# -*- coding: utf-8 -*-

#    Copyright (C) 2014 Yahoo! Inc. 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.

import logging
import random

import six

from taskflow.engines.worker_based import protocol as pr
from taskflow.utils import lock_utils as lu

LOG = logging.getLogger(__name__)


class Cache(object):
    """Represents thread-safe cache."""

    def __init__(self):
        self._data = {}
        self._lock = lu.ReaderWriterLock()

    def get(self, key):
        """Retrieve a value from the cache."""
        with self._lock.read_lock():
            return self._data.get(key)

    def set(self, key, value):
        """Set a value in the cache."""
        with self._lock.write_lock():
            self._data[key] = value
            LOG.debug("Cache updated. Capacity: %s", len(self._data))

    def delete(self, key):
        """Delete a value from the cache."""
        with self._lock.write_lock():
            self._data.pop(key, None)

    def cleanup(self, on_expired_callback=None):
        """Delete out-dated values from the cache."""
        with self._lock.write_lock():
            expired_values = [(k, v) for k, v in six.iteritems(self._data)
                              if v.expired]
            for (k, _v) in expired_values:
                self._data.pop(k, None)
        if on_expired_callback:
            for (_k, v) in expired_values:
                on_expired_callback(v)


class RequestsCache(Cache):
    """Represents thread-safe requests cache."""

    def get_waiting_requests(self, tasks):
        """Get list of waiting requests by tasks."""
        waiting_requests = []
        with self._lock.read_lock():
            for request in six.itervalues(self._data):
                if request.state == pr.WAITING and request.task_cls in tasks:
                    waiting_requests.append(request)
        return waiting_requests


class WorkersCache(Cache):
    """Represents thread-safe workers cache."""

    def get_topic_by_task(self, task):
        """Get topic for a given task."""
        available_topics = []
        with self._lock.read_lock():
            for topic, tasks in six.iteritems(self._data):
                if task in tasks:
                    available_topics.append(topic)
        return random.choice(available_topics) if available_topics else None