import functools
import logging
from collections import defaultdict
from inspect import signature
from warnings import warn

from twisted.internet.defer import Deferred, DeferredList
from twisted.python.failure import Failure

from scrapy.settings import Settings
from scrapy.utils.datatypes import SequenceExclude
from scrapy.utils.defer import mustbe_deferred, defer_result
from scrapy.utils.deprecate import ScrapyDeprecationWarning
from scrapy.utils.request import request_fingerprint
from scrapy.utils.misc import arg_to_iter
from scrapy.utils.log import failure_to_exc_info

logger = logging.getLogger(__name__)


class MediaPipeline:

    LOG_FAILED_RESULTS = True

    class SpiderInfo:
        def __init__(self, spider):
            self.spider = spider
            self.downloading = set()
            self.downloaded = {}
            self.waiting = defaultdict(list)

    def __init__(self, download_func=None, settings=None):
        self.download_func = download_func
        self._expects_item = {}

        if isinstance(settings, dict) or settings is None:
            settings = Settings(settings)
        resolve = functools.partial(self._key_for_pipe,
                                    base_class_name="MediaPipeline",
                                    settings=settings)
        self.allow_redirects = settings.getbool(
            resolve('MEDIA_ALLOW_REDIRECTS'), False
        )
        self._handle_statuses(self.allow_redirects)

        # Check if deprecated methods are being used and make them compatible
        self._make_compatible()

    def _handle_statuses(self, allow_redirects):
        self.handle_httpstatus_list = None
        if allow_redirects:
            self.handle_httpstatus_list = SequenceExclude(range(300, 400))

    def _key_for_pipe(self, key, base_class_name=None, settings=None):
        """
        >>> MediaPipeline()._key_for_pipe("IMAGES")
        'IMAGES'
        >>> class MyPipe(MediaPipeline):
        ...     pass
        >>> MyPipe()._key_for_pipe("IMAGES", base_class_name="MediaPipeline")
        'MYPIPE_IMAGES'
        """
        class_name = self.__class__.__name__
        formatted_key = f"{class_name.upper()}_{key}"
        if (
            not base_class_name
            or class_name == base_class_name
            or settings and not settings.get(formatted_key)
        ):
            return key
        return formatted_key

    @classmethod
    def from_crawler(cls, crawler):
        try:
            pipe = cls.from_settings(crawler.settings)
        except AttributeError:
            pipe = cls()
        pipe.crawler = crawler
        return pipe

    def open_spider(self, spider):
        self.spiderinfo = self.SpiderInfo(spider)

    def process_item(self, item, spider):
        info = self.spiderinfo
        requests = arg_to_iter(self.get_media_requests(item, info))
        dlist = [self._process_request(r, info, item) for r in requests]
        dfd = DeferredList(dlist, consumeErrors=True)
        return dfd.addCallback(self.item_completed, item, info)

    def _process_request(self, request, info, item):
        fp = request_fingerprint(request)
        cb = request.callback or (lambda _: _)
        eb = request.errback
        request.callback = None
        request.errback = None

        # Return cached result if request was already seen
        if fp in info.downloaded:
            return defer_result(info.downloaded[fp]).addCallbacks(cb, eb)

        # Otherwise, wait for result
        wad = Deferred().addCallbacks(cb, eb)
        info.waiting[fp].append(wad)

        # Check if request is downloading right now to avoid doing it twice
        if fp in info.downloading:
            return wad

        # Download request checking media_to_download hook output first
        info.downloading.add(fp)
        dfd = mustbe_deferred(self.media_to_download, request, info, item=item)
        dfd.addCallback(self._check_media_to_download, request, info, item=item)
        dfd.addBoth(self._cache_result_and_execute_waiters, fp, info)
        dfd.addErrback(lambda f: logger.error(
            f.value, exc_info=failure_to_exc_info(f), extra={'spider': info.spider})
        )
        return dfd.addBoth(lambda _: wad)  # it must return wad at last

    def _make_compatible(self):
        """Make overridable methods of MediaPipeline and subclasses backwards compatible"""
        methods = [
            "file_path", "media_to_download", "media_downloaded",
            "file_downloaded", "image_downloaded", "get_images"
        ]

        for method_name in methods:
            method = getattr(self, method_name, None)
            if callable(method):
                setattr(self, method_name, self._compatible(method))

    def _compatible(self, func):
        """Wrapper for overridable methods to allow backwards compatibility"""
        self._check_signature(func)

        @functools.wraps(func)
        def wrapper(*args, **kwargs):
            if self._expects_item[func.__name__]:
                return func(*args, **kwargs)

            kwargs.pop('item', None)
            return func(*args, **kwargs)

        return wrapper

    def _check_signature(self, func):
        sig = signature(func)
        self._expects_item[func.__name__] = True

        if 'item' not in sig.parameters:
            old_params = str(sig)[1:-1]
            new_params = old_params + ", *, item=None"
            warn(f'{func.__name__}(self, {old_params}) is deprecated, '
                 f'please use {func.__name__}(self, {new_params})',
                 ScrapyDeprecationWarning, stacklevel=2)
            self._expects_item[func.__name__] = False

    def _modify_media_request(self, request):
        if self.handle_httpstatus_list:
            request.meta['handle_httpstatus_list'] = self.handle_httpstatus_list
        else:
            request.meta['handle_httpstatus_all'] = True

    def _check_media_to_download(self, result, request, info, item):
        if result is not None:
            return result
        if self.download_func:
            # this ugly code was left only to support tests. TODO: remove
            dfd = mustbe_deferred(self.download_func, request, info.spider)
            dfd.addCallbacks(
                callback=self.media_downloaded, callbackArgs=(request, info), callbackKeywords={'item': item},
                errback=self.media_failed, errbackArgs=(request, info))
        else:
            self._modify_media_request(request)
            dfd = self.crawler.engine.download(request, info.spider)
            dfd.addCallbacks(
                callback=self.media_downloaded, callbackArgs=(request, info), callbackKeywords={'item': item},
                errback=self.media_failed, errbackArgs=(request, info))
        return dfd

    def _cache_result_and_execute_waiters(self, result, fp, info):
        if isinstance(result, Failure):
            # minimize cached information for failure
            result.cleanFailure()
            result.frames = []
            result.stack = None

            # This code fixes a memory leak by avoiding to keep references to
            # the Request and Response objects on the Media Pipeline cache.
            #
            # What happens when the media_downloaded callback raises an
            # exception, for example a FileException('download-error') when
            # the Response status code is not 200 OK, is that the original
            # StopIteration exception (which in turn contains the failed
            # Response and by extension, the original Request) gets encapsulated
            # within the FileException context.
            #
            # Originally, Scrapy was using twisted.internet.defer.returnValue
            # inside functions decorated with twisted.internet.defer.inlineCallbacks,
            # encapsulating the returned Response in a _DefGen_Return exception
            # instead of a StopIteration.
            #
            # To avoid keeping references to the Response and therefore Request
            # objects on the Media Pipeline cache, we should wipe the context of
            # the encapsulated exception when it is a StopIteration instance
            #
            # This problem does not occur in Python 2.7 since we don't have
            # Exception Chaining (https://www.python.org/dev/peps/pep-3134/).
            context = getattr(result.value, '__context__', None)
            if isinstance(context, StopIteration):
                setattr(result.value, '__context__', None)

        info.downloading.remove(fp)
        info.downloaded[fp] = result  # cache result
        for wad in info.waiting.pop(fp):
            defer_result(result).chainDeferred(wad)

    # Overridable Interface
    def media_to_download(self, request, info, *, item=None):
        """Check request before starting download"""
        pass

    def get_media_requests(self, item, info):
        """Returns the media requests to download"""
        pass

    def media_downloaded(self, response, request, info, *, item=None):
        """Handler for success downloads"""
        return response

    def media_failed(self, failure, request, info):
        """Handler for failed downloads"""
        return failure

    def item_completed(self, results, item, info):
        """Called per item when all media requests has been processed"""
        if self.LOG_FAILED_RESULTS:
            for ok, value in results:
                if not ok:
                    logger.error(
                        '%(class)s found errors processing %(item)s',
                        {'class': self.__class__.__name__, 'item': item},
                        exc_info=failure_to_exc_info(value),
                        extra={'spider': info.spider}
                    )
        return item

    def file_path(self, request, response=None, info=None, *, item=None):
        """Returns the path where downloaded media should be stored"""
        pass
