#!/usr/bin/env perl

use strict;
use warnings;
use Getopt::Long;
use Date::Calc qw(Delta_Days Parse_Date Today);
use Crypt::OpenSSL::X509;

# Basic Arguments
our $ARG_WARNING_DAYS = 14;
our $ARG_CRITICAL_DAYS = 7;

# Arguments for network check
our $ARG_ADDRESS = '';
our $ARG_HOSTNAME = ''; # Only used for HTTP SNI
our $ARG_PORT = 443;
our $ARG_OPENSSL = '/usr/bin/openssl';
our $ARG_STARTTLS = '';

# Argument for file check
our $ARG_FILE = '';
our $ARG_COMMON_NAME = '';

main();

sub main {
	parseArguments();
	my $certificate = retrieveCertificate();

	my $x509 = Crypt::OpenSSL::X509->new_from_string(
		$certificate, Crypt::OpenSSL::X509::FORMAT_PEM
	);

	decideExitCode(
		calculateDaysLeft($x509->notAfter()),
		extractCommonName($x509->subject())
		);
}

sub decideExitCode {
	my ( $daysLeft, $commonName ) = @_;

	if ( length($ARG_COMMON_NAME) != 0 ) {
		# Common name check wanted
		if ( $ARG_COMMON_NAME ne $commonName ) {
			printf("CRITICAL - Common name does not match. Got: %s\n",
				$commonName);
			exit(2);
		}
	}

	# Check if certificate is already expired
	# Display an appropriate string then
	if ( $daysLeft <= 0 ) {
		printf("CRITICAL - Certificate is expired\n");
		exit(2);
	}

	# Days left check
	if ( $daysLeft <= $ARG_CRITICAL_DAYS ) {
		printf("CRITICAL - %d days left\n", $daysLeft);
		exit(2);
	}
	elsif ( $daysLeft <= $ARG_WARNING_DAYS ) {
		printf("WARNING - %d days left\n", $daysLeft);
		exit(1);
	}
	else {
		printf("OK - %d days left\n", $daysLeft);
		exit(0);
	}
}

sub parseArguments {
	GetOptions (
		'address=s' => \$ARG_ADDRESS,
		'port=s' => \$ARG_PORT,
		'hostname=s' => \$ARG_HOSTNAME,
		'common-name=s' => \$ARG_COMMON_NAME,
		'file=s' => \$ARG_FILE,
		'warn=i' => \$ARG_WARNING_DAYS,
		'crit=i' => \$ARG_CRITICAL_DAYS,
		'openssl=s' => \$ARG_OPENSSL,
		'starttls=s' => \$ARG_STARTTLS
	);

	validateArguments();
}

sub validateArguments {
	# Common Arguments
	if ( ! isInteger($ARG_WARNING_DAYS) ) {
		exitUnknown("Argument --warn is not numeric");
	}

	if ( ! isInteger($ARG_CRITICAL_DAYS) ) {
		exitUnknown("Argument --crit is not numeric");
	}

	if ( $ARG_CRITICAL_DAYS > $ARG_WARNING_DAYS ) {
		exitUnknown(sprintf(
			'Critical value (%d) is greater than warning value (%d)',
			$ARG_CRITICAL_DAYS,
			$ARG_WARNING_DAYS
			));
	}

	# Decide which mode
	if ( length ($ARG_FILE) == 0 ) {
		# Network mode
		# Validate network parameter
		validateNetworkArguments();
	}
	else {
		# File mode
		# Validate file parameter
		validateFileArguments();
	}
}

sub validateNetworkArguments {
	if ( ! -e $ARG_OPENSSL ) {
		exitUnknown(sprintf("OpenSSL not found under %s", $ARG_OPENSSL));
	}

	if ( length($ARG_ADDRESS) == 0) {
		exitUnknown("Argument --address is not set");
	}

	if ( ! isInteger($ARG_PORT) ) {
		exitUnknown("Argument --port is not numeric");
	}

	if ( $ARG_PORT <= 0 || $ARG_PORT >= 65535 ) {
		exitUnknown("Argument --port is out of bounds! Valid: 1-65535");
	}
}

sub validateFileArguments {
	if ( ! -e $ARG_FILE ) {
		exitUnknown(sprintf(
			"Certificate under %s not found",
			$ARG_FILE
			));
	}
}

sub isInteger {
	my $possibleInteger = shift;

	return 1 if ( $possibleInteger =~ /\d+/ );
	return 0;
}

sub exitUnknown {
	printf("UNKNOWN - %s\n", shift);
	exit 3;
}

sub retrieveCertificate {
	my $certificate = '';

	if ( length($ARG_FILE) == 0 ) {
		# Network mode
		# Fetch certificate and return it as a string

		# Check if we have to set SNI
		my $sniPart = '';

		if ( length($ARG_HOSTNAME) != 0 ) {
			$sniPart = sprintf("-servername %s", $ARG_HOSTNAME);
		}

		# Check if we have to set starttls protocol
		my $starttlsPart = '';

		if ( length($ARG_STARTTLS) != 0 ) {
			$starttlsPart = sprintf("-starttls %s", $ARG_STARTTLS);
		}

		# Build command
		my $command = sprintf(
			"echo \"\" | %s s_client -connect %s:%d %s %s 2> /dev/null | %s x509 2> /dev/null",
			$ARG_OPENSSL,
			$ARG_ADDRESS,
			$ARG_PORT,
			$starttlsPart,
			$sniPart,
			$ARG_OPENSSL
			);

		$certificate = `$command`;
	}
	else {
		# File mode
		# Fetch certificate from file and return it as string
		open(CERT, $ARG_FILE);
		my $line = '';

		while ( $line = <CERT> ) {
			$certificate .= $line;
		}

		close(CERT);
	}

	if ( $certificate !~ /BEGIN CERTIFICATE/ ) {
		exitUnknown("Didn't receive a certificate");
	}

	return $certificate;
}

sub calculateDaysLeft {
	my $expireDate = shift;

	my ($year, $month, $day) = Parse_Date($expireDate);
	my ( $nowYear, $nowMonth, $nowDay) = Today();

	return Delta_Days($nowYear, $nowMonth, $nowDay,
		$year, $month, $day);
}

sub extractCommonName {
	my $possibleCommonName = shift;

	if ( $possibleCommonName =~ m/CN=(.*)/ ) {
		# Strip possible E-Mail address
        my $cn = $1;
        $cn =~ s/,.*//;

        return $cn;
	}
	else {
		exitUnknown("No common name given");
	}
}