feat: Implement basic general folder support (#2051)

- Related: #1748

src/ha/get-entities.ts

@@ -0,0 +1,14 @@
+import { HomeAssistant } from './types';
+
+/**
+ * Get entities from the HASS object.
+ * @param hass
+ * @param domain
+ * @returns A list of entities ids.
+ */
+export const getEntitiesFromHASS = (hass: HomeAssistant, domain?: string): string[] => {
+  const entities = Object.keys(hass.states).filter(
+    (eid) => !domain || eid.substring(0, eid.indexOf('.')) === domain,
+  );
+  return entities.sort();
+};