import random


class RequestPoll:
    """Iterator that yields random requests and keeps statistic."""

    def __init__(self, time_to_finish, intensity_of_service_flow):
        self.time_to_finish = time_to_finish
        self.intensity_of_service_flow = intensity_of_service_flow

    def __str__(self):
        return (
            'Total: {}\n'.format(self.total()) +
            'Processed: {}\n'.format(self.qty_of_processed_requests) +
            'Refused: {}\n'.format(self.qty_of_refused_requests) +
            'Proportion of processed requests: {}\n'.format(self.proportion_of_processed_requests()) +
            'Probability of refuse: {}\n'.format(self.probability_of_refuse()) +
            'Absolute bandwidth: {}'.format(self.abs_bandwidth())
        )

    def __iter__(self):
        self.system_uptime = 0
        self.time_when_channel_will_be_free = 0
        self.qty_of_processed_requests = 0
        self.qty_of_refused_requests = 0
        return self

    def __next__(self):
        if self.system_uptime > self.time_to_finish:
            raise StopIteration
        time_when_request_came_in = random.random()
        self.system_uptime += time_when_request_came_in

        if self._can_system_process_request():
            self.qty_of_processed_requests += 1

            time_for_which_request_has_taken_channel = random \
                .expovariate(self.intensity_of_service_flow)
            self.time_when_channel_will_be_free = self.system_uptime \
                + time_for_which_request_has_taken_channel

            return 'request added to queue at {}'.format(self.system_uptime)
        else:
            self.qty_of_refused_requests += 1

            return 'requests refused at {}'.format(self.system_uptime)

    def _can_system_process_request(self):
        return self.system_uptime >= self.time_when_channel_will_be_free

    def total(self):
        return self.qty_of_processed_requests + self.qty_of_refused_requests

    def abs_bandwidth(self):
        return self.qty_of_processed_requests / self.time_to_finish

    def proportion_of_processed_requests(self):
        return self.qty_of_processed_requests / self.total()

    def probability_of_refuse(self):
        return self.qty_of_refused_requests / self.total()

intensity_of_service_flow = 0.5
time_to_finish = 70
request_poll = RequestPoll(time_to_finish, intensity_of_service_flow)

for request in request_poll:
    print(request)

print(request_poll)