refactor: add an AbstractSubject that implements Subject

src/js/teaching_unit/model.ts

@@ -1,20 +1,19 @@
-import { Observer, Subject } from "../utils";
+import { AbstractSubject } from "../utils";
 
 export enum State {
   Unselected,
   Selected,
   Validated,
 }
 
-export class TeachingUnit implements Subject {
+export class TeachingUnit extends AbstractSubject {
   public title: string;
   public code: string;
   public ects: number;
   public state: State;
 
-  private observers: Observer[] = [];
-
   constructor(title: string, code: string, ects: number, state?: State) {
+    super();
     this.title = title;
     this.code = code;
     this.ects = ects;
@@ -44,30 +43,6 @@ export class TeachingUnit implements Subject {
     );
   }
 
-  public attach(observer: Observer): void {
-    const isExist = this.observers.includes(observer);
-    if (isExist) {
-      throw new Error("Observer has been attached already");
-    }
-
-    this.observers.push(observer);
-  }
-
-  public detach(observer: Observer): void {
-    const observerIndex = this.observers.indexOf(observer);
-    if (observerIndex === -1) {
-      throw new Error("Nonexistent observer");
-    }
-
-    this.observers.splice(observerIndex, 1);
-  }
-
-  public notify(): void {
-    for (const observer of this.observers) {
-      observer.update(this);
-    }
-  }
-
   public toggle() {
     switch (this.state) {
       case State.Unselected:

src/js/utils.ts

@@ -7,3 +7,31 @@ export interface Subject {
 export interface Observer {
   update(subject: Subject): void;
 }
+
+export abstract class AbstractSubject implements Subject {
+  private observers: Observer[] = [];
+
+  public attach(observer: Observer): void {
+    const isExist = this.observers.includes(observer);
+    if (isExist) {
+      throw new Error("Observer has been attached already");
+    }
+
+    this.observers.push(observer);
+  }
+
+  public detach(observer: Observer): void {
+    const observerIndex = this.observers.indexOf(observer);
+    if (observerIndex === -1) {
+      throw new Error("Nonexistent observer");
+    }
+
+    this.observers.splice(observerIndex, 1);
+  }
+
+  public notify(): void {
+    for (const observer of this.observers) {
+      observer.update(this);
+    }
+  }
+}