producer/consumerlocator.py

#!/usr/bin/env python

"""
Consumer locator module, that manages the list of consumers.
"""

import datetime
from communicator import Communicator
import os
from redisconnector import RedisConnector
import logging

__author__ = "@dscharnitzky"
__copyright__ = "Copyright 2020, GoldenPogácsa Team"
__module_name__ = "consumerlocator"
__version__text__ = "1"

KNOWNCONSUMER = os.getenv("PRODUCER_KNOWNCONSUMER", '10.69.42.1')
LOGGER = logging.getLogger(__name__)


class ConsumerLocator:
    """
    Component responsible for managing the list of consumers. Requires an instance of :class:`communicator.Communicator`
    """

    def __init__(self, communicator: Communicator, redisconnector: RedisConnector):
        """**Constructor:**
        Initializes the object.

        Gets the known consumer's IP address from the PRODUCER_KNOWNCONSUMER envar.

        :param communicator: the :class:'communicator.Communicator' instance that will be used for the low level communication.
        """
        self.red = redisconnector
        self.red.consumerlist = [{"Host": KNOWNCONSUMER, "State": True, "LastOk": datetime.datetime.now().timestamp()}]
        self.red.currentconsumer = self.red.consumerlist[0]
        self.communicator = communicator

    def learnconsumerlist(self) -> None:
        """"Learns the list of consumers from the current consumer.
        
        Calls :func:`communicator.Communicator.didiscoveravailableconsumers`, adds the learned consumers to the list
        if are not present, and then calls :func:`consumerlocator.ConsumerLocator.updateconsumerlist`
        
        :returns: None
        """
        recievedconsumerlist = self.communicator.discoveravailableconsumers()
        if not recievedconsumerlist:
            return

        consumer_list = self.red.consumerlist

        for recconsumer in recievedconsumerlist:
            contains = False
            for consumer in consumer_list:
                if consumer["Host"] == recconsumer:
                    contains = True

            if not contains:
                LOGGER.info(f"Learned about new consumer at {recconsumer}")
                consumer_list.append(
                    {"Host": recconsumer, "State": True, "LastOk": datetime.datetime.now().timestamp()})

        self.red.consumerlist = consumer_list
        self.updateconsumerlist()

    def updateconsumerlist(self) -> None:
        """ Updates the consumer list based on their availability.
        
        Marks for each consumer if they are available or not. If a consumer is not available for some time (1 hour),
        the it will be deleted from the list.
        
        :return: None
        """
        removelist = []
        consumer_list = self.red.consumerlist

        for consumer in consumer_list:
            if not self.communicator.checkconsumer(consumer["Host"]):
                consumer["State"] = False
                if datetime.datetime.now() - datetime.datetime.fromtimestamp(consumer["LastOk"]) > datetime.timedelta(
                        seconds=15):
                    removelist.append(consumer)
            else:
                consumer["LastOk"] = datetime.datetime.now().timestamp()
                consumer["State"] = True
        for rem in removelist:
            consumer_list.remove(rem)

        self.red.consumerlist = consumer_list

    def updateconsumer(self):
        """If the current consumer is not available, checks all the consumers in the list and updates the current one.
       
        Calls :func:`consumerlocator.ConsumerLocator.checkcurrentconsumer` and if needed
        :func:`consumerlocator.ConsumerLocator.updateconsumerlist`. Sets the :class:`communicator.Communicator`
        current instance with :func:`communicator.Communicator.set_currentconsumer`.
        
        :return: the current consumer or None if there are no available customers at the moment.
        """

        if not self.checkcurrentconsumer():
            self.updateconsumerlist()
            newcurrentconsumer = None

            for consumer in self.red.consumerlist:
                if consumer["State"]:
                    newcurrentconsumer = consumer
                    break

            self.red.currentconsumer = newcurrentconsumer
            if self.red.currentconsumer is not None:
                LOGGER.warning(f"Falling back to consumer at {newcurrentconsumer['Host']}")
                self.learnconsumerlist()

        if self.red.currentconsumer is not None:
            self.communicator.set_currentconsumer(self.red.currentconsumer["Host"])
            return self.red.currentconsumer["Host"]
        else:
            return None

    def getcurrentconsumer(self) -> str:
        """Returns the currently selected consumer's IP address.
        
        :return: the current consumer
        """
        return self.red.currentconsumer["Host"]

    def checkcurrentconsumer(self) -> bool:
        """Check the current consumer's health.
        
        :return: True if OK, False if fail
        """
        if self.red.currentconsumer is None:
            return False
        return self.communicator.checkconsumer(self.red.currentconsumer["Host"])