var db = require('redis').createClient();

 exports.book = function(req, res) {
  stats(function(free) {
   if (free > 0) {
     var code = "XCP"+Math.floor(Math.random()*1000);
     db.sadd("open", code);
   }
   show(res, 'book', (free>0)?0:1, code);
  });
 };

 exports.checkin = function(req, res) {
   var code = req.body.code;
  db.srem("open", code, function(err, rp) {
   if (rp > 0) {
     db.sadd("checkedIn", code);
   }
   show(res, 'checkin', (rp>0)?0:1, code);
  });
 };

 exports.checkout = function(req, res) {
   var code = req.body.code; // closure
   db.srem("checkedIn", code, function(err, rp) {
   show(res, 'checkout', (rp>0)?0:1, code);
  });
 };