# Copyright (c) 2014 Prashanth Raghu.
# 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.

import functools

import msgpack
from oslo_utils import timeutils
import redis

from zaqar.common import decorators
from zaqar import storage
from zaqar.storage import errors
from zaqar.storage.redis import utils

QUEUES_SET_STORE_NAME = 'queues_set'
MESSAGE_IDS_SUFFIX = 'messages'


class QueueController(storage.Queue):
    """Implements queue resource operations using Redis.

    Queues are scoped by project, which is prefixed to the
    queue name.

    Redis Data Structures:

    1. Queue Index (Redis sorted set):

        Set of all queues for the given project, ordered by name.

        Key: <project_id>.queues_set

        +--------+-----------------------------+
        |  Id    |  Value                      |
        +========+=============================+
        |  name  |  <project_id>.<queue_name>  |
        +--------+-----------------------------+

    2. Queue Information (Redis hash):

        Key: <project_id>.<queue_name>

        +----------------------+---------+
        |  Name                |  Field  |
        +======================+=========+
        |  metadata            |  m      |
        +----------------------+---------+
        |  creation timestamp  |  t      |
        +----------------------+---------+
    """

    def __init__(self, *args, **kwargs):
        super(QueueController, self).__init__(*args, **kwargs)
        self._client = self.driver.connection
        self._packer = msgpack.Packer(encoding='utf-8',
                                      use_bin_type=True).pack
        self._unpacker = functools.partial(msgpack.unpackb, encoding='utf-8')

    @decorators.lazy_property(write=False)
    def _claim_ctrl(self):
        return self.driver.claim_controller

    @decorators.lazy_property(write=False)
    def _subscription_ctrl(self):
        return self.driver.subscription_controller

    def _get_queue_info(self, queue_key, fields, transform=str):
        """Get one or more fields from Queue Info."""

        values = self._client.hmget(queue_key, fields)
        return [transform(v) for v in values] if transform else values

    @utils.raises_conn_error
    @utils.retries_on_connection_error
    def _list(self, project=None, marker=None,
              limit=storage.DEFAULT_QUEUES_PER_PAGE, detailed=False):
        client = self._client
        qset_key = utils.scope_queue_name(QUEUES_SET_STORE_NAME, project)
        marker = utils.scope_queue_name(marker, project)
        rank = client.zrank(qset_key, marker)
        start = rank + 1 if rank else 0

        cursor = (q for q in client.zrange(qset_key, start,
                                           start + limit - 1))
        marker_next = {}

        def denormalizer(info, name):
            queue = {'name': utils.descope_queue_name(name)}
            marker_next['next'] = queue['name']
            if detailed:
                queue['metadata'] = info[1]

            return queue

        yield utils.QueueListCursor(self._client, cursor, denormalizer)
        yield marker_next and marker_next['next']

    def _get(self, name, project=None):
        """Obtain the metadata from the queue."""
        try:
            return self.get_metadata(name, project)
        except errors.QueueDoesNotExist:
            return {}

    @utils.raises_conn_error
    def _create(self, name, metadata=None, project=None):
        # TODO(prashanthr_): Implement as a lua script.
        queue_key = utils.scope_queue_name(name, project)
        qset_key = utils.scope_queue_name(QUEUES_SET_STORE_NAME, project)

        # Check if the queue already exists.
        if self._exists(name, project):
            return False

        queue = {
            'c': 0,
            'cl': 0,
            'm': self._packer(metadata or {}),
            't': timeutils.utcnow_ts()
        }

        # Pipeline ensures atomic inserts.
        with self._client.pipeline() as pipe:
            pipe.zadd(qset_key, 1, queue_key).hmset(queue_key, queue)

            try:
                pipe.execute()
            except redis.exceptions.ResponseError:
                return False

        return True

    @utils.raises_conn_error
    @utils.retries_on_connection_error
    def _exists(self, name, project=None):
        # TODO(prashanthr_): Cache this lookup
        queue_key = utils.scope_queue_name(name, project)
        qset_key = utils.scope_queue_name(QUEUES_SET_STORE_NAME, project)

        return self._client.zrank(qset_key, queue_key) is not None

    @utils.raises_conn_error
    @utils.retries_on_connection_error
    def set_metadata(self, name, metadata, project=None):
        if not self.exists(name, project):
            raise errors.QueueDoesNotExist(name, project)

        key = utils.scope_queue_name(name, project)
        fields = {'m': self._packer(metadata)}

        self._client.hmset(key, fields)

    @utils.raises_conn_error
    @utils.retries_on_connection_error
    def get_metadata(self, name, project=None):
        if not self.exists(name, project):
            raise errors.QueueDoesNotExist(name, project)

        queue_key = utils.scope_queue_name(name, project)
        metadata = self._get_queue_info(queue_key, b'm', None)[0]

        return self._unpacker(metadata)

    @utils.raises_conn_error
    @utils.retries_on_connection_error
    def _delete(self, name, project=None):
        queue_key = utils.scope_queue_name(name, project)
        qset_key = utils.scope_queue_name(QUEUES_SET_STORE_NAME, project)

        # NOTE(prashanthr_): Pipelining is used to mitigate race conditions
        with self._client.pipeline() as pipe:
            pipe.zrem(qset_key, queue_key)
            pipe.delete(queue_key)
            pipe.execute()

    @utils.raises_conn_error
    @utils.retries_on_connection_error
    def _stats(self, name, project=None):
        pass