from __future__ import absolute_import

from django.conf import settings
import pika
import logging
import ujson
import random
import time
import threading
import atexit
from collections import defaultdict

from zerver.lib.utils import statsd
from typing import Any, Callable

# This simple queuing library doesn't expose much of the power of
# rabbitmq/pika's queuing system; its purpose is to just provide an
# interface for external files to put things into queues and take them
# out from bots without having to import pika code all over our codebase.
class SimpleQueueClient(object):
    def __init__(self):
        self.log = logging.getLogger('zulip.queue')
        self.queues = set() # type: Set[str]
        self.channel = None # type: Any
        self.consumers = defaultdict(set) # type: Dict[str, Set[Any]]
        # Disable RabbitMQ heartbeats since BlockingConnection can't process them
        self.rabbitmq_heartbeat = 0
        self._connect()

    def _connect(self):
        start = time.time()
        self.connection = pika.BlockingConnection(self._get_parameters())
        self.channel    = self.connection.channel()
        self.log.info('SimpleQueueClient connected (connecting took %.3fs)' % (time.time() - start,))

    def _reconnect(self):
        self.connection = None
        self.channel = None
        self.queues = set()
        self._connect()

    def _get_parameters(self):
        # We explicitly disable the RabbitMQ heartbeat feature, since
        # it doesn't make sense with BlockingConnection
        credentials = pika.PlainCredentials(settings.RABBITMQ_USERNAME,
                                            settings.RABBITMQ_PASSWORD)
        return pika.ConnectionParameters(settings.RABBITMQ_HOST,
                                         heartbeat_interval=self.rabbitmq_heartbeat,
                                         credentials=credentials)

    def _generate_ctag(self, queue_name):
        return "%s_%s" % (queue_name, str(random.getrandbits(16)))

    def _reconnect_consumer_callback(self, queue, consumer):
        self.log.info("Queue reconnecting saved consumer %s to queue %s" % (consumer, queue))
        self.ensure_queue(queue, lambda: self.channel.basic_consume(consumer,
                                                                    queue=queue,
                                                                    consumer_tag=self._generate_ctag(queue)))

    def _reconnect_consumer_callbacks(self):
        for queue, consumers in self.consumers.items():
            for consumer in consumers:
                self._reconnect_consumer_callback(queue, consumer)

    def close(self):
        if self.connection:
            self.connection.close()

    def ready(self):
        return self.channel is not None

    def ensure_queue(self, queue_name, callback):
        '''Ensure that a given queue has been declared, and then call
           the callback with no arguments.'''
        if not self.connection.is_open:
            self._connect()

        if queue_name not in self.queues:
            self.channel.queue_declare(queue=queue_name, durable=True)
            self.queues.add(queue_name)
        callback()

    def publish(self, queue_name, body):
        def do_publish():
            self.channel.basic_publish(
                            exchange='',
                            routing_key=queue_name,
                            properties=pika.BasicProperties(delivery_mode=2),
                            body=body)

            statsd.incr("rabbitmq.publish.%s" % (queue_name,))

        self.ensure_queue(queue_name, do_publish)

    def json_publish(self, queue_name, body):
        try:
            self.publish(queue_name, ujson.dumps(body))
        except (AttributeError, pika.exceptions.AMQPConnectionError):
            self.log.warning("Failed to send to rabbitmq, trying to reconnect and send again")
            self._reconnect()

            self.publish(queue_name, ujson.dumps(body))

    def register_consumer(self, queue_name, consumer):
        def wrapped_consumer(ch, method, properties, body):
            try:
                consumer(ch, method, properties, body)
                ch.basic_ack(delivery_tag=method.delivery_tag)
            except Exception as e:
                ch.basic_nack(delivery_tag=method.delivery_tag)
                raise e

        self.consumers[queue_name].add(wrapped_consumer)
        self.ensure_queue(queue_name,
            lambda: self.channel.basic_consume(wrapped_consumer, queue=queue_name,
                consumer_tag=self._generate_ctag(queue_name)))

    def register_json_consumer(self, queue_name, callback):
        def wrapped_callback(ch, method, properties, body):
            return callback(ujson.loads(body))
        return self.register_consumer(queue_name, wrapped_callback)

    def drain_queue(self, queue_name, json=False):
        "Returns all messages in the desired queue"
        messages = []
        def opened():
            while True:
                (meta, _, message) = self.channel.basic_get(queue_name)

                if not message:
                    break;

                self.channel.basic_ack(meta.delivery_tag)
                if json:
                    message = ujson.loads(message)
                messages.append(message)

        self.ensure_queue(queue_name, opened)
        return messages

    def start_consuming(self):
        self.channel.start_consuming()

    def stop_consuming(self):
        self.channel.stop_consuming()

# Patch pika.adapters.TornadoConnection so that a socket error doesn't
# throw an exception and disconnect the tornado process from the rabbitmq
# queue. Instead, just re-connect as usual
class ExceptionFreeTornadoConnection(pika.adapters.TornadoConnection):
    def _adapter_disconnect(self):
        try:
            super(ExceptionFreeTornadoConnection, self)._adapter_disconnect()
        except (pika.exceptions.ProbableAuthenticationError,
                pika.exceptions.ProbableAccessDeniedError,
                pika.exceptions.IncompatibleProtocolError) as e:
            logging.warning("Caught exception '%r' in ExceptionFreeTornadoConnection when \
calling _adapter_disconnect, ignoring" % (e,))


class TornadoQueueClient(SimpleQueueClient):
    # Based on:
    # https://pika.readthedocs.io/en/0.9.8/examples/asynchronous_consumer_example.html
    def __init__(self):
        super(TornadoQueueClient, self).__init__()
        # Enable rabbitmq heartbeat since TornadoConection can process them
        self.rabbitmq_heartbeat = None
        self._on_open_cbs = [] # type: List[Callable[[], None]]

    def _connect(self, on_open_cb = None):
        self.log.info("Beginning TornadoQueueClient connection")
        if on_open_cb:
            self._on_open_cbs.append(on_open_cb)
        self.connection = ExceptionFreeTornadoConnection(
            self._get_parameters(),
            on_open_callback = self._on_open,
            stop_ioloop_on_close = False)
        self.connection.add_on_close_callback(self._on_connection_closed)

    def _reconnect(self):
        self.connection = None
        self.channel = None
        self.queues = set()
        self._connect()

    def _on_open(self, connection):
        self.connection.channel(
            on_open_callback = self._on_channel_open)

    def _on_channel_open(self, channel):
        self.channel = channel
        for callback in self._on_open_cbs:
            callback()
        self._reconnect_consumer_callbacks()
        self.log.info('TornadoQueueClient connected')

    def _on_connection_closed(self, connection, reply_code, reply_text):
        self.log.warning("TornadoQueueClient lost connection to RabbitMQ, reconnecting...")
        from tornado import ioloop

        # Try to reconnect in two seconds
        retry_seconds = 2
        def on_timeout():
            try:
                self._reconnect()
            except pika.exceptions.AMQPConnectionError:
                self.log.critical("Failed to reconnect to RabbitMQ, retrying...")
                ioloop.IOLoop.instance().add_timeout(time.time() + retry_seconds, on_timeout)

        ioloop.IOLoop.instance().add_timeout(time.time() + retry_seconds, on_timeout)

    def ensure_queue(self, queue_name, callback):
        def finish(frame):
            self.queues.add(queue_name)
            callback()

        if queue_name not in self.queues:
            # If we're not connected yet, send this message
            # once we have created the channel
            if not self.ready():
                self._on_open_cbs.append(lambda: self.ensure_queue(queue_name, callback))
                return

            self.channel.queue_declare(queue=queue_name, durable=True, callback=finish)
        else:
            callback()

    def register_consumer(self, queue_name, consumer):
        def wrapped_consumer(ch, method, properties, body):
            consumer(ch, method, properties, body)
            ch.basic_ack(delivery_tag=method.delivery_tag)

        if not self.ready():
            self.consumers[queue_name].add(wrapped_consumer)
            return

        self.consumers[queue_name].add(wrapped_consumer)
        self.ensure_queue(queue_name,
            lambda: self.channel.basic_consume(wrapped_consumer, queue=queue_name,
                consumer_tag=self._generate_ctag(queue_name)))

queue_client = None # type: SimpleQueueClient
def get_queue_client():
    global queue_client
    if queue_client is None:
        if settings.RUNNING_INSIDE_TORNADO and settings.USING_RABBITMQ:
            queue_client = TornadoQueueClient()
        elif settings.USING_RABBITMQ:
            queue_client = SimpleQueueClient()

    return queue_client

def setup_tornado_rabbitmq():
    # When tornado is shut down, disconnect cleanly from rabbitmq
    if settings.USING_RABBITMQ:
        atexit.register(lambda: queue_client.close())

# We using a simple lock to prevent multiple RabbitMQ messages being
# sent to the SimpleQueueClient at the same time; this is a workaround
# for an issue with the pika BlockingConnection where using
# BlockingConnection for multiple queues causes the channel to
# randomly close.
queue_lock = threading.RLock()

def queue_json_publish(queue_name, event, processor):
    with queue_lock:
        if settings.USING_RABBITMQ:
            get_queue_client().json_publish(queue_name, event)
        else:
            processor(event)