gwei-alert-bot/src/blockchain.ts

import 'dotenv/config.js';
import { WebSocketProvider, formatUnits } from 'ethers';
import { Observable } from 'rxjs';
import { map, scan } from 'rxjs/operators';

import { GasPrices } from '../types/gasPrices';

const rpcUrl = process.env.RPC_URL || "wss://ropsten.infura.io/ws/v3/YOUR_INFURA_PROJECT_ID";

const provider = new WebSocketProvider(rpcUrl);

const blockGasPricesObservable = new Observable<GasPrices>((observer) => {
  provider.on('block', async (blockNumber) => {
    try {
      const block = await provider.getBlock(blockNumber, true);

      if (!block) throw new Error(`Error fetching block! ${blockNumber}`);

      const gasPrices = block.prefetchedTransactions.map((tx) => tx.gasPrice);
      const fast = Number(formatUnits(gasPrices[Math.floor(gasPrices.length * 0.1)], "gwei"));
      const average = Number(formatUnits(gasPrices[Math.floor(gasPrices.length / 2)], "gwei"));
      const slow = Number(formatUnits(gasPrices[Math.floor(gasPrices.length * 0.95)], "gwei"));

      // Log averages every 10 blocks
      if (blockNumber % 10 == 0) console.log(`Found new block data for ${blockNumber}! Base average transaction cost: ${slow} Gwei`)

      observer.next({ fast, average, slow } as GasPrices);
    } catch (error) {
      observer.error(`Error fetching block! ${error}`);
    }
  });
});

const averageGasPricesObservable = blockGasPricesObservable.pipe(
  scan((acc, curr) => [...acc.slice(-19), curr], [] as GasPrices[]),
  map((blocks) => {
    const fastSum = blocks.reduce((sum, block) => sum + block.fast, 0);
    const averageSum = blocks.reduce((sum, block) => sum + block.average, 0);
    const slowSum = blocks.reduce((sum, block) => sum + block.slow, 0);
    return {
      fast: Math.round(fastSum / blocks.length),
      average: Math.round(averageSum / blocks.length),
      slow: Math.round(slowSum / blocks.length),
    };
  })
);

export { averageGasPricesObservable };