# Copyright (c) 2012 OpenStack Foundation.
# All Rights Reserved.
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

"""
Policy engine for neutron.  Largely copied from nova.
"""

import collections
import logging as std_logging
import re

from oslo_config import cfg
from oslo_log import log as logging
from oslo_policy import policy
from oslo_utils import excutils
from oslo_utils import importutils
import six

from neutron.api.v2 import attributes
from neutron.common import constants as const
from neutron.common import exceptions
from neutron.i18n import _LE, _LW


LOG = logging.getLogger(__name__)

_ENFORCER = None
ADMIN_CTX_POLICY = 'context_is_admin'
ADVSVC_CTX_POLICY = 'context_is_advsvc'


def reset():
    global _ENFORCER
    if _ENFORCER:
        _ENFORCER.clear()
        _ENFORCER = None


def init(conf=cfg.CONF, policy_file=None):
    """Init an instance of the Enforcer class."""

    global _ENFORCER
    if not _ENFORCER:
        _ENFORCER = policy.Enforcer(conf, policy_file=policy_file)
        _ENFORCER.load_rules(True)


def refresh(policy_file=None):
    """Reset policy and init a new instance of Enforcer."""
    reset()
    init(policy_file=policy_file)


def get_resource_and_action(action, pluralized=None):
    """Extract resource and action (write, read) from api operation."""
    data = action.split(':', 1)[0].split('_', 1)
    resource = pluralized or ("%ss" % data[-1])
    return (resource, data[0] != 'get')


def set_rules(policies, overwrite=True):
    """Set rules based on the provided dict of rules.

    :param policies: New policies to use. It should be an instance of dict.
    :param overwrite: Whether to overwrite current rules or update them
                          with the new rules.
    """

    LOG.debug("Loading policies from file: %s", _ENFORCER.policy_path)
    init()
    _ENFORCER.set_rules(policies, overwrite)


def _is_attribute_explicitly_set(attribute_name, resource, target, action):
    """Verify that an attribute is present and is explicitly set."""
    if 'update' in action:
        # In the case of update, the function should not pay attention to a
        # default value of an attribute, but check whether it was explicitly
        # marked as being updated instead.
        return (attribute_name in target[const.ATTRIBUTES_TO_UPDATE] and
                target[attribute_name] is not attributes.ATTR_NOT_SPECIFIED)
    return ('default' in resource[attribute_name] and
            attribute_name in target and
            target[attribute_name] is not attributes.ATTR_NOT_SPECIFIED and
            target[attribute_name] != resource[attribute_name]['default'])


def _should_validate_sub_attributes(attribute, sub_attr):
    """Verify that sub-attributes are iterable and should be validated."""
    validate = attribute.get('validate')
    return (validate and isinstance(sub_attr, collections.Iterable) and
            any([k.startswith('type:dict') and
                 v for (k, v) in six.iteritems(validate)]))


def _build_subattr_match_rule(attr_name, attr, action, target):
    """Create the rule to match for sub-attribute policy checks."""
    # TODO(salv-orlando): Instead of relying on validator info, introduce
    # typing for API attributes
    # Expect a dict as type descriptor
    validate = attr['validate']
    key = list(filter(lambda k: k.startswith('type:dict'), validate.keys()))
    if not key:
        LOG.warn(_LW("Unable to find data type descriptor for attribute %s"),
                 attr_name)
        return
    data = validate[key[0]]
    if not isinstance(data, dict):
        LOG.debug("Attribute type descriptor is not a dict. Unable to "
                  "generate any sub-attr policy rule for %s.",
                  attr_name)
        return
    sub_attr_rules = [policy.RuleCheck('rule', '%s:%s:%s' %
                                       (action, attr_name,
                                        sub_attr_name)) for
                      sub_attr_name in data if sub_attr_name in
                      target[attr_name]]
    return policy.AndCheck(sub_attr_rules)


def _process_rules_list(rules, match_rule):
    """Recursively walk a policy rule to extract a list of match entries."""
    if isinstance(match_rule, policy.RuleCheck):
        rules.append(match_rule.match)
    elif isinstance(match_rule, policy.AndCheck):
        for rule in match_rule.rules:
            _process_rules_list(rules, rule)
    return rules


def _build_match_rule(action, target, pluralized):
    """Create the rule to match for a given action.

    The policy rule to be matched is built in the following way:
    1) add entries for matching permission on objects
    2) add an entry for the specific action (e.g.: create_network)
    3) add an entry for attributes of a resource for which the action
       is being executed (e.g.: create_network:shared)
    4) add an entry for sub-attributes of a resource for which the
       action is being executed
       (e.g.: create_router:external_gateway_info:network_id)
    """
    match_rule = policy.RuleCheck('rule', action)
    resource, is_write = get_resource_and_action(action, pluralized)
    # Attribute-based checks shall not be enforced on GETs
    if is_write:
        # assigning to variable with short name for improving readability
        res_map = attributes.RESOURCE_ATTRIBUTE_MAP
        if resource in res_map:
            for attribute_name in res_map[resource]:
                if _is_attribute_explicitly_set(attribute_name,
                                                res_map[resource],
                                                target, action):
                    attribute = res_map[resource][attribute_name]
                    if 'enforce_policy' in attribute:
                        attr_rule = policy.RuleCheck('rule', '%s:%s' %
                                                     (action, attribute_name))
                        # Build match entries for sub-attributes
                        if _should_validate_sub_attributes(
                                attribute, target[attribute_name]):
                            attr_rule = policy.AndCheck(
                                [attr_rule, _build_subattr_match_rule(
                                    attribute_name, attribute,
                                    action, target)])
                        match_rule = policy.AndCheck([match_rule, attr_rule])
    return match_rule


# This check is registered as 'tenant_id' so that it can override
# GenericCheck which was used for validating parent resource ownership.
# This will prevent us from having to handling backward compatibility
# for policy.json
# TODO(salv-orlando): Reinstate GenericCheck for simple tenant_id checks
@policy.register('tenant_id')
class OwnerCheck(policy.Check):
    """Resource ownership check.

    This check verifies the owner of the current resource, or of another
    resource referenced by the one under analysis.