backend/utils/sendEmail.js

const { google } = require('googleapis');
const { oAuth2Client } = require('../config/googleOAuth');

const sendEmail = async (recipient, subject, htmlContent, attachment = null, attachmentName = '') => {
    try {
        const gmail = google.gmail({ version: 'v1', auth: oAuth2Client });

        // Unique boundary string
        const boundary = "----=_NextPart_001";
        let rawEmail = [
            `To: ${recipient}`,
            `Subject: ${subject}`,
            `MIME-Version: 1.0`,
        ];

        if (attachment && attachment.buffer) {
            const encodedAttachment = Buffer.isBuffer(attachment.buffer) 
                ? attachment.buffer.toString('base64')
                : Buffer.from(attachment.buffer).toString('base64');
                
            const formattedAttachment = encodedAttachment.match(/.{1,76}/g).join("\n");

            rawEmail.push(
                `Content-Type: multipart/mixed; boundary="${boundary}"`,
                "",
                `--${boundary}`,
                "Content-Type: text/html; charset=UTF-8",
                "",
                htmlContent,
                "",
                `--${boundary}`,
                `Content-Type: ${attachment.mimetype}; name="${attachmentName}"`,
                `Content-Disposition: attachment; filename="${attachmentName}"`,
                "Content-Transfer-Encoding: base64",
                "",
                formattedAttachment,
                "",
                `--${boundary}--`
            );
        } else {
            rawEmail.push("Content-Type: text/html; charset=UTF-8", "", htmlContent);
        }

        const encodedEmail = Buffer.from(rawEmail.join("\r\n"))
            .toString("base64")
            .replace(/\+/g, "-")
            .replace(/\//g, "_")
            .replace(/=+$/, ""); // Remove padding `=` characters

        await gmail.users.messages.send({
            userId: "me",
            requestBody: { raw: encodedEmail },
        });

        console.log(`✅ Email sent successfully to ${recipient}`);
    } catch (error) {
        console.log(`❌ Failed to send email to ${recipient}:`, error);
        throw error;
    }
};

module.exports = { sendEmail };