import { MongoClient } from 'mongodb';

let mongo;
let db;
let functionCollection = {};

export function init(connectionString) {
  try {
    mongo = new MongoClient(connectionString);
    db = mongo.db();
    return mongo.connect().then(() => Promise.resolve(functionCollection));
  } catch (e) {
    return Promise.reject(e);
  }
}

functionCollection.subscribe = function subscribe (collectionName, filter) {
  let collection = db.collection(collectionName);
  return collection
    .find(filter, {})
    .toArray();
}

functionCollection.persist = function persist (collectionName, filter, fieldName, value) {
  let collection = db.collection(collectionName);
  let newValue = { $set: {} };
  newValue.$set[fieldName + ".modifiedAt"] = Date.now();
  newValue.$set[fieldName + ".modifiedBy"] = "anonymous";
  newValue.$set[fieldName + ".transientValue"] = value;

  return collection.updateMany(filter, newValue, { upsert: true });
}

functionCollection.publish = function publish (b) {
  console.log('publish')
}

functionCollection.close = function close () {
  return mongo.close();
}

functionCollection.purge = function purge (collectionNames) {
  let promises = [];

  for (let i = 0; i < collectionNames.length; i++) {
    const collection = db.collection(collectionNames[i]);
    promises.push(collection.drop());
  }
  return Promise.all(promises);
}