#!/usr/bin/perl

use warnings;
use strict;
use JSON;
use LWP::UserAgent;
use Encode qw(encode);
use Data::Dumper;
use Compress::Zlib;
use Getopt::Long;
use Config::Any;

my $config = '/etc/systemd/journal-gelf.yml';
my $conf = {};

if (-e $config) { 
  print "Reading config file $config\n";
  $conf = Config::Any->load_files( { files => [ $config ], flatten_to_hash => 1, use_ext => 1 } )->{$config};
}

GetOptions (
  'state=s'    => \$conf->{state},
  'compress!'  => \$conf->{compress},
  'url=s'      => \$conf->{url},
  'username=s' => \$conf->{username},
  'password=s' => \$conf->{password}
);

$conf->{state}    //= '/var/lib/systemd-journal-gelf/state';
$conf->{compress} //= 1;

if (
     not $conf->{url} or
     ($conf->{username} and not $conf->{password}) or
     (not $conf->{username} and $conf->{password})
  ){
  help();
  die;
}

print "Starting the Systemd Journal GELF uploader daemon\n";

my $ua = LWP::UserAgent->new(
  # env_proxy => 1,
  keep_alive => 1
);
$ua->default_header( 'Content-Type' => 'application/json' );
if ( $conf->{compress} ){
  $ua->default_header( 'Accept-Encoding' => HTTP::Message::decodable );
  $ua->default_header( 'Content-Encoding' => 'gzip' );
}

# Check if the state file exists and contains a valid cursor
my $cursor_arg = '';
open CURSOR, "+<", $conf->{state};
if (-e $conf->{state}){
  my $cursor = <CURSOR>;
  close CURSOR;
  if ($cursor and $cursor =~ m/^s=[a-z\d]+;i=[a-z\d]+;b=[a-z\d]+;m=[a-z\d]+;t=[a-z\d]+;x=[a-z\d]+$/){
    print "Valid cursor found in " . $conf->{state} . ", will start back from here\n";
    $cursor_arg = " --after-cursor='" . $cursor . "'";
  } else {
    print $conf->{state} . " contains an invalid cursor, so we're wiping it\n";
    unlink $conf->{state};
  }
}

open JOURNAL, "journalctl -f -o json$cursor_arg |";
while (my $entry = <JOURNAL>){
  my $msg = from_json($entry);
  my $gelf = {
    version => 1.1,
    short_message => $msg->{MESSAGE},
    host => $msg->{_HOSTNAME},
    timestamp => int ($msg->{__REALTIME_TIMESTAMP} / (1000 * 1000)),
    level => $msg->{PRIORITY}
  };
  foreach (grep !/^MESSAGE|_HOSTNAME|__REALTIME_TIMESTAMP|PRIORITY$/,  keys %$msg){
    my $key = lc (($_ =~ m/^_/) ? $_ : '_' . $_);
    $gelf->{$key} = $msg->{$_};
  }
  my $retry = 0;
  my $resp;
  do {
    if ($retry > 0){
      print "Sending message to " . $conf->{url} . " failed : got code " .
        $resp->code . " (" . $resp->message . "). Tring again in $retry seconds\n";
      sleep $retry;
    }
    $resp = $ua->post($conf->{url}, Content => Compress::Zlib::memGzip(encode('utf-8', to_json($gelf))));
    $retry = ($retry > 0) ? $retry * 2 : 1;
  } while ($resp->code != 202 and $retry < 600);
  if ($resp->code == 202){
    open CURSOR, ">", $conf->{state};
    print CURSOR $msg->{__CURSOR};
    close CURSOR
  } else {
    die "Error sending data to GELF server\n";
  }
}

sub help {
  print <<"_EOF"

Usage: $0 --url=<URL> [--compress|--no-compress] [--user=production --password=secr3t] [--state=/path/to/file]

  * --url is the http or https URL where you will push your gelf formated logs. This is mandatory
  * --compress or --no-compress : will turn on or off gzip compression of logs. Default is on, but can be usefull to disable for debugging
  * --username and --password may be used if URL is protected with a basic auth mecanism. Either both or none must be provided
  * --state can be used to specify where to record the last correctly sent message, so we can start from here when
    systemd-journal-gelf is restarted or if there's a network problem. Default value is /var/lib/systemd-journal-gelf/state

_EOF
}