Button webhook

button.js

module['exports'] = function counter (hook) {
  var expectedEvent = "magicButton";
  function authorized() {
    return hook.params.event === expectedEvent;
  }

  function increment(key, callback) {
    var datastore = hook.datastore;
    datastore.get(key, function (err, counter) {
      if(err) {
        callback(err);
      } else {
        counter = (counter || 0) + 1;
        datastore.set(key, counter, function (err) {
          if(err) {
            callback(err);
          } else {
            callback(null, counter);
          }
        });
      }
    });
  }

  function outputResult(err, result) {
    var data;
    if(err) {
      data = { error: err.message };
    } else {
      data = { result: result };
    }
    hook.res.end(JSON.stringify(data, true, 2));
  }

  // check that the event name in the hook matches the expected name
  if(!authorized()) {
    outputResult({ message: 'Unexpected event'});
    return;
  }
  
  // increment a key in the cloud datastore
  increment('counter', outputResult);
};