import type { User } from "$lib/server/database";

import Crypto from "node:crypto";

interface UserSession {
	user: User;
	last_active: Date;
}

export interface TokenInfo {
	user_id: number;
	creation_time: Date;
	expiry_time: Date;
}

class LoginError extends Error {
	constructor(message: string) {
		super(message);
	}
}

class UserLoginError extends LoginError {
	user_id: number;

	constructor(user_id: number, message: string) {
		super(message);
		this.user_id = user_id;
	}
}


const TOKEN_LENGTH = 256;

const active_users = new Map<number, UserSession>();
const active_session_tokens = new Map<string, TokenInfo>();


function issue_access_token_for_user(user: User, expiry_date: Date): string {

	let user_session = active_users.get(user.id);
	if (user_session === undefined) {
		user_session = {
			user: user,
			last_active: new Date()
		} as UserSession;

		active_users.set(user.id, user_session);
	}

	/* | Token (256) | Expiry date as getTime | */
	const token_info: TokenInfo = {
		user_id: user.id,
		creation_time: new Date(),
		expiry_time:  expiry_date
	}
	const session_token = Buffer.concat(
		[ Crypto.randomBytes(TOKEN_LENGTH / 4 * 3), 
		  Buffer.from(token_info.creation_time.getTime().toFixed(0)) ]
		).toString("base64");

	if (active_session_tokens.has(session_token)) {
		throw new UserLoginError(user.id, "Tried issuing a duplicate session token.");
	}

	active_session_tokens.set(session_token, token_info);

	return session_token;
}

function get_user_by_access_token(token: string): User | null {

	const token_info = active_session_tokens.get(token);

	if (token_info === undefined || token_info.expiry_time.getTime() < Date.now()) {
		return null;
	}

	const user = active_users.get(token_info.user_id);

	if (user === undefined) {
		return null;
	}

	user.last_active = new Date();
	
	return user.user;
}

function logout_user_session(token: string): boolean {
	const token_info = active_session_tokens.get(token);

	if (!token_info) {
		console.log("this shouldn't happen.");
		return false;
	}

	token_info.expiry_time = new Date(0);

	return true;
}

async function __clean_session_store() {
	console.log("cleaning sessions");

	const active_users_session = new Set<number>();
	active_session_tokens.forEach((token_info, token, token_map) => {
		if (token_info.expiry_time.getTime() < Date.now()) {
			token_map.delete(token);
		} else {
			active_users_session.add(token_info.user_id);
		}
	});
	
	active_users.forEach((user_info, user_id, user_map) => {
		if (user_info.last_active.getTime() + 15*60*1000 < Date.now() && !active_users.has(user_id)) {
			user_map.delete(user_id)
		}
	});
}

export default class SessionStore {
	static issue_access_token_for_user = issue_access_token_for_user;
	static get_user_by_access_token = get_user_by_access_token;
	static logout_user_session = logout_user_session;
}

setInterval(__clean_session_store, 15*60*1000);