const crypto = require('crypto');

class SessionError extends Error {};

function SessionManager (){
	// default session length - you might want to
	// set this to something small during development
	const CookieMaxAgeMs = 600000;

	// keeping the session data inside a closure to keep them protected
	const sessions = {};

	// might be worth thinking about why we create these functions
	// as anonymous functions (per each instance) and not as prototype methods
	this.createSession = (response, username, maxAge = CookieMaxAgeMs) => {
		const token = crypto.randomBytes(15).toString('hex');
		const sessionObj = {
			username: username,
			created: new Date(),
			maxAge: maxAge
		};

		response.cookie("cpen322-session", token, { maxAge });
		sessions[token] = sessionObj;

		setTimeout(() => {
			delete sessions[token];
		}, maxAge);
	};

	this.deleteSession = (request) => {
		if(request.session && sessions[request.session]){
			delete sessions[request.session];
		}
		delete request.username;
		delete request.session;
	};

	this.middleware = (request, response, next) => {
		// AI used to generate regex rule to select cookie
		const tokenString = request.headers.cookie;
		const match = tokenString ? tokenString.match(/cpen322-session=([^;]*)/) : null;
		const token =  match ? match[1] : null;

		if(!token || !(sessions[token])) {
			next(new SessionError("Session not found"));
			return;
		}	

		request.username = sessions[token].username;
		request.session = token;
		next();
	};

	// this function is used by the test script.
	// you can use it if you want.
	this.getUsername = (token) => ((token in sessions) ? sessions[token].username : null);
};

// SessionError class is available to other modules as "SessionManager.Error"
SessionManager.Error = SessionError;

module.exports = SessionManager;