import base64
import re
import six
import warnings

from django.http import HttpResponse
from django.utils.decorators import method_decorator
from django.views.decorators.csrf import csrf_exempt
from django.views.generic import View

from ..exceptions import AnymailInsecureWebhookWarning, AnymailWebhookValidationFailure
from ..utils import get_anymail_setting, collect_all_methods


class AnymailBasicAuthMixin(object):
    """Implements webhook basic auth as mixin to AnymailBaseWebhookView."""

    # Whether to warn if basic auth is not configured.
    # For most ESPs, basic auth is the only webhook security,
    # so the default is True. Subclasses can set False if
    # they enforce other security (like signed webhooks).
    warn_if_no_basic_auth = True

    # List of allowable HTTP basic-auth 'user:pass' strings.
    basic_auth = None  # (Declaring class attr allows override by kwargs in View.as_view.)

    def __init__(self, **kwargs):
        self.basic_auth = get_anymail_setting('webhook_authorization', default=[],
                                              kwargs=kwargs)  # no esp_name -- auth is shared between ESPs
        # Allow a single string:
        if isinstance(self.basic_auth, six.string_types):
            self.basic_auth = [self.basic_auth]
        if self.warn_if_no_basic_auth and len(self.basic_auth) < 1:
            warnings.warn(
                "Your Anymail webhooks are insecure and open to anyone on the web. "
                "You should set WEBHOOK_AUTHORIZATION in your ANYMAIL settings. "
                "See 'Securing webhooks' in the Anymail docs.",
                AnymailInsecureWebhookWarning)
        # noinspection PyArgumentList
        super(AnymailBasicAuthMixin, self).__init__(**kwargs)

    def validate_request(self, request):
        """If configured for webhook basic auth, validate request has correct auth."""
        if self.basic_auth:
            valid = False
            try:
                authtype, authdata = request.META['HTTP_AUTHORIZATION'].split()
                if authtype.lower() == "basic":
                    auth = base64.b64decode(authdata).decode('utf-8')
                    if auth in self.basic_auth:
                        valid = True
            except (IndexError, KeyError, TypeError, ValueError):
                valid = False
            if not valid:
                # noinspection PyUnresolvedReferences
                raise AnymailWebhookValidationFailure(
                    "Missing or invalid basic auth in Anymail %s webhook" % self.esp_name)


# Mixin note: Django's View.__init__ doesn't cooperate with chaining,
# so all mixins that need __init__ must appear before View in MRO.
class AnymailBaseWebhookView(AnymailBasicAuthMixin, View):
    """Base view for processing ESP event webhooks

    ESP-specific implementations should subclass
    and implement parse_events. They may also
    want to implement validate_request
    if additional security is available.
    """

    def __init__(self, **kwargs):
        super(AnymailBaseWebhookView, self).__init__(**kwargs)
        self.validators = collect_all_methods(self.__class__, 'validate_request')

    # Subclass implementation:

    # Where to send events: either ..signals.inbound or ..signals.tracking
    signal = None

    def validate_request(self, request):
        """Check validity of webhook post, or raise AnymailWebhookValidationFailure.

        AnymailBaseWebhookView includes basic auth validation.
        Subclasses can implement (or provide via mixins) if the ESP supports
        additional validation (such as signature checking).

        *All* definitions of this method in the class chain (including mixins)
        will be called. There is no need to chain to the superclass.
        (See self.run_validators and collect_all_methods.)
        """
        # if request.POST['signature'] != expected_signature:
        #     raise AnymailWebhookValidationFailure("...message...")
        # (else just do nothing)
        pass

    def parse_events(self, request):
        """Return a list of normalized AnymailWebhookEvent extracted from ESP post data.

        Subclasses must implement.
        """
        raise NotImplementedError()

    # HTTP handlers (subclasses shouldn't need to override):

    http_method_names = ["post", "head", "options"]

    def head(self, request, *args, **kwargs):
        # Some ESPs verify the webhook with a HEAD request at configuration time
        return HttpResponse()

    @method_decorator(csrf_exempt)
    def post(self, request, *args, **kwargs):
        # Normal Django exception handling will do the right thing:
        # - AnymailWebhookValidationFailure will turn into an HTTP 400 response
        #   (via Django SuspiciousOperation handling)
        # - Any other errors (e.g., in signal dispatch) will turn into HTTP 500
        #   responses (via normal Django error handling). ESPs generally
        #   treat that as "try again later".
        self.run_validators(request)
        events = self.parse_events(request)
        esp_name = self.esp_name
        for event in events:
            self.signal.send(sender=self.__class__, event=event, esp_name=esp_name)
        return HttpResponse()

    # Request validation (subclasses shouldn't need to override):

    def run_validators(self, request):
        for validator in self.validators:
            validator(self, request)

    @property
    def esp_name(self):
        """
        Read-only name of the ESP for this webhook view.

        (E.g., MailgunTrackingWebhookView will return "Mailgun")
        """
        return re.sub(r'(Tracking|Inbox)WebhookView$', "", self.__class__.__name__)