//
// Middleware to handle returning the expiry time for the session.
// This will allow clients to accurately manage session keep alive requests.
//
// In a similar manner to the swagger respone validator, we replace res.end()
// with our own function, so that we will be called at the end of the response
// tree.
// etc.
//
'use strict';
var debug = require('debug')('webconsole-api:cors-middleware');
var sessionTimeout = require(global.pathPrefix + 'utils.js').sessionTimeout;

module.exports = middleware;

/**
 * Define a middleware function to add the session expiry to responses, so that
 * clients can manage the session keepalive effectively.
 *
 * @param {Object} req      - the express request
 * @param {Object} res      - the express response
 */
function reportSessionExpiry(req, res) {
    const session = req.session;
    if (session && session.lastModified) {
        let expiry = new Date(session.lastModified);
        expiry.setMinutes(expiry.getMinutes() + sessionTimeout);

        const now = new Date();

        const secondsLeft = Math.floor((expiry.getTime() - now.getTime()) / 1000);

        res.setHeader('X-BRIDGE-SESSION-EXPIRY', secondsLeft);
    }
}

/**
 * Define a middleware function to add the session expiry to responses, so that
 * clients can manage the session keepalive effectively.
 * This uses a replacement for the original res.end so that we get called at
 * the end as part of the response.
 *
 * @param {Object} req      - the express request
 * @param {Object} res      - the express response
 * @param {function} next   - the callback for the next middleware in the chain
 *
 * @returns {any}           - the result of the next() callback
 */
function middleware(req, res, next) {
    // Store the original end so we can restore it later
    var originalEnd = res.end;

    // Replace the end with our own function
    res.end = function(data, encoding) {
        //
        // Put the real end back
        //
        res.end = originalEnd;

        //
        // Add our header
        //
        reportSessionExpiry(req, res);

        //
        // Call the original end function to continue
        //
        res.end(data, encoding);
    };

    //
    // Call the next item on the stack
    //
    return next();
}