#!/usr/bin/perl
#
# I have finally got sick of typing something like:
#
# tail -f logs/debug/2014/0623.log | grep -i mdip | grep -vi p[io]ng
#
# Do a tail -f of one of the current day's log files, the default is 'debug' but
# one can follow any of the others by putting enough of the directory
# as an argument so that it can find it eg: 
#
# logf [perl regex] ...
# logf sys [perl regex] ...
# logf -100 [dir] [perl regex] ...
#
# NOTE: You can have many regexes and they all have to match (an implied '&&')
# NOTE: Also you preceed any regex with the '!' character to indicate negation (like "| grep -v regex")
#
# logf udpr           - yields all udpr messages
# logf \!udpr         - yields everything except udpr messages. Note the shell escape character
# logf udpr ping      - yields udpr ping messages
# logf udpr \!p[io]ng - yields all udpr messages that aren't pings
#
# Copyright (c) 2014 Dirk Koopman, Tobit Computer Co Ltd
#

use strict;
use IO::Handle;
use IO::Select;
use File::Basename;
use Cwd;

my $me = fileparse($0);
my $cwd = fileparse(getcwd);

my $base = "logs";
my $ofn;

if (@ARGV[0] =~ /^-[\?h]/) {
	print "usage:   $0 [-<count>] [<directory name fragment>] [<regex>]\n";
	print "  e.g:   $0\n"; 
    print "         $0 deb\n";
	print "         $0 -100 cdr\n";
	print "         $0 udpr\n";
	print "         $0 sys tcp\n";
	print "\n    any regexes are caseless\n\n";
	print "default: $0 -40 debug\n";

	exit(0);
}

my $lines = shift if ($ARGV[0] =~ /\-\d+/);
$lines ||= -40;

my $sort = shift || "debug";
my @dirs;
my $end;

opendir(my $dh, $base) or die "cannot open log directory '$base' ($!)";
@dirs = grep {!/^\./} readdir($dh);
closedir $dh;

my @pattern;
my ($dir) = grep {/^$sort/} @dirs;
if ($dir) {
	@pattern = @ARGV;
} else {
	@pattern = ($sort, @ARGV);
	$dir = "debug";
}

my $s = IO::Select->new;
$s->add(\*STDIN);
autoflush STDIN, 0;
autoflush STDOUT, 0;

$SIG{TERM} = $SIG{INT} = sub {++$end};

while (!$end) {
	my $fn;
	my ($dd,$mm,$yy) = (gmtime)[3,4,5];
	++$mm;
	$yy += 1900;

	my $fn = sprintf "$base/$dir/%04d/%02d%02d", $yy, $mm, $dd;
	if (-e "$fn.log") {
		$fn = "$fn.log";
	} elsif (-e "$fn.csv") {
		$fn = "$fn.csv";
	} else {
		if ($fn ne $ofn) {
			print "Waiting for $fn to appear...\n";
			STDOUT->flush;
			$ofn = $fn;
		}
		sleep 1;
		next;
	}

	my $state = 1;

	# open the file, seek to the end, then seek backward from the end a bit and start reading
	# but ignore the first line 'cos it will be incomplete. 
	open I, $fn or die "cannot open $fn ($!)\n";
	my $pos = sysseek(I, 0, 2);
	if ($pos <= int(abs($lines * 80))) {
		sysseek(I, 0, 0);
	} else {
		sysseek(I, $pos + ($lines * 80), 0);     # remember lines is (-)ve
	}

	my $count;
	while (!$end) {

		if ($state) {
			my $l;
			my $r = sysread(I, $l, 4096);
			if (defined $r && length $l) {
				my @lines = split /\cM?\cJ/, $l;
				foreach my $s (@lines) {
					if (@pattern) {
						unless (match($s)) {
							next;
						}
					}
					print "\n".$s;
				}
			}
			$count = 0;
		}

		if (wait_for_stdin(0.1)) {
			$state ^= 1;
			print $state ? "\nRunning..." : "\nStopped...";
		}
		sysseek(I, 0, 1);
		STDOUT->flush;

		# move onto the next file if we roll over midnight
		my ($d) = (gmtime)[3];
		last if ($d != $dd);
	}
	close I;
}

print "\n";
exit(0);

sub match
{
	my $count = 0;
	foreach my $p (@pattern) {
		if ($p =~ /^!/) {
			my $r = substr $p, 1;
			last if $_[0] =~ m{$r}i;
		} else {
			last unless $_[0] =~ m{$p}i;
		}
		++$count;
	}
	return $count == @pattern;
}

sub wait_for_stdin
{
	my $t = shift;
	if ($s->can_read($t)) {
		my $l = <STDIN>;
		if ($l =~ /^q/i) {
			print "\n";
			exit(0);
		}
		return 1;
	}
	return 0;
}