#!/usr/bin/perl

my $pidfile;
my $logfile;
my $init;
my $kill;
my $killsig = 9;
my $restart;

while ($ARGV[0] =~ /^\-/) {
    my $opt = shift @ARGV;
    print STDERR "opt='$opt'\n";
    if ($opt eq '-f' || $opt eq '--pidfile') {
	$pidfile = shift @ARGV;
    }
    elsif ($opt eq '-l' || $opt eq '--logfile') {
	$logfile = shift @ARGV;
    }
    elsif ($opt eq '-i' || $opt eq '--initfile') {
	$init = shift @ARGV;
    }
    elsif ($opt eq '-r' || $opt eq '--restart') {
        $restart = 1;
    }
    elsif ($opt eq '-k' || $opt eq '--kill') {
        $kill = 1;
    }
    elsif ($opt eq '-s' || $opt eq '--kill-sig') {
        $killsig = shift @ARGV;
    }
    elsif ($opt eq '-h' || '--help') {
        print usage();
        exit 0;
    }
}
if (!$pidfile) {
    $pidfile = $ARGV[0].".pid";
}

my $pid;
if (-f $pidfile) {
    open(F,$pidfile);
    $pid = <F>;
    chomp $pid;
    close(F);
}

if ($kill || $restart) {
    my $ok = 1;
    if ($pid) {
        # -ve PID kills process group
        # http://stackoverflow.com/questions/2618403/how-to-kill-all-subprocesses-of-shell
        if (system("kill -$killsig -$pid")) {
            # failed to kill
            if (is_running($pid)) {
                print STDERR "Cannot kill $pid\n";
                die;
            }
            else {
                if ($kill) {
                    print STDERR "Cannot kill $pid, as it is not running\n";
                }
            }
        }
        else {
            if (is_running($pid)) {
                print STDERR "attempt to kill -s $killsig $pid failed\n";
                die;
            }
            else {
                print STDERR "Killed $pid\n";
                if ($restart) {
                    sleep(3);
                }
            }
        }
    }
    else {
        print STDERR "No process running\n";
        if ($kill) {
            die;
        }
    }
    if ($kill) {
        exit 0;
    }
}

if ($pid) {
    if (is_running($pid)) {
        print STDERR "process running: $pid\n";
        exit 0;
    }
    print STDERR "process not found: $pid -- will start a new process\n";
}
else {
    print STDERR "No existing process\n";
}

open(F,">$pidfile") || die $pidfile;
print F "$$\n";
close(F);

my $cmd = "@ARGV";

if ($init) {
    $cmd = ". $init; $cmd";
}

if ($logfile) {
    print STDERR "Logging to $logfile\n";
    print STDERR "running command $cmd\n";
    system("$cmd > $logfile 2>&1");
    system("tail -f $logfile");
}
else {
    print "running command $cmd\n";
    system($cmd);
}

exit 0;

sub scriptname {
    my @p = split(/\//,$0);
    pop @p;
}

sub is_running {
    my $pid = shift;
    my @procs = split(/\n/,`ps ax`);
    my $is_running = 0;
    foreach (@procs) {
	my ($x) = split(' ',$_);
	#print STDERR "$foo // $x ps: $_\n";
	if ($x eq $pid) {
	    $is_running = 1;
            break;
	}
    }
    return $is_running;
}

sub usage {
    my $sn = scriptname();

    <<EOM;
$sn [--pidfile PIDFILE] [--logfile LOGFILE] CMD [ARGS]

Example crontab:
* * * * 45 staying-alive.pl "my-server"

EOM
}