"""passbook SAML IDP Views"""
from typing import Optional

from django.contrib.auth import logout
from django.contrib.auth.mixins import AccessMixin
from django.core.exceptions import ValidationError
from django.core.validators import URLValidator
from django.http import HttpRequest, HttpResponse, HttpResponseBadRequest
from django.shortcuts import get_object_or_404, redirect, render, reverse
from django.utils.datastructures import MultiValueDictKeyError
from django.utils.decorators import method_decorator
from django.utils.translation import gettext as _
from django.views import View
from django.views.decorators.csrf import csrf_exempt
from signxml.util import strip_pem_header
from structlog import get_logger

from passbook.audit.models import Event, EventAction
from passbook.core.models import Application
from passbook.lib.mixins import CSRFExemptMixin
from passbook.lib.utils.template import render_to_string
from passbook.policies.engine import PolicyEngine
from passbook.providers.saml import exceptions
from passbook.providers.saml.models import SAMLProvider

LOGGER = get_logger()
URL_VALIDATOR = URLValidator(schemes=("http", "https"))


def _generate_response(request: HttpRequest, provider: SAMLProvider):
    """Generate a SAML response using processor_instance and return it in the proper Django
    response."""
    try:
        provider.processor.init_deep_link(request, "")
        ctx = provider.processor.generate_response()
        ctx["remote"] = provider
        ctx["is_login"] = True
    except exceptions.UserNotAuthorized:
        return render(request, "saml/idp/invalid_user.html")

    return render(request, "saml/idp/login.html", ctx)


class AccessRequiredView(AccessMixin, View):
    """Mixin class for Views using a provider instance"""

    _provider: Optional[SAMLProvider] = None

    @property
    def provider(self) -> SAMLProvider:
        """Get provider instance"""
        if not self._provider:
            application = get_object_or_404(
                Application, slug=self.kwargs["application"]
            )
            self._provider = get_object_or_404(SAMLProvider, pk=application.provider_id)
        return self._provider

    def _has_access(self) -> bool:
        """Check if user has access to application"""
        policy_engine = PolicyEngine(
            self.provider.application.policies.all(), self.request.user, self.request
        )
        policy_engine.build()
        return policy_engine.passing

    def dispatch(self, request, *args, **kwargs):
        if not request.user.is_authenticated:
            return self.handle_no_permission()
        if not self._has_access():
            return render(
                request,
                "login/denied.html",
                {
                    "title": _("You don't have access to this application"),
                    "is_login": True,
                },
            )
        return super().dispatch(request, *args, **kwargs)


class LoginBeginView(AccessRequiredView):
    """Receives a SAML 2.0 AuthnRequest from a Service Provider and
    stores it in the session prior to enforcing login."""

    @method_decorator(csrf_exempt)
    def dispatch(self, request, application):
        if request.method == "POST":
            source = request.POST
        else:
            source = request.GET

        # Store these values now, because Django's login cycle won't preserve them.
        try:
            request.session["SAMLRequest"] = source["SAMLRequest"]
        except (KeyError, MultiValueDictKeyError):
            return HttpResponseBadRequest("the SAML request payload is missing")

        request.session["RelayState"] = source.get("RelayState", "")
        return redirect(
            reverse(
                "passbook_providers_saml:saml-login-process",
                kwargs={"application": application},
            )
        )


class RedirectToSPView(AccessRequiredView):
    """Return autosubmit form"""

    def get(self, request, acs_url, saml_response, relay_state):
        """Return autosubmit form"""
        return render(
            request,
            "core/autosubmit_form.html",
            {
                "url": acs_url,
                "attrs": {"SAMLResponse": saml_response, "RelayState": relay_state},
            },
        )


class LoginProcessView(AccessRequiredView):
    """Processor-based login continuation.
    Presents a SAML 2.0 Assertion for POSTing back to the Service Provider."""

    # pylint: disable=unused-argument
    def get(self, request: HttpRequest, application: str) -> HttpResponse:
        """Handle get request, i.e. render form"""
        # User access gets checked in dispatch
        if self.provider.application.skip_authorization:
            ctx = self.provider.processor.generate_response()
            # Log Application Authorization
            Event.new(
                EventAction.AUTHORIZE_APPLICATION,
                authorized_application=self.provider.application,
                skipped_authorization=True,
            ).from_http(request)
            return RedirectToSPView.as_view()(
                request=request,
                acs_url=ctx["acs_url"],
                saml_response=ctx["saml_response"],
                relay_state=ctx["relay_state"],
            )
        try:
            return _generate_response(request, self.provider)
        except exceptions.CannotHandleAssertion as exc:
            LOGGER.debug(exc)
        return HttpResponseBadRequest()

    # pylint: disable=unused-argument
    def post(self, request, application: str) -> HttpResponse:
        """Handle post request, return back to ACS"""
        # User access gets checked in dispatch
        if request.POST.get("ACSUrl", None):
            # User accepted request
            Event.new(
                EventAction.AUTHORIZE_APPLICATION,
                authorized_application=self.provider.application,
                skipped_authorization=False,
            ).from_http(request)
            return RedirectToSPView.as_view()(
                request=request,
                acs_url=request.POST.get("ACSUrl"),
                saml_response=request.POST.get("SAMLResponse"),
                relay_state=request.POST.get("RelayState"),
            )
        try:
            return _generate_response(request, self.provider)
        except exceptions.CannotHandleAssertion as exc:
            LOGGER.debug(exc)
        return HttpResponseBadRequest()


class LogoutView(CSRFExemptMixin, AccessRequiredView):
    """Allows a non-SAML 2.0 URL to log out the user and
    returns a standard logged-out page. (SalesForce and others use this method,
    though it's technically not SAML 2.0)."""

    # pylint: disable=unused-argument
    def get(self, request, application):
        """Perform logout"""
        logout(request)

        redirect_url = request.GET.get("redirect_to", "")

        try:
            URL_VALIDATOR(redirect_url)
        except ValidationError:
            pass
        else:
            return redirect(redirect_url)

        return render(request, "saml/idp/logged_out.html")


class SLOLogout(CSRFExemptMixin, AccessRequiredView):
    """Receives a SAML 2.0 LogoutRequest from a Service Provider,
    logs out the user and returns a standard logged-out page."""

    # pylint: disable=unused-argument
    def post(self, request, application):
        """Perform logout"""
        request.session["SAMLRequest"] = request.POST["SAMLRequest"]
        # TODO: Parse SAML LogoutRequest from POST data, similar to login_process().
        # TODO: Modify the base processor to handle logouts?
        # TODO: Combine this with login_process(), since they are so very similar?
        # TODO: Format a LogoutResponse and return it to the browser.
        # XXX: For now, simply log out without validating the request.
        logout(request)
        return render(request, "saml/idp/logged_out.html")


class DescriptorDownloadView(AccessRequiredView):
    """Replies with the XML Metadata IDSSODescriptor."""

    def get(self, request, application):
        """Replies with the XML Metadata IDSSODescriptor."""
        entity_id = self.provider.issuer
        slo_url = request.build_absolute_uri(
            reverse(
                "passbook_providers_saml:saml-logout",
                kwargs={"application": application},
            )
        )
        sso_url = request.build_absolute_uri(
            reverse(
                "passbook_providers_saml:saml-login",
                kwargs={"application": application},
            )
        )
        pubkey = strip_pem_header(self.provider.signing_cert.replace("\r", "")).replace(
            "\n", ""
        )
        ctx = {
            "entity_id": entity_id,
            "cert_public_key": pubkey,
            "slo_url": slo_url,
            "sso_url": sso_url,
        }
        metadata = render_to_string("saml/xml/metadata.xml", ctx)
        response = HttpResponse(metadata, content_type="application/xml")
        response["Content-Disposition"] = (
            'attachment; filename="' '%s_passbook_meta.xml"' % self.provider.name
        )
        return response


class InitiateLoginView(AccessRequiredView):
    """IdP-initiated Login"""

    # pylint: disable=unused-argument
    def get(self, request, application):
        """Initiates an IdP-initiated link to a simple SP resource/target URL."""
        self.provider.processor.init_deep_link(request, "")
        self.provider.processor.is_idp_initiated = True
        return _generate_response(request, self.provider)