index.js

const Store = require('./libs/store.js');

module.exports = (opts = {}) => {
    const { key = 'koa:sess', store = new Store() } = opts;

    return async (ctx, next) => {
        let id = ctx.cookies.get(key, opts);
        let need_refresh = false;

        if (!id) {
            ctx.session = {};
        } else {
            ctx.session = await store.get(id, ctx);

            // reassigning session ID if current is not found
            if (ctx.session == null) {
                id = await store.getID(24);
                need_refresh = true;
            }

            // check session must be a no-null object
            if (typeof ctx.session !== 'object' || ctx.session == null) {
                ctx.session = {};
            }
        }

        const old = JSON.stringify(ctx.session);

        // add refresh function
        ctx.session.refresh = () => {need_refresh = true}

        await next();

        // remove refresh function
        if (ctx.session && 'refresh' in ctx.session) {
            delete ctx.session.refresh
        }

        const sess = JSON.stringify(ctx.session);

        // if not changed
        if (!need_refresh && old == sess) return;

        // if is an empty object
        if (sess == '{}') {
            ctx.session = null;
        }

        // need clear old session
        if (id && !ctx.session) {
            await store.destroy(id, ctx);
            ctx.cookies.set(key, null);
            return;
        }

        // set/update session
        const sid = await store.set(ctx.session, Object.assign({}, opts, {sid: id}), ctx);
        if (!id || id !== sid || need_refresh) ctx.cookies.set(key, sid, opts);
    }
}

// Reeexport Store to not use reference to internal files
module.exports.Store = Store;