import base64
import logging

from django.conf import settings
from django.contrib import messages
from django.contrib.auth import get_user_model
from django.contrib.auth.backends import ModelBackend
from django.contrib.auth.tokens import default_token_generator
from django.contrib.auth.models import User
from django.core.urlresolvers import reverse as django_reverse
from django.db import transaction
from django.utils.translation import ugettext as _

from mozilla_django_oidc.auth import OIDCAuthenticationBackend

from kitsune.sumo.urlresolvers import reverse
from kitsune.users.models import Profile
from kitsune.users.utils import get_oidc_fxa_setting, add_to_contributors


log = logging.getLogger('k.users')


class ModelBackendAllowInactive(ModelBackend):
    """
    Standard model authentication that also allows inactive users.

    This is necessary as new registered users are marked inactive
    but still logged in automatically. Some control around logging
    in as an active user is still retained via the ``only_active``
    argument of ``kitsune.users.forms.AuthenticationForm``.
    """

    def user_can_authenticate(self, user):
        """
        Allow users with is_active=False.
        """
        return True


class TokenLoginBackend(object):
    """Authenticates users based on tokens that can be passed in urls.

    Tokens are the string '{username}:{token}' base64 encoded, where
    username is the username of the user to be logged in, and token is
    a token generated by `django.contrib.auth.tokens.default_token_generator`
    for that user.

    A user can only be logged in once for each token, because the token
    creation process includes the last login time for a user. Once a
    user logs in, the token won't work again. The token will also stop
    working if the user's password changes.

    :returns: A user object if the user is authenticated succesfully, or
        None if the user was not authenticated.
    """

    def authenticate(self, auth):
        try:
            decoded = base64.b64decode(auth)
        except (TypeError, UnicodeDecodeError):
            return None

        if ':' not in decoded:
            return None
        username, token = decoded.split(':')
        try:
            user = User.objects.get(username=username)
        except User.DoesNotExist:
            return None

        match = default_token_generator.check_token(user, token)
        if match:
            return user
        else:
            return None

    def get_user(self, user_id):
        try:
            user = User.objects.get(pk=user_id)
            user.backend = 'kitsune.users.auth.TokenLoginMiddleware'
            return user
        except User.DoesNotExist:
            return None


def get_auth_str(user):
    """Creates an auth string based on {username}:{token}"""
    token = default_token_generator.make_token(user)
    auth = '{0}:{1}'.format(user.username, token)
    return base64.b64encode(auth)


class SumoOIDCAuthBackend(OIDCAuthenticationBackend):

    def authenticate(self, request, **kwargs):
        """Authenticate a user based on the OIDC code flow."""

        # If the request has the /fxa/callback/ path then probably there is a login
        # with Firefox Accounts. In this case just return None and let
        # the FxA backend handle this request.
        if request and not request.path == django_reverse('oidc_authentication_callback'):
            return None

        return super(SumoOIDCAuthBackend, self).authenticate(request, **kwargs)


class FXAAuthBackend(OIDCAuthenticationBackend):

    @staticmethod
    def get_settings(attr, *args):
        """Override settings for Firefox Accounts Provider."""
        val = get_oidc_fxa_setting(attr)
        if val is not None:
            return val
        return super(FXAAuthBackend, FXAAuthBackend).get_settings(attr, *args)

    def create_user(self, claims):
        """Override create user method to mark the profile as migrated."""

        user = super(FXAAuthBackend, self).create_user(claims)
        # Create a user profile for the user and populate it with data from
        # Firefox Accounts
        profile, _ = Profile.objects.get_or_create(user=user)
        profile.is_fxa_migrated = True
        profile.fxa_uid = claims.get('uid')
        profile.fxa_avatar = claims.get('avatar', '')
        profile.name = claims.get('displayName', '')
        # Let's get the first element even if it's an empty string
        # A few assertions return a locale of None so we need to default to empty string
        fxa_locale = (claims.get('locale', '') or '').split(',')[0]
        if fxa_locale in settings.SUMO_LANGUAGES:
            profile.locale = fxa_locale
        else:
            profile.locale = settings.LANGUAGE_CODE

        profile.save()

        # This is a new sumo profile, redirect to the edit profile page
        self.request.session['oidc_login_next'] = reverse('users.edit_my_profile')
        messages.info(self.request, 'fxa_notification_created')

        if self.request.session.get('is_contributor', False):
            add_to_contributors(user, self.request.LANGUAGE_CODE)
            del self.request.session['is_contributor']

        return user

    def filter_users_by_claims(self, claims):
        """Match users by FxA uid or email."""
        fxa_uid = claims.get('uid')
        user_model = get_user_model()
        users = user_model.objects.none()

        # something went terribly wrong. Return None
        if not fxa_uid:
            log.warning(u'Failed to get Firefox Account UID.')
            return users

        # A existing user is attempting to connect a Firefox Account to the SUMO profile
        # NOTE: this section will be dropped when the migration is complete
        if self.request and self.request.user and self.request.user.is_authenticated():
            return [self.request.user]

        users = user_model.objects.filter(profile__fxa_uid=fxa_uid)

        if not users:
            # We did not match any users so far. Let's call the super method
            # which will try to match users based on email
            users = super(FXAAuthBackend, self).filter_users_by_claims(claims)
        return users

    def update_user(self, user, claims):
        """Update existing user with new claims, if necessary save, and return user"""
        profile = user.profile
        fxa_uid = claims.get('uid')
        email = claims.get('email')
        user_attr_changed = False
        # Check if the user has active subscriptions
        subscriptions = claims.get('subscriptions')

        if not profile.is_fxa_migrated:
            # Check if there is already a Firefox Account with this ID
            if Profile.objects.filter(fxa_uid=fxa_uid).exists():
                msg = _('This Firefox Account is already used in another profile.')
                messages.error(self.request, msg)
                return None

            # If it's not migrated, we can assume that there isn't an FxA id too
            profile.is_fxa_migrated = True
            profile.fxa_uid = fxa_uid
            # This is the first time an existing user is using FxA. Redirect to profile edit
            # in case the user wants to update any settings.
            self.request.session['oidc_login_next'] = reverse('users.edit_my_profile')
            messages.info(self.request, 'fxa_notification_updated')

        # There is a change in the email in Firefox Accounts. Let's update user's email
        # unless we have a superuser
        if user.email != email and not user.is_staff:
            if User.objects.exclude(id=user.id).filter(email=email).exists():
                msg = _(u'The email used with this Firefox Account is already '
                        'linked in another profile.')
                messages.error(self.request, msg)
                return None
            user.email = email
            user_attr_changed = True

        # Follow avatars from FxA profiles
        profile.fxa_avatar = claims.get('avatar', '')
        # Update subscriptions status
        profile.has_subscriptions = bool(subscriptions)

        # Users can select their own display name.
        if not profile.name:
            profile.name = claims.get('displayName', '')

        with transaction.atomic():
            if user_attr_changed:
                user.save()
            profile.save()
        return user

    def authenticate(self, request, **kwargs):
        """Authenticate a user based on the OIDC/oauth2 code flow."""

        # If the request has the /oidc/callback/ path then probably there is a login
        # attempt in the admin interface. In this case just return None and let
        # the OIDC backend handle this request.
        if request and request.path == django_reverse('oidc_authentication_callback'):
            return None

        return super(FXAAuthBackend, self).authenticate(request, **kwargs)
