# vi: ts=4 expandtab
#
#    Copyright (C) 2014 Canonical Ltd.
#
#    Author: Scott Moser <scott.moser@canonical.com>
#
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License version 3, as
#    published by the Free Software Foundation.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with this program.  If not, see <http://www.gnu.org/licenses/>.

"""
**Summary:** reboot system into another init.

**Description:** This module provides a way for the user to boot with systemd
even if the image is set to boot with upstart.  It should be run as one of the
first ``cloud_init_modules``, and will switch the init system and then issue a
reboot. The next boot will come up in the target init system and no action will
be taken.

This should be inert on non-ubuntu systems, and also exit quickly.

It can be configured with the following option structure::

    init_switch:
      target: systemd (can be 'systemd' or 'upstart')
      reboot: true (reboot if a change was made, or false to not reboot)

.. note::

    Best effort is made, but it's possible
    this system will break, and probably won't interact well with any other
    mechanism you've used to switch the init system.
"""

from cloudinit.distros import ubuntu
from cloudinit import log as logging
from cloudinit.settings import PER_INSTANCE
from cloudinit import util

import os
import time

frequency = PER_INSTANCE
REBOOT_CMD = ["/sbin/reboot", "--force"]

DEFAULT_CONFIG = {
    'init_switch': {'target': None, 'reboot': True}
}

SWITCH_INIT = """
#!/bin/sh
# switch_init: [upstart | systemd]

is_systemd() {
   [ "$(dpkg-divert --listpackage /sbin/init)" = "systemd-sysv" ]
}
debug() { echo "$@" 1>&2; }
fail() { echo "$@" 1>&2; exit 1; }

if [ "$1" = "systemd" ]; then
   if is_systemd; then
      debug "already systemd, nothing to do"
   else
      [ -f /lib/systemd/systemd ] || fail "no systemd available";
      dpkg-divert --package systemd-sysv --divert /sbin/init.diverted \\
          --rename /sbin/init
   fi
   [ -f /sbin/init ] || ln /lib/systemd/systemd /sbin/init
elif [ "$1" = "upstart" ]; then
   if is_systemd; then
      rm -f /sbin/init
      dpkg-divert --package systemd-sysv --rename --remove /sbin/init
   else
      debug "already upstart, nothing to do."
   fi
else
  fail "Error. expect 'upstart' or 'systemd'"
fi
"""


def handle(name, cfg, cloud, log, args):
    """Handler method activated by cloud-init."""

    if not isinstance(cloud.distro, ubuntu.Distro):
        log.debug("%s: distro is '%s', not ubuntu. returning",
                  name, cloud.distro.__class__)
        return

    cfg = util.mergemanydict([cfg, DEFAULT_CONFIG])
    target = cfg['init_switch']['target']
    reboot = cfg['init_switch']['reboot']

    if len(args) != 0:
        target = args[0]
        if len(args) > 1:
            reboot = util.is_true(args[1])

    if not target:
        log.debug("%s: target=%s. nothing to do", name, target)
        return

    if not util.which('dpkg'):
        log.warn("%s: 'dpkg' not available. Assuming not ubuntu", name)
        return

    supported = ('upstart', 'systemd')
    if target not in supported:
        log.warn("%s: target set to %s, expected one of: %s",
                 name, target, str(supported))

    if os.path.exists("/run/systemd/system"):
        current = "systemd"
    else:
        current = "upstart"

    if current == target:
        log.debug("%s: current = target = %s. nothing to do", name, target)
        return

    try:
        util.subp(['sh', '-s', target], data=SWITCH_INIT)
    except util.ProcessExecutionError as e:
        log.warn("%s: Failed to switch to init '%s'. %s", name, target, e)
        return

    if util.is_false(reboot):
        log.info("%s: switched '%s' to '%s'. reboot=false, not rebooting.",
                 name, current, target)
        return

    try:
        log.warn("%s: switched '%s' to '%s'. rebooting.",
                 name, current, target)
        logging.flushLoggers(log)
        _fire_reboot(log, wait_attempts=4, initial_sleep=4)
    except Exception as e:
        util.logexc(log, "Requested reboot did not happen!")
        raise


def _fire_reboot(log, wait_attempts=6, initial_sleep=1, backoff=2):
    util.subp(REBOOT_CMD)
    start = time.time()
    wait_time = initial_sleep
    for _i in range(0, wait_attempts):
        time.sleep(wait_time)
        wait_time *= backoff
        elapsed = time.time() - start
        log.debug("Rebooted, but still running after %s seconds", int(elapsed))
    # If we got here, not good
    elapsed = time.time() - start
    raise RuntimeError(("Reboot did not happen"
                        " after %s seconds!") % (int(elapsed)))
