How to build a transfer notification bot with Envio HyperIndex

# default config...
field_selection:
    transaction_fields:
      - hash

import axios from "axios";
import { CHAT_ID, BOT_TOKEN } from "../constants";

export const sendMessageToTelegram = async (message: string): Promise<void> => {
  try {
    const apiUrl = `https://api.telegram.org/bot${BOT_TOKEN}/sendMessage`;

    await axios.post(apiUrl, {
      chat_id: CHAT_ID,
      text: message,
      parse_mode: "HTML",
    });
  } catch (error) {
    console.error("Error sending message:", error);
  }
};

export const EXPLORER_URL_MONAD = "https://testnet.monadvision.com/";

// Threshold for WMON transfer amount above which the bot sends a notification
export const THRESHOLD_WEI: string = process.env.ENVIO_THRESHOLD_WEI ?? "1000000000000000000"; // in wei

export const BOT_TOKEN = process.env.ENVIO_BOT_TOKEN; // Telegram bot token
export const CHAT_ID = process.env.ENVIO_TELEGRAM_CHAT_ID; // WMON Transfers Notification Channel ID

// Function to get explorer url for the provided address
export const explorerUrlAddress = (address: string) =>
  EXPLORER_URL_MONAD + "address/" + address;

// Function to get explorer url for the provided transaction hash
export const explorerUrlTx = (txHash: string) =>
  EXPLORER_URL_MONAD + "tx/" + txHash;

import {
  WrappedMonad,
} from "generated";
import { isIndexingAtHead, weiToEth } from "./libs/helpers";
import { sendMessageToTelegram } from "./libs/telegram";
import { THRESHOLD_WEI, explorerUrlAddress, explorerUrlTx } from "./constants";

// Other event handlers can be removed...

WrappedMonad.Transfer.handler(async ({ event, context }) => {
    const from_address = event.params.src;
    const to_address = event.params.dst;

  if (isIndexingAtHead(event.block.timestamp) && event.params.wad >= BigInt(THRESHOLD_WEI)) {
    // Only send a message when the indexer is indexing event from the time it was started and not historical transfers, and only message if the transfer amount is greater than or equal to THRESHOLD_WEI.

    // Example message
    // WMON Transfer ALERT: A new transfer has been made by 0x65C3564f1DD63eA81C11D8FE9a93F8FFb5615233 to 0xBA5Cf1c0c1238F60832618Ec49FC81e8C7C0CF01 for 2.0000 WMON! 🔥 - View on Explorer

    const msg = `WMON Transfer ALERT: A new transfer has been made by <a href="${explorerUrlAddress(from_address)}">${from_address}</a> to <a href="${explorerUrlAddress(to_address)}">${to_address}</a> for ${weiToEth(event.params.wad)} WMON! 🔥 - <a href="${explorerUrlTx(
      event.transaction.hash
    )}">View on Explorer</a>`;

    await sendMessageToTelegram(msg);
  }
});

// Used to ensure notifications are only sent while indexing at the head and not historical sync
const INDEXER_START_TIMESTAMP = Math.floor(new Date().getTime() / 1000);

export const isIndexingAtHead = (timestamp: number): boolean => {
    return timestamp >= INDEXER_START_TIMESTAMP;
}

// Convert wei to ether for human readability
export const weiToEth = (bigIntNumber: bigint): string => {
  // Convert BigInt to string
  const numberString = bigIntNumber.toString();

  const decimalPointsInEth = 18;

  // Extract integer part and decimal part
  const integerPart = numberString.substring(
    0,
    numberString.length - decimalPointsInEth
  );

  const decimalPart = numberString.slice(-decimalPointsInEth);

  // Insert decimal point
  const decimalString =
    (integerPart ? integerPart : "0") +
    "." +
    decimalPart.padStart(decimalPointsInEth, "0");

  // Add negative sign if necessary
  return decimalString.slice(0, -14);
};