#!/usr/bin/python3

import os
import re
import string
import subprocess
import tempfile


class GrubUpdater(object):

  _VOLUME_ID_REGEX = re.compile(b'^Volume id: (?P<volume_id>.+)$', re.MULTILINE)
  _HOTKEYS = string.digits + string.ascii_letters

  def __init__(self, image_dir, boot_dir):
    self._image_dir = image_dir
    self._boot_dir = boot_dir

    assert self._image_dir.startswith(self._boot_dir)

    self._image_path = '/' + os.path.relpath(self._image_dir, self._boot_dir)

  def _GetVolumeID(self, path):
    isoinfo = subprocess.check_output([
      'isoinfo',
      '-d',
      '-i', path,
    ])
    match = self._VOLUME_ID_REGEX.search(isoinfo)
    return match.group('volume_id').decode('ascii')

  def Update(self):
    grub_dir = os.path.join(self._boot_dir, 'grub')

    with tempfile.NamedTemporaryFile('w', dir=grub_dir, delete=False) as fh:
      current = os.readlink(os.path.join(self._image_dir, 'current'))

      fh.write("""
set timeout=5
set default=%(default_image_filename)s
""" % {
        'default_image_filename': os.path.basename(current),
      })

      files = []
      for filename in os.listdir(self._image_dir):
        if not filename.endswith('.iso'):
          continue
        files.append(filename)

      for i, filename in enumerate(sorted(files, reverse=True)):
        fh.write("""
menuentry "%(image_filename)s (%(volume_id)s)" --hotkey=%(hotkey)s {
  search --no-floppy --file --set=root %(image_path)s/%(image_filename)s
  iso_path="%(image_path)s/%(image_filename)s"
  export iso_path
  loopback loop "%(image_path)s/%(image_filename)s"
  set root=(loop)
  configfile /boot/grub/loopback.cfg
}
""" % {
          'image_filename': filename,
          'image_path': self._image_path,
          'hotkey': self._HOTKEYS[i],
          'volume_id': self._GetVolumeID(os.path.join(self._image_dir, filename)),
        })

      fh.flush()
      os.rename(fh.name, os.path.join(grub_dir, 'grub.cfg'))