refactor: use range query for canteen module

src/app/modules/data/data.provider.ts

@@ -14,8 +14,16 @@
  */
 import {Injectable} from '@angular/core';
 import {Client} from '@openstapps/api/lib/client';
-import {SCSearchRequest, SCSearchResponse, SCThingOriginType, SCThings, SCThingType} from '@openstapps/core';
+import {
+  SCMultiSearchRequest, SCMultiSearchResponse,
+  SCSearchRequest,
+  SCSearchResponse,
+  SCThingOriginType,
+  SCThings,
+  SCThingType,
+} from '@openstapps/core';
 import {SCSaveableThing} from '@openstapps/core';
+import {chunk, fromPairs, toPairs} from 'lodash-es';
 import {environment} from '../../../environments/environment';
 import {StorageProvider} from '../storage/storage.provider';
 import {StAppsWebHttpClient} from './stapps-web-http-client.provider';
@@ -35,6 +43,20 @@ export enum DataScope {
   providedIn: 'root',
 })
 export class DataProvider {
+
+  /**
+   * TODO
+   */
+  get storagePrefix(): string {
+    return this._storagePrefix;
+  }
+
+  /**
+   * TODO
+   */
+  set storagePrefix(storagePrefix) {
+    this._storagePrefix = storagePrefix;
+  }
   /**
    * TODO
    */
@@ -43,6 +65,10 @@ export class DataProvider {
    * Version of the app (used for the header in communication with the backend)
    */
   appVersion = environment.backend_version;
+  /**
+   * Maximum number of sub-queries in a multi-query allowed by the backend
+   */
+  backendQueriesLimit = 5;
   /**
    * TODO
    */
@@ -144,6 +170,18 @@ export class DataProvider {
     return this.storageProvider.has(this.getDataKey(uid));
   }
 
+  /**
+   * Performs multiple searches at once and returns their responses
+   *
+   * @param query - query to send to the backend (auto-splits according to the backend limit)
+   */
+  async multiSearch(query: SCMultiSearchRequest): Promise<SCMultiSearchResponse> {
+    // partition object into chunks, process those requests in parallel, then merge their responses again
+    return Object.assign({}, ...(await Promise.all(chunk(toPairs(query), this.backendQueriesLimit)
+      .map((request) => this.client.multiSearch(fromPairs(request))),
+    )));
+  }
+
   /**
    * Save a data item
    *
@@ -174,18 +212,4 @@ export class DataProvider {
   async search(query: SCSearchRequest): Promise<SCSearchResponse> {
     return (this.client.search(query));
   }
-
-  /**
-   * TODO
-   */
-  get storagePrefix(): string {
-    return this._storagePrefix;
-  }
-
-  /**
-   * TODO
-   */
-  set storagePrefix(storagePrefix) {
-    this._storagePrefix = storagePrefix;
-  }
 }