import random
from collections import deque
from datetime import datetime
from time import time

from twisted.internet import defer, task

from scrapy import signals
from scrapy.core.downloader.handlers import DownloadHandlers
from scrapy.core.downloader.middleware import DownloaderMiddlewareManager
from scrapy.resolver import dnscache
from scrapy.utils.defer import mustbe_deferred
from scrapy.utils.httpobj import urlparse_cached


class Slot:
    """Downloader slot"""

    def __init__(self, concurrency, delay, randomize_delay):
        self.concurrency = concurrency
        self.delay = delay
        self.randomize_delay = randomize_delay

        self.active = set()
        self.queue = deque()
        self.transferring = set()
        self.lastseen = 0
        self.latercall = None

    def free_transfer_slots(self):
        return self.concurrency - len(self.transferring)

    def download_delay(self):
        if self.randomize_delay:
            return random.uniform(0.5 * self.delay, 1.5 * self.delay)
        return self.delay

    def close(self):
        if self.latercall and self.latercall.active():
            self.latercall.cancel()

    def __repr__(self):
        cls_name = self.__class__.__name__
        return (
            f"{cls_name}(concurrency={self.concurrency!r}, "
            f"delay={self.delay:.2f}, "
            f"randomize_delay={self.randomize_delay!r})"
        )

    def __str__(self):
        return (
            f"<downloader.Slot concurrency={self.concurrency!r} "
            f"delay={self.delay:.2f} randomize_delay={self.randomize_delay!r} "
            f"len(active)={len(self.active)} len(queue)={len(self.queue)} "
            f"len(transferring)={len(self.transferring)} "
            f"lastseen={datetime.fromtimestamp(self.lastseen).isoformat()}>"
        )


def _get_concurrency_delay(concurrency, spider, settings):
    delay = settings.getfloat("DOWNLOAD_DELAY")
    if hasattr(spider, "download_delay"):
        delay = spider.download_delay

    if hasattr(spider, "max_concurrent_requests"):
        concurrency = spider.max_concurrent_requests

    return concurrency, delay


class Downloader:

    DOWNLOAD_SLOT = "download_slot"

    def __init__(self, crawler):
        self.settings = crawler.settings
        self.signals = crawler.signals
        self.slots = {}
        self.active = set()
        self.handlers = DownloadHandlers(crawler)
        self.total_concurrency = self.settings.getint("CONCURRENT_REQUESTS")
        self.domain_concurrency = self.settings.getint("CONCURRENT_REQUESTS_PER_DOMAIN")
        self.ip_concurrency = self.settings.getint("CONCURRENT_REQUESTS_PER_IP")
        self.randomize_delay = self.settings.getbool("RANDOMIZE_DOWNLOAD_DELAY")
        self.middleware = DownloaderMiddlewareManager.from_crawler(crawler)
        self._slot_gc_loop = task.LoopingCall(self._slot_gc)
        self._slot_gc_loop.start(60)

    def fetch(self, request, spider):
        def _deactivate(response):
            self.active.remove(request)
            return response

        self.active.add(request)
        dfd = self.middleware.download(self._enqueue_request, request, spider)
        return dfd.addBoth(_deactivate)

    def needs_backout(self):
        return len(self.active) >= self.total_concurrency

    def _get_slot(self, request, spider):
        key = self._get_slot_key(request, spider)
        if key not in self.slots:
            conc = (
                self.ip_concurrency if self.ip_concurrency else self.domain_concurrency
            )
            conc, delay = _get_concurrency_delay(conc, spider, self.settings)
            self.slots[key] = Slot(conc, delay, self.randomize_delay)

        return key, self.slots[key]

    def _get_slot_key(self, request, spider):
        if self.DOWNLOAD_SLOT in request.meta:
            return request.meta[self.DOWNLOAD_SLOT]

        key = urlparse_cached(request).hostname or ""
        if self.ip_concurrency:
            key = dnscache.get(key, key)

        return key

    def _enqueue_request(self, request, spider):
        key, slot = self._get_slot(request, spider)
        request.meta[self.DOWNLOAD_SLOT] = key

        def _deactivate(response):
            slot.active.remove(request)
            return response

        slot.active.add(request)
        self.signals.send_catch_log(
            signal=signals.request_reached_downloader, request=request, spider=spider
        )
        deferred = defer.Deferred().addBoth(_deactivate)
        slot.queue.append((request, deferred))
        self._process_queue(spider, slot)
        return deferred

    def _process_queue(self, spider, slot):
        from twisted.internet import reactor

        if slot.latercall and slot.latercall.active():
            return

        # Delay queue processing if a download_delay is configured
        now = time()
        delay = slot.download_delay()
        if delay:
            penalty = delay - now + slot.lastseen
            if penalty > 0:
                slot.latercall = reactor.callLater(
                    penalty, self._process_queue, spider, slot
                )
                return

        # Process enqueued requests if there are free slots to transfer for this slot
        while slot.queue and slot.free_transfer_slots() > 0:
            slot.lastseen = now
            request, deferred = slot.queue.popleft()
            dfd = self._download(slot, request, spider)
            dfd.chainDeferred(deferred)
            # prevent burst if inter-request delays were configured
            if delay:
                self._process_queue(spider, slot)
                break

    def _download(self, slot, request, spider):
        # The order is very important for the following deferreds. Do not change!

        # 1. Create the download deferred
        dfd = mustbe_deferred(self.handlers.download_request, request, spider)

        # 2. Notify response_downloaded listeners about the recent download
        # before querying queue for next request
        def _downloaded(response):
            self.signals.send_catch_log(
                signal=signals.response_downloaded,
                response=response,
                request=request,
                spider=spider,
            )
            return response

        dfd.addCallback(_downloaded)

        # 3. After response arrives, remove the request from transferring
        # state to free up the transferring slot so it can be used by the
        # following requests (perhaps those which came from the downloader
        # middleware itself)
        slot.transferring.add(request)

        def finish_transferring(_):
            slot.transferring.remove(request)
            self._process_queue(spider, slot)
            self.signals.send_catch_log(
                signal=signals.request_left_downloader, request=request, spider=spider
            )
            return _

        return dfd.addBoth(finish_transferring)

    def close(self):
        self._slot_gc_loop.stop()
        for slot in self.slots.values():
            slot.close()

    def _slot_gc(self, age=60):
        mintime = time() - age
        for key, slot in list(self.slots.items()):
            if not slot.active and slot.lastseen + slot.delay < mintime:
                self.slots.pop(key).close()
