feat: add data generation logic and history file class

backend/classes/HistoryFile.js

@@ -0,0 +1,82 @@
+import path from 'path';
+import fs from 'fs';
+
+export default class HistoryFile {
+  constructor(fileName) {
+    this.path = path.join(process.cwd(), fileName);
+    this.history = [];
+    this.load();
+  }
+
+  /**
+   * Writes history to file
+   * @returns {boolean} true if successful, false otherwise
+   */
+  writeToFile() {
+    try {
+      fs.writeFileSync(this.path, JSON.stringify(this.history));
+      return true;
+    } catch (err) {
+      console.error(`Failed to write data to history file: ${err.message}`);
+      return false;
+    }
+  }
+
+  /**
+   * Reads history file, and returns it as JSON
+   * @returns {array}
+   */
+  readFromFile() {
+    try {
+      const raw = fs.readFileSync(this.path, 'utf-8');
+      return JSON.parse(raw);
+    } catch (err) {
+      console.warn(`Failed at reading history, using empty history: ${err.message}`);
+      return [];
+    }
+  }
+
+  /**
+   * Loads history file, if it exists
+   * If not, creates empty file
+   */
+  load() {
+    if (fs.existsSync(this.path)) {
+      // Read file, and update this.history
+      const data = this.readFromFile();
+      this.history = data;
+    } else {
+      // Create empty history file, if doesn't exist
+      this.writeToFile();
+    }
+  }
+
+  /**
+   * Saves most recent 15 entries to history file
+   */
+  save() {
+    // If there's more than 15 entries, we need to save only most recent 15 ones
+    if (this.history.length > 15) {
+      this.history = this.history.slice(this.history.length - 15);
+    }
+
+    // Write to history file
+    this.writeToFile();
+  }
+
+  /**
+   * Appends new entry to history file
+   * Returns most recent entry
+   * @param {number} number
+   * @returns {object}
+   */
+  append(number) {
+    const data = { number, timestamp: Date.now() };
+    // Push new entry to history
+    this.history.push(data);
+    // Save history file, and keep only 15 entries
+    this.save();
+    // Return most recent entry
+    return data;
+  }
+}

backend/data.json

@@ -0,0 +1 @@
+[]

backend/index.js

@@ -1,8 +1,15 @@
-const WebSocket = require('ws');
+import { WebSocketServer } from 'ws';
+import HistoryFile from './classes/HistoryFile.js';
 
-const wss = new WebSocket.Server({ port: 8080 });
+// Define WebSocket server
+const wss = new WebSocketServer({ port: 8080 });
+// Define History file class
+// For managing data state beyond restart
+const history = new HistoryFile('data.json');
 
 wss.on('connection', (ws) => {
+  // On successful connection, we send history data to the client
+  // After that, we procceed sending data update every 10 seconds
   console.log('Client connected');
 
   ws.on('message', (message) => {

backend/package.json

@@ -1,6 +1,7 @@
 {
   "name": "backend",
   "version": "1.0.0",
+  "type": "module",
   "main": "index.js",
   "scripts": {
     "dev": "nodemon index.js",

backend/utils/random.js

@@ -0,0 +1,33 @@
+/**
+ * Generates a random integer between min and max (inclusive)
+ * @param {number} min
+ * @param {number} max
+ * @returns {number}
+ */
+export function randomInt(min, max) {
+  return Math.floor(Math.random() * (max - min + 1)) + min;
+}
+
+/**
+ * Generates a random number based on previous number, and provided range
+ * Also taking into account global provided min and max values
+ * @param {number} previousNumber
+ * @param {number} range (0 - 1)
+ * @param {number} min
+ * @param {number} max
+ * @returns {number}
+ */
+export function randomInRange(previousNumber, range, min, max) {
+  // Decides on min max range for the next number
+  // based on range, and previous number
+  const integerRange = previousNumber * range; // +- 0.3 -> 30%
+  // Calculate min, and check if its less that global min (eg. 0)
+  let newMin = previousNumber - integerRange;
+  if (newMin < min) newMin = min; // sets to global min, for example 0
+
+  // calculate max, and check if number is above the global set max (eg. 100)
+  let newMax = previousNumber + integerRange;
+  if (newMax > max) newMax = max; // sets to global max, for example 100
+
+  return Math.floor(randomInt(newMin, newMax));
+}