IcingaDB: Sync affects_children as part of runtime state updates

lib/icinga/checkable-dependency.cpp

@@ -122,6 +122,35 @@ bool Checkable::IsReachable(DependencyType dt, Dependency::Ptr *failedDependency
 	return true;
 }
 
+/**
+ * Checks whether the last check result of this Checkable affects its child dependencies.
+ *
+ * A Checkable affects its child dependencies if it runs into a non-OK state and results in any of its child
+ * Checkables to become unreachable. Though, that unavailable dependency may not necessarily cause the child
+ * Checkable to be in unreachable state as it might have some other dependencies that are still reachable, instead
+ * it just indicates whether the edge/connection between this and the child Checkable is broken or not.
+ *
+ * @return bool - Returns true if the Checkable affects its child dependencies, otherwise false.
+ */
+bool Checkable::AffectsChildren() const
+{
+	if (!GetLastCheckResult() || !IsReachable()) {
+		// If there is no check result, or the Checkable is not reachable, we can't safely determine whether
+		// the Checkable affects its child dependencies.
+		return false;
+	}
+
+	for (auto& dep : GetReverseDependencies()) {
+		if (!dep->IsAvailable(DependencyState)) {
+			// If one of the child dependency is not available, then it's definitely due to the
+			// current Checkable state, so we don't need to verify the remaining ones.
+			return true;
+		}
+	}
+
+	return false;
+}
+
 std::set<Checkable::Ptr> Checkable::GetParents() const
 {
 	std::set<Checkable::Ptr> parents;

lib/icinga/checkable.hpp

@@ -82,6 +82,7 @@ public:
 	void AddGroup(const String& name);
 
 	bool IsReachable(DependencyType dt = DependencyState, intrusive_ptr<Dependency> *failedDependency = nullptr, int rstack = 0) const;
+	bool AffectsChildren() const;
 
 	AcknowledgementType GetAcknowledgement();
 

lib/icingadb/icingadb-objects.cpp

@@ -2828,6 +2828,7 @@ Dictionary::Ptr IcingaDB::SerializeState(const Checkable::Ptr& checkable)
 	attrs->Set("check_attempt", checkable->GetCheckAttempt());
 
 	attrs->Set("is_active", checkable->IsActive());
+	attrs->Set("affects_children", checkable->AffectsChildren());
 
 	CheckResult::Ptr cr = checkable->GetLastCheckResult();