implement pruning code

src/loaders/ApiBasedRepositoryLoader.ts

@@ -1,5 +1,5 @@
 import { GetterSetterRepository } from "../repositories/GetterSetterRepository";
-import { IEta, IRoute, IShuttle, IStop, ISystem } from "../entities/entities";
+import { IEntityWithId, IEta, IRoute, IShuttle, IStop, ISystem } from "../entities/entities";
 
 export class ApiResponseError extends Error {
   constructor(message: string) {
@@ -17,12 +17,25 @@ export class ApiBasedRepositoryLoader {
   ) {
   }
 
+  private async constructExistingEntityIdSet<T extends IEntityWithId>(entitySearchCallback: () => Promise<T[]>) {
+    const existingEntities = await entitySearchCallback();
+    const ids = new Set<string>();
+    existingEntities.forEach((entity) => {
+      ids.add(entity.id);
+    });
+    return ids;
+  }
+
   public async fetchAndUpdateSystemData() {
     const params = {
       getSystems: "2",
     };
     const query = new URLSearchParams(params).toString();
 
+    const systemIds = await this.constructExistingEntityIdSet(async () => {
+      return await this.repository.getSystems();
+    })
+
     try {
       const response = await fetch(`${this.baseUrl}?${query}`);
       const json = await response.json();
@@ -41,10 +54,18 @@ export class ApiBasedRepositoryLoader {
           };
 
           await this.repository.addOrUpdateSystem(constructedSystem);
+          if (systemIds.has(constructedSystem.id)) {
+            systemIds.delete(constructedSystem.id);
+          }
         }));
       } else {
         throw new Error("Received JSON object does not contain `all` field")
       }
+
+      // Prune systems
+      await Promise.all(Array.from(systemIds).map(async (systemId) => {
+        await this.repository.removeSystemIfExists(systemId);
+      }));
     } catch(e: any) {
       throw new ApiResponseError(e.message);
     }