from urllib.parse import urlparse, urlunparse

from django.conf import settings
# Avoid shadowing the login() and logout() views below.
from django.contrib.auth import (
    REDIRECT_FIELD_NAME, get_user_model, login as auth_login,
    logout as auth_logout, update_session_auth_hash,
)
from django.contrib.auth.decorators import login_required
from django.contrib.auth.forms import (
    AuthenticationForm, PasswordChangeForm, PasswordResetForm, SetPasswordForm,
)
from django.contrib.auth.tokens import default_token_generator
from django.contrib.sites.shortcuts import get_current_site
from django.core.exceptions import ValidationError
from django.http import HttpResponseRedirect, QueryDict
from django.shortcuts import resolve_url
from django.urls import reverse_lazy
from django.utils.decorators import method_decorator
from django.utils.http import (
    url_has_allowed_host_and_scheme, urlsafe_base64_decode,
)
from django.utils.translation import gettext_lazy as _
from django.views.decorators.cache import never_cache
from django.views.decorators.csrf import csrf_protect
from django.views.decorators.debug import sensitive_post_parameters
from django.views.generic.base import TemplateView
from django.views.generic.edit import FormView

UserModel = get_user_model()


class SuccessURLAllowedHostsMixin:
    success_url_allowed_hosts = set()

    def get_success_url_allowed_hosts(self):
        return {self.request.get_host(), *self.success_url_allowed_hosts}


class LoginView(SuccessURLAllowedHostsMixin, FormView):
    """
    Display the login form and handle the login action.
    """
    form_class = AuthenticationForm
    authentication_form = None
    next_page = None
    redirect_field_name = REDIRECT_FIELD_NAME
    template_name = 'registration/login.html'
    redirect_authenticated_user = False
    extra_context = None

    @method_decorator(sensitive_post_parameters())
    @method_decorator(csrf_protect)
    @method_decorator(never_cache)
    def dispatch(self, request, *args, **kwargs):
        if self.redirect_authenticated_user and self.request.user.is_authenticated:
            redirect_to = self.get_success_url()
            if redirect_to == self.request.path:
                raise ValueError(
                    "Redirection loop for authenticated user detected. Check that "
                    "your LOGIN_REDIRECT_URL doesn't point to a login page."
                )
            return HttpResponseRedirect(redirect_to)
        return super().dispatch(request, *args, **kwargs)

    def get_success_url(self):
        return self.get_redirect_url() or self.get_default_redirect_url()

    def get_redirect_url(self):
        """Return the user-originating redirect URL if it's safe."""
        redirect_to = self.request.POST.get(
            self.redirect_field_name,
            self.request.GET.get(self.redirect_field_name, '')
        )
        url_is_safe = url_has_allowed_host_and_scheme(
            url=redirect_to,
            allowed_hosts=self.get_success_url_allowed_hosts(),
            require_https=self.request.is_secure(),
        )
        return redirect_to if url_is_safe else ''

    def get_default_redirect_url(self):
        """Return the default redirect URL."""
        return resolve_url(self.next_page or settings.LOGIN_REDIRECT_URL)

    def get_form_class(self):
        return self.authentication_form or self.form_class

    def get_form_kwargs(self):
        kwargs = super().get_form_kwargs()
        kwargs['request'] = self.request
        return kwargs

    def form_valid(self, form):
        """Security check complete. Log the user in."""
        auth_login(self.request, form.get_user())
        return HttpResponseRedirect(self.get_success_url())

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        current_site = get_current_site(self.request)
        context.update({
            self.redirect_field_name: self.get_redirect_url(),
            'site': current_site,
            'site_name': current_site.name,
            **(self.extra_context or {})
        })
        return context


class LogoutView(SuccessURLAllowedHostsMixin, TemplateView):
    """
    Log out the user and display the 'You are logged out' message.
    """
    next_page = None
    redirect_field_name = REDIRECT_FIELD_NAME
    template_name = 'registration/logged_out.html'
    extra_context = None

    @method_decorator(never_cache)
    def dispatch(self, request, *args, **kwargs):
        auth_logout(request)
        next_page = self.get_next_page()
        if next_page:
            # Redirect to this page until the session has been cleared.
            return HttpResponseRedirect(next_page)
        return super().dispatch(request, *args, **kwargs)

    def post(self, request, *args, **kwargs):
        """Logout may be done via POST."""
        return self.get(request, *args, **kwargs)

    def get_next_page(self):
        if self.next_page is not None:
            next_page = resolve_url(self.next_page)
        elif settings.LOGOUT_REDIRECT_URL:
            next_page = resolve_url(settings.LOGOUT_REDIRECT_URL)
        else:
            next_page = self.next_page

        if (self.redirect_field_name in self.request.POST or
                self.redirect_field_name in self.request.GET):
            next_page = self.request.POST.get(
                self.redirect_field_name,
                self.request.GET.get(self.redirect_field_name)
            )
            url_is_safe = url_has_allowed_host_and_scheme(
                url=next_page,
                allowed_hosts=self.get_success_url_allowed_hosts(),
                require_https=self.request.is_secure(),
            )
            # Security check -- Ensure the user-originating redirection URL is
            # safe.
            if not url_is_safe:
                next_page = self.request.path
        return next_page

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        current_site = get_current_site(self.request)
        context.update({
            'site': current_site,
            'site_name': current_site.name,
            'title': _('Logged out'),
            **(self.extra_context or {})
        })
        return context


def logout_then_login(request, login_url=None):
    """
    Log out the user if they are logged in. Then redirect to the login page.
    """
    login_url = resolve_url(login_url or settings.LOGIN_URL)
    return LogoutView.as_view(next_page=login_url)(request)


def redirect_to_login(next, login_url=None, redirect_field_name=REDIRECT_FIELD_NAME):
    """
    Redirect the user to the login page, passing the given 'next' page.
    """
    resolved_url = resolve_url(login_url or settings.LOGIN_URL)

    login_url_parts = list(urlparse(resolved_url))
    if redirect_field_name:
        querystring = QueryDict(login_url_parts[4], mutable=True)
        querystring[redirect_field_name] = next
        login_url_parts[4] = querystring.urlencode(safe='/')

    return HttpResponseRedirect(urlunparse(login_url_parts))


# Class-based password reset views
# - PasswordResetView sends the mail
# - PasswordResetDoneView shows a success message for the above
# - PasswordResetConfirmView checks the link the user clicked and
#   prompts for a new password
# - PasswordResetCompleteView shows a success message for the above

class PasswordContextMixin:
    extra_context = None

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context.update({
            'title': self.title,
            **(self.extra_context or {})
        })
        return context


class PasswordResetView(PasswordContextMixin, FormView):
    email_template_name = 'registration/password_reset_email.html'
    extra_email_context = None
    form_class = PasswordResetForm
    from_email = None
    html_email_template_name = None
    subject_template_name = 'registration/password_reset_subject.txt'
    success_url = reverse_lazy('password_reset_done')
    template_name = 'registration/password_reset_form.html'
    title = _('Password reset')
    token_generator = default_token_generator

    @method_decorator(csrf_protect)
    def dispatch(self, *args, **kwargs):
        return super().dispatch(*args, **kwargs)

    def form_valid(self, form):
        opts = {
            'use_https': self.request.is_secure(),
            'token_generator': self.token_generator,
            'from_email': self.from_email,
            'email_template_name': self.email_template_name,
            'subject_template_name': self.subject_template_name,
            'request': self.request,
            'html_email_template_name': self.html_email_template_name,
            'extra_email_context': self.extra_email_context,
        }
        form.save(**opts)
        return super().form_valid(form)


INTERNAL_RESET_SESSION_TOKEN = '_password_reset_token'


class PasswordResetDoneView(PasswordContextMixin, TemplateView):
    template_name = 'registration/password_reset_done.html'
    title = _('Password reset sent')


class PasswordResetConfirmView(PasswordContextMixin, FormView):
    form_class = SetPasswordForm
    post_reset_login = False
    post_reset_login_backend = None
    reset_url_token = 'set-password'
    success_url = reverse_lazy('password_reset_complete')
    template_name = 'registration/password_reset_confirm.html'
    title = _('Enter new password')
    token_generator = default_token_generator

    @method_decorator(sensitive_post_parameters())
    @method_decorator(never_cache)
    def dispatch(self, *args, **kwargs):
        assert 'uidb64' in kwargs and 'token' in kwargs

        self.validlink = False
        self.user = self.get_user(kwargs['uidb64'])

        if self.user is not None:
            token = kwargs['token']
            if token == self.reset_url_token:
                session_token = self.request.session.get(INTERNAL_RESET_SESSION_TOKEN)
                if self.token_generator.check_token(self.user, session_token):
                    # If the token is valid, display the password reset form.
                    self.validlink = True
                    return super().dispatch(*args, **kwargs)
            else:
                if self.token_generator.check_token(self.user, token):
                    # Store the token in the session and redirect to the
                    # password reset form at a URL without the token. That
                    # avoids the possibility of leaking the token in the
                    # HTTP Referer header.
                    self.request.session[INTERNAL_RESET_SESSION_TOKEN] = token
                    redirect_url = self.request.path.replace(token, self.reset_url_token)
                    return HttpResponseRedirect(redirect_url)

        # Display the "Password reset unsuccessful" page.
        return self.render_to_response(self.get_context_data())

    def get_user(self, uidb64):
        try:
            # urlsafe_base64_decode() decodes to bytestring
            uid = urlsafe_base64_decode(uidb64).decode()
            user = UserModel._default_manager.get(pk=uid)
        except (TypeError, ValueError, OverflowError, UserModel.DoesNotExist, ValidationError):
            user = None
        return user

    def get_form_kwargs(self):
        kwargs = super().get_form_kwargs()
        kwargs['user'] = self.user
        return kwargs

    def form_valid(self, form):
        user = form.save()
        del self.request.session[INTERNAL_RESET_SESSION_TOKEN]
        if self.post_reset_login:
            auth_login(self.request, user, self.post_reset_login_backend)
        return super().form_valid(form)

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        if self.validlink:
            context['validlink'] = True
        else:
            context.update({
                'form': None,
                'title': _('Password reset unsuccessful'),
                'validlink': False,
            })
        return context


class PasswordResetCompleteView(PasswordContextMixin, TemplateView):
    template_name = 'registration/password_reset_complete.html'
    title = _('Password reset complete')

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context['login_url'] = resolve_url(settings.LOGIN_URL)
        return context


class PasswordChangeView(PasswordContextMixin, FormView):
    form_class = PasswordChangeForm
    success_url = reverse_lazy('password_change_done')
    template_name = 'registration/password_change_form.html'
    title = _('Password change')

    @method_decorator(sensitive_post_parameters())
    @method_decorator(csrf_protect)
    @method_decorator(login_required)
    def dispatch(self, *args, **kwargs):
        return super().dispatch(*args, **kwargs)

    def get_form_kwargs(self):
        kwargs = super().get_form_kwargs()
        kwargs['user'] = self.request.user
        return kwargs

    def form_valid(self, form):
        form.save()
        # Updating the password logs out all other sessions for the user
        # except the current one.
        update_session_auth_hash(self.request, form.user)
        return super().form_valid(form)


class PasswordChangeDoneView(PasswordContextMixin, TemplateView):
    template_name = 'registration/password_change_done.html'
    title = _('Password change successful')

    @method_decorator(login_required)
    def dispatch(self, *args, **kwargs):
        return super().dispatch(*args, **kwargs)