"""
This is a middleware to respect robots.txt policies. To activate it you must
enable this middleware and enable the ROBOTSTXT_OBEY setting.

"""

import logging

from twisted.internet.defer import Deferred, maybeDeferred
from scrapy.exceptions import NotConfigured, IgnoreRequest
from scrapy.http import Request
from scrapy.utils.httpobj import urlparse_cached
from scrapy.utils.log import failure_to_exc_info
from scrapy.utils.misc import load_object

logger = logging.getLogger(__name__)


class RobotsTxtMiddleware:
    DOWNLOAD_PRIORITY = 1000

    def __init__(self, crawler):
        if not crawler.settings.getbool('ROBOTSTXT_OBEY'):
            raise NotConfigured
        self._default_useragent = crawler.settings.get('USER_AGENT', 'Scrapy')
        self._robotstxt_useragent = crawler.settings.get('ROBOTSTXT_USER_AGENT', None)
        self.crawler = crawler
        self._parsers = {}
        self._parserimpl = load_object(crawler.settings.get('ROBOTSTXT_PARSER'))

        # check if parser dependencies are met, this should throw an error otherwise.
        self._parserimpl.from_crawler(self.crawler, b'')

    @classmethod
    def from_crawler(cls, crawler):
        return cls(crawler)

    def process_request(self, request, spider):
        if request.meta.get('dont_obey_robotstxt'):
            return
        d = maybeDeferred(self.robot_parser, request, spider)
        d.addCallback(self.process_request_2, request, spider)
        return d

    def process_request_2(self, rp, request, spider):
        if rp is None:
            return

        useragent = self._robotstxt_useragent
        if not useragent:
            useragent = request.headers.get(b'User-Agent', self._default_useragent)
        if not rp.allowed(request.url, useragent):
            logger.debug("Forbidden by robots.txt: %(request)s",
                         {'request': request}, extra={'spider': spider})
            self.crawler.stats.inc_value('robotstxt/forbidden')
            raise IgnoreRequest("Forbidden by robots.txt")

    def robot_parser(self, request, spider):
        url = urlparse_cached(request)
        netloc = url.netloc

        if netloc not in self._parsers:
            self._parsers[netloc] = Deferred()
            robotsurl = f"{url.scheme}://{url.netloc}/robots.txt"
            robotsreq = Request(
                robotsurl,
                priority=self.DOWNLOAD_PRIORITY,
                meta={'dont_obey_robotstxt': True}
            )
            dfd = self.crawler.engine.download(robotsreq, spider)
            dfd.addCallback(self._parse_robots, netloc, spider)
            dfd.addErrback(self._logerror, robotsreq, spider)
            dfd.addErrback(self._robots_error, netloc)
            self.crawler.stats.inc_value('robotstxt/request_count')

        if isinstance(self._parsers[netloc], Deferred):
            d = Deferred()

            def cb(result):
                d.callback(result)
                return result
            self._parsers[netloc].addCallback(cb)
            return d
        else:
            return self._parsers[netloc]

    def _logerror(self, failure, request, spider):
        if failure.type is not IgnoreRequest:
            logger.error("Error downloading %(request)s: %(f_exception)s",
                         {'request': request, 'f_exception': failure.value},
                         exc_info=failure_to_exc_info(failure),
                         extra={'spider': spider})
        return failure

    def _parse_robots(self, response, netloc, spider):
        self.crawler.stats.inc_value('robotstxt/response_count')
        self.crawler.stats.inc_value(f'robotstxt/response_status_count/{response.status}')
        rp = self._parserimpl.from_crawler(self.crawler, response.body)
        rp_dfd = self._parsers[netloc]
        self._parsers[netloc] = rp
        rp_dfd.callback(rp)

    def _robots_error(self, failure, netloc):
        if failure.type is not IgnoreRequest:
            key = f'robotstxt/exception_count/{failure.type}'
            self.crawler.stats.inc_value(key)
        rp_dfd = self._parsers[netloc]
        self._parsers[netloc] = None
        rp_dfd.callback(None)
