#!/usr/bin/env python

import re
import datetime

def count_dhcp_leases():
    regex_leaseblock = re.compile(r"lease (?P<ip>\d+\.\d+\.\d+\.\d+) {(?P<config>[\s\S]+?)\n}")
    regex_properties = re.compile(r"\s+(?P<key>\S+) (?P<value>[\s\S]+?);")
    leases = 0
    with open("/var/lib/dhcp/dhcpd.leases") as lease_file:
        macs = set()
        for match in regex_leaseblock.finditer(lease_file.read()):
             block = match.groupdict()
             properties = {key: value for (key, value) in regex_properties.findall(block['config'])}
             if properties['binding'].split(' ')[1] == 'active' and properties['ends'] != 'never':
                 dt_ends = datetime.datetime.strptime(properties['ends'][2:], "%Y/%m/%d %H:%M:%S")
                 if dt_ends > datetime.datetime.utcnow() and properties['hardware'].startswith('ethernet'):
                     macs.add(properties['hardware'][9:])
        leases = len(macs)
    return leases

if __name__ == "__main__":
    print count_dhcp_leases()