feat: listen to group events (#90)

This allows you to listen for user joins or leaves, description updates, subject updates, picture updates, and group settings updates.

Co-authored-by: Pedro S. Lopez <pedroslopez@me.com>

src/structures/GroupNotification.js

@@ -0,0 +1,104 @@
+'use strict';
+
+const Base = require('./Base');
+
+/**
+ * Represents a GroupNotification on WhatsApp
+ * @extends {Base}
+ */
+class GroupNotification extends Base {
+    constructor(client, data) {
+        super(client);
+
+        if(data) this._patch(data);
+    }
+
+    _patch(data) {
+        /**
+         * ID that represents the groupNotification
+         * @type {object}
+         */
+        this.id = data.id;
+
+        /**
+         * Extra content
+         * @type {string}
+         */
+        this.body = data.body || '';
+
+        /** 
+         * GroupNotification type
+         * @type {GroupNotificationTypes}
+         */
+        this.type = data.subtype;
+        
+        /**
+         * Unix timestamp for when the groupNotification was created
+         * @type {number}
+         */
+        this.timestamp = data.t;
+
+        /**
+         * ID for the Chat that this groupNotification was sent for.
+         * 
+         * @type {string}
+         */
+        this.chatId = typeof (data.to) === 'object' ? data.to._serialized : data.to;
+
+        /**
+         * ContactId for the user that produced the GroupNotification.
+         * @type {string}
+         */
+        this.author = typeof (data.author) === 'object' ? data.author._serialized : data.author;
+        
+        /**
+         * Contact IDs for the users that were affected by this GroupNotification.
+         * @type {Array<string>}
+         */
+        this.recipientIds = [];
+
+        if (data.recipients) {
+            this.recipientIds = data.recipients;
+        }
+
+        return super._patch(data);
+    }
+
+    /**
+     * Returns the Chat this groupNotification was sent in
+     * @returns {Promise<Chat>}
+     */
+    getChat() {
+        return this.client.getChatById(this.chatId);
+    }
+
+    /**
+     * Returns the Contact this GroupNotification was produced by
+     * @returns {Promise<Contact>}
+     */
+    getContact() {
+        return this.client.getContactById(this.author);
+    }
+
+    /**
+     * Returns the Contacts affected by this GroupNotification.
+     * @returns {Promise<Array<Contact>>}
+     */
+    async getRecipients() {
+        return await Promise.all(this.recipientIds.map(async m => await this.client.getContactById(m)));
+    }
+
+    /**
+     * Sends a message to the same chat this GroupNotification was produced in.
+     * 
+     * @param {string|MessageMedia|Location} content 
+     * @param {object} options
+     * @returns {Promise<Message>}
+     */
+    async reply(content, options={}) {
+        return this.client.sendMessage(this.chatId, content, options);
+    }
+    
+}
+
+module.exports = GroupNotification;