#! /usr/bin/python
###
### Report on available package updates, including security updates.

import time as T
import os as OS
import errno as E

import apt_pkg as APT
import apt.cache as AC

###--------------------------------------------------------------------------
### Some utility functions.

def cache_up_to_date_p():
  """Answer whether the cache is up-to-date."""

  ## I use the same stamp file as APT's standard periodic update service.
  ## This needs prodding via a hook in the APT configuration.
  now = T.time()
  try:
    last = OS.path.getmtime('/var/lib/apt/periodic/update-stamp')
  except OSError, err:
    if err.errno == E.ENOENT:
      return False
  return now - last < 86400

def upgradable_packages():
  """Return a list of packages for which updates are available."""
  cache = AC.Cache()
  return [pkg for pkg in cache if pkg.is_upgradable]

def security_updates_p(pkg):
  """Answer whether any update for PKG is security-relevant."""

  ## There doesn't seem to be a good way of doing this.  For distributions
  ## like `testing', security updates are folded into the main distribution
  ## after the usual triage process, so they stop looking like security
  ## updates.  Worse, for `unstable' there aren't distinct security updates
  ## anyway: they're all just thrown into the mixer.  The good way to tell
  ## would be to fetch the changelog and look for urgent changes.  Debian's
  ## Aptitude checks explicitly for `security.debian.org'.  This check at
  ## least also captures Ubuntu.
  for v in pkg.versions:
    if v < pkg.installed:
      continue
    for o in v.origins:
      if o.site.startswith('security.'):
        return True
  return False

###--------------------------------------------------------------------------
### Main program.

if not cache_up_to_date_p():
  print 'W: package cache is more than 24 hours of date'
updates = upgradable_packages()
if updates:
  plural = len(updates) != 1
  print 'I: updates available for %d %s' % \
        (len(updates), plural and 'packages' or 'package')
sec = [pkg for pkg in updates if security_updates_p(pkg)]
if sec:
  plural = len(sec) != 1
  print 'W: security updates available for %d %s' % \
        (len(sec), plural and 'packages' or 'package')

###----- That's all, folks --------------------------------------------------