#!/usr/bin/env python3

import socket
import ssl
import datetime
import json


CONFIGFILE='/etc/snmp/certificate.json'
# {"domains": [
#     {"fqdn": "www.mydomain.com"},
#     {"fqdn": "www2.mydomain.com"}
# ]
# }


def get_certificate_data(domain, port=443):

    context = ssl.create_default_context()
    conn = context.wrap_socket(
        socket.socket(socket.AF_INET),
        server_hostname=domain,
    )
    # 3 second timeout because Lambda has runtime limitations
    conn.settimeout(3.0)

    try:
        conn.connect((domain, port))
        error_msg = None
    except ConnectionRefusedError as e:
        error_msg = e
    ssl_info = conn.getpeercert()
    return ssl_info, error_msg


output = {}
output['error'] = 0
output['errorString'] = ""
output['version'] = 1

with open(CONFIGFILE, 'r') as json_file:
    try:
        configfile = json.load(json_file)
    except json.decoder.JSONDecodeError as e:
        output['error'] = 1
        output['errorString'] = "Configfile Error: '%s'" % e

if not output['error']:
    output_data_list = []
    for domain in configfile['domains']:
        output_data = {}

        if 'port' not in domain.keys():
            domain['port'] = 443
        certificate_data, error_msg = get_certificate_data(domain['fqdn'], domain['port'])

        output_data['cert_name'] = domain['fqdn']

        if not error_msg:
            ssl_date_format = r'%b %d %H:%M:%S %Y %Z'
            validity_end = datetime.datetime.strptime(certificate_data['notAfter'], ssl_date_format)
            validity_start = datetime.datetime.strptime(certificate_data['notBefore'], ssl_date_format)
            cert_age = datetime.datetime.now() - validity_start
            cert_still_valid = validity_end - datetime.datetime.now()

            output_data['age'] = cert_age.days
            output_data['remaining_days'] = cert_still_valid.days

        else:
            output_data['age'] = None
            output_data['remaining_days'] = None
            output['error'] = 1
            output['errorString'] = "%s: %s" % (domain['fqdn'], error_msg)

        output_data_list.append(output_data)

    output['data'] = output_data_list

print(json.dumps(output))