Deploy a contract when gas is cheap

deploy.ts

// $ yarn hardhat run --network mainnet scripts/deploy.ts

import {BigNumber} from '@ethersproject/bignumber';
import {formatUnits, parseUnits} from '@ethersproject/units';
import {ethers} from 'hardhat';

async function main() {
  const gasPrice = await waitForGasPriceBelow(parseUnits('40', 'gwei'));

  const Greeter = await ethers.getContractFactory('Greeter');
  const greeter = await Greeter.deploy({gasPrice});
  console.log('Greeter address:', greeter.address);
  await greeter.deployed();
  console.log('Deployed!');
}

async function waitForGasPriceBelow(max: BigNumber): Promise<BigNumber> {
  console.log('Waiting for gas price below', formatUnits(max, 'gwei'), 'gwei');
  while (true) {
    const price = await ethers.provider.getGasPrice();
    console.log(new Date().toLocaleString(), 'Gas Price:', formatUnits(price, 'gwei'), 'gwei');
    if (price.lte(max)) {
      console.log('Good enough!');
      return price;
    }
    await new Promise((resolve) => setTimeout(resolve, 30_000));
  }
}

main()
  .then(() => process.exit(0))
  .catch((error) => {
    console.error(error);
    process.exit(1);
  });