[ENG-8247] Ability to delete draft preprints from database (#11191)

## Purpose
User should be able to delete draft preprints, so that we don't save them in database

## Changes
Added `delete` method.
User can delete a preprint only if it's in initial state, so it means this preprint is a draft

## Ticket
https://openscience.atlassian.net/browse/ENG-8247

Author: ihorsokhanexoft

api/preprints/views.py

@@ -279,7 +279,7 @@ def create(self, request, *args, **kwargs):
         return super().create(request, *args, **kwargs)
 
 
-class PreprintDetail(PreprintOldVersionsImmutableMixin, PreprintMetricsViewMixin, JSONAPIBaseView, generics.RetrieveUpdateAPIView, PreprintMixin, WaterButlerMixin):
+class PreprintDetail(PreprintOldVersionsImmutableMixin, PreprintMetricsViewMixin, JSONAPIBaseView, generics.RetrieveUpdateDestroyAPIView, PreprintMixin, WaterButlerMixin):
     """The documentation for this endpoint can be found [here](https://developer.osf.io/#operation/preprints_read).
     """
     permission_classes = (
@@ -326,6 +326,11 @@ def get_parser_context(self, http_request):
         res['legacy_type_allowed'] = True
         return res
 
+    def delete(self, request, *args, **kwargs):
+        if self.get_preprint().machine_state == 'initial':
+            return super().delete(request, *args, **kwargs)
+
+        raise ValidationError('You cannot delete created preprint')
 
 class PreprintNodeRelationship(PreprintOldVersionsImmutableMixin, JSONAPIBaseView, generics.RetrieveUpdateAPIView, PreprintMixin):
     permission_classes = (

api_tests/preprints/views/test_preprint_detail.py

@@ -195,15 +195,41 @@ def published_preprint(self, user):
     def url(self, user):
         return f'/{API_BASE}preprints/{{}}/'
 
-    def test_cannot_delete_preprints(
-            self, app, user, url, unpublished_preprint, published_preprint):
-        res = app.delete(url.format(unpublished_preprint._id), auth=user.auth, expect_errors=True)
-        assert res.status_code == 405
-        assert unpublished_preprint.deleted is None
-
-        res = app.delete(url.format(published_preprint._id), auth=user.auth, expect_errors=True)
-        assert res.status_code == 405
-        assert published_preprint.deleted is None
+    def test_can_delete_draft_preprints(
+        self, app, user, url, unpublished_preprint
+    ):
+
+        url = f'/{API_BASE}preprints/{unpublished_preprint._id}/'
+        res = app.delete(url, auth=user.auth)
+        assert res.status_code == 204
+
+        res = app.get(url, auth=user.auth, expect_errors=True)
+        assert res.status_code == 404
+
+    def test_cannot_delete_published_preprints(self, app, user, url, published_preprint):
+        url = f'/{API_BASE}preprints/{published_preprint._id}/'
+
+        res = app.delete(url, auth=user.auth, expect_errors=True)
+        assert res.json['errors'][0]['detail'] == 'You cannot delete created preprint'
+        res = app.get(url, auth=user.auth)
+        assert res.status_code == 200
+
+    def test_cannot_delete_in_moderation_preprints(self, app, user, url):
+        pre_moderation_preprint = PreprintFactory(creator=user, reviews_workflow='pre-moderation')
+        post_moderation_preprint = PreprintFactory(creator=user, reviews_workflow='post-moderation')
+
+        url = f'/{API_BASE}preprints/{pre_moderation_preprint._id}/'
+        res = app.delete(url, auth=user.auth, expect_errors=True)
+        assert res.json['errors'][0]['detail'] == 'You cannot delete created preprint'
+        res = app.get(url, auth=user.auth)
+        assert res.status_code == 200
+
+        url = f'/{API_BASE}preprints/{post_moderation_preprint._id}/'
+
+        res = app.delete(url, auth=user.auth, expect_errors=True)
+        assert res.json['errors'][0]['detail'] == 'You cannot delete created preprint'
+        res = app.get(url, auth=user.auth)
+        assert res.status_code == 200
 
 
 @pytest.mark.django_db