exports.addUser = async function addUser(name, email, password) {
  const client = await db.loadUsersCollection();
  const validatedName = validateAuth.validateName(name);
  const validatedEmail = validateAuth.validateEmail(email);
  const validatedPassword = validateAuth.validatePassword(password);
  const session = client.startSession();
  session.startTransaction();
  const userCollection = client.db('recruitment').collection('recruitment');
  try{
    const opts = { session, returnOriginal: false, new: true,
      writeConcern: { w: "majority", wtimeout: 5000 } };
    const result = await userCollection.insertOne({ name: validatedName, email: validatedEmail, password: validatedPassword, role: 'applicant' }, opts);
    await session.commitTransaction().then((data) => console.log("Success"));
    session.endSession();
    return result.ops[0]._id;
  }catch(error){
    await session.abortTransaction().then((data) => {
      console.log("Transaction error: " + data);
    }).catch((error) => {
      console.log("Transaction error: " + error);
    });
    console.log("fail");
    session.endSession();
    if(error.code == 11000){
      console.log("Duplicate user: " + error);
    } else {
      console.log("Error: "+ error);
    }
  }
}

##DB##
exports.loadUsersCollection = async function loadUsersCollection() {
  const fn = async function () {
    const client = await mongodb.MongoClient.connect(' mongodb://IV1201:IV1201@recruitment-shard-00-00-gxbqo.mongodb.net:27017,recruitment-shard-00-01-gxbqo.mongodb.net:27017,recruitment-shard-00-02-gxbqo.mongodb.net:27017/test?ssl=true&replicaSet=recruitment-shard-0&authSource=admin&retryWrites=true', {
      useNewUrlParser: true,
      replicaSet: 'recruitment-shard-0' ,
      readConcern: { level: "majority" }
    });
    return client;
  }
  return await retry(fn, MAX_RETRIES, MONGO_NETWORK_ERROR, ERROR_MESSAGE);
}