import hashlib
import hmac
import logging
import requests
from datetime import timedelta

from django.utils import timezone

from allauth.socialaccount import app_settings, providers
from allauth.socialaccount.helpers import (
    complete_social_login,
    render_authentication_error,
)
from allauth.socialaccount.models import SocialLogin, SocialToken
from allauth.socialaccount.providers.oauth2.views import (
    OAuth2Adapter,
    OAuth2CallbackView,
    OAuth2LoginView,
)

from .forms import FacebookConnectForm
from .provider import GRAPH_API_URL, GRAPH_API_VERSION, FacebookProvider


logger = logging.getLogger(__name__)


def compute_appsecret_proof(app, token):
    # Generate an appsecret_proof parameter to secure the Graph API call
    # see https://developers.facebook.com/docs/graph-api/securing-requests
    msg = token.token.encode('utf-8')
    key = app.secret.encode('utf-8')
    appsecret_proof = hmac.new(
        key,
        msg,
        digestmod=hashlib.sha256).hexdigest()
    return appsecret_proof


def fb_complete_login(request, app, token):
    provider = providers.registry.by_id(FacebookProvider.id, request)
    resp = requests.get(
        GRAPH_API_URL + '/me',
        params={
            'fields': ','.join(provider.get_fields()),
            'access_token': token.token,
            'appsecret_proof': compute_appsecret_proof(app, token)
        })
    resp.raise_for_status()
    extra_data = resp.json()
    login = provider.sociallogin_from_response(request, extra_data)
    return login


class FacebookOAuth2Adapter(OAuth2Adapter):
    provider_id = FacebookProvider.id
    provider_default_auth_url = (
        'https://www.facebook.com/{}/dialog/oauth'.format(
            GRAPH_API_VERSION))

    settings = app_settings.PROVIDERS.get(provider_id, {})

    authorize_url = settings.get('AUTHORIZE_URL', provider_default_auth_url)
    access_token_url = GRAPH_API_URL + '/oauth/access_token'
    expires_in_key = 'expires_in'

    def complete_login(self, request, app, access_token, **kwargs):
        return fb_complete_login(request, app, access_token)


oauth2_login = OAuth2LoginView.adapter_view(FacebookOAuth2Adapter)
oauth2_callback = OAuth2CallbackView.adapter_view(FacebookOAuth2Adapter)


def login_by_token(request):
    ret = None
    auth_exception = None
    if request.method == 'POST':
        form = FacebookConnectForm(request.POST)
        if form.is_valid():
            try:
                provider = providers.registry.by_id(
                    FacebookProvider.id, request)
                login_options = provider.get_fb_login_options(request)
                app = provider.get_app(request)
                access_token = form.cleaned_data['access_token']
                expires_at = None
                if login_options.get('auth_type') == 'reauthenticate':
                    info = requests.get(
                        GRAPH_API_URL + '/oauth/access_token_info',
                        params={'client_id': app.client_id,
                                'access_token': access_token}).json()
                    nonce = provider.get_nonce(request, pop=True)
                    ok = nonce and nonce == info.get('auth_nonce')
                else:
                    ok = True
                if ok and provider.get_settings().get('EXCHANGE_TOKEN'):
                    resp = requests.get(
                        GRAPH_API_URL + '/oauth/access_token',
                        params={'grant_type': 'fb_exchange_token',
                                'client_id': app.client_id,
                                'client_secret': app.secret,
                                'fb_exchange_token': access_token}).json()
                    access_token = resp['access_token']
                    expires_in = resp.get('expires_in')
                    if expires_in:
                        expires_at = timezone.now() + timedelta(
                            seconds=int(expires_in))
                if ok:
                    token = SocialToken(app=app,
                                        token=access_token,
                                        expires_at=expires_at)
                    login = fb_complete_login(request, app, token)
                    login.token = token
                    login.state = SocialLogin.state_from_request(request)
                    ret = complete_social_login(request, login)
            except requests.RequestException as e:
                logger.exception('Error accessing FB user profile')
                auth_exception = e
    if not ret:
        ret = render_authentication_error(request,
                                          FacebookProvider.id,
                                          exception=auth_exception)
    return ret
