Add guarded content draft and publication services

apps/content/models.py

@@ -70,6 +70,12 @@ class SiteIdentity(models.Model):
 
     class Meta:
         constraints = [models.CheckConstraint(condition=Q(id=1), name="content_single_site")]
+        permissions = [
+            ("change_content_draft", "Can change content drafts"),
+            ("preview_content_draft", "Can preview content drafts"),
+            ("publish_content", "Can publish content"),
+            ("restore_content", "Can restore published content"),
+        ]
 
     def clean(self):
         if self.published_revision_id and self.published_revision.site_id != self.pk:
@@ -114,6 +120,14 @@ class SiteRevision(models.Model):
         if not self.logo_id and self.logo_alt:
             raise ValidationError({"logo_alt": "Alt text requires a logo."})
 
+    def save(self, *args, **kwargs):
+        if self.pk:
+            previous = type(self).objects.get(pk=self.pk)
+            protected = ("site_id", "number", "official_name", "short_name", "faculty_subline", "description", "logo_id", "logo_alt", "navigation", "contacts", "footer_copy", "seo_title", "seo_description", "seo_image_id", "created_by_id", "source_seed_key", "source_seed_version", "content_checksum")
+            if any(getattr(self, field) != getattr(previous, field) for field in protected):
+                raise ValidationError("Site revision content is immutable.")
+        return super().save(*args, **kwargs)
+
 
 class EditorialPage(models.Model):
     slug = models.CharField(max_length=20, unique=True)
@@ -155,6 +169,16 @@ class PageRevision(models.Model):
         for field in ("title", "intro", "seo_title", "seo_description"):
             validators.text(getattr(self, field), self._meta.get_field(field).max_length, required=field != "intro")
 
+    def save(self, *args, **kwargs):
+        if self.pk:
+            previous = type(self).objects.get(pk=self.pk)
+            protected = ("page_id", "number", "title", "intro", "seo_title", "seo_description", "seo_image_id", "created_by_id", "source_seed_key", "source_seed_version")
+            if any(getattr(self, field) != getattr(previous, field) for field in protected):
+                raise ValidationError("Page revision content is immutable.")
+            if self.content_checksum != previous.content_checksum and previous.content_checksum:
+                raise ValidationError("Page revision checksum is immutable.")
+        return super().save(*args, **kwargs)
+
 
 class PageSection(models.Model):
     revision = models.ForeignKey(PageRevision, on_delete=models.CASCADE, related_name="sections")
@@ -226,6 +250,16 @@ class PageSection(models.Model):
         if self.body and self.entries:
             raise ValidationError("Use body or entries, not both.")
 
+    def save(self, *args, **kwargs):
+        if self.pk:
+            raise ValidationError("Page sections are immutable; create a new revision.")
+        if self.revision.status != "draft":
+            raise ValidationError("Sections can only be added to a draft revision.")
+        return super().save(*args, **kwargs)
+
+    def delete(self, *args, **kwargs):
+        raise ValidationError("Page sections are immutable; create a new revision.")
+
 
 class PublicationAudit(models.Model):
     actor = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.PROTECT)
@@ -238,3 +272,11 @@ class PublicationAudit(models.Model):
 
     class Meta:
         constraints = [models.CheckConstraint(condition=(Q(site__isnull=False, page__isnull=True) | Q(site__isnull=True, page__isnull=False)), name="content_audit_one_target")]
+
+    def save(self, *args, **kwargs):
+        if self.pk:
+            raise ValidationError("Publication audit records are append only.")
+        return super().save(*args, **kwargs)
+
+    def delete(self, *args, **kwargs):
+        raise ValidationError("Publication audit records are append only.")