borgwarehouse/pages/api/account/updateUsername.js

//Lib
import { promises as fs } from 'fs';
import path from 'path';
import { authOptions } from '../auth/[...nextauth]';
import { getServerSession } from 'next-auth/next';

export default async function handler(req, res) {
    if (req.method == 'PUT') {
        //Verify that the user is logged in.
        const session = await getServerSession(req, res, authOptions);
        if (!session) {
            res.status(401).json({ message: 'You must be logged in.' });
            return;
        }

        //The data we expect to receive
        let { username } = req.body;

        //Read the users file
        //Find the absolute path of the json directory
        const jsonDirectory = path.join(process.cwd(), '/config');
        let usersList = await fs.readFile(
            jsonDirectory + '/users.json',
            'utf8'
        );
        //Parse the usersList
        usersList = JSON.parse(usersList);

        //1 : We check that we receive data.
        if (!username) {
            //If a variable is empty.
            res.status(400).json({ message: 'A field is missing.' });
            return;
        }

        //2 : control the data
        const usernameRegex = new RegExp(/^[a-z]{5,15}$/);
        if (!usernameRegex.test(username)) {
            res.status(400).json({
                message: 'Only a-z characters are allowed (5 to 15 char.)',
            });
            return;
        }

        //3 : Verify that the user of the session exists
        const userIndex = usersList
            .map((user) => user.username)
            .indexOf(session.user.name);
        if (userIndex === -1) {
            res.status(400).json({
                message:
                    'User is incorrect. Please, logout to update your session.',
            });
            return;
        }

        //4 : Change the username
        try {
            //Modify the username for the user
            let newUsersList = usersList.map((user) =>
                user.username == session.user.name
                    ? { ...user, username: username }
                    : user
            );
            //Stringify the new users list
            newUsersList = JSON.stringify(newUsersList);
            //Write the new JSON
            await fs.writeFile(
                jsonDirectory + '/users.json',
                newUsersList,
                (err) => {
                    if (err) console.log(err);
                }
            );
            res.status(200).json({ message: 'Successful API send' });
        } catch (error) {
            //Log for backend
            console.log(error);
            //Log for frontend
            if (error.code == 'ENOENT') {
                res.status(500).json({
                    status: 500,
                    message: 'No such file or directory',
                });
            } else {
                res.status(500).json({
                    status: 500,
                    message: 'API error, contact the administrator',
                });
            }
            return;
        }
    } else {
        res.status(405).json({ message: 'Bad request on API' });
    }
}