# Copyright (C) 2014 Canonical Ltd.
#
# Author: Scott Moser <scott.moser@canonical.com>
#
# This file is part of cloud-init. See LICENSE file for license information.

"""
Ubuntu Init Switch
------------------
**Summary:** reboot system into another init.

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.

.. 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.

**Internal name:** ``cc_ubuntu_init_switch``

**Module frequency:** once per instance

**Supported distros:** ubuntu

**Config keys**::

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

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
"""

distros = ['ubuntu']


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)))

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