add mediator design pattern real world example

Author: samuel.casanova

src/Mediator/RealWorld/Output.txt

@@ -0,0 +1,12 @@
+Subscribing Lightning
+Subscribing Doc
+Subscribing Mater
+Publishing message "Catchaw" to the group
+Message received by Doc: Catchaw
+Message received by Mater: Catchaw
+Publishing message "Ey kid" to the group
+Message received by Lightning: Ey kid
+Message received by Mater: Ey kid
+Publishing message "Tomato" to the group
+Message received by Lightning: Tomato
+Message received by Doc: Tomato

src/Mediator/RealWorld/index.ts

@@ -0,0 +1,70 @@
+/**
+ * EN: Real World Example for the Mediator design pattern
+ *
+ * Need: To have a messaging application to notify groups of people. Users
+ * should not know about each other.
+ *
+ * Solution: Create a mediator to manage subscriptions and messages
+ */
+
+/**
+ * EN: Extending the Mediator interface to have a payload to include messages
+ */
+interface Mediator {
+    notify(sender: object, event: string, payload?: string): void;
+}
+
+/**
+ * EN: The user plays the role of the independent component. It has an
+ * instance of the mediator.
+ */
+class User {
+    constructor(public name: string, private mediator: Mediator) {
+        this.mediator.notify(this, 'subscribe');
+    }
+
+    receiveMessage(message: string) {
+        console.log(`Message received by ${this.name}: ${message}`);
+    }
+
+    publishMessage(message: string) {
+        this.mediator.notify(this, 'publish', message);
+    }
+}
+
+/**
+ * EN: The app is the concrete Mediator and implements all the events that
+ * collaborators can notify: subscribe and publish
+ */
+class ChatAppMediator implements Mediator {
+    private users: User[] = [];
+
+    public notify(sender: object, event: string, payload?: string): void {
+        if (event === 'subscribe') {
+            const user = sender as User;
+            console.log(`Subscribing ${user.name}`);
+            this.users.push(user);
+        }
+
+        if (event === 'publish') {
+            console.log(`Publishing message "${payload}" to the group`);
+            const usersExcludingSender = this.users.filter(u => u !== sender);
+            for (const user of usersExcludingSender) {
+                user.receiveMessage(payload);
+            }
+        }
+    }
+}
+
+/**
+ * EN: The client code. Creating a user automatically subscribes them to the
+ * group.
+ */
+const chatAppMediator = new ChatAppMediator();
+const user1 = new User('Lightning', chatAppMediator);
+const user2 = new User('Doc', chatAppMediator);
+const user3 = new User('Mater', chatAppMediator);
+
+user1.publishMessage('Catchaw');
+user2.publishMessage('Ey kid');
+user3.publishMessage('Tomato');