from __future__ import absolute_import

from typing import Any, Dict

from django.utils.module_loading import import_string
from django.utils.translation import ugettext as _
from django.views.decorators.csrf import csrf_exempt, csrf_protect

from zerver.decorator import authenticated_json_view, authenticated_rest_api_view, \
        process_as_post
from zerver.lib.response import json_method_not_allowed, json_unauthorized
from django.http import HttpRequest, HttpResponse, HttpResponseRedirect
from django.conf import settings

METHODS = ('GET', 'HEAD', 'POST', 'PUT', 'DELETE', 'PATCH')
FLAGS = ('override_api_url_scheme')

@csrf_exempt
def rest_dispatch(request, **kwargs):
    # type: (HttpRequest, **Any) -> HttpResponse
    """Dispatch to a REST API endpoint.

    Unauthenticated endpoints should not use this, as authentication is verified
    in the following ways:
        * for paths beginning with /api, HTTP Basic auth
        * for paths beginning with /json (used by the web client), the session token

    This calls the function named in kwargs[request.method], if that request
    method is supported, and after wrapping that function to:

        * protect against CSRF (if the user is already authenticated through
          a Django session)
        * authenticate via an API key (otherwise)
        * coerce PUT/PATCH/DELETE into having POST-like semantics for
          retrieving variables

    Any keyword args that are *not* HTTP methods are passed through to the
    target function.

    Never make a urls.py pattern put user input into a variable called GET, POST,
    etc, as that is where we route HTTP verbs to target functions.
    """
    supported_methods = {} # type: Dict[str, Any]

    # duplicate kwargs so we can mutate the original as we go
    for arg in list(kwargs):
        if arg in METHODS:
            supported_methods[arg] = kwargs[arg]
            del kwargs[arg]

    if request.method == 'OPTIONS':
        response = HttpResponse(status=204) # No content
        response['Allow'] = ', '.join(supported_methods.keys())
        response['Content-Length'] = "0"
        return response

    # Override requested method if magic method=??? parameter exists
    method_to_use = request.method
    if request.POST and 'method' in request.POST:
        method_to_use = request.POST['method']
    if method_to_use == "SOCKET" and "zulip.emulated_method" in request.META:
        method_to_use = request.META["zulip.emulated_method"]

    if method_to_use in supported_methods:
        entry = supported_methods[method_to_use]
        if isinstance(entry, tuple):
            target_function, view_flags = entry
            target_function = import_string(target_function)
        else:
            target_function = import_string(supported_methods[method_to_use])
            view_flags = set()

        # Set request._query for update_activity_user(), which is called
        # by some of the later wrappers.
        request._query = target_function.__name__

        # We want to support authentication by both cookies (web client)
        # and API keys (API clients). In the former case, we want to
        # do a check to ensure that CSRF etc is honored, but in the latter
        # we can skip all of that.
        #
        # Security implications of this portion of the code are minimal,
        # as we should worst-case fail closed if we miscategorise a request.

        # for some special views (e.g. serving a file that has been
        # uploaded), we support using the same url for web and API clients.
        if ('override_api_url_scheme' in view_flags
                and request.META.get('HTTP_AUTHORIZATION', None) is not None):
            # This request  API based authentication.
            target_function = authenticated_rest_api_view()(target_function)
        # /json views (web client) validate with a session token (cookie)
        elif not request.path.startswith("/api") and request.user.is_authenticated():
            # Authenticated via sessions framework, only CSRF check needed
            target_function = csrf_protect(authenticated_json_view(target_function))

        # most clients (mobile, bots, etc) use HTTP Basic Auth and REST calls, where instead of
        # username:password, we use email:apiKey
        elif request.META.get('HTTP_AUTHORIZATION', None):
            # Wrap function with decorator to authenticate the user before
            # proceeding
            target_function = authenticated_rest_api_view()(target_function)
        # Pick a way to tell user they're not authed based on how the request was made
        else:
            # If this looks like a request from a top-level page in a
            # browser, send the user to the login page
            if 'text/html' in request.META.get('HTTP_ACCEPT', ''):
                return HttpResponseRedirect('%s/?next=%s' % (settings.HOME_NOT_LOGGED_IN, request.path))
            # Ask for basic auth (email:apiKey)
            elif request.path.startswith("/api"):
                return json_unauthorized(_("Not logged in: API authentication or user session required"))
            # Session cookie expired, notify the client
            else:
                return json_unauthorized(_("Not logged in: API authentication or user session required"),
                                         www_authenticate='session')

        if request.method not in ["GET", "POST"]:
            # process_as_post needs to be the outer decorator, because
            # otherwise we might access and thus cache a value for
            # request.REQUEST.
            target_function = process_as_post(target_function)

        return target_function(request, **kwargs)

    return json_method_not_allowed(list(supported_methods.keys()))