# Copyright 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.

"""
Base utilities to build API operation managers and objects on top of.
"""

import copy

from ceilometerclient import exc
from ceilometerclient.openstack.common.apiclient import base
from ceilometerclient.openstack.common.apiclient import exceptions


def getid(obj):
    """Extracts object ID.

    Abstracts the common pattern of allowing both an object or an
    object's ID (UUID) as a parameter when dealing with relationships.
    """
    try:
        return obj.id
    except AttributeError:
        return obj


class Manager(object):
    """Managers interact with a particular type of API.

    It works with samples, meters, alarms, etc. and provide CRUD operations for
    them.
    """
    resource_class = None

    def __init__(self, api):
        self.api = api

    @property
    def client(self):
        """Compatible with latest oslo-incubator.apiclient code."""
        return self.api

    def _create(self, url, body):
        body = self.api.post(url, json=body).json()
        if body:
            return self.resource_class(self, body)

    def _list(self, url, response_key=None, obj_class=None, body=None,
              expect_single=False):
        try:
            resp = self.api.get(url)
        except exceptions.NotFound:
            raise exc.HTTPNotFound
        if not resp.content:
            raise exc.HTTPNotFound
        body = resp.json()

        if obj_class is None:
            obj_class = self.resource_class

        if response_key:
            try:
                data = body[response_key]
            except KeyError:
                return []
        else:
            data = body
        if expect_single:
            data = [data]
        return [obj_class(self, res, loaded=True) for res in data if res]

    def _update(self, url, body, response_key=None):
        body = self.api.put(url, json=body).json()
        # PUT requests may not return a body
        if body:
            return self.resource_class(self, body)

    def _delete(self, url):
        self.api.delete(url)


class Resource(base.Resource):
    """A resource represents a particular instance of an object.

    Resource might be tenant, user, etc.
    This is pretty much just a bag for attributes.

    :param manager: Manager object
    :param info: dictionary representing resource attributes
    :param loaded: prevent lazy-loading if set to True
    """

    def to_dict(self):
        return copy.deepcopy(self._info)
