#!/usr/bin/python
# -*- coding: utf-8 -*-

# Copyright: (c) 2016, Shinichi TAMURA (@tmshn)
# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)

from __future__ import absolute_import, division, print_function
__metaclass__ = type

ANSIBLE_METADATA = {'metadata_version': '1.1',
                    'status': ['preview'],
                    'supported_by': 'community'}

DOCUMENTATION = '''
---
module: timezone
short_description: Configure timezone setting
description:
  - This module configures the timezone setting, both of the system clock and of the hardware clock. If you want to set up the NTP, use M(service) module.
  - It is recommended to restart C(crond) after changing the timezone, otherwise the jobs may run at the wrong time.
  - Several different tools are used depending on the OS/Distribution involved.
    For Linux it can use C(timedatectl) or edit C(/etc/sysconfig/clock) or C(/etc/timezone) and C(hwclock).
    On SmartOS, C(sm-set-timezone), for macOS, C(systemsetup), for BSD, C(/etc/localtime) is modified.
  - As of version 2.3 support was added for SmartOS and BSDs.
  - As of version 2.4 support was added for macOS.
  - Windows, AIX and HPUX are not supported, please let us know if you find any other OS/distro in which this fails.
version_added: "2.2"
options:
  name:
    description:
      - Name of the timezone for the system clock.
        Default is to keep current setting. B(At least one of name and
        hwclock are required.)
  hwclock:
    description:
      - Whether the hardware clock is in UTC or in local timezone.
        Default is to keep current setting.
        Note that this option is recommended not to change and may fail
        to configure, especially on virtual environments such as AWS.
        B(At least one of name and hwclock are required.)
        I(Only used on Linux.)
    aliases: [ rtc ]
    choices: [ "UTC", "local" ]
notes:
  - On SmartOS the C(sm-set-timezone) utility (part of the smtools package) is required to set the zone timezone
author:
  - Shinichi TAMURA (@tmshn)
  - Jasper Lievisse Adriaanse (@jasperla)
  - Indrajit Raychaudhuri (@indrajitr)
'''

RETURN = '''
diff:
  description: The differences about the given arguments.
  returned: success
  type: complex
  contains:
    before:
      description: The values before change
      type: dict
    after:
      description: The values after change
      type: dict
'''

EXAMPLES = '''
- name: set timezone to Asia/Tokyo
  timezone:
    name: Asia/Tokyo
'''

import errno
import filecmp
import os
import platform
import random
import re
import string
import filecmp

from ansible.module_utils.basic import AnsibleModule, get_platform, get_distribution
from ansible.module_utils.six import iteritems


class Timezone(object):
    """This is a generic Timezone manipulation class that is subclassed based on platform.

    A subclass may wish to override the following action methods:
        - get(key, phase)   ... get the value from the system at `phase`
        - set(key, value)   ... set the value to the current system
    """

    def __new__(cls, module):
        """Return the platform-specific subclass.

        It does not use load_platform_subclass() because it needs to judge based
        on whether the `timedatectl` command exists and is available.

        Args:
            module: The AnsibleModule.
        """
        if get_platform() == 'Linux':
            timedatectl = module.get_bin_path('timedatectl')
            if timedatectl is not None:
                rc, stdout, stderr = module.run_command(timedatectl)
                if rc == 0:
                    return super(Timezone, SystemdTimezone).__new__(SystemdTimezone)
                else:
                    module.warn('timedatectl command was found but not usable: %s. using other method.' % stderr)
                    return super(Timezone, NosystemdTimezone).__new__(NosystemdTimezone)
            else:
                return super(Timezone, NosystemdTimezone).__new__(NosystemdTimezone)
        elif re.match('^joyent_.*Z', platform.version()):
            # get_platform() returns SunOS, which is too broad. So look at the
            # platform version instead. However we have to ensure that we're not
            # running in the global zone where changing the timezone has no effect.
            zonename_cmd = module.get_bin_path('zonename')
            if zonename_cmd is not None:
                (rc, stdout, _) = module.run_command(zonename_cmd)
                if rc == 0 and stdout.strip() == 'global':
                    module.fail_json(msg='Adjusting timezone is not supported in Global Zone')

            return super(Timezone, SmartOSTimezone).__new__(SmartOSTimezone)
        elif re.match('^Darwin', platform.platform()):
            return super(Timezone, DarwinTimezone).__new__(DarwinTimezone)
        elif re.match('^(Free|Net|Open)BSD', platform.platform()):
            return super(Timezone, BSDTimezone).__new__(BSDTimezone)
        else:
            # Not supported yet
            return super(Timezone, Timezone).__new__(Timezone)

    def __init__(self, module):
        """Initialize of the class.

        Args:
            module: The AnsibleModule.
        """
        super(Timezone, self).__init__()
        self.msg = []
        # `self.value` holds the values for each params on each phases.
        # Initially there's only info of "planned" phase, but the
        # `self.check()` function will fill out it.
        self.value = dict()
        for key in module.argument_spec:
            value = module.params[key]
            if value is not None:
                self.value[key] = dict(planned=value)
        self.module = module

    def abort(self, msg):
        """Abort the process with error message.

        This is just the wrapper of module.fail_json().

        Args:
            msg: The error message.
        """
        error_msg = ['Error message:', msg]
        if len(self.msg) > 0:
            error_msg.append('Other message(s):')
            error_msg.extend(self.msg)
        self.module.fail_json(msg='\n'.join(error_msg))

    def execute(self, *commands, **kwargs):
        """Execute the shell command.

        This is just the wrapper of module.run_command().

        Args:
            *commands: The command to execute.
                It will be concatenated with single space.
            **kwargs:  Only 'log' key is checked.
                If kwargs['log'] is true, record the command to self.msg.

        Returns:
            stdout: Standard output of the command.
        """
        command = ' '.join(commands)
        (rc, stdout, stderr) = self.module.run_command(command, check_rc=True)
        if kwargs.get('log', False):
            self.msg.append('executed `%s`' % command)
        return stdout

    def diff(self, phase1='before', phase2='after'):
        """Calculate the difference between given 2 phases.

        Args:
            phase1, phase2: The names of phase to compare.

        Returns:
            diff: The difference of value between phase1 and phase2.
                This is in the format which can be used with the
                `--diff` option of ansible-playbook.
        """
        diff = {phase1: {}, phase2: {}}
        for key, value in iteritems(self.value):
            diff[phase1][key] = value[phase1]
            diff[phase2][key] = value[phase2]
        return diff

    def check(self, phase):
        """Check the state in given phase and set it to `self.value`.

        Args:
            phase: The name of the phase to check.

        Returns:
            NO RETURN VALUE
        """
        if phase == 'planned':
            return
        for key, value in iteritems(self.value):
            value[phase] = self.get(key, phase)

    def change(self):
        """Make the changes effect based on `self.value`."""
        for key, value in iteritems(self.value):
            if value['before'] != value['planned']:
                self.set(key, value['planned'])

    # ===========================================
    # Platform specific methods (must be replaced by subclass).

    def get(self, key, phase):
        """Get the value for the key at the given phase.

        Called from self.check().

        Args:
            key:   The key to get the value
            phase: The phase to get the value

        Return:
            value: The value for the key at the given phase.
        """
        self.abort('get(key, phase) is not implemented on target platform')

    def set(self, key, value):
        """Set the value for the key (of course, for the phase 'after').

        Called from self.change().

        Args:
            key: Key to set the value
            value: Value to set
        """
        self.abort('set(key, value) is not implemented on target platform')

    def _verify_timezone(self):
        tz = self.value['name']['planned']
        tzfile = '/usr/share/zoneinfo/%s' % tz
        if not os.path.isfile(tzfile):
            self.abort('given timezone "%s" is not available' % tz)
        return tzfile


class SystemdTimezone(Timezone):
    """This is a Timezone manipulation class for systemd-powered Linux.

    It uses the `timedatectl` command to check/set all arguments.
    """

    regexps = dict(
        hwclock=re.compile(r'^\s*RTC in local TZ\s*:\s*([^\s]+)', re.MULTILINE),
        name=re.compile(r'^\s*Time ?zone\s*:\s*([^\s]+)', re.MULTILINE)
    )

    subcmds = dict(
        hwclock='set-local-rtc',
        name='set-timezone'
    )

    def __init__(self, module):
        super(SystemdTimezone, self).__init__(module)
        self.timedatectl = module.get_bin_path('timedatectl', required=True)
        self.status = dict()
        # Validate given timezone
        if 'name' in self.value:
            self._verify_timezone()

    def _get_status(self, phase):
        if phase not in self.status:
            self.status[phase] = self.execute(self.timedatectl, 'status')
        return self.status[phase]

    def get(self, key, phase):
        status = self._get_status(phase)
        value = self.regexps[key].search(status).group(1)
        if key == 'hwclock':
            # For key='hwclock'; convert yes/no -> local/UTC
            if self.module.boolean(value):
                value = 'local'
            else:
                value = 'UTC'
        return value

    def set(self, key, value):
        # For key='hwclock'; convert UTC/local -> yes/no
        if key == 'hwclock':
            if value == 'local':
                value = 'yes'
            else:
                value = 'no'
        self.execute(self.timedatectl, self.subcmds[key], value, log=True)


class NosystemdTimezone(Timezone):
    """This is a Timezone manipulation class for non systemd-powered Linux.

    For timezone setting, it edits the following file and reflect changes:
        - /etc/sysconfig/clock  ... RHEL/CentOS
        - /etc/timezone         ... Debian/Ubuntu
    For hwclock setting, it executes `hwclock --systohc` command with the
    '--utc' or '--localtime' option.
    """

    conf_files = dict(
        name=None,  # To be set in __init__
        hwclock=None,  # To be set in __init__
        adjtime='/etc/adjtime'
    )

    # It's fine if all tree config files don't exist
    allow_no_file = dict(
        name=True,
        hwclock=True,
        adjtime=True
    )

    regexps = dict(
        name=None,  # To be set in __init__
        hwclock=re.compile(r'^UTC\s*=\s*([^\s]+)', re.MULTILINE),
        adjtime=re.compile(r'^(UTC|LOCAL)$', re.MULTILINE)
    )

    dist_regexps = dict(
        SuSE=re.compile(r'^TIMEZONE\s*=\s*"?([^"\s]+)"?', re.MULTILINE),
        redhat=re.compile(r'^ZONE\s*=\s*"?([^"\s]+)"?', re.MULTILINE)
    )

    dist_tzline_format = dict(
        SuSE='TIMEZONE="%s"\n',
        redhat='ZONE="%s"\n'
    )

    def __init__(self, module):
        super(NosystemdTimezone, self).__init__(module)
        # Validate given timezone
        if 'name' in self.value:
            tzfile = self._verify_timezone()
            # `--remove-destination` is needed if /etc/localtime is a symlink so
            # that it overwrites it instead of following it.
            self.update_timezone = ['%s --remove-destination %s /etc/localtime' % (self.module.get_bin_path('cp', required=True), tzfile)]
        self.update_hwclock = self.module.get_bin_path('hwclock', required=True)
        # Distribution-specific configurations
        if self.module.get_bin_path('dpkg-reconfigure') is not None:
            # Debian/Ubuntu
            if 'name' in self.value:
                self.update_timezone = ['%s -sf %s /etc/localtime' % (self.module.get_bin_path('ln', required=True), tzfile),
                                        '%s --frontend noninteractive tzdata' % self.module.get_bin_path('dpkg-reconfigure', required=True)]
            self.conf_files['name'] = '/etc/timezone'
            self.conf_files['hwclock'] = '/etc/default/rcS'
            self.regexps['name'] = re.compile(r'^([^\s]+)', re.MULTILINE)
            self.tzline_format = '%s\n'
        else:
            # RHEL/CentOS/SUSE
            if self.module.get_bin_path('tzdata-update') is not None:
                # tzdata-update cannot update the timezone if /etc/localtime is
                # a symlink so we have to use cp to update the time zone which
                # was set above.
                if not os.path.islink('/etc/localtime'):
                    self.update_timezone = [self.module.get_bin_path('tzdata-update', required=True)]
                # else:
                #   self.update_timezone       = 'cp --remove-destination ...' <- configured above
            self.conf_files['name'] = '/etc/sysconfig/clock'
            self.conf_files['hwclock'] = '/etc/sysconfig/clock'
            try:
                f = open(self.conf_files['name'], 'r')
            except IOError as err:
                if self._allow_ioerror(err, 'name'):
                    # If the config file doesn't exist detect the distribution and set regexps.
                    distribution = get_distribution()
                    if distribution == 'SuSE':
                        # For SUSE
                        self.regexps['name'] = self.dist_regexps['SuSE']
                        self.tzline_format = self.dist_tzline_format['SuSE']
                    else:
                        # For RHEL/CentOS
                        self.regexps['name'] = self.dist_regexps['redhat']
                        self.tzline_format = self.dist_tzline_format['redhat']
                else:
                    self.abort('could not read configuration file "%s"' % self.conf_files['name'])
            else:
                # The key for timezone might be `ZONE` or `TIMEZONE`
                # (the former is used in RHEL/CentOS and the latter is used in SUSE linux).
                # So check the content of /etc/sysconfig/clock and decide which key to use.
                sysconfig_clock = f.read()
                f.close()
                if re.search(r'^TIMEZONE\s*=', sysconfig_clock, re.MULTILINE):
                    # For SUSE
                    self.regexps['name'] = self.dist_regexps['SuSE']
                    self.tzline_format = self.dist_tzline_format['SuSE']
                else:
                    # For RHEL/CentOS
                    self.regexps['name'] = self.dist_regexps['redhat']
                    self.tzline_format = self.dist_tzline_format['redhat']

    def _allow_ioerror(self, err, key):
        # In some cases, even if the target file does not exist,
        # simply creating it may solve the problem.
        # In such cases, we should continue the configuration rather than aborting.
        if err.errno != errno.ENOENT:
            # If the error is not ENOENT ("No such file or directory"),
            # (e.g., permission error, etc), we should abort.
            return False
        return self.allow_no_file.get(key, False)

    def _edit_file(self, filename, regexp, value, key):
        """Replace the first matched line with given `value`.

        If `regexp` matched more than once, other than the first line will be deleted.

        Args:
            filename: The name of the file to edit.
            regexp:   The regular expression to search with.
            value:    The line which will be inserted.
            key:      For what key the file is being editted.
        """
        # Read the file
        try:
            file = open(filename, 'r')
        except IOError as err:
            if self._allow_ioerror(err, key):
                lines = []
            else:
                self.abort('tried to configure %s using a file "%s", but could not read it' % (key, filename))
        else:
            lines = file.readlines()
            file.close()
        # Find the all matched lines
        matched_indices = []
        for i, line in enumerate(lines):
            if regexp.search(line):
                matched_indices.append(i)
        if len(matched_indices) > 0:
            insert_line = matched_indices[0]
        else:
            insert_line = 0
        # Remove all matched lines
        for i in matched_indices[::-1]:
            del lines[i]
        # ...and insert the value
        lines.insert(insert_line, value)
        # Write the changes
        try:
            file = open(filename, 'w')
        except IOError:
            self.abort('tried to configure %s using a file "%s", but could not write to it' % (key, filename))
        else:
            file.writelines(lines)
            file.close()
        self.msg.append('Added 1 line and deleted %s line(s) on %s' % (len(matched_indices), filename))

    def _get_value_from_config(self, key, phase):
        filename = self.conf_files[key]
        try:
            file = open(filename, mode='r')
        except IOError as err:
            if self._allow_ioerror(err, key):
                if key == 'hwclock':
                    return 'n/a'
                elif key == 'adjtime':
                    return 'UTC'
                elif key == 'name':
                    return 'n/a'
            else:
                self.abort('tried to configure %s using a file "%s", but could not read it' % (key, filename))
        else:
            status = file.read()
            file.close()
            try:
                value = self.regexps[key].search(status).group(1)
            except AttributeError:
                if key == 'hwclock':
                    # If we cannot find UTC in the config that's fine.
                    return 'n/a'
                elif key == 'adjtime':
                    # If we cannot find UTC/LOCAL in /etc/cannot that means UTC
                    # will be used by default.
                    return 'UTC'
                elif key == 'name':
                    if phase == 'before':
                        # In 'before' phase UTC/LOCAL doesn't need to be set in
                        # the timezone config file, so we ignore this error.
                        return 'n/a'
                    else:
                        self.abort('tried to configure %s using a file "%s", but could not find a valid value in it' % (key, filename))
            else:
                if key == 'hwclock':
                    # convert yes/no -> UTC/local
                    if self.module.boolean(value):
                        value = 'UTC'
                    else:
                        value = 'local'
                elif key == 'adjtime':
                    # convert LOCAL -> local
                    if value != 'UTC':
                        value = value.lower()
        return value

    def get(self, key, phase):
        planned = self.value[key]['planned']
        if key == 'hwclock':
            value = self._get_value_from_config(key, phase)
            if value == planned:
                # If the value in the config file is the same as the 'planned'
                # value, we need to check /etc/adjtime.
                value = self._get_value_from_config('adjtime', phase)
        elif key == 'name':
            value = self._get_value_from_config(key, phase)
            if value == planned:
                # If the planned values is the same as the one in the config file
                # we need to check if /etc/localtime is also set to the 'planned' zone.
                if os.path.islink('/etc/localtime'):
                    # If /etc/localtime is a symlink and is not set to the TZ we 'planned'
                    # to set, we need to return the TZ which the symlink points to.
                    if os.path.exists('/etc/localtime'):
                        # We use readlink() because on some distros zone files are symlinks
                        # to other zone files, so it's hard to get which TZ is actually set
                        # if we follow the symlink.
                        path = os.readlink('/etc/localtime')
                        linktz = re.search(r'/usr/share/zoneinfo/(.*)', path, re.MULTILINE)
                        if linktz:
                            valuelink = linktz.group(1)
                            if valuelink != planned:
                                value = valuelink
                        else:
                            # Set current TZ to 'n/a' if the symlink points to a path
                            # which isn't a zone file.
                            value = 'n/a'
                    else:
                        # Set current TZ to 'n/a' if the symlink to the zone file is broken.
                        value = 'n/a'
                else:
                    # If /etc/localtime is not a symlink best we can do is compare it with
                    # the 'planned' zone info file and return 'n/a' if they are different.
                    try:
                        if not filecmp.cmp('/etc/localtime', '/usr/share/zoneinfo/' + planned):
                            return 'n/a'
                    except:
                        return 'n/a'
        else:
            self.abort('unknown parameter "%s"' % key)
        return value

    def set_timezone(self, value):
        self._edit_file(filename=self.conf_files['name'],
                        regexp=self.regexps['name'],
                        value=self.tzline_format % value,
                        key='name')
        for cmd in self.update_timezone:
            self.execute(cmd)

    def set_hwclock(self, value):
        if value == 'local':
            option = '--localtime'
            utc = 'no'
        else:
            option = '--utc'
            utc = 'yes'
        if self.conf_files['hwclock'] is not None:
            self._edit_file(filename=self.conf_files['hwclock'],
                            regexp=self.regexps['hwclock'],
                            value='UTC=%s\n' % utc,
                            key='hwclock')
        self.execute(self.update_hwclock, '--systohc', option, log=True)

    def set(self, key, value):
        if key == 'name':
            self.set_timezone(value)
        elif key == 'hwclock':
            self.set_hwclock(value)
        else:
            self.abort('unknown parameter "%s"' % key)


class SmartOSTimezone(Timezone):
    """This is a Timezone manipulation class for SmartOS instances.

    It uses the C(sm-set-timezone) utility to set the timezone, and
    inspects C(/etc/default/init) to determine the current timezone.

    NB: A zone needs to be rebooted in order for the change to be
    activated.
    """

    def __init__(self, module):
        super(SmartOSTimezone, self).__init__(module)
        self.settimezone = self.module.get_bin_path('sm-set-timezone', required=False)
        if not self.settimezone:
            module.fail_json(msg='sm-set-timezone not found. Make sure the smtools package is installed.')

    def get(self, key, phase):
        """Lookup the current timezone name in `/etc/default/init`. If anything else
        is requested, or if the TZ field is not set we fail.
        """
        if key == 'name':
            try:
                f = open('/etc/default/init', 'r')
                for line in f:
                    m = re.match('^TZ=(.*)$', line.strip())
                    if m:
                        return m.groups()[0]
            except:
                self.module.fail_json(msg='Failed to read /etc/default/init')
        else:
            self.module.fail_json(msg='%s is not a supported option on target platform' % key)

    def set(self, key, value):
        """Set the requested timezone through sm-set-timezone, an invalid timezone name
        will be rejected and we have no further input validation to perform.
        """
        if key == 'name':
            cmd = 'sm-set-timezone %s' % value

            (rc, stdout, stderr) = self.module.run_command(cmd)

            if rc != 0:
                self.module.fail_json(msg=stderr)

            # sm-set-timezone knows no state and will always set the timezone.
            # XXX: https://github.com/joyent/smtools/pull/2
            m = re.match(r'^\* Changed (to)? timezone (to)? (%s).*' % value, stdout.splitlines()[1])
            if not (m and m.groups()[-1] == value):
                self.module.fail_json(msg='Failed to set timezone')
        else:
            self.module.fail_json(msg='%s is not a supported option on target platform' % key)


class DarwinTimezone(Timezone):
    """This is the timezone implementation for Darwin which, unlike other *BSD
    implementations, uses the `systemsetup` command on Darwin to check/set
    the timezone.
    """

    regexps = dict(
        name=re.compile(r'^\s*Time ?Zone\s*:\s*([^\s]+)', re.MULTILINE)
    )

    def __init__(self, module):
        super(DarwinTimezone, self).__init__(module)
        self.systemsetup = module.get_bin_path('systemsetup', required=True)
        self.status = dict()
        # Validate given timezone
        if 'name' in self.value:
            self._verify_timezone()

    def _get_current_timezone(self, phase):
        """Lookup the current timezone via `systemsetup -gettimezone`."""
        if phase not in self.status:
            self.status[phase] = self.execute(self.systemsetup, '-gettimezone')
        return self.status[phase]

    def _verify_timezone(self):
        tz = self.value['name']['planned']
        # Lookup the list of supported timezones via `systemsetup -listtimezones`.
        # Note: Skip the first line that contains the label 'Time Zones:'
        out = self.execute(self.systemsetup, '-listtimezones').splitlines()[1:]
        tz_list = list(map(lambda x: x.strip(), out))
        if tz not in tz_list:
            self.abort('given timezone "%s" is not available' % tz)
        return tz

    def get(self, key, phase):
        if key == 'name':
            status = self._get_current_timezone(phase)
            value = self.regexps[key].search(status).group(1)
            return value
        else:
            self.module.fail_json(msg='%s is not a supported option on target platform' % key)

    def set(self, key, value):
        if key == 'name':
            self.execute(self.systemsetup, '-settimezone', value, log=True)
        else:
            self.module.fail_json(msg='%s is not a supported option on target platform' % key)


class BSDTimezone(Timezone):
    """This is the timezone implementation for *BSD which works simply through
    updating the `/etc/localtime` symlink to point to a valid timezone name under
    `/usr/share/zoneinfo`.
    """

    def __init__(self, module):
        super(BSDTimezone, self).__init__(module)

    def __get_timezone(self):
        zoneinfo_dir = '/usr/share/zoneinfo/'
        localtime_file = '/etc/localtime'

        # Strategy 1:
        #   If /etc/localtime does not exist, assum the timezone is UTC.
        if not os.path.exists(localtime_file):
            self.module.warn('Could not read /etc/localtime. Assuming UTC.')
            return 'UTC'

        # Strategy 2:
        #   Return planned timezone as current timezone if their content matches.
        #   This is bad design to see `self.value` here,
        #   but it's intended to avoid useless diff.
        planned = self.value['name']['planned']
        try:
            already_planned_state = filecmp.cmp(os.path.join(zoneinfo_dir, planned), localtime_file)
        except OSError:
            # Even if reading planned zoneinfo file gives an OSError, don't abort here,
            # because a bit more detailed check will be done in `set`.
            already_planned_state = False
        if already_planned_state:
            return planned

        # Strategy 3:
        #   Follow symlink of /etc/localtime
        zoneinfo_file = localtime_file
        while not zoneinfo_file.startswith(zoneinfo_dir):
            try:
                zoneinfo_file = os.readlink(localtime_file)
            except OSError:
                # OSError means "end of symlink chain" or broken link.
                break
        else:
            return zoneinfo_file.replace(zoneinfo_dir, '')

        # Strategy 4:
        #   Check all files in /usr/share/zoneinfo and return first match.
        for dname, _, fnames in os.walk(zoneinfo_dir):
            for fname in fnames:
                zoneinfo_file = os.path.join(dname, fname)
                if filecmp.cmp(zoneinfo_file, localtime_file):
                    return zoneinfo_file.replace(zoneinfo_dir, '')

        # Strategy 5:
        #   As a fall-back, return 'UTC' as default assumption.
        self.module.warn('Could not identify timezone name from /etc/localtime. Assuming UTC.')
        return 'UTC'

    def get(self, key, phase):
        """Lookup the current timezone by resolving `/etc/localtime`."""
        if key == 'name':
            return self.__get_timezone()
        else:
            self.module.fail_json(msg='%s is not a supported option on target platform' % key)

    def set(self, key, value):
        if key == 'name':
            # First determine if the requested timezone is valid by looking in
            # the zoneinfo directory.
            zonefile = '/usr/share/zoneinfo/' + value
            try:
                if not os.path.isfile(zonefile):
                    self.module.fail_json(msg='%s is not a recognized timezone' % value)
            except:
                self.module.fail_json(msg='Failed to stat %s' % zonefile)

            # Now (somewhat) atomically update the symlink by creating a new
            # symlink and move it into place. Otherwise we have to remove the
            # original symlink and create the new symlink, however that would
            # create a race condition in case another process tries to read
            # /etc/localtime between removal and creation.
            suffix = "".join([random.choice(string.ascii_letters + string.digits) for x in range(0, 10)])
            new_localtime = '/etc/localtime.' + suffix

            try:
                os.symlink(zonefile, new_localtime)
                os.rename(new_localtime, '/etc/localtime')
            except:
                os.remove(new_localtime)
                self.module.fail_json(msg='Could not update /etc/localtime')
        else:
            self.module.fail_json(msg='%s is not a supported option on target platform' % key)


def main():
    # Construct 'module' and 'tz'
    module = AnsibleModule(
        argument_spec=dict(
            hwclock=dict(type='str', choices=['local', 'UTC'], aliases=['rtc']),
            name=dict(type='str'),
        ),
        required_one_of=[
            ['hwclock', 'name']
        ],
        supports_check_mode=True,
    )
    tz = Timezone(module)

    # Check the current state
    tz.check(phase='before')
    if module.check_mode:
        diff = tz.diff('before', 'planned')
        # In check mode, 'planned' state is treated as 'after' state
        diff['after'] = diff.pop('planned')
    else:
        # Make change
        tz.change()
        # Check the current state
        tz.check(phase='after')
        # Examine if the current state matches planned state
        (after, planned) = tz.diff('after', 'planned').values()
        if after != planned:
            tz.abort('still not desired state, though changes have made - '
                     'planned: %s, after: %s' % (str(planned), str(after)))
        diff = tz.diff('before', 'after')

    changed = (diff['before'] != diff['after'])
    if len(tz.msg) > 0:
        module.exit_json(changed=changed, diff=diff, msg='\n'.join(tz.msg))
    else:
        module.exit_json(changed=changed, diff=diff)


if __name__ == '__main__':
    main()
