[epa-orchestrator] Add noop relation handler for sunbeam-machine relation

Add relation handler for the subordinate charm

Change-Id: I0d561fda38bfef5262e9d9a88ce5ac97f0cfea31
Signed-off-by: Ahmad Hassan <ahmad.hassan@canonical.com>

charms/epa-orchestrator/src/charm.py

@@ -20,15 +20,38 @@ This charm is used to install the epa-orchestrator snap as a part of the opensta
 """
 
 import logging
+from typing import (
+    List,
+)
 
 import charms.operator_libs_linux.v2.snap as snap
 import ops
 import ops_sunbeam.charm as sunbeam_charm
+import ops_sunbeam.relation_handlers as sunbeam_rhandlers
 import ops_sunbeam.tracing as sunbeam_tracing
 
 logger = logging.getLogger(__name__)
 
 
+@sunbeam_tracing.trace_type
+class SunbeamMachineRequiresHandler(sunbeam_rhandlers.RelationHandler):
+    """Handler for sunbeam-machine relation on the requires side."""
+
+    def setup_event_handler(self):
+        """Noop event handler for sunbeam-machine relation."""
+        return ops.framework.Object(self.charm, self.relation_name)
+
+    def interface_properties(self) -> dict:
+        """Return empty interface properties."""
+        return {}
+
+    @property
+    def ready(self) -> bool:
+        """Report if relation is ready."""
+        relations = self.model.relations.get(self.relation_name, [])
+        return len(relations) > 0
+
+
 @sunbeam_tracing.trace_sunbeam_charm(extra_types=(snap.SnapCache, snap.Snap))
 class EpaOrchestratorCharm(sunbeam_charm.OSBaseOperatorCharmSnap):
     """Charm the service."""
@@ -45,7 +68,7 @@ class EpaOrchestratorCharm(sunbeam_charm.OSBaseOperatorCharmSnap):
         """Returns the snap channel."""
         return str(self.model.config["snap-channel"])
 
-    def ensure_services_running(self, enable) -> None:
+    def ensure_services_running(self, enable: bool = True) -> None:
         """Override to prevent service start - this snap has no services."""
         logger.debug(
             "Skipping service start - %s snap has no services", self.snap_name
@@ -59,6 +82,23 @@ class EpaOrchestratorCharm(sunbeam_charm.OSBaseOperatorCharmSnap):
         )
         pass
 
+    def relation_ready(self, event) -> None:
+        """Noop callback for sunbeam-machine relation."""
+        pass
+
+    def get_relation_handlers(
+        self, handlers: List[sunbeam_rhandlers.RelationHandler] = None
+    ) -> List[sunbeam_rhandlers.RelationHandler]:
+        """Relation handlers for the service."""
+        handlers = handlers or []
+        if self.can_add_handler("sunbeam-machine", handlers):
+            self.sunbeam_machine = SunbeamMachineRequiresHandler(
+                self, "sunbeam-machine", self.relation_ready, mandatory=True
+            )
+            handlers.append(self.sunbeam_machine)
+
+        return super().get_relation_handlers(handlers)
+
 
 if __name__ == "__main__":  # pragma: nocover
     ops.main(EpaOrchestratorCharm)

charms/epa-orchestrator/tests/unit/test_charm.py

@@ -86,3 +86,11 @@ class TestEpaOrchestratorCharm(test_utils.CharmTestCase):
 
         # Should return None (no-op)
         self.assertIsNone(result)
+
+    def test_all_relations(self):
+        """Test that all relation handlers are properly configured."""
+        self.harness.begin()
+
+        self.assertFalse(self.harness.charm.sunbeam_machine.ready)
+        self.harness.add_relation("sunbeam-machine", "sunbeam-machine")
+        self.assertTrue(self.harness.charm.sunbeam_machine.ready)