custom-gas-station.ts

import Web3 from "web3";
import {
  CustomGasChainId,
  TxSpeed,
  verifyValidOption,
  txSpeeds,
  customGasChainIds,
} from "./utils";

type chainMethods = Record<CustomGasChainId, () => Promise<string>>;

export class CustomGasStation {
  private chain: CustomGasChainId;
  private speed: TxSpeed;
  private chainMethods: chainMethods = {
    137: this.fetchMaticMainnetGasPrice.bind(this),
  };
  constructor(chain: number, speed: string) {
    this.speed = verifyValidOption(speed, txSpeeds);
    this.chain = verifyValidOption(chain, customGasChainIds);
  }

  async getCustomGasPrice() {
    return this.chainMethods[this.chain]();
  }

  private async fetchMaticMainnetGasPrice() {
    const res = await fetch("https://gasstation-mainnet.matic.network/v2");
    const jsonRes = await res.json();
    const gasPrice = jsonRes[this.speed].maxFee;
    const gweiGasPrice = Web3.utils.toWei(gasPrice.toFixed(2), "Gwei");
    return gweiGasPrice.toString();
  }
}