createMail.js

const {google} = require('googleapis');
const mailComposer = require('nodemailer/lib/mail-composer');
	
class CreateMail {

  	constructor(auth, to, sub, body, task, attachmentSrc) {
        this.me = 'receiver@test.com';
        this.task = task;
        this.auth = auth;
        this.to = to;
        this.sub = sub;
        this.body = body;
        this.gmail = google.gmail({version: 'v1', auth});
        this.attachment = attachmentSrc;	
	}

	// Creates the mail body and encodes it to base64 format.
	makeBody() {
		let mail = new mailComposer({
			to: this.to,
			html: this.body, // can be changed to play 'text: this.body'
			subject: this.sub,
			textEncoding: "base64"
		});
		
		//Compiles and encodes the mail.
		mail.compile().build((err, msg) => {
			if (err){
				return console.log('Error compiling email ' + error);
			} 
		
			const encodedMessage = Buffer.from(msg)
			  .toString('base64')
			  .replace(/\+/g, '-')
			  .replace(/\//g, '_')
			  .replace(/=+$/, '');
			
			if(this.task === 'mail'){
				this.sendMail(encodedMessage);
			}
			else{
				this.saveDraft(encodedMessage);
			}
		});
	}

	// Send the message to specified receiver.
	sendMail(encodedMessage) {
		this.gmail.users.messages.send({
			userId: this.me,
			resource: {
				raw: encodedMessage,
			}
		}, (err, result) => {
			if(err){
				return console.log('NODEMAILER - The API returned an error: ' + err);
			}
				
			console.log("NODEMAILER - Sending email reply from server:", result.data);
		});
	}

	// Saves the draft.
    saveDraft(encodedMessage) {
		this.gmail.users.drafts.create({
			'userId': this.me,
			'resource': {
			  'message': {
				'raw': encodedMessage
			  }
			}
		})
		.then(res => console.log("Draft created : ", res.data))
    }

	// Deletes the draft.
    deleteDraft(id) {
		this.attachment.gmail.users.drafts.delete({
			id: id,
			userId: this.me 
		});
    }

	//Lists all drafts.
    listAllDrafts() {
        this.gmail.users.drafts.list({
            userId: this.me
        }, (err, res) => {
        	if(err) {
            	console.log(err);
        	}
			else {
				console.log(res.data);
			}
    	});
    }
}

module.exports = CreateMail;