#!/usr/bin/env perl

use strict;
use warnings;
use 5.020;

our $VERSION = '0.00';

use File::Path qw(make_path);
use File::Slurp qw(read_file write_file);
use Net::MQTT::Simple;
use YAML::XS;

sub load_config {
	my ($config_file) = @_;
	my $content       = read_file($config_file);
	my $yaml          = Load($content);
	return $yaml;
}

my ($config_file) = @ARGV;

if ( not defined $config_file ) {
	die("Usage: $0 <config.yaml>\n");
}

my $user_config = load_config($config_file);
my $outdir      = $user_config->{directory};
my $server      = $user_config->{server};
my %config;

for my $subscription ( @{ $user_config->{subscriptions} } ) {
	$config{ $subscription->{topic} } = {};
	for my $key (qw(freshness norm_factor)) {
		if ( exists $subscription->{$key} ) {
			$config{ $subscription->{topic} }{$key} = $subscription->{$key};
		}
	}
}

if ( not defined $outdir ) {
	die("Error: configuration must specify an output directory\n");
}
if ( not defined $server ) {
	die("Error: configuration must specify a server\n");
}

my %subscription;

for my $name ( keys %config ) {
	$subscription{$name} = sub {
		my ( $topic, $message ) = @_;
		my $basedir = "${outdir}/${topic}";

		$basedir =~ s{ / [^/]+ $ }{}x;

		if ( exists $config{$name}{norm_factor} ) {
			$message *= $config{$name}{norm_factor};
		}

		if ( not -e $basedir ) {
			make_path($basedir);
		}

		write_file( "${outdir}/${topic}", $message );
	};

	if ( exists $config{$name}{freshness} and $name =~ m{ [*] }x ) {
		say STDERR
		  "Warning: $name: freshness checks on subscriptions containing "
		  . "an asterisk ('*') are not supported.";
		say STDERR "         I will not check this topic's freshness";
		delete $config{$name}{freshness};
	}
	if ( exists $config{$name}{freshness} and $name =~ m{ [#] }x ) {
		say STDERR
		  "Warning: $name: freshness checks on subscriptions containing "
		  . "multi-level wildcards ('#') are not yet supported.";
		say STDERR "         I will not check this topic's freshness";
		delete $config{$name}{freshness};
	}

}

sub check_freshness {
	my ( $topic, $now ) = @_;

	my $glob_expr = $topic;
	$glob_expr =~ s{ [+] }{*}gx;

	for my $file ( glob("${outdir}/${glob_expr}") ) {
		my $mtime = ( stat($file) )[9];

		if ( -f $file and $now - $mtime > $config{$topic}{freshness} ) {
			unlink($file)
			  or say STDERR
			  "Unable to delete ${file} during freshness check: $!";
		}
	}
}

my $mqtt = Net::MQTT::Simple->new($server);
$mqtt->subscribe(%subscription);

while (1) {
	$mqtt->tick(30);

	my $now = time();

	for my $topic ( keys %config ) {
		if ( exists $config{$topic}{freshness} ) {
			check_freshness( $topic, $now );
		}
	}
}

__END__

=head1 NAME

mqttsyncdir-subscriber - map MQTT messages to filesystem entries

=head1 SYNOPSIS

B<mqttsyncdir-subscriber> I<config.yaml>

=head1 VERSION

0.00

=head1 DESCRIPTION



=head1 OPTIONS

None yet.

=head1 EXIT STATUS

=head1 CONFIGURATION

=head2 EXAMPLE CONFIGURATION

=begin text

The following configuration will subscribe to three topics, normalize message
bodies of one of them and also remove stale data in two cases.

directory: /srv/mqtt
server: mqtt.example
subscriptions:
  - topic: sensor/+/temperature
    freshness: 600
  - topic: sensor/+/voltage
    freshness: 600
    norm_factor: 0.000001
  - topic: counter/whatever

=end text

This configuration file will subscribe to the topics C<< sensor/+/temperature >>,
C<< sensor/+/voltage >>, and C<< counter/whatever >>. Each time a message is
posted to one of them, the appropriate file in F</srv/mqtt> will be updated.

So, assuming the message C<< 12.5 >> is posted to C<<
sensor/outdoor/temperature >>, the string C<< 12.5 >> will be written to
F</srv/mqtt/sensor/outdoor/temperature>. The message C<< 10700000 >> to
C<< sensor/main_battery/voltage >> will result in C<< 10.7 >> being written
to F</srv/mqtt/sensor/main_battery/voltage>. Any file belonging to the topics
C<< sensor/+/temperature >> or C<< sensor/+/voltage >> which did not receive
an update in the last 10 minutes will be deleted.

=head1 DEPENDENCIES

=over

=item * Net::MQTT::Simple

=back

=head1 BUGS AND LIMITATIONS

=head1 AUTHOR

Copyright (C) 2017-2018 by Daniel Friesel E<lt>derf@finalrewind.orgE<gt>

=head1 LICENSE

  0. You just DO WHAT THE FUCK YOU WANT TO.