Initial work on #2: Reverting a merged branch

netbox_branching/choices.py

@@ -9,6 +9,7 @@ class BranchStatusChoices(ChoiceSet):
     READY = 'ready'
     SYNCING = 'syncing'
     MERGING = 'merging'
+    REVERTING = 'reverting'
     MERGED = 'merged'
     FAILED = 'failed'
 
@@ -18,6 +19,7 @@ class BranchStatusChoices(ChoiceSet):
         (READY, _('Ready'), 'green'),
         (SYNCING, _('Syncing'), 'orange'),
         (MERGING, _('Merging'), 'orange'),
+        (REVERTING, _('Reverting'), 'orange'),
         (MERGED, _('Merged'), 'blue'),
         (FAILED, _('Failed'), 'red'),
     )
@@ -27,9 +29,11 @@ class BranchEventTypeChoices(ChoiceSet):
     PROVISIONED = 'provisioned'
     SYNCED = 'synced'
     MERGED = 'merged'
+    REVERTED = 'reverted'
 
     CHOICES = (
         (PROVISIONED, _('Provisioned'), 'green'),
         (SYNCED, _('Synced'), 'cyan'),
         (MERGED, _('Merged'), 'blue'),
+        (REVERTED, _('Reverted'), 'blue'),
     )

netbox_branching/jobs.py

@@ -10,6 +10,7 @@
 __all__ = (
     'MergeBranchJob',
     'ProvisionBranchJob',
+    'RevertBranchJob',
     'SyncBranchJob',
 )
 
@@ -109,3 +110,24 @@ def run(self, commit=True, *args, **kwargs):
             branch.merge(user=self.job.user, commit=commit)
         except AbortTransaction:
             logger.info("Dry run completed; rolling back changes")
+
+
+class RevertBranchJob(JobRunner):
+    """
+    Revert changes from a merged Branch.
+    """
+    class Meta:
+        name = 'Revert branch'
+
+    def run(self, commit=True, *args, **kwargs):
+        # Initialize logging
+        logger = logging.getLogger('netbox_branching.branch.revert')
+        logger.setLevel(logging.DEBUG)
+        logger.addHandler(ListHandler(queue=get_job_log(self.job)))
+
+        # Merge the Branch
+        try:
+            branch = self.job.object
+            branch.revert(user=self.job.user, commit=commit)
+        except AbortTransaction:
+            logger.info("Dry run completed; rolling back changes")

netbox_branching/models/branches.py

@@ -107,6 +107,10 @@ def is_active(self):
     def ready(self):
         return self.status == BranchStatusChoices.READY
 
+    @property
+    def merged(self):
+        return self.status == BranchStatusChoices.MERGED
+
     @cached_property
     def schema_name(self):
         schema_prefix = get_plugin_config('netbox_branching', 'schema_prefix')
@@ -299,6 +303,67 @@ def merge(self, user, commit=True):
 
     merge.alters_data = True
 
+    def revert(self, user, commit=True):
+        """
+        Undo all changes associated with a previously merged Branch in the main schema by replaying them in
+        reverse order and calling undo() on each.
+        """
+        logger = logging.getLogger('netbox_branching.branch.revert')
+        logger.info(f'Reverting branch {self} ({self.schema_name})')
+
+        if not self.merged:
+            raise Exception(f"Only merged branches can be reverted.")
+
+        # Retrieve applied changes before we update the Branch's status
+        changes = self.get_changes().order_by('-time')
+
+        # Update Branch status
+        Branch.objects.filter(pk=self.pk).update(status=BranchStatusChoices.REVERTING)
+
+        # Create a dummy request for the event_tracking() context manager
+        request = RequestFactory().get(reverse('home'))
+
+        # Prep & connect the signal receiver for recording AppliedChanges
+        handler = partial(record_applied_change, branch=self)
+        post_save.connect(handler, sender=ObjectChange_, weak=False)
+
+        try:
+            with transaction.atomic():
+                # Undo each change from the Branch
+                for change in changes:
+                    with event_tracking(request):
+                        logger.debug(f'Undoing change: {change}')
+                        request.id = change.request_id
+                        request.user = change.user
+                        change.undo()
+                if not commit:
+                    raise AbortTransaction()
+
+        except Exception as e:
+            logger.error(e)
+            # Disconnect signal receiver & restore original branch status
+            post_save.disconnect(handler, sender=ObjectChange_)
+            Branch.objects.filter(pk=self.pk).update(status=BranchStatusChoices.READY)
+            raise e
+
+        # Update the Branch's status to "ready"
+        self.status = BranchStatusChoices.READY
+        self.merged_time = None
+        self.merged_by = None
+        self.save()
+        BranchEvent.objects.create(branch=self, user=user, type=BranchEventTypeChoices.REVERTED)
+
+        # TODO: Introduce branch_reverted signal
+        # Emit branch_merged signal
+        # branch_merged.send(sender=self.__class__, branch=self, user=user)
+
+        logger.info('Reversion completed')
+
+        # Disconnect the signal receiver
+        post_save.disconnect(handler, sender=ObjectChange_)
+
+    merge.alters_data = True
+
     def provision(self, user):
         """
         Create the schema & replicate main tables.

netbox_branching/models/changes.py

@@ -60,6 +60,39 @@ def apply(self, using=DEFAULT_DB_ALIAS):
 
     apply.alters_data = True
 
+    def undo(self, using=DEFAULT_DB_ALIAS):
+        """
+        Revert a previously applied change using the specified database connection.
+        """
+        model = self.changed_object_type.model_class()
+
+        # Deleting a previously created object
+        if self.action == ObjectChangeActionChoices.ACTION_CREATE:
+            try:
+                instance = model.objects.get(pk=self.changed_object_id)
+                print(f'Undoing creation of {model._meta.verbose_name} {instance}')
+                instance.delete(using=using)
+            except model.DoesNotExist:
+                print(f'{model._meta.verbose_name} ID {self.changed_object_id} does not exist; skipping')
+
+        # Reverting a modification to an object
+        elif self.action == ObjectChangeActionChoices.ACTION_UPDATE:
+            instance = model.objects.using(using).get(pk=self.changed_object_id)
+            update_object(instance, self.diff()['pre'], using=using)
+
+        # Restoring a deleted object
+        elif self.action == ObjectChangeActionChoices.ACTION_DELETE:
+            instance = deserialize_object(model, self.prechange_data, pk=self.changed_object_id)
+            print(f'Restoring {model._meta.verbose_name} {instance}')
+            instance.object.full_clean()
+            instance.save(using=using)
+
+        # Rebuild the MPTT tree where applicable
+        if issubclass(model, MPTTModel):
+            model.objects.rebuild()
+
+    undo.alters_data = True
+
 
 class ChangeDiff(models.Model):
     branch = models.ForeignKey(

netbox_branching/templates/netbox_branching/branch.html

@@ -34,6 +34,10 @@
     <a href="{% url 'plugins:netbox_branching:branch_merge' pk=object.pk %}" class="btn btn-primary">
       <i class="mdi mdi-merge"></i> {% trans "Merge" %}
     </a>
+  {% elif perms.netbox_branching.revert_branch and object.merged %}
+    <a href="{% url 'plugins:netbox_branching:branch_revert' pk=object.pk %}" class="btn btn-primary">
+      <i class="mdi mdi-arrow-u-left-top"></i> {% trans "Revert" %}
+    </a>
   {% else %}
     <button type="button" class="btn btn-primary disabled" aria-disabled="true">
       <i class="mdi mdi-merge"></i> {% trans "Merge" %}

netbox_branching/views.py

@@ -10,7 +10,8 @@
 from netbox.views import generic
 from utilities.views import ViewTab, register_model_view
 from . import filtersets, forms, tables
-from .jobs import MergeBranchJob, SyncBranchJob
+from .choices import BranchStatusChoices
+from .jobs import MergeBranchJob, RevertBranchJob, SyncBranchJob
 from .models import ChangeDiff, Branch
 
 
@@ -151,6 +152,9 @@ class BaseBranchActionView(generic.ObjectView):
     form = forms.BranchActionForm
     template_name = 'netbox_branching/branch_action.html'
     action = None
+    valid_states = (
+        BranchStatusChoices.READY,
+    )
 
     def get_required_permission(self):
         return f'netbox_branching.{self.action}_branch'
@@ -181,8 +185,10 @@ def post(self, request, **kwargs):
         branch = self.get_object(**kwargs)
         form = forms.BranchActionForm(branch, request.POST)
 
-        if not branch.ready:
-            messages.error(request, _("The branch must be in the ready state to perform this action."))
+        if branch.status not in self.valid_states:
+            messages.error(request, _(
+                "The branch must be in one of the following states to perform this action: {valid_states}"
+            ).format(valid_states=', '.join(self.valid_states)))
         elif form.is_valid():
             return self.do_action(branch, request, form)
 
@@ -226,6 +232,25 @@ def do_action(self, branch, request, form):
         return redirect(branch.get_absolute_url())
 
 
+@register_model_view(Branch, 'revert')
+class BranchRevertView(BaseBranchActionView):
+    action = 'revert'
+    valid_states = (
+        BranchStatusChoices.MERGED,
+    )
+
+    def do_action(self, branch, request, form):
+        # Enqueue a background job to revert the Branch
+        RevertBranchJob.enqueue(
+            instance=branch,
+            user=request.user,
+            commit=form.cleaned_data['commit']
+        )
+        messages.success(request, f"Reverting branch {branch}")
+
+        return redirect(branch.get_absolute_url())
+
+
 class BranchBulkImportView(generic.BulkImportView):
     queryset = Branch.objects.all()
     model_form = forms.BranchImportForm