Simple in-memory session handler

session.js

/* eslint-env es6 */

'use strict';

const EventEmitter = require('events');
const crypto = require('crypto');

class Session extends EventEmitter {
    constructor() {
        super();

        this.timer = false;
        this.sessions = new Map();
        this.ttl = [];
    }

    create(id, data, ttl) {
        id = id || crypto.randomBytes(10).toString('hex');
        ttl = Number(ttl) || false;

        let exists = this.sessions.has(id);

        this.sessions.set(id, {
            id,
            data,
            ttl
        });

        if (ttl) {
            this.updateTTL(id, ttl);
        }

        this.emit(exists ? 'updated' : 'created', id, data);
        return id;
    }

    check(id) {
        if (!this.sessions.has(id)) {
            return false;
        }
        let data = this.sessions.get(id).data;
        let ttl = this.sessions.get(id).ttl;
        if (!ttl) {
            return data;
        }
        this.updateTTL(id, ttl);
        return data;
    }

    updateTTL(id, ttl) {
        let nextTimeout = Date.now() + ttl;
        let checks = 2;
        for (let i = this.ttl.length - 1; i >= 0; i--) {
            if (this.ttl[i].id === id) {
                // remove existing
                this.ttl.splice(i, 1);
                if (--checks === 0) {
                    break;
                }
            } else if (this.ttl[i].timeout < nextTimeout) {
                // add new
                this.ttl.splice(i + 1, 0, {
                    timeout: nextTimeout,
                    id
                });
                nextTimeout = false;
                if (--checks === 0) {
                    break;
                }
            }
        }
        if (nextTimeout) {
            // we have a new closest TTL
            clearTimeout(this.timer);
            this.ttl.unshift({
                timeout: nextTimeout,
                id
            });
            this.timer = setTimeout(() => this.checkTTL(), ttl + 10);
        }
    }

    checkTTL() {
        clearTimeout(this.timer);
        let remove = 0;
        let time = Date.now();
        for (let i = 0, len = this.ttl.length; i < len; i++) {
            if (this.ttl[i].timeout <= time) {
                this.emit('expired', this.ttl[i].id, this.sessions.get(this.ttl[i].id));
                this.sessions.delete(this.ttl[i].id);
                remove++;
            } else {
                break;
            }
        }
        if (remove) {
            this.ttl.splice(0, remove);
        }
        if (this.ttl.length) {
            this.timer = setTimeout(() => this.checkTTL(), this.ttl[0].timeout + 10);
        }
    }
}

module.exports = Session;