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

  /*============== VARIABLE DECLARATION ==============*/
// Mongo set-up variables
const mongoEndpoint = process.env.ME_CONFIG_MONGODB_SERVER;
const mongoPort = parseInt(process.env.ME_CONFIG_MONGODB_PORT);
const mongoDatabase = process.env.ME_CONFIG_MONGODB_DB;
const mongoCollection = process.env.ME_CONFIG_MONGODB_COLLECTION;

// Minio set-up variables
const minioEndpoint = process.env.MINIO_ENDPOINT;
const minioBucket = process.env.MINIO_BUCKET;
const minioPort = parseInt(process.env.MINIO_SERVING_PORT);
const minioKey = process.env.MINIO_ACCESS_KEY;
const minioSecret = process.env.MINIO_SECRET_KEY;

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

// Create Mongo client
const MONGO_URI = `mongodb://${mongoEndpoint}:${mongoPort}`;
const mongoClient = new MongoClient(MONGO_URI);


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

  console.log('server.js has been launched')

  const app = express();

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

  // Notify connection
  console.log(`Connection established with Mongo Database at ${MONGO_URI}`);

  // 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: minioEndpoint,
      port: minioPort,
      useSSL: false,
      accessKey: minioKey,
      secretKey: minioSecret
    });

    // 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);