Implements task saving and retrieving.

src/app/core/service/task.service.ts

@@ -0,0 +1,32 @@
+import { Injectable } from '@angular/core';
+import { BehaviorSubject, Observable } from 'rxjs';
+import { Task } from '../entity/task';
+import { TaskPersistenceService } from './task-persistence.service';
+
+@Injectable({
+  providedIn: 'root'
+})
+export class TaskService {
+  _tasks: BehaviorSubject<Task[]> = new BehaviorSubject<Task[]>([]);
+
+  constructor(
+    private _taskPersistenceService: TaskPersistenceService
+  ) {
+    const tasks = this._taskPersistenceService.getAll() || [];
+    this._tasks.next(tasks);
+  }
+
+  get tasks(): Observable<Task[]> {
+    return this._tasks.asObservable();
+  }
+
+  add(task: Task): void {
+    const tasks = this._tasks.value;
+    tasks.push(task);
+    this._tasks.next(tasks);
+  }
+
+  _saveTasks(): void {
+    this._taskPersistenceService.save(this._tasks.value);
+  }
+}