const { MongoClient } = require("mongodb");
const express = require('express');
const minio = require('minio');

  /*============== VARIABLE DECLARATION ==============*/
// Mongo set-up variables
const mongoCollection = process.env.MONGO_COLLECTION || 'eventlog';
const mongoUri = process.env.MONGO_URI || 'mongodb://127.0.0.1:27017/default?replicaSet=rs0';

// Minio set-up variables
const minioURI = new URL(process.env.MINIO_URI || 'http://kspace-mugshot:2mSI6HdbJ8@127.0.0.1:9000/kspace-mugshot');
const minioBucket = minioURI.pathname.substring(1);

// Stream set-up variables
let changeStream;
const options = { fullDocument: "updateLookup" };
const pipeline = [];
const PORT = process.env.PORT || 3002;

// Create Mongo client
const mongoClient = new MongoClient(mongoUri);


/*============== CODE ==============*/
async function run() {

  console.log('server.js has been launched');
  const app = express();

  // Configuring mongoDB connection
  await mongoClient.connect();
  const collection = mongoClient.db().collection(mongoCollection);

  // Opening event listener on the database
  changeStream = collection.watch(pipeline, options);
  console.log("Started watching changes in database");

  app.get('/events', async function (request, response) {
    let eventArray = [];

    let minioClient = new minio.Client({
      endPoint: minioURI.hostname,
      port: parseInt(minioURI.port) || (minioURI.protocol == 'https' ? 443 : 80),
      useSSL: minioURI.protocol == 'https',
      accessKey: minioURI.username,
      secretKey: minioURI.password
    });

    // notifies GET requests
    console.log('/events was requested');

    // Setting the header to event-stream for Server Sent Events (Eventsource)
    const header = { 'Content-Type': 'text/event-stream', 'Connection': 'keep-alive' };
    response.writeHead(200, "OK", header);
    response.write('Connection established \n\n');

    // Triggers callback on every change in collection set up
    changeStream.on("change", data => {

      // Retrieves modified document on the db and stores it
      let document = JSON.stringify(data.fullDocument);
      eventArray = [document, ...eventArray];

      // Fetch screenshot if there is one
      if (data.fullDocument.screenshot_count) {
        minioClient.presignedUrl('GET', minioBucket, `${data.fullDocument.camera}/${data.fullDocument._id}/1.jpg`, 60 * 60, (err, presignedUrl) => {
          if (err) { return console.log(err) };
          const realURL = JSON.stringify({ picUrl: presignedUrl });
          eventArray = [realURL, ...eventArray];
        })
      };

      // sends updated array
      response.write(`data: [${[...eventArray]}]\n\n`);
    });
  });

  app.listen(PORT);
  console.log(`Server listening at 127.0.0.1:${PORT}`);
}

run().catch(console.dir);