#!/usr/bin/perl
###############################################################################
#
# Copyright (c) 2012  Ramon Novoa  <rnovoa@artica.es>
# Copyright (c) 2012  Artica Soluciones Tecnologicas S.L.
#
# grep_log_module Perl script to search log files for a matching pattern. The
#                 last searched position is saved in an index file so that
#                 consecutive runs do not return the same results. The log file
#                 inode number is also saved to detect log rotation.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; version 2 of the License.
# 
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.	
#
###############################################################################

use strict;
use File::Basename;

# Output format (module or log_module).
my $Output = 'log_module';

# Be verbose
my $Verbose = 0;

# Index file storage directory, with a trailing '/'
my $Idx_dir='/tmp/';

# Log file
my $Log_file = '';

# Module name
my $Module_name = "default_log";

# Index file
my $Idx_file = '';

# Log file position index
my $Idx_pos = 0;

# Log file inode number
my $Idx_ino = '';

# Regular expression to be matched
my $Reg_exp = '';

###############################################################################
# SUB error_msg
# Print an error message and exit.
###############################################################################
sub error_msg ($) {
	my $err_msg = $_[0];

	if (! -z $err_msg) {
		print(stderr "[error] $err_msg.\n");
	}

	exit 1;
}

###############################################################################
# SUB print_help
# Print a help message.
###############################################################################
sub print_help () {
	print "Usage: $0 <log_file> <module_name> <pattern>\n";
}

###############################################################################
# SUB log_msg
# Print a log message.
###############################################################################
sub log_msg ($) {
	my $log_msg = $_[0];

	if (! -z $log_msg && $Verbose == 1) {
		print(stdout "[log] $log_msg.\n");
	}
}

###############################################################################
# SUB load_idx
# Load index file.
###############################################################################
sub load_idx () {
	my $line;
	my $current_ino;

	log_msg("Loading index file $Idx_file");

	open(IDXFILE, $Idx_file) || error_msg("Error opening file $Idx_file: " .
	                                         $!);

	# Read position and date
	$line = <IDXFILE>;
	($Idx_pos, $Idx_ino) = split(' ', $line);

	close(IDXFILE);

	# Reset the file index if the file has changed
	$current_ino = (stat($Log_file))[1];
	if ($current_ino != $Idx_ino) {
		log_msg("File changed, resetting index");

		$Idx_pos = 0;
		$Idx_ino = $current_ino;
	}

	return;
}

###############################################################################
# SUB save_idx
# Save index file.
###############################################################################
sub save_idx () {

	log_msg("Saving index file $Idx_file");

	open(IDXFILE, "> $Idx_file") || error_msg("Error opening file $Idx_file: "
	                                          . $!);
	print (IDXFILE $Idx_pos . " " . $Idx_ino);
	close(IDXFILE);

	return;
}

###############################################################################
# SUB create_idx
# Create index file.
###############################################################################
sub create_idx () {
	my $first_line;

	log_msg("Creating index file $Idx_file");

	open(LOGFILE, $Log_file) || error_msg("Error opening file $Log_file: " .
	                                     $!);

	# Go to EOF and save the position
	seek(LOGFILE, 0, 2);
	$Idx_pos = tell(LOGFILE);

	close(LOGFILE);

	# Save the file inode number
	$Idx_ino = (stat($Log_file))[1];

	# Save the index file
	save_idx();

	return;
}

###############################################################################
# SUB parse_log
# Parse log file starting from position $Idx_pos.
###############################################################################
sub parse_log () {
	my $line;

	log_msg("Parsing log file $Log_file");

	# Open log file for reading
	open(LOGFILE, $Log_file) || error_msg("Error opening file $Log_file: " .
	                                     $!);

	# Go to starting position. 
	seek(LOGFILE, $Idx_pos, 0);

	# Parse log file
	my @data;
	while ($line = <LOGFILE>) {
		if ($line =~ m/$Reg_exp/i) {
			push (@data, $line);
		}
	}

	$Idx_pos = tell(LOGFILE);
	close(LOGFILE);

	# Save the index file
	save_idx();

	return @data;
}

###############################################################################
# SUB parse_log
# Print log data to stdout.
###############################################################################
sub print_log (@) {
	my @data = @_;

	# No data
	if ($#data < 0) {
		return;
	}
	
	# Log module
	if ($Output eq 'log_module') {
		my $output = "<log_module>\n";
		$output .= "<source><![CDATA[" . $Module_name . "]]></source>\n";
		$output .= "<data><![CDATA[";
		foreach my $line (@data) {
			$output .= $line;
		}
		$output .= "]]></data>";
		$output .= "</log_module>\n";

		print stdout $output;
	}
	# Regular module
	else {
		my $output = "<module>\n";
		$output .= "<name><![CDATA[" . $Module_name . "]]></name>\n";
		$output .= "<type><![CDATA[async_string]]></type>\n";
		$output .= "<datalist>\n";
		foreach my $line (@data) {
			$output .= "<data><value><![CDATA[$line]]></value></data>\n";
		}
		$output .= "</datalist>\n";
		$output .= "</module>\n";

		print stdout $output;
	}
}

###############################################################################
###############################################################################
## Main
###############################################################################
###############################################################################

# Check command line parameters
if ($#ARGV != 2) {
	print_help();
	exit 1;
}

$Log_file = $ARGV[0];
$Module_name = $ARGV[1];
$Reg_exp = $ARGV[2];

# Create index file storage directory
if ( ! -d $Idx_dir) {
	mkdir($Idx_dir) || error_msg("Error creating directory $Idx_dir: "
	                             . $!);
}

# Check that log file exists
if (! -e $Log_file) {
	error_msg("File $Log_file does not exist");
}

# Create index file if it does not exist
$Idx_file=$Idx_dir . $Module_name . "_" . basename($Log_file) . ".idx";
if (! -e $Idx_file) {
	create_idx();
	exit 0;
}

# Load index file
load_idx();

# Parse log file
my @data = parse_log();

# Print output to stdout
print_log (@data);

exit 0;