feat: Implement basic general folder support (#2051)

- Related: #1748

src/ha/entity-state-translation.ts

@@ -0,0 +1,50 @@
+import { HassEntity } from 'home-assistant-js-websocket';
+import { computeDomain } from './compute-domain.js';
+import { Entity } from './registry/entity/types.js';
+import { HomeAssistant } from './types.js';
+
+/**
+ * Get the translation of an entity state. Inspired by:
+ * https://github.com/home-assistant/frontend/blob/dev/src/common/entity/compute_state_display.ts#L204-L218
+ *
+ * This may no longer be necessary to custom implement if `custom-card-helpers`
+ * is updated to reflect how the Home Assistant frontend now [as of 2023-03-04]
+ * computes state display (e.g. supports usage of `translation_key`).
+ *
+ * https://github.com/custom-cards/custom-card-helpers/blob/master/src/compute-state-display.ts
+ *
+ */
+export const getEntityStateTranslation = (
+  hass: HomeAssistant,
+  entityID: string,
+  options?: {
+    entity?: Entity;
+    state?: string;
+  },
+): string | null => {
+  const stateObj: HassEntity | undefined = hass.states[entityID];
+  const state = options?.state ? options.state : stateObj ? stateObj.state : null;
+
+  if (!state) {
+    return null;
+  }
+
+  const domain = computeDomain(entityID);
+  const attributes = stateObj ? stateObj.attributes : null;
+
+  return (
+    // Return the translation_key translation.
+    (options?.entity?.translation_key &&
+      hass.localize(
+        `component.${options.entity.platform}.entity.${domain}` +
+          `.${options.entity.translation_key}.state.${state}`,
+      )) ||
+    // Return device class translation
+    (attributes?.device_class &&
+      hass.localize(`component.${domain}.state.${attributes.device_class}.${state}`)) ||
+    // Return default translation
+    hass.localize(`component.${domain}.state._.${state}`) ||
+    // We don't know! Return the raw state.
+    state
+  );
+};