Creating custom email template for nodemailer in firebase cloud functions?

Can anyone weigh in on how to create a dynamic email template to use with firebase cloud functions? Basically, I have created a function that will be invoked on hitting a /sendEmail endpoint. It holds data in req body, I am retrieving that data and sending it via email using nodemailer.

I am getting a path error if I want to use handlebars to create the template. The error is that no such file or directory exists. I tried two different paths, the first one under functions/src/email/template.html and the second one is at the same level as the functions folder.

sendMail Function

const transporter = nodemailer.createTransport({
            service: 'gmail',
            auth: {
                user: 'example@gmail.com',
                pass: 'dqsdsqdqsdsq'
            }
        });
        const filePath = path.join(__dirname, 'functions/src/Email/template.html');
        const source = fs.readFileSync(filePath, 'utf-8').toString();
        const template = handlebars.compile(source);
        const replacements = {
            schoolName: schoolName,
            className: className,
            date: new Date(),
            responsibiltyId: responsibiltyId,
            memorialId: memorialId
        };
        const htmlToSend = template(replacements);
        const mailOptions = {
            from: 'ADMIN <example@gmail.com>', // Something like: Jane Doe <janedoe@gmail.com>
            to: destination,
            subject: `Session Codes for Class ${className} | ${schoolName} | ${new Date()}`, // email subject
            html: htmlToSend
        };
        return transporter.sendMail(mailOptions, (error, info) => {
            if (error) {
                return handleError(res, error);
            }
            return res.status(200).json({
                timestamp: new Date(),
                status: 200,
                message: `Email has been sent successfuly to ${destination}`,
                extra: ''
            });
        });