'period_end_type',

            'period_ends',

            'agreement_terms',

            'attestation_of_copyright',

        ]

    def clean_period_ends(self):

        if 'period_begins' in self.cleaned_data and 'period_ends' in self.cleaned_data and self.cleaned_data['period_begins'] and self.cleaned_data['period_ends'] and self.cleaned_data['period_begins'] > self.cleaned_data['period_ends']:

            raise ValidationError('End of period is before start')

        if self.cleaned_data['period_end_type'] == 'a specific past date' and not self.cleaned_data['period_ends']:

            raise ValidationError('This field is required')

    template_name = 'assignment/assignment_form.html'

    def form_valid(self, form):

        intro = 'The following copyright assignment has been submitted:\n\n'

        body = intro + '\n'.join(['{}: {}'.format(k, v) for k, v in form.cleaned_data.items() if k != 'agreement_terms'])

        send_mail(

            'Copyright assignment form: {}'.format(form.cleaned_data['full_name']),

            body,

            'ben@sturm.com.au',

            ['denver@sfconservancy.org', 'bsturmfels@sfconservancy.org'],

        )

        return super().form_valid(form)

    def get_success_url(self, *args, **kwargs):

        return reverse_lazy('assignment-thanks', kwargs={'pk': str(self.object.uuid)})

class AssignmentThanksView(DetailView):

    model = Assignment

    template_name = 'assignment/thanks.html'

    def get_context_data(self, **kwargs):

        context = super().get_context_data(**kwargs)

        context['form'] = AssignmentForm(instance=self.object)

        for _, field in context['form'].fields.items():