'use strict';

/**

* Observer Pattern - Defines a one-to-many relationships where there is a Subject

* and many Observers. Like the name suggests, the Observers observe the Subject,

* receive notifications from the Subject when something has changed. This concept

* is similar to Followers and Following in Twitter.

*

* Example - In picture sharing application like Instagram, on your dashboard you

* find pictures of the users you are following. That user may or may not know

* you are following him/her. The observer in this case refers to you following a

* user and the user becomes the subject.

*

*/

class NotificationData {

constructor(data) {

if(this.validData(data)) {

this.data = data;

} else {

this.data = {};

}

}

validData(data) {

// Data validation before you can return the correct data

console.log("No need validation")

// Create your logic if you need validation if not return true

return true;

}

}

class Subject {

constructor(name) {

// Create a new Array of Observers

this.observers = [];

this.name = name;

}

addObserver(observer) {

this.observers.push(observer);

}

removeObserver(observer) {

var index = this.observers.indexOf(observer);

this.observers.splice(index, 1);

}

notifyObservers(notificationData) {

this.observers.forEach((observer) => observer.update(notificationData));

}

}

class Observer {

constructor(name) {

this.newPosts = [];

this.isOnline = false;

this.name = name;

}

update() {

// When notification received, update something

console.log("Nothing to update over here");

}

}

class NewPost extends NotificationData {

validData(data) {

// Check if data has url and description if not it is not a valid data

if(data.hasOwnProperty('name') && data.hasOwnProperty('url') && data.hasOwnProperty('description')) {

return true;

} else {

return false;

}

}

}

class User extends Subject {

createPost(url, description) {

var data = {

name: this.name,

url: url,

description: description

}

var newPost = new NewPost(data).data;

this.notifyObservers(newPost);

}

}

class Follower extends Observer {

update(data) {

// After updating, send out notifications to Followers

this.newPosts.push(data);

if(this.isOnline) {

this.display();

this.seen();

}

}

seen() {

this.newPosts = [];

}

setOnline(b) {

this.isOnline = b;

// Display new data after going online

this.display();

this.seen();

}

display() {

console.log(this.name + ":" + JSON.stringify(this.newPosts));

this.seen();

}

}

// Initiate a really popular woman

let chloe = new User("Chloe");

// Initiate the Followers

let tom = new Follower("Tom");

let jack = new Follower("Jack");

// Let the guys follow Chloe

chloe.addObserver(tom);

chloe.addObserver(jack);

// Let Tom be offline while Jack be online, so Jack will receive instant notification

jack.setOnline(true);

// Chloe creates a post and Jack will receive updates while Tom has to wait to be online

console.log("Only Jack received the new post");

chloe.createPost("http://www.myselfie.com/selfie1.png", "Selfie taken at home");

console.log("Now Jack received another new post");

chloe.createPost("http://www.mymodelshoot.com/modelshoot1.png", "Model shoot");

console.log("Now Tom goes online");

tom.setOnline(true);

console.log("Now Chloe creates another post and both guys receive it");

chloe.createPost("http://www.ootd.com/ootd.png", "#ootd");

console.log("Chloe finds Tom creepy, removes him, then creates a new post");

chloe.removeObserver(tom);

chloe.createPost("http://www.ootd2.com/ootd2.png", "#ootd");