Calculations and Scripting

We will be using a simple fromula given below to calculate and trace the real-time balance changes. To execute this formula through code we will build two files (namely balance.js and index.js).

Current Balance = sum(all_balance_updates) + steam_balance_updates

Initialise and Installing Dependencies

To initiate the project run the following command.

npm init -y

Before going further make sure that all the dependencies are installed. The dependencies are listed below:

• axios
• dotenv
• express
• ws

Use the following command to install these dependencies.

npm install axios dotenv express ws

Create Balance Script

This script will calculate the summation of all the Balance Updates till yet, giving the current balance of a particular currency (Ethereum in this example) for the wallet. Follow the steps given below to build the script

1. Import the dependencies

const axios = require('axios');

require('dotenv').config()

NOTE: Make sure to create a .env file and create a AUTH_TOKEN variable to store your Bitquery Access Token. To know more about the access token click here.

2. Create a standard config for the getBalance function. This includes the API url we are trying to hit, access token to authenticate the request, and the request body as data.

let data = JSON.stringify({
    "query": "{\n  EVM(dataset: combined, network: eth) {\n    BalanceUpdates(\n      where: {BalanceUpdate: {Address: {is: \"\"}}, Currency: {SmartContract: {is: \"0x\"}}}\n    ) {\n      sum(of: BalanceUpdate_Amount)\n    }\n  }\n}\n",
    "variables": "{}"
 });

let config = {
   method: 'post',
   maxBodyLength: Infinity,
   url: 'https://streaming.bitquery.io/graphql',
   headers: { 
      'Content-Type': 'application/json', 
      'X-API-KEY': 'BQYuTITWanwYGz0YLGdcWSADO74o5RTX', 
      'Authorization': `Bearer ${process.env.AUTH_TOKEN}`
   },
   data : data
};

Please note that the data part is a standard case, but will be modified upon the user input.

3. Create the asynchronous getBalance function.

const getBalance = async (config) => {
    try {
        const response = await axios.request(config);
        // console.log(response.data.data.EVM.BalanceUpdates[0].sum)
        return response.data.data.EVM.BalanceUpdates[0].sum;        
    } catch (error) {
        return error;
    }

}

4. Export the requirements from the file.

module.exports = {getBalance, config};

Create Index Script

In this file we will write code to:

• Get Balance using the getBalance function from balance.js.
• Create an express server so that we can render a simple UI.
• Run a websoket connection to get real-time balance updates.

1. Import the requirements.

const express = require('express');
const path = require('path');
const { getBalance, config } = require('./balance.js');
require('dotenv').config();

2. Initiate the express server and declare the address variable.

const app = express();
app.use(express.static(path.join(__dirname)));
app.use(express.json());

let currentAddress = '';  // Default address if none provided

3. Creating the endpoint to handle address input from frontend.

app.post('/track-balance', (req, res) => {
    const { address } = req.body;
    if (!address) {
        return res.status(400).json({ success: false, message: 'Address required' });
    }
    currentAddress = address;
    res.json({ success: true });
});

4. Creating the endpoint to get the balance from getBalance function.

app.get('/get-balance', async (req, res) => {
    try {
        // Update the address in the config dynamically
        config.data = JSON.stringify({
            "query": `{\n  EVM(dataset: combined, network: eth) {\n    BalanceUpdates(\n      where: {BalanceUpdate: {Address: {is: \"${currentAddress}\"}}, Currency: {SmartContract: {is: \"0x\"}}}\n    ) {\n      sum(of: BalanceUpdate_Amount)\n    }\n  }\n}\n`,
            "variables": "{}"
        });

        const balance = await getBalance(config);
        res.json({ balance: balance || '0' });
    } catch (error) {
        console.error('Error fetching balance:', error);
        res.status(500).json({ error: 'Error fetching balance' });
    }
});

5. Start WebSocket connection for real-time updates.

const { WebSocket } = require("ws");

const bitqueryConnection = new WebSocket(
  "wss://streaming.bitquery.io/graphql?token=" + process.env.AUTH_TOKEN,
  ["graphql-ws"],
);

bitqueryConnection.on("open", () => {
  console.log("Connected to Bitquery.");

  const initMessage = JSON.stringify({ type: "connection_init" });
  bitqueryConnection.send(initMessage);
});

bitqueryConnection.on("message", async (data) => {
  const response = JSON.parse(data);
  
  if (response.type === "connection_ack") {
    const subscriptionMessage = JSON.stringify({
      type: "start",
      id: "1",
      payload: {
        query: `
        subscription {
            EVM{
                BalanceUpdates(
                    where: {
                        BalanceUpdate: {
                            Address: {
                                is: "${currentAddress}"
                            }
                        }, 
                        Currency: {SmartContract: {is: "0x"}}
                    }
                ) {
                    BalanceUpdate {
                        Amount
                    }
                }
            }
        }`,
      },
    });

    bitqueryConnection.send(subscriptionMessage);
    console.log("Subscription message sent.");
  }
});

bitqueryConnection.on("error", (error) => {
  console.error("WebSocket Error:", error);
});

6. Start the Express server.

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
  console.log(`Server is running on port ${PORT}`);
});

Now we need to build a simple UI using HTML, CSS and Javascript to make this project inituitive.