ".vacation.msg") 
		{
			print "You already have a message file in ~/.vacation.msg.\n";
			$see = &yorn("Would you like to see it? ");
			system $pager, ".vacation.msg" if $see;
			print "\n" if $see;
			$edit = &yorn("Would you like to edit it? ");
		}
		else 
		{
			&make_default;
			print <<EOF;
I've created a default vacation message in ~/.vacation.msg.  This
message will be automatically returned to anyone sending you mail while
you're out.

You will now enter your favorite editor ($editor) 
to edit the messasge to your own tastes. Remember that the first 
line shall start with "Subject: ", and that the second line shall
be empty.

EOF
			$| = 1;
			print "Press return to continue. "; 
			<STDIN>;
			$edit = 1;
		}
		last unless $edit;
		system $editor, ".vacation.msg";
		last;
	}
	if (&yorn("Would you like to enable the vacation feature now? ")) 
	{
		&enable;
	}
	else 
	{
		print "Ok, vacation feature NOT enabled.\n";
	}
	exit;
}

######################################################################
#
# Enable the vacation feature. If no .forward file exists one is 
# created. If a .forward file exists, a line enabling the vacation
# program is appended to it.
#
######################################################################

sub enable 
{
	if (-f ".forward")
	{
		open(FOR, ">>.forward") || 
			die "$CMDNAME: Can't open .forward\n";
		print FOR "\"|$vacation $user\"\n";
		close FOR;
	} 
	else
	{
		open(FOR, ">.forward") || 
			die "$CMDNAME: Can't create .forward\n";
		print FOR "\\$user, \"|$vacation $user\"\n";
		close FOR;
	}
	print <<EOF;
Ok, vacation feature ENABLED. Please remember to turn it off when
you get back from vacation. Bon voyage!
EOF
} 

######################################################################
#
# Disable the vacation feature. The line enabling the vacation
# program is deleted from the .forward file.
#
######################################################################

sub disable 
{
	open(FOR, "|$ed -s .forward") ||
		die "$CMDNAME: Can't open pipe to ed .forward\n";
	print FOR "g|$vacation|d\nw\nq\n";
	close FOR;
	if (-z ".forward") 
	{
		unlink(".forward"); 
	}
	print "Back to normal reception of mail.\n";
} 

######################################################################
#
# A default .vacation.msg file is created.
#
######################################################################

sub make_default 
{
	return if $edit;
	open(MSG, ">.vacation.msg") || 
		die "$CMDNAME: Can't create .vacation.msg\n";
	print MSG <<EOF;
Subject: I am away from my mail

I will not be reading my mail for a while. Your mail regarding 
\$SUBJECT will be read when I return.
EOF
	close MSG;
} 


######################################################################
#
# Ask a question and read an answer being y(es) or n(o).
#
######################################################################

sub yorn 
{
	local($answer);
	for (;;) 
	{
		print $_[0];
		$answer = <STDIN>;
		last if $answer =~ /^[yn]/i;
		print "Please answer \"yes\" or \"no\" (\"y\" or \"n\")\n";
	}
	print "\n";
	$answer =~ /^y/i;
}