var cookieparser = require('cookie-parser');
var debug = require('debug')('express-socket.io-session');
var hash = require('./lib/hash');
// The express session object will be set
// in socket.handskake.session.

/**
 * Returns a middleware function that acts on socket.handshake
 *
 * @param {Function} expressSessionMiddleware - An express-session middleware function to reuse with io.use
 * @param {Function} cookieParserMiddleware - An express-session middleware function to reuse with express-session
 * @param {Object} options - An object with some options for overriding default behaviour.
 *   - {Boolean} autSave - If true, the session variables will be saved asyncrhonously to express-session driver
 *                         by wrapping the method socket.on
 */
module.exports = function(
	expressSessionMiddleware,
	cookieParserMiddleware,
	options
) {
	var socketIoSharedSessionMiddleware;

	// Accept options as second argument if only 2 parameters passed
	if (arguments.length == 2 && typeof cookieParserMiddleware === 'object') {
		options = cookieParserMiddleware;
		cookieParserMiddleware = undefined;
	}

	if (typeof cookieParserMiddleware === 'undefined') {
		debug(
			'No cookie-parser instance passed as argument. Creating a cookie-parser ' +
				'instance with default values'
		);
		cookieParserMiddleware = cookieparser();
	}
	options = options || {};
	var saveUninitializedSession = options.saveUninitialized;
	debug('Creating socket.io middleware');

	socketIoSharedSessionMiddleware = function(socket, next) {
		var req = socket.handshake;
		var res = {
			end: function() {}
		};
		// originalHash, savedHash, originalId, cookieId
		// are variables present for replicating express-session autoSaving behaviour
		var originalHash, savedHash;
		var originalId;
		var cookieId;
		var _onevent = socket.onevent;
		// Override socket.on if autoSave = true;
		if (options.autoSave === true) {
			debug(
				'Using autoSave feature. express-session middleware will be called on every event received'
			);
			socket.onevent = function() {
				debug(
					'Executing socket.onevent monkeypatched by express-socket.io-session'
				);
				var _args = arguments;
				originalHash = savedHash = hash(req.session);
				cookieId = req.sessionID;
				originalId = req.sessionID;
				_onevent.apply(socket, _args);
				process.nextTick(function() {
					if (shouldSave(req)) {
						req.session.touch();
						req.session.save();
					}
				});
			};
		}
		//Parse session cookie
		cookieParserMiddleware(req, res, function(err) {
			if (err) {
				debug('cookieParser errored');
				return next(err);
			}
			expressSessionMiddleware(req, res, function(req, res) {
				next();
			});
		});
		/*
		 * These functions hash, isModified, isSaved, shouldSave
		 * and shouldDestroy are canibalized from express-session
		 * in order to this module being able to comply with the autoSave options.
		 */

		// check if session has been modified
		function isModified(sess) {
			return originalId !== sess.id || originalHash !== hash(sess);
		}

		// check if session has been saved
		function isSaved(sess) {
			return originalId === sess.id && savedHash === hash(sess);
		}

		// determine if session should be saved to store
		function shouldSave(req) {
			// cannot set cookie without a session ID
			if (typeof req.sessionID !== 'string') {
				debug(
					'session ignored because of bogus req.sessionID %o',
					req.sessionID
				);
				return false;
			}

			return !saveUninitializedSession && cookieId !== req.sessionID
				? isModified(req.session)
				: !isSaved(req.session);
		}
	};

	return socketIoSharedSessionMiddleware;
};