server.js

    require("dotenv").config();
    const multer = require("multer");
    const mongoose = require("mongoose");
    const bcrypt = require("bcrypt");
    const File = require("./models/file");
    const express=  require("express");
    const req = require("express/lib/request");
    const app = express();
    app.use(express.urlencoded({ extended: true}));

    const upload = multer({dest: "uploads"});

    mongoose.connect(process.env.DATABASE_URL);

    app.set("view engine", "ejs");

    app.get("/",(req,res) => {
        res.render("index")
    })

    app.post("/upload",upload.single("file"), async (req,res) => {
        const fileData = {
            path: req.file.path,
            originalName: req.file.originalname
        }
        if(req.body.password != null && req.body.password !== ""){
            fileData.password = await bcrypt.hash(req.body.password, 10);
        }
        const file = await File.create(fileData);
        
        res.render("index",{fileLink: `${req.headers.origin}/file/${file.id}`})
    })

    app.get("/file/:id",handleDownload);
    app.post("/file/:id",handleDownload);

    async function handleDownload(req,res) {
        const file = await File.findById(req.params.id);

        if(file.password != null) {
            if(req.body.password == null) {
                res.render("password");
                return;
            }
        }
        //if compares whether inputted password and hashed password is matching
        if(!(await bcrypt.compare(req.body.password, file.password))) {
            res.render("password",{error: true});
            return
        }

        await file.save();

        res.download(file.path,file.originalName);
    }

    app.listen(process.env.PORT);