Manage preview-confirm step with Django Form

oneanddone/tasks/forms.py

@@ -21,6 +21,21 @@ class Meta:
         fields = ('text',)
 
 
+class PreviewConfirmationForm(forms.Form):
+    """ Used to create a multi-step object-creation/update process, with a
+        chance to preview and cancel changes before committing them.
+    """
+    submission_stages = ('fill', 'preview', 'confirm')
+    stage = forms.CharField(widget=forms.HiddenInput())
+
+    def clean(self):
+        cleaned_data = super(PreviewConfirmationForm, self).clean()
+        if cleaned_data.get('stage') not in self.submission_stages:
+            raise forms.ValidationError(_('Form data is missing or has been '
+                                          'tampered.'))
+        return cleaned_data
+
+
 class TaskInvalidationCriterionForm(forms.Form):
     criterion = forms.ModelChoiceField(queryset=
                                        TaskInvalidationCriterion.objects.all())

oneanddone/tasks/templates/tasks/confirmation.html

@@ -17,13 +17,13 @@ <h1>{{ title }}</h1>
       <form method="post">
         {{ csrf() }}
         {{ hiddenform([batch_form, task_form], [criterion_formset]) }}
-        <input type="hidden" name="stage" value="initial" />
+        {{ stage_form__fill }}
         <button type="submit" class="button">{{ _('No, cancel import') }}</button>
       </form>
       <form method="post">
         {{ csrf() }}
         {{ hiddenform([batch_form, task_form], [criterion_formset]) }}
-        <input type="hidden" name="stage" value="confirm" />
+        {{ stage_form__confirm }}
         <button type="submit" class="button">{{ _('Yes, import tasks') }}</button>
       </form>
     </div>

oneanddone/tasks/templates/tasks/form.html

@@ -47,7 +47,7 @@ <h4>{{ title }}</h4>
       </div>
     {% endif %}
     {% if action == 'Import' %}
-      <input type="hidden" name="stage" value="preview" />
+      {{ stage_form__preview }}
       {{ form_field(batch_form['description'], help_text=True) }}
       {{ form_field(batch_form['query'], help_text=True) }}
       <div class="subsection content-container">

oneanddone/tasks/views.py

@@ -17,7 +17,8 @@
 
 from oneanddone.base.util import get_object_or_none, SortHeaders
 from oneanddone.tasks.filters import ActivityFilterSet, TasksFilterSet
-from oneanddone.tasks.forms import (FeedbackForm, TaskImportBatchForm,
+from oneanddone.tasks.forms import (FeedbackForm, PreviewConfirmationForm,
+                                    TaskImportBatchForm,
                                     TaskInvalidCriteriaFormSet, TaskForm)
 from oneanddone.tasks.mixins import (APIRecordCreatorMixin,
                                      APIOnlyCreatorMayDeleteMixin)
@@ -219,18 +220,24 @@ def get_forms(self):
         kwargs = {'initial': None}
         if self.request.method == 'POST':
             kwargs['data'] = self.request.POST
-
-        batch_form = TaskImportBatchForm(instance=None,
-                                         prefix='batch', **kwargs)
+        batch_form = TaskImportBatchForm(instance=None, prefix='batch',
+                                         **kwargs)
         criterion_formset = TaskInvalidCriteriaFormSet(prefix='criterion',
                                                        **kwargs)
         kwargs['initial'] = {'end_date': date.today() + timedelta(days=30),
                              'repeatable': False}
         task_form = TaskForm(instance=None, prefix='task', **kwargs)
 
-        return {'criterion_formset': criterion_formset,
-                'batch_form': batch_form,
-                'task_form': task_form}
+        forms = {'criterion_formset': criterion_formset,
+                 'batch_form': batch_form,
+                 'task_form': task_form}
+
+        # Create a hidden form for each possible PreviewConfirmationForm stage.
+        # These forms are used to signal what the next stage should be.
+        make_stage = lambda x: PreviewConfirmationForm(data={'stage': x})
+        stages = PreviewConfirmationForm.submission_stages
+        forms.update({'stage_form__' + s: make_stage(s) for s in stages})
+        return forms
 
     def get_context_data(self, **kwargs):
         ctx = super(ImportTasksView, self).get_context_data(**kwargs)
@@ -253,20 +260,20 @@ def forms_valid(self, forms):
             return self.render_to_response(self.get_context_data(**ctx))
 
     def forms_invalid(self, forms):
-        self.stage = 'initial'
+        self.stage = 'fill'
         return self.render_to_response(self.get_context_data(**forms))
 
     def get(self, request, *args, **kwargs):
         # Assume this is a fresh start to the import process
-        self.stage = None
+        self.stage = 'fill'
         forms = self.get_forms()
         assert forms['criterion_formset'].total_form_count() == 1
         return self.render_to_response(self.get_context_data(**forms))
 
     def post(self, request, *args, **kwargs):
-        stage = self._update_stage()
+        self.stage = self.request.POST.get('stage', 'fill')
         forms = self.get_forms()
-        if stage == 'initial':
+        if self.stage == 'fill':
             return self.render_to_response(self.get_context_data(**forms))
 
         if all([form.is_valid() for form in forms.values()]):
@@ -277,8 +284,8 @@ def post(self, request, *args, **kwargs):
     def done(self, forms):
         bugs = forms['batch_form'].cleaned_data['_fresh_bugs']
         import_batch = forms['batch_form'].save(self.request.user)
-        criterion_objs = [criterion_form.cleaned_data['criterion'] for criterion_form in
-                          forms['criterion_formset'].forms]
+        criterion_objs = [criterion_form.cleaned_data['criterion'] for
+                          criterion_form in forms['criterion_formset'].forms]
         for criterion in criterion_objs:
             criterion.batches.add(import_batch)
             criterion.save()
@@ -300,12 +307,6 @@ def done(self, forms):
         messages.success(self.request, _('{num} tasks created.').format(num=str(len(bugs))))
         return redirect('tasks.list')
 
-    def _update_stage(self):
-        self.stage = self.request.POST.get('stage')
-        if self.stage not in ['initial', 'preview', 'confirm']:
-            raise ValidationError(_('Form data is missing or has been tampered.'))
-        return self.stage
-
 
 class CreateTaskView(LoginRequiredMixin, MyStaffUserRequiredMixin, generic.CreateView):
     model = Task