Thought works assignment without using any 3rd party npm modules.

thoughtWorksAssignment.js

const http  = require('http');
const fs = require('fs');
const path = require('path');
const https = require("https");
const querystring = require('querystring');
const td = new Date("2018-09-01")

const config = {
    "userId" : "HhjEtD0rD",
    "endpoints" : {
        "host" : "https://http-hunt.thoughtworks-labs.net",
        "challengeUri" : "/challenge",
        "inputUri" : "/challenge/input",
        "outputUri" : "/challenge/output"
    }
};


function requestResponseHandler(request, response){
    console.log(`Request came: ${request.url}`);
    const contentType = getContentType(request.url);
    
    if(request.url === '/'){
        sendFileResponse('index.html', 'text/html', response)
    }else if(request.url === '/challenge'){
        const url = config.endpoints.host+config.endpoints.challengeUri;
        https.get(url, {headers: {
            'userId': config.userId
        }}, res => {
            res.setEncoding("utf8");
            let body = "";
            res.on("data", data => {
                body += data;
            });
            res.on("end", () => {
                sendResponse(body, contentType, response)
            });
        });
    }else if(request.url === '/challenge/input'){
        const url = config.endpoints.host+config.endpoints.inputUri;
        https.get(url, {headers: {
            'userId': config.userId
        }}, res => {
            res.setEncoding("utf8");
            let body = "";
            res.on("data", data => {
                body += data;
            });
            res.on("end", () => {
                sendResponse(body, contentType, response)
            });
        });
    }else if(request.url === '/challenge/start'){

        const inputUrl = config.endpoints.host+config.endpoints.inputUri;
        const outputUrl = config.endpoints.host+config.endpoints.outputUri;
        
        https.get(inputUrl, {headers: {
            'userId': config.userId,
            'Content-Type': contentType
        }}, res => {
            res.setEncoding("utf8");
            let body = "";
            res.on("data", data => {
                body += data;
            });
            res.on("end", () => {
                
                let data = JSON.parse(body);
                let catMap = {};
                let totalValue = 0;

                for (var i=0; i<data.length; i++){
                    var sd = new Date(data[i].startDate)

                    if (data[i].endDate != null){
                        var ed = new Date(data[i].endDate)
                        if (td - sd >= 0 && ed - td >= 0){
                            if(catMap[data[i].category]){
                                catMap[data[i].category]++;
                            }else {
                                catMap[data[i].category] = 1;
                            }

                            totalValue += data[i].price 
                        }
                    }else if (td - sd >= 0 && data[i].endDate == null) {
                        if(catMap[data[i].category]){
                            catMap[data[i].category]++;
                        }else {
                            catMap[data[i].category] = 1;
                        }
                        totalValue += data[i].price 
                    }
                }
                
                
                let input = JSON.stringify({"totalValue":totalValue});

                let req = https.request(outputUrl, {
                    method: 'POST', 
                    headers: {
                        'userId': config.userId,
                        'Content-Type': contentType,
                        'Content-Length': input.length
                    }}, res => {
                        res.setEncoding("utf8");
                        let body = "";
                        res.on("data", data => {
                            body += data;
                        });
                        res.on("end", () => {
                            sendResponse(body, contentType, response)
                        });
                    });
                    
                    req.on('error', (e) => {
                        console.error(e);
                        sendResponse(JSON.stringify(e), contentType, response)
                    });
                    
                    req.write(input);
                    req.end();
                });
            });
        }
    }
    
    function sendFileResponse(url, contentType, res){
        let file = path.join(__dirname, url);
        fs.readFile(file, (err, content) => {
            if(err){
                res.writeHead(404);
                res.write(`File '${file}' Not Found!`);
                res.end();
                console.log("Response: 404 ${file}, err");
            }else{
                res.writeHead(200, {'Content-Type': contentType});
                res.write(content);
                res.end();
                console.log(`Response: 200 ${file}`);
            }
        })
    }
    
    
    function sendResponse(content, contentType, res){
        res.writeHead(200, {'Content-Type': contentType});
        res.write(content);
        res.end();
        console.log(`Response: 200`);
    }
    
    function getContentType(url){
        switch (path.extname(url)) {
            case '.html':
            return 'text/html';
            case '.css':
            return 'text/css';
            case '.js':
            return 'text/javascript';
            case '.json':
            return 'application/json';
            default:
            return 'application/json';
        }
    }
    
    const httpServer = http.createServer(requestResponseHandler);
    
    httpServer.listen(8000, () => {
        console.log('Node.JS static file server is listening on port 8000')
    })