feat(challenge23): create table for testing table challenge

libs/testing-table/backend/src/index.ts

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+export * from './lib/fake-backend.service';

libs/testing-table/backend/src/lib/fake-backend.service.ts

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+import { Injectable } from '@angular/core';
+import { SortDirection } from '@angular/material/sort';
+import { User, randUser } from '@ngneat/falso';
+import { map, take, timer } from 'rxjs';
+
+type SortDirectionIndex = 1 | -1 | 0;
+
+const sort: Record<SortDirection, SortDirectionIndex> = {
+  asc: 1,
+  desc: -1,
+  '': 0,
+};
+
+@Injectable({ providedIn: 'root' })
+export class FakeBackendService {
+  private readonly users = randUser({ length: 10 });
+
+  getUsers = (active: keyof User, dir: SortDirection, pageIndex: number) =>
+    timer(0, 1000).pipe(
+      take(1),
+      map(() => this.sortByKey(this.users, active, sort[dir]))
+    );
+
+  private sortByKey(
+    arr: User[],
+    key: keyof User,
+    direction: SortDirectionIndex
+  ): User[] {
+    return arr.sort((a, b) => {
+      const valueA = a[key];
+      const valueB = b[key];
+
+      if (valueA < valueB) {
+        return -1 * direction;
+      } else if (valueA > valueB) {
+        return 1 * direction;
+      } else {
+        return 0;
+      }
+    });
+  }
+}