"""Sign-in with Authelia and linking it to an existing account (accounts/oidc.py)."""
import logging

from django.conf import settings
from django.contrib import messages
from django.contrib.auth import login
from django.contrib.auth.decorators import login_required
from django.shortcuts import redirect
from django.utils import timezone
from django.utils.http import url_has_allowed_host_and_scheme
from django.views.decorators.http import require_http_methods

from . import oidc
from .models import OidcIdentity

log = logging.getLogger(__name__)

SESSION_KEY = 'oidc_flow'


def _redirect_uri(request):
    return settings.OIDC_REDIRECT_URI or request.build_absolute_uri('/accounts/oidc/callback/')


def _safe_next(request, value):
    if value and url_has_allowed_host_and_scheme(value, allowed_hosts={request.get_host()},
                                                 require_https=request.is_secure()):
        return value
    return '/'


def oidc_context(request):
    """What the settings page shows about the provider."""
    return {
        'oidc_enabled': oidc.enabled(),
        'oidc_provider': settings.OIDC_PROVIDER_NAME,
        'oidc_identities': list(request.user.oidc_identities.all()) if request.user.is_authenticated else [],
    }


@require_http_methods(['GET'])
def oidc_start(request):
    """Off to the provider. `?link=1` (signed in) links the account instead of signing in."""
    if not oidc.enabled():
        messages.error(request, 'Die Anmeldung über Authelia ist auf diesem Server nicht eingerichtet.')
        return redirect('login')
    link = request.GET.get('link') == '1'
    if link and not request.user.is_authenticated:
        return redirect('login')
    flow = oidc.new_flow()
    flow['link'] = link
    flow['next'] = _safe_next(request, request.GET.get('next', ''))
    try:
        url = oidc.authorize_url(flow, _redirect_uri(request))
    except oidc.OidcError as exc:
        log.warning('oidc start: %s', exc)
        messages.error(request, 'Authelia ist gerade nicht erreichbar.')
        return redirect('settings' if link else 'login')
    request.session[SESSION_KEY] = flow
    return redirect(url)


@require_http_methods(['GET'])
def oidc_callback(request):
    flow = request.session.pop(SESSION_KEY, None)
    fail_to = 'login'
    if flow and flow.get('link'):
        fail_to = 'settings'
    if not flow or request.GET.get('state') != flow.get('state'):
        messages.error(request, 'Die Anmeldung über Authelia ist abgelaufen. Bitte noch einmal.')
        return redirect(fail_to)
    if request.GET.get('error'):
        messages.error(request, 'Authelia hat die Anmeldung abgebrochen.')
        return redirect(fail_to)
    code = request.GET.get('code', '')
    try:
        claims = oidc.exchange_code(code, flow, _redirect_uri(request))
    except oidc.OidcError as exc:
        log.warning('oidc callback: %s', exc)
        messages.error(request, 'Die Anmeldung über Authelia hat nicht geklappt.')
        return redirect(fail_to)

    issuer = settings.OIDC_ISSUER.rstrip('/')
    sub = claims['sub']
    shown = {
        'username': (claims.get('preferred_username') or '')[:150],
        'email': (claims.get('email') or '')[:254],
    }
    identity = OidcIdentity.objects.filter(issuer=issuer, sub=sub).select_related('user').first()

    if flow.get('link'):
        if not request.user.is_authenticated:
            return redirect('login')
        if identity and identity.user_id != request.user.id:
            messages.error(request, 'Dieses Authelia-Konto ist schon mit einem anderen diora-Konto verknüpft.')
            return redirect('settings')
        if identity is None:
            OidcIdentity.objects.create(user=request.user, issuer=issuer, sub=sub, **shown)
        else:
            OidcIdentity.objects.filter(pk=identity.pk).update(**shown)
        messages.success(request, f'Authelia-Konto „{shown["username"] or sub}“ verknüpft. '
                                  'Du kannst dich jetzt auch darüber anmelden.')
        return redirect('settings')

    if identity is None:
        messages.error(request, 'Dieses Authelia-Konto ist mit keinem diora-Konto verknüpft. '
                                'Melde dich einmal mit Passwort an und verknüpfe es in den Einstellungen.')
        return redirect('login')
    if not identity.user.is_active:
        messages.error(request, 'Dieses diora-Konto ist gesperrt.')
        return redirect('login')
    OidcIdentity.objects.filter(pk=identity.pk).update(last_login_at=timezone.now(), **shown)
    login(request, identity.user, backend='django.contrib.auth.backends.ModelBackend')
    # The page asks for the book key (static/js/app/33-unlock.js); a password login
    # brings it along, this one cannot.
    return redirect(flow.get('next') or '/')


@login_required
@require_http_methods(['POST'])
def oidc_unlink(request, pk):
    OidcIdentity.objects.filter(user=request.user, pk=pk).delete()
    messages.success(request, 'Verknüpfung mit Authelia gelöst.')
    return redirect('settings')