#!/usr/bin/perl
use warnings;
use strict;
use English;
use POSIX;
use JSON;
use Net::MQTT::Simple;

my $file = shift;
my $host = shift;

my $json = JSON->new->allow_nonref;
my $mqtt;

my $values;
my $pvalues;
my $serial;

sub read_json_file {
	my $filename = shift;
	my $content;

	open FILE, '<', $filename or die "read $filename: $!";
	{ local $/; undef $/; $content = <FILE> }
	close FILE;

	return $json->decode($content);
}

if (defined($host)) {
	$mqtt = Net::MQTT::Simple->new($host) or die "mqtt init (server $host)"
}

for (;;) {
	$values = read_json_file($file);
	$serial = $values->{'serial'};
	for my $key ('co2', 'temperature', 'humidity') {
		next if defined($pvalues->{$key}) and $pvalues->{$key} eq $values->{$key};
		my $topic = "sensors/" . $key . "/scd4x/" . $serial;
		if (defined($mqtt)) {
			$mqtt->retain( $topic => $values->{$key} );
		} else {
			my $ts = POSIX::ctime(time());
			chomp($ts);
			printf("[%s] %-40s: %s\n",
			       $ts, $topic, $values->{$key});
		}
	}
	$pvalues = $values;
	sleep 60;
}