"""
This is the Scrapy engine which controls the Scheduler, Downloader and Spider.

For more information see docs/topics/architecture.rst

"""
import logging
from time import time
from typing import (
    TYPE_CHECKING,
    Any,
    Callable,
    Generator,
    Iterable,
    Iterator,
    Optional,
    Set,
    Type,
    Union,
    cast,
)

from twisted.internet.defer import Deferred, inlineCallbacks, succeed
from twisted.internet.task import LoopingCall
from twisted.python.failure import Failure

from scrapy import signals
from scrapy.core.downloader import Downloader
from scrapy.core.scraper import Scraper
from scrapy.exceptions import CloseSpider, DontCloseSpider
from scrapy.http import Request, Response
from scrapy.logformatter import LogFormatter
from scrapy.settings import BaseSettings, Settings
from scrapy.signalmanager import SignalManager
from scrapy.spiders import Spider
from scrapy.utils.log import failure_to_exc_info, logformatter_adapter
from scrapy.utils.misc import create_instance, load_object
from scrapy.utils.reactor import CallLaterOnce

if TYPE_CHECKING:
    from scrapy.core.scheduler import BaseScheduler
    from scrapy.crawler import Crawler

logger = logging.getLogger(__name__)


class Slot:
    def __init__(
        self,
        start_requests: Iterable[Request],
        close_if_idle: bool,
        nextcall: CallLaterOnce,
        scheduler: "BaseScheduler",
    ) -> None:
        self.closing: Optional[Deferred] = None
        self.inprogress: Set[Request] = set()
        self.start_requests: Optional[Iterator[Request]] = iter(start_requests)
        self.close_if_idle: bool = close_if_idle
        self.nextcall: CallLaterOnce = nextcall
        self.scheduler: "BaseScheduler" = scheduler
        self.heartbeat: LoopingCall = LoopingCall(nextcall.schedule)

    def add_request(self, request: Request) -> None:
        self.inprogress.add(request)

    def remove_request(self, request: Request) -> None:
        self.inprogress.remove(request)
        self._maybe_fire_closing()

    def close(self) -> Deferred:
        self.closing = Deferred()
        self._maybe_fire_closing()
        return self.closing

    def _maybe_fire_closing(self) -> None:
        if self.closing is not None and not self.inprogress:
            if self.nextcall:
                self.nextcall.cancel()
                if self.heartbeat.running:
                    self.heartbeat.stop()
            self.closing.callback(None)


class ExecutionEngine:
    def __init__(self, crawler: "Crawler", spider_closed_callback: Callable) -> None:
        self.crawler: "Crawler" = crawler
        self.settings: Settings = crawler.settings
        self.signals: SignalManager = crawler.signals
        assert crawler.logformatter
        self.logformatter: LogFormatter = crawler.logformatter
        self.slot: Optional[Slot] = None
        self.spider: Optional[Spider] = None
        self.running: bool = False
        self.paused: bool = False
        self.scheduler_cls: Type["BaseScheduler"] = self._get_scheduler_class(
            crawler.settings
        )
        downloader_cls: Type[Downloader] = load_object(self.settings["DOWNLOADER"])
        self.downloader: Downloader = downloader_cls(crawler)
        self.scraper = Scraper(crawler)
        self._spider_closed_callback: Callable = spider_closed_callback
        self.start_time: Optional[float] = None

    def _get_scheduler_class(self, settings: BaseSettings) -> Type["BaseScheduler"]:
        from scrapy.core.scheduler import BaseScheduler

        scheduler_cls: Type = load_object(settings["SCHEDULER"])
        if not issubclass(scheduler_cls, BaseScheduler):
            raise TypeError(
                f"The provided scheduler class ({settings['SCHEDULER']})"
                " does not fully implement the scheduler interface"
            )
        return scheduler_cls

    @inlineCallbacks
    def start(self) -> Generator[Deferred, Any, None]:
        if self.running:
            raise RuntimeError("Engine already running")
        self.start_time = time()
        yield self.signals.send_catch_log_deferred(signal=signals.engine_started)
        self.running = True
        self._closewait: Deferred = Deferred()
        yield self._closewait

    def stop(self) -> Deferred:
        """Gracefully stop the execution engine"""

        @inlineCallbacks
        def _finish_stopping_engine(_: Any) -> Generator[Deferred, Any, None]:
            yield self.signals.send_catch_log_deferred(signal=signals.engine_stopped)
            self._closewait.callback(None)

        if not self.running:
            raise RuntimeError("Engine not running")

        self.running = False
        dfd = (
            self.close_spider(self.spider, reason="shutdown")
            if self.spider is not None
            else succeed(None)
        )
        return dfd.addBoth(_finish_stopping_engine)

    def close(self) -> Deferred:
        """
        Gracefully close the execution engine.
        If it has already been started, stop it. In all cases, close the spider and the downloader.
        """
        if self.running:
            return self.stop()  # will also close spider and downloader
        if self.spider is not None:
            return self.close_spider(
                self.spider, reason="shutdown"
            )  # will also close downloader
        self.downloader.close()
        return succeed(None)

    def pause(self) -> None:
        self.paused = True

    def unpause(self) -> None:
        self.paused = False

    def _next_request(self) -> None:
        if self.slot is None:
            return

        assert self.spider is not None  # typing

        if self.paused:
            return None

        while (
            not self._needs_backout()
            and self._next_request_from_scheduler() is not None
        ):
            pass

        if self.slot.start_requests is not None and not self._needs_backout():
            try:
                request = next(self.slot.start_requests)
            except StopIteration:
                self.slot.start_requests = None
            except Exception:
                self.slot.start_requests = None
                logger.error(
                    "Error while obtaining start requests",
                    exc_info=True,
                    extra={"spider": self.spider},
                )
            else:
                self.crawl(request)

        if self.spider_is_idle() and self.slot.close_if_idle:
            self._spider_idle()

    def _needs_backout(self) -> bool:
        assert self.slot is not None  # typing
        assert self.scraper.slot is not None  # typing
        return (
            not self.running
            or bool(self.slot.closing)
            or self.downloader.needs_backout()
            or self.scraper.slot.needs_backout()
        )

    def _next_request_from_scheduler(self) -> Optional[Deferred]:
        assert self.slot is not None  # typing
        assert self.spider is not None  # typing

        request = self.slot.scheduler.next_request()
        if request is None:
            return None

        d = self._download(request)
        d.addBoth(self._handle_downloader_output, request)
        d.addErrback(
            lambda f: logger.info(
                "Error while handling downloader output",
                exc_info=failure_to_exc_info(f),
                extra={"spider": self.spider},
            )
        )

        def _remove_request(_: Any) -> None:
            assert self.slot
            self.slot.remove_request(request)

        d.addBoth(_remove_request)
        d.addErrback(
            lambda f: logger.info(
                "Error while removing request from slot",
                exc_info=failure_to_exc_info(f),
                extra={"spider": self.spider},
            )
        )
        slot = self.slot
        d.addBoth(lambda _: slot.nextcall.schedule())
        d.addErrback(
            lambda f: logger.info(
                "Error while scheduling new request",
                exc_info=failure_to_exc_info(f),
                extra={"spider": self.spider},
            )
        )
        return d

    def _handle_downloader_output(
        self, result: Union[Request, Response, Failure], request: Request
    ) -> Optional[Deferred]:
        assert self.spider is not None  # typing

        if not isinstance(result, (Request, Response, Failure)):
            raise TypeError(
                f"Incorrect type: expected Request, Response or Failure, got {type(result)}: {result!r}"
            )

        # downloader middleware can return requests (for example, redirects)
        if isinstance(result, Request):
            self.crawl(result)
            return None

        d = self.scraper.enqueue_scrape(result, request, self.spider)
        d.addErrback(
            lambda f: logger.error(
                "Error while enqueuing downloader output",
                exc_info=failure_to_exc_info(f),
                extra={"spider": self.spider},
            )
        )
        return d

    def spider_is_idle(self) -> bool:
        if self.slot is None:
            raise RuntimeError("Engine slot not assigned")
        if not self.scraper.slot.is_idle():  # type: ignore[union-attr]
            return False
        if self.downloader.active:  # downloader has pending requests
            return False
        if self.slot.start_requests is not None:  # not all start requests are handled
            return False
        if self.slot.scheduler.has_pending_requests():
            return False
        return True

    def crawl(self, request: Request) -> None:
        """Inject the request into the spider <-> downloader pipeline"""
        if self.spider is None:
            raise RuntimeError(f"No open spider to crawl: {request}")
        self._schedule_request(request, self.spider)
        self.slot.nextcall.schedule()  # type: ignore[union-attr]

    def _schedule_request(self, request: Request, spider: Spider) -> None:
        self.signals.send_catch_log(
            signals.request_scheduled, request=request, spider=spider
        )
        if not self.slot.scheduler.enqueue_request(request):  # type: ignore[union-attr]
            self.signals.send_catch_log(
                signals.request_dropped, request=request, spider=spider
            )

    def download(self, request: Request) -> Deferred:
        """Return a Deferred which fires with a Response as result, only downloader middlewares are applied"""
        if self.spider is None:
            raise RuntimeError(f"No open spider to crawl: {request}")
        return self._download(request).addBoth(self._downloaded, request)

    def _downloaded(
        self, result: Union[Response, Request, Failure], request: Request
    ) -> Union[Deferred, Response, Failure]:
        assert self.slot is not None  # typing
        self.slot.remove_request(request)
        return self.download(result) if isinstance(result, Request) else result

    def _download(self, request: Request) -> Deferred:
        assert self.slot is not None  # typing

        self.slot.add_request(request)

        def _on_success(result: Union[Response, Request]) -> Union[Response, Request]:
            if not isinstance(result, (Response, Request)):
                raise TypeError(
                    f"Incorrect type: expected Response or Request, got {type(result)}: {result!r}"
                )
            if isinstance(result, Response):
                if result.request is None:
                    result.request = request
                assert self.spider is not None
                logkws = self.logformatter.crawled(result.request, result, self.spider)
                if logkws is not None:
                    logger.log(
                        *logformatter_adapter(logkws), extra={"spider": self.spider}
                    )
                self.signals.send_catch_log(
                    signal=signals.response_received,
                    response=result,
                    request=result.request,
                    spider=self.spider,
                )
            return result

        def _on_complete(_: Any) -> Any:
            assert self.slot is not None
            self.slot.nextcall.schedule()
            return _

        assert self.spider is not None
        dwld = self.downloader.fetch(request, self.spider)
        dwld.addCallbacks(_on_success)
        dwld.addBoth(_on_complete)
        return dwld

    @inlineCallbacks
    def open_spider(
        self, spider: Spider, start_requests: Iterable = (), close_if_idle: bool = True
    ) -> Generator[Deferred, Any, None]:
        if self.slot is not None:
            raise RuntimeError(f"No free spider slot when opening {spider.name!r}")
        logger.info("Spider opened", extra={"spider": spider})
        nextcall = CallLaterOnce(self._next_request)
        scheduler = create_instance(
            self.scheduler_cls, settings=None, crawler=self.crawler
        )
        start_requests = yield self.scraper.spidermw.process_start_requests(
            start_requests, spider
        )
        self.slot = Slot(start_requests, close_if_idle, nextcall, scheduler)
        self.spider = spider
        if hasattr(scheduler, "open"):
            yield scheduler.open(spider)
        yield self.scraper.open_spider(spider)
        assert self.crawler.stats
        self.crawler.stats.open_spider(spider)
        yield self.signals.send_catch_log_deferred(signals.spider_opened, spider=spider)
        self.slot.nextcall.schedule()
        self.slot.heartbeat.start(5)

    def _spider_idle(self) -> None:
        """
        Called when a spider gets idle, i.e. when there are no remaining requests to download or schedule.
        It can be called multiple times. If a handler for the spider_idle signal raises a DontCloseSpider
        exception, the spider is not closed until the next loop and this function is guaranteed to be called
        (at least) once again. A handler can raise CloseSpider to provide a custom closing reason.
        """
        assert self.spider is not None  # typing
        expected_ex = (DontCloseSpider, CloseSpider)
        res = self.signals.send_catch_log(
            signals.spider_idle, spider=self.spider, dont_log=expected_ex
        )
        detected_ex = {
            ex: x.value
            for _, x in res
            for ex in expected_ex
            if isinstance(x, Failure) and isinstance(x.value, ex)
        }
        if DontCloseSpider in detected_ex:
            return None
        if self.spider_is_idle():
            ex = detected_ex.get(CloseSpider, CloseSpider(reason="finished"))
            assert isinstance(ex, CloseSpider)  # typing
            self.close_spider(self.spider, reason=ex.reason)

    def close_spider(self, spider: Spider, reason: str = "cancelled") -> Deferred:
        """Close (cancel) spider and clear all its outstanding requests"""
        if self.slot is None:
            raise RuntimeError("Engine slot not assigned")

        if self.slot.closing is not None:
            return self.slot.closing

        logger.info(
            "Closing spider (%(reason)s)", {"reason": reason}, extra={"spider": spider}
        )

        dfd = self.slot.close()

        def log_failure(msg: str) -> Callable:
            def errback(failure: Failure) -> None:
                logger.error(
                    msg, exc_info=failure_to_exc_info(failure), extra={"spider": spider}
                )

            return errback

        dfd.addBoth(lambda _: self.downloader.close())
        dfd.addErrback(log_failure("Downloader close failure"))

        dfd.addBoth(lambda _: self.scraper.close_spider(spider))
        dfd.addErrback(log_failure("Scraper close failure"))

        if hasattr(self.slot.scheduler, "close"):
            dfd.addBoth(lambda _: cast(Slot, self.slot).scheduler.close(reason))
            dfd.addErrback(log_failure("Scheduler close failure"))

        dfd.addBoth(
            lambda _: self.signals.send_catch_log_deferred(
                signal=signals.spider_closed,
                spider=spider,
                reason=reason,
            )
        )
        dfd.addErrback(log_failure("Error while sending spider_close signal"))

        def close_stats(_: Any) -> None:
            assert self.crawler.stats
            self.crawler.stats.close_spider(spider, reason=reason)

        dfd.addBoth(close_stats)
        dfd.addErrback(log_failure("Stats close failure"))

        dfd.addBoth(
            lambda _: logger.info(
                "Spider closed (%(reason)s)",
                {"reason": reason},
                extra={"spider": spider},
            )
        )

        dfd.addBoth(lambda _: setattr(self, "slot", None))
        dfd.addErrback(log_failure("Error while unassigning slot"))

        dfd.addBoth(lambda _: setattr(self, "spider", None))
        dfd.addErrback(log_failure("Error while unassigning spider"))

        dfd.addBoth(lambda _: self._spider_closed_callback(spider))

        return dfd
