"""
NETCONF for APK Distributions server:
    ietf-system module

Copyright © 2020 Adélie Software in the Public Benefit, Inc.

Released under the terms of the NCSA license.  See the LICENSE file included
with this source distribution for more information.

SPDX-License-Identifier: NCSA
"""

import logging
import os.path
import pathlib
import platform
import subprocess

from datetime import datetime
from socket import gethostname, sethostname

from lxml.etree import QName  # pylint: disable=E0611
from netconf import error, util

from ncserver.base.log import HOSTNAME_CHANGED, log_config_change, \
                              log_operation
from ncserver.base.util import _, ensure_leaf, handle_list_operation, \
                               node_operation, yang_dt_for_timestamp
from ncserver.util import maybe_raise_on_invalid_node, system_boot_time


LOGGER = logging.getLogger(__name__)
"""The object used for logging informational messages."""


M_ABI_VERSION = 1
"""The ABI version of this NETCONF module."""


M_PREFIX = "sys"
"""The XML tag prefix for this module's tags."""


M_NS = "urn:ietf:params:xml:ns:yang:ietf-system"
"""The XML namespace for this module."""


M_NAME = "ietf-system"
"""The YANG model name for this module."""


M_REVISION = "2014-08-06"
"""The YANG revision date for this module."""


M_IMPORTS = {
    'ietf-yang-types@2013-07-15': {
        'ns': "urn:ietf:params:xml:ns:yang:ietf-yang-types", 'prefix': "yang"
    },
    'ietf-inet-types@2013-07-15': {
        'ns': "urn:ietf:params:xml:ns:yang:ietf-inet-types", 'prefix': "inet"
    },
    'ietf-netconf-acm@2018-02-14': {
        'ns': "urn:ietf:params:xml:ns:yang:ietf-netconf-acm", 'prefix': "nacm"
    },
    'iana-crypt-hash@2014-08-06': {
        'ns': "urn:ietf:params:xml:ns:yang:iana-crypt-hash", 'prefix': "ianach"
    }
}
"""The imported YANG modules for this module."""


M_FEATURES = ['ntp']
"""The supported features declared in YANG for this module."""


_CONTACT_PATH = '/etc/netconf/contact.txt'
"""The file path for the contents of /sys:system/contact."""


_LOCATION_PATH = '/etc/netconf/location.txt'
"""The file path for the contents of /sys:system/location."""


class NTPServer:  # pylint: disable=R0902
    """Represents an NTP server entry."""
    def __init__(self, host: str, **kwargs):
        """Create a new NTP server entry.

        :param str host:
        The host, in IP or DNS form.
        """
        self.host = host
        self.mode = kwargs.pop('mode', 'pool')
        if self.mode in ('server', 'peer'):
            self.key = kwargs.pop('key', None)
        else:
            self.key = None
        self.burst = kwargs.pop('burst', False)
        self.iburst = kwargs.pop('iburst', False)
        self.version = kwargs.pop('version', None)
        self.prefer = kwargs.pop('prefer', False)
        self.minpoll = kwargs.pop('minpoll', None)
        self.maxpoll = kwargs.pop('maxpoll', None)
        if self.mode == 'poll':
            self.preempt = kwargs.pop('preempt', False)
        else:
            self.preempt = False

    def __repr__(self):
        """Return a representation of this object."""
        args = {'mode': '"' + self.mode + '"'}
        if self.burst:
            args['burst'] = True
        if self.iburst:
            args['iburst'] = True
        if self.version is not None:
            args['version'] = '"' + self.version + '"'
        if self.prefer:
            args['prefer'] = True
        if self.minpoll is not None:
            args['minpoll'] = '"' + self.minpoll + '"'
        if self.maxpoll is not None:
            args['maxpoll'] = '"' + self.maxpoll + '"'

        if self.mode in ('server', 'peer') and self.key is not None:
            args['key'] = '"' + self.key + '"'
        if self.mode == 'poll' and self.preempt:
            args['preempt'] = True

        nondef_args = ', '.join(
                ['{}={}'.format(*item) for item in args.items()]
        )
        return "NTPServer('{host}', {nondef_args})".format(
                host=self.host, nondef_args=nondef_args
        )

    def __str__(self):  # pylint: disable=R0912
        """Return the configuration line for this server."""
        line = self.mode + ' '

        if ':' in self.host and '[' not in self.host:
            if '%' in self.host:
                addr, dev = self.host.split('%')
                line += '[' + addr + ']%' + dev
            else:
                line += '[' + self.host + ']'
        else:
            line += self.host

        if self.mode in ('server', 'peer') and self.key is not None:
            line += ' key ' + self.key

        if self.mode in ('pool', 'server'):
            if self.burst:
                line += ' burst'
            if self.iburst:
                line += ' iburst'

        if self.version is not None:
            line += ' version ' + str(self.version)

        if self.prefer:
            line += ' prefer'

        if self.minpoll is not None:
            line += ' minpoll ' + self.minpoll
        if self.maxpoll is not None:
            line += ' maxpoll ' + self.maxpoll

        if self.mode == 'pool' and self.preempt:
            line += ' preempt'

        return line

    @classmethod
    def from_line(cls, line: str):
        """Create an NTPServer object from a configuration file line."""
        tokens = line.strip().split(' ')
        tokens.reverse()

        kwargs = {'mode': tokens.pop()}
        host = tokens.pop()

        bool_keys = ('burst', 'iburst', 'prefer', 'preempt')
        value_keys = ('key', 'version', 'minpoll', 'maxpoll')

        while len(tokens) > 0:
            key = tokens.pop()
            if key in bool_keys:
                kwargs[key] = True
            elif key in value_keys:
                kwargs[key] = tokens.pop()
            else:
                LOGGER.warning('unknown NTP server conf key: %s', key)

        return cls(host, **kwargs)


def _parse_ntp_config() -> dict:
    """Parse /etc/ntp.conf and return the configuration.

    The return value is a dictionary with the following keys:

        * servers: a list of NTPServer objects.
    """
    conf = open('/etc/ntp.conf', 'r')
    lines = conf.readlines()
    conf.close()

    result = {'servers': list()}

    for line in lines:
        line.strip()
        if line.startswith('#') or len(line) == 0:
            continue
        if any([line.startswith(word) for word in ('server', 'pool', 'peer')]):
            result['servers'].append(NTPServer.from_line(line))
        else:
            LOGGER.warning('unhandled NTP configuration line: %s', line)

    return result


def _parse_ntp_conf_to(sys_node):
    """Parse NTP configuration into /sys:system/ntp format."""
    root = util.subelm(sys_node, 'sys:ntp')

    if not os.path.exists('/etc/ntp.conf'):
        root.append(util.leaf_elm('sys:enabled', 'false'))
        return

    conf = _parse_ntp_config()
    for server in conf['servers']:
        serv_node = util.subelm(root, 'sys:server')
        serv_node.append(util.leaf_elm('sys:name', server.host))
        serv_node.append(util.leaf_elm('sys:association-type', server.mode))
        serv_node.append(util.leaf_elm('sys:iburst',
                                       str(server.iburst).lower()))
        serv_node.append(util.leaf_elm('sys:prefer',
                                       str(server.prefer).lower()))
        udp = util.subelm(serv_node, 'sys:udp')
        udp.append(util.leaf_elm('sys:address', server.host))
    return


def _parse_resolv_conf() -> dict:
    """Parse /etc/resolv.conf and return the configuration.

    The return value is a dictionary with the following keys:

        * resolvers: a dict, with each key being the name of the resolver
                     and the value being the resolver IP

        * search: a list, containing search domains

        * attempts: the number of attempts to resolve a name

        * timeout: the timeout in seconds to resolve a name
    """
    with open('/etc/resolv.conf', 'r') as rconf_f:
        rconf = rconf_f.readlines()

    # Stores the last NAME: line seen.
    last_name = 'Resolver'
    # Containers for actual data.
    resolvers = dict()
    search = list()
    # musl defaults; see musl:include/resolv.h
    attempts = 2
    attempts_default = True
    timeout = 5
    timeout_default = True

    for line in rconf:
        line = line.rstrip()
        if line.startswith('# NAME: '):
            last_name = line[8:]
        elif line.startswith('nameserver '):
            if len(resolvers) >= 3:
                continue  # invalid configuration, so don't report it.
            if last_name in resolvers:
                last_name = last_name + "-1"
            resolvers[last_name] = line[11:]
        elif line.startswith('options attempts:'):
            try:
                # musl caps attempts at 10
                attempts = min(10, int(line[17:]))
                attempts_default = False
            except ValueError:
                LOGGER.warning(_("invalid resolv.conf: non-integral attempts"))
        elif line.startswith('options timeout:'):
            try:
                # musl caps timeout at 60
                timeout = min(60, int(line[16:]))
                timeout_default = False
            except ValueError:
                LOGGER.warning(_("invalid resolv.conf: non-integral timeout"))
        # This logic is taken directly from musl source code.
        elif line.startswith('domain') or line.startswith('search'):
            search = line[7:].split(' ')

    return {'resolvers': resolvers, 'search': search, 'attempts': attempts,
            'timeout': timeout, 'attempts_default': attempts_default,
            'timeout_default': timeout_default}


def _parse_resolv_conf_to(sys_node):
    """Parse /etc/resolv.conf into /sys:system/dns-resolver format."""
    root = util.subelm(sys_node, 'sys:dns-resolver')

    resolv_conf = _parse_resolv_conf()

    for domain in resolv_conf['search']:
        root.append(util.leaf_elm('sys:search', domain))

    for pair in resolv_conf['resolvers'].items():
        res = util.subelm(root, 'sys:server')
        res.append(util.leaf_elm('sys:name', pair[0]))
        udp = util.subelm(res, 'sys:udp-and-tcp')
        udp.append(util.leaf_elm('sys:address', pair[1]))

    opts = util.subelm(root, 'sys:options')
    opts.append(util.leaf_elm('sys:timeout', resolv_conf['timeout']))
    opts.append(util.leaf_elm('sys:attempts', resolv_conf['attempts']))


def _parse_authn_to(sys_node):
    """Parse current config into /sys:system/authentication format."""
    sys_node.append(util.leaf_elm('sys:authentication', ''))


def running(node):
    """Retrieve the running configuration for this system."""
    sys = util.subelm(node, 'sys:system')

    if os.path.exists(_CONTACT_PATH):
        with open(_CONTACT_PATH, 'r') as contact_f:
            sys.append(util.leaf_elm('sys:contact', contact_f.read()))
    else:
        sys.append(util.leaf_elm('sys:contact', ''))

    if os.path.exists(_LOCATION_PATH):
        with open(_LOCATION_PATH, 'r') as loc_f:
            sys.append(util.leaf_elm('sys:location', loc_f.read()))
    else:
        sys.append(util.leaf_elm('sys:location', ''))

    sys.append(util.leaf_elm('sys:hostname', gethostname()))

    _parse_ntp_conf_to(sys)
    _parse_resolv_conf_to(sys)
    _parse_authn_to(sys)


def operational(node):
    """Retrieve the operational configuration for this system."""
    running(node)  # Include the running configuration.
    state = util.subelm(node, 'sys:system-state')

    plat = util.subelm(state, 'sys:platform')
    plat.append(util.leaf_elm('sys:os-name', platform.system()))
    plat.append(util.leaf_elm('sys:os-release', platform.release()))
    try:
        osv = subprocess.run(['/bin/sh', '-c',
                              '( . /etc/os-release && echo -n $PRETTY_NAME )'],
                             stdout=subprocess.PIPE, check=True)
        version = osv.stdout.decode('utf-8')
    except subprocess.CalledProcessError:
        version = "Unknown Distribution"
    plat.append(util.leaf_elm('sys:os-version', version))
    plat.append(util.leaf_elm('sys:machine', platform.machine()))

    clock = util.subelm(state, 'sys:clock')
    clock.append(util.leaf_elm(
        'sys:current-datetime',
        yang_dt_for_timestamp(datetime.now().timestamp())
    ))

    clock.append(util.leaf_elm('sys:boot-datetime', system_boot_time()))


# -- Editing functions --


def _save_resolv_conf(conf: dict):
    """Save the current configuration to /etc/resolv.conf."""
    rcfile = open('/etc/resolv.conf', 'w')
    rcfile.write("# Generated by NETCONFAPK\n")
    rcfile.write("# This file will be overwritten upon configuration.  "
                 "Do not edit directly.\n\n")

    if 'attempts' in conf and not conf.get('attempts_default', False):
        rcfile.write("options attempts:{}\n".format(conf['attempts']))

    if 'timeout' in conf and not conf.get('timeout_default', False):
        rcfile.write("options timeout:{}\n".format(conf['timeout']))

    if len(conf.get('search', list())) > 0:
        rcfile.write("search {}\n".format(" ".join(conf['search'])))

    for pair in conf.get('resolvers', dict()).items():
        rcfile.write("# NAME: {}\nnameserver {}\n".format(pair[0], pair[1]))

    rcfile.close()


def _edit_dns_option(session, rpc, node, def_op, curr):
    """Edit DNS option configuration."""
    root_op = node_operation(node, def_op)

    if root_op in ['replace', 'delete', 'remove']:
        # delete must raise if no options are set.
        if root_op == 'delete':
            if ('attempts' not in curr or curr.get('attempts_default', False))\
              or ('timeout' not in curr or curr.get('timeout_default', False)):
                raise error.DataMissingAppError(rpc)

        curr.pop('attempts', None)
        curr.pop('timeout', None)
    elif root_op == 'create':
        if 'attempts' in curr and not curr.get('attempts_default', False) \
          or 'timeout' in curr and not curr.get('timeout_default', False):
            raise error.DataExistsAppError(rpc)

    for opt in node:
        option = QName(opt.tag).localname
        operation = node_operation(opt, root_op)
        ensure_leaf(rpc, opt)

        if option == 'attempts':
            limit = 10
        elif option == 'timeout':
            limit = 60
        else:
            raise error.UnknownElementAppError(rpc, opt)

        if operation in ['delete', 'remove']:
            if option in curr:
                log_config_change(session, opt.tag, '( deleted )')
                del curr[option]
            continue

        try:
            value = int(opt.text)
            log_config_change(session, opt.tag, value)
        except ValueError as value:
            raise error.InvalidValueAppError(rpc) from value

        curr[option] = min(limit, value)
        curr['{}_default'.format(option)] = False

    _save_resolv_conf(curr)


def _edit_dns_search(session, rpc, node, def_op, curr: dict):
    """Edit DNS search-domain configuration."""
    operation = node_operation(node, def_op)

    log_config_change(session, 'sys:search', operation + ':' + node.text)
    handle_list_operation(rpc, curr['search'], node, operation)
    _save_resolv_conf(curr)


def _edit_dns_server(session, rpc, node, def_op, curr: dict):
    # yes, this function is too complex.
    # pylint: disable=R0912,R0914,R0915
    """Edit DNS nameserver configuration."""
    operation = node_operation(node, def_op)
    xmlmap = {'':  'urn:ietf:params:xml:ns:yang:ietf-system'}
    name = node.find('name', xmlmap)

    # XXX TODO: log changes

    # This lets us handle cases where there are no resolvers yet.
    # We set the dict key to the value in case we used the default.
    resolvers = curr.get('resolvers', dict())
    curr['resolvers'] = resolvers

    if name is None:
        raise error.MissingElementAppError(
                rpc, '{urn:ietf:params:xml:ns:yang:ietf-system}name'
        )
    name = name.text

    if operation in ['delete', 'remove']:
        if operation == 'delete' and name not in resolvers.keys():
            raise error.DataMissingAppError(rpc)

        resolvers.pop(name, None)
        _save_resolv_conf(curr)
        return

    insert = node.attrib.get('{urn:ietf:params:xml:ns:yang:1}insert', None)
    other_key = node.attrib.get('{urn:ietf:params:xml:ns:yang:1}key', None)
    value = None

    for opt in node:
        opt_name = QName(opt.tag).localname
        if opt_name == 'name':
            continue  # already handled

        if opt_name == 'udp-and-tcp':
            for subopt in opt:
                if QName(subopt.tag).localname != 'address':
                    raise error.UnknownElementAppError(rpc, subopt)
                value = subopt.text
        else:
            raise error.UnknownElementAppError(rpc, opt)

    if operation == 'create':
        if name in resolvers:
            raise error.DataExistsAppError(rpc)

        if len(resolvers) >= 3:
            # there is no guidance in the RFC for what to do with this...
            raise error.BadElementAppError(rpc, node)

        if insert is None:
            insert = 'last'
    elif operation in ['merge', 'replace']:
        if value is None:
            raise error.MissingElementAppError(
                    rpc, '{urn:ietf:params:xml:ns:yang:ietf-system}udp-and-tcp'
            )

        if name not in resolvers and len(resolvers) >= 3:
            # ditto from above
            raise error.BadElementAppError(rpc, node)

    # Okay, we have to juggle everything around.
    if insert is None or insert == 'last':
        resolvers[name] = value
    elif insert == 'first':
        # update always adds keys to the end of a dict.
        curr['resolvers'] = {name: value}
        curr['resolvers'].update(resolvers)
    elif insert in ('before', 'after'):
        if other_key is None:
            raise error.MissingAttributeAppError(
                    rpc, node, '{urn:ietf:params:xml:ns:yang:1}key'
            )

        if other_key not in resolvers:
            raise error.DataMissingAppError(rpc)

        work = dict()
        for r_name, r_ip in resolvers.items():
            if r_name == other_key and insert == 'before':
                work[name] = value
            work[r_name] = r_ip
            if r_name == other_key and insert == 'after':
                work[name] = value

        curr['resolvers'] = work
    else:
        raise error.BadAttributeAppError(
                rpc, node, '{urn:ietf:params:xml:ns:yang:1}insert'
        )

    _save_resolv_conf(curr)


def _is_resolv_conf_empty(curr: dict) -> bool:
    """Determine if a DNS configuration is empty/default."""
    return (
        len(curr.get('resolvers', dict())) == 0 and
        len(curr.get('search', list())) == 0 and
        ('attempts' not in curr or curr.get('attempts_default', True)) and
        ('timeout' not in curr or curr.get('timeout_default', True))
    )


def _edit_dns(session, rpc, node, def_op):
    """Edit the DNS configuration for this system."""
    curr = _parse_resolv_conf()

    root_op = node_operation(node, def_op)
    if root_op == 'replace':
        curr = {}
    elif root_op == 'remove':
        curr = {}
        log_config_change(session, 'sys:dns-resolver', '( deleted )')
        _save_resolv_conf(curr)
    elif root_op == 'delete':
        if _is_resolv_conf_empty(curr):
            raise error.DataMissingAppError(rpc)
        curr = {}
        log_config_change(session, 'sys:dns-resolver', '( deleted )')
        _save_resolv_conf(curr)
    elif root_op == 'create':
        if not _is_resolv_conf_empty(curr):
            raise error.DataExistsAppError(rpc)

    editors = {'options': _edit_dns_option, 'search': _edit_dns_search,
               'server': _edit_dns_server}

    for key_node in node:
        key = QName(key_node.tag).localname
        if key not in editors:
            raise error.UnknownElementAppError(rpc, key)

        editors[key](session, rpc, key_node, root_op, curr)


def _edit_file(session, rpc, node, def_op):
    """Edit a file-based configuration for this system."""
    operation = node_operation(node, def_op)
    ensure_leaf(rpc, node)

    paths = {'contact': _CONTACT_PATH, 'location': _LOCATION_PATH}
    selected = paths[QName(node.tag).localname]
    already = os.path.exists(selected)

    if operation == 'create' and already:
        raise error.DataExistsAppError(rpc)

    if operation == 'delete' and not already:
        raise error.DataMissingAppError(rpc)

    if operation in ['delete', 'remove']:
        if already:
            log_config_change(session, node.tag, '( deleted )')
            pathlib.Path(selected).unlink()
        return

    log_config_change(session, node.tag, node.text)
    with open(selected, 'wt') as myfile:
        myfile.write(node.text)


def _edit_hostname(session, rpc, node, def_op):
    """Edit the hostname for this system."""
    operation = node_operation(node, def_op)
    ensure_leaf(rpc, node)

    # you can't *unset* a hostname.
    if operation in ['delete', 'remove']:
        raise error.OperationNotSupportedAppError(rpc)

    if operation == 'create':
        raise error.DataExistsAppError(rpc)

    if operation not in ['merge', 'replace']:
        raise error.OperationNotSupportedAppError(rpc)

    newname = node.text
    log_config_change(session, 'sys:hostname', newname)
    with open('/etc/hostname', 'wt') as hostfile:
        hostfile.write(newname + '\n')
    sethostname(newname)
    HOSTNAME_CHANGED.call(newname)


def _edit_ntp(session, rpc, node, def_op):
    """Edit NTP configuration for this system."""


def edit(session, rpc, node, def_op):
    """Edit the configuration for this system."""
    methods = {'dns-resolver': _edit_dns,
               'contact': _edit_file, 'location': _edit_file,
               'hostname': _edit_hostname,
               'ntp': _edit_ntp}

    for subsystem in node:
        name = QName(subsystem.tag).localname
        if name in methods:
            methods[name](session, rpc, subsystem, def_op)
        else:
            maybe_raise_on_invalid_node(M_NS, rpc, subsystem)


def rpc_system_shutdown(session, _, *params):
    """Shutdown the system."""
    log_operation(session, "shutting down the system")
    subprocess.Popen(["/sbin/poweroff"])
    return util.elm('nc:ok')


def rpc_system_restart(session, _, *params):
    """Restart the system."""
    log_operation(session, "restarting the system")
    subprocess.Popen(["/sbin/reboot"])
    return util.elm('nc:ok')


M_RPCS = {'system-shutdown': rpc_system_shutdown,
          'system-restart': rpc_system_restart}
"""The RPCs implemented by this module."""