#!/usr/bin/python

import fcntl
import errno
import os
import logging
import sys
import simplejson
import fcntl

starting_mac_prefix='aa:00:00'

class FileLock(object):
  def __init__(self, fd, filename):
    self.fd = fd
    self.filename = filename

  @classmethod
  def Open(cls, filename):
    # Using "os.open" is necessary to allow both opening existing file
    # read/write and creating if not existing. Vanilla "open" will truncate an
    # existing file -or- allow creating if not existing.
    return cls(os.fdopen(os.open(filename, os.O_RDWR | os.O_CREAT), "w+"),
               filename)

  def __del__(self):
    self.Close()

  def Close(self):
    if hasattr(self, "fd") and self.fd:
      self.fd.close()
      self.fd = None

  def _flock(self, flag):
    self._Lock(self.fd, flag)

  @staticmethod
  def _Lock(fd, flag):
    fcntl.flock(fd, flag)

  def Exclusive(self):
    self._flock(fcntl.LOCK_EX)

  def Unlock(self):
    self._flock(fcntl.LOCK_UN)
    

def get_data():
  f = open('test', 'r')
  data = simplejson.load(f)
  f.close()
  high = data['high']
  pool = set(data['pool'])
  return high, pool

def update_data(high, pool):
  data = dict()
  data['pool'] = list(pool)
  data['high'] = high
  f = open('test', 'w')
  f.write(simplejson.dumps(data, indent=2))
  f.close()

def init(prefix):
  pool=set()
  high=prefix
  update_data(high, pool)

def find_prefix(high, pool):
  try:
    prefix = pool.pop()
    new_high = high
  except KeyError:
    a = hex(int(high.replace(":",""),16) + 1).replace("0x",'')
    prefix = ":".join([a[x:x+2] for x in xrange(0,len(a),2)])
    new_high = prefix    

  return prefix, new_high, pool

  

  


def main(argv):
  if len(argv) < 2:
    print "Usage: " + argv[0] + "init/get/put"
    return 1

  action=argv[1]

  lock = FileLock.Open('prefix.lock')
  lock.Exclusive()


  if action == "get":
    (high, pool) = get_data()
    (prefix, new_high, new_pool) = find_prefix(high, pool)
    update_data(new_high, new_pool)
    print prefix

  elif action == "put":
    if len(argv) < 3 :
      lock.Unlock()
      print "Usage: " + argv[0] + "put prefix"
      return 1

    (high, pool) = get_data()
    prefix = argv[2]
    pool.add(prefix)
    update_data(high, pool)

  elif action == "init":
    if len(argv) < 3:
      lock.Unlock()
      print "Usage: " + argv[0] + "init prefix"
      return 1

    prefix = argv[2]
    init(prefix)
    
  lock.Unlock()
  return 0

if __name__ == '__main__':
  sys.exit(main(sys.argv))