Add a star to a collection given a user

collectionFactory.js

  var addStar = function(data) {
    return $http({
      method: 'POST',
      url: '/api/collection/addStar',
      data: data
    }).then(function(response) {
      return response.data;
    });
  };

mongo.js

// If the provided user has not already starred this
// collection, adds a star to the collection
//
// Expects data to have _id and user properties:
//  {
//    _id: the collection to add to
//    user: [
//      {
//        provider: String,
//        id: String,
//        fullName: String,
//        givenName: String
//      }
//    ]
//  }
// Returns a promise that resolves to the updated collections
mongo.addStar = function(data) {
  // Stringify the user
  // This should be unique to every user
  var userString = data.user.provider + data.user.id;
  return Collection.findByIdAndUpdate(data._id, {
    $addToSet: { userStars: userString }
  }).exec()
  .then(function(collection) {
    var update = {};
    update._id = collection._id;
    update.stars = collection.userStars.length;
    return mongo.update(update);
  });
};

server.js

// add a star to a collection
// this will check if the given user has already stared the collection
// and if not, add the user to userStars and increment stars.
// responds with the collection, updated or not
app.post('/api/collection/addStar', function(req, res) {
  mongo.addStar(req.body).then(function(collection) {
    res.end(JSON.stringify(collection));
  });
});