feat: Implement basic general folder support (#2051)

- Related: #1748

src/ha/registry/entity/index.ts

@@ -0,0 +1,90 @@
+import { errorToConsole } from '../../../utils/basic.js';
+import { HomeAssistant } from '../../types.js';
+import { homeAssistantWSRequest } from '../../ws-request.js';
+import {
+  Entity,
+  EntityCache,
+  EntityList,
+  entityListSchema,
+  EntityRegistryManager,
+  entitySchema,
+} from './types.js';
+
+// This class manages interactions with entities, caching results and fetching
+// as necessary. Some calls require every entity to be fetched, which may be
+// non-trivial in size (after which they are cached forever).
+
+export class EntityRegistryManagerLive implements EntityRegistryManager {
+  protected _cache: EntityCache;
+  protected _fetchedEntityList = false;
+
+  constructor(cache: EntityCache) {
+    this._cache = cache;
+  }
+
+  public async getEntity(hass: HomeAssistant, entityID: string): Promise<Entity | null> {
+    const cachedEntity = this._cache.get(entityID);
+    if (cachedEntity) {
+      return cachedEntity;
+    }
+
+    let entity: Entity | null = null;
+    try {
+      entity = await homeAssistantWSRequest<Entity>(hass, entitySchema, {
+        type: 'config/entity_registry/get',
+        entity_id: entityID,
+      });
+    } catch (e) {
+      errorToConsole(e as Error);
+      return null;
+    }
+    this._cache.set(entity.entity_id, entity);
+    return entity;
+  }
+
+  public async getMatchingEntities(
+    hass: HomeAssistant,
+    func: (arg: Entity) => boolean,
+  ): Promise<Entity[]> {
+    await this.fetchEntityList(hass);
+    return this._cache.getMatches(func);
+  }
+
+  public async getEntities(
+    hass: HomeAssistant,
+    entityIDs: string[],
+  ): Promise<Map<string, Entity>> {
+    const output: Map<string, Entity> = new Map();
+    const _storeEntity = async (entityID: string): Promise<void> => {
+      const entity = await this.getEntity(hass, entityID);
+
+      if (entity) {
+        // When asked to fetch multiple entities, ignore missing entities (they
+        // will just not feature in the output).
+        output.set(entityID, entity);
+      }
+    };
+    await Promise.all(entityIDs.map(_storeEntity));
+    return output;
+  }
+
+  public async fetchEntityList(hass: HomeAssistant): Promise<void> {
+    if (this._fetchedEntityList) {
+      return;
+    }
+
+    let entityList: EntityList | null = null;
+    try {
+      entityList = await homeAssistantWSRequest<EntityList>(hass, entityListSchema, {
+        type: 'config/entity_registry/list',
+      });
+    } catch (e) {
+      errorToConsole(e as Error);
+      return;
+    }
+    entityList.forEach((entity) => {
+      this._cache.set(entity.entity_id, entity);
+    });
+    this._fetchedEntityList = true;
+  }
+}