mkdir hardhat-tutorial
  cd hardhat-tutorial
  npm init --yes
  npm install --save-dev hardhat

  npx hardhat

  npm install --save-dev @nomiclabs/hardhat-waffle ethereum-waffle chai @nomiclabs/hardhat-ethers ethers

  npm install @openzeppelin/contracts

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.4;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract Exchange is ERC20 {

    address public cryptoDevTokenAddress;

    // Exchange is inheriting ERC20, becase our exchange would keep track of Crypto Dev LP tokens
    constructor(address _CryptoDevtoken) ERC20("CryptoDev LP Token", "CDLP") {
        require(_CryptoDevtoken != address(0), "Token address passed is a null address");
        cryptoDevTokenAddress = _CryptoDevtoken;
    }

    /** 
    * @dev Returns the amount of `Crypto Dev Tokens` held by the contract
    */
    function getReserve() public view returns (uint) {
        return ERC20(cryptoDevTokenAddress).balanceOf(address(this));
    }

    /**
    * @dev Adds liquidity to the exchange.
    */
    function addLiquidity(uint _amount) public payable returns (uint) {
        uint liquidity;
        uint ethBalance = address(this).balance;
        uint cryptoDevTokenReserve = getReserve();
        ERC20 cryptoDevToken = ERC20(cryptoDevTokenAddress);
        /* 
            If the reserve is empty, intake any user supplied value for 
            `Ether` and `Crypto Dev` tokens because there is no ratio currently
        */
        if(cryptoDevTokenReserve == 0) {
            // Transfer the `cryptoDevToken` address from the user's account to the contract
            cryptoDevToken.transferFrom(msg.sender, address(this), _amount);
            // Take the current ethBalance and mint `ethBalance` amount of LP tokens to the user.
            // `liquidity` provided is equal to `ethBalance` because this is the first time user 
            // is adding `Eth` to the contract, so whatever `Eth` contract has is equal to the one supplied 
            // by the user in the current `addLiquidity` call
            // `liquidity` tokens that need to be minted to the user on `addLiquidity` call shouls always be proportional
            // to the Eth specified by the user
            liquidity = ethBalance;
            _mint(msg.sender, liquidity);
        } else {
            /* 
                If the reserve is not empty, intake any user supplied value for 
                `Ether` and determine according to the ratio how many `Crypto Dev` tokens
                need to be supplied to prevent any large price impacts because of the additional
                liquidity
            */
            // EthReserve should be the current ethBalance subtracted by the value of ether sent by the user
            // in the current `addLiquidity` call
            uint ethReserve =  ethBalance - msg.value;
            // Ratio should always be maintained so that there are no major price impacts when adding liquidity
            // Ration here is -> (cryptoDevTokenAmount user can add/cryptoDevTokenReserve in the contract) = (Eth Sent by the user/Eth Reserve in the contract);
            // So doing some maths, (cryptoDevTokenAmount user can add) = (Eth Sent by the user * cryptoDevTokenReserve /Eth Reserve);
            uint cryptoDevTokenAmount = (msg.value * cryptoDevTokenReserve)/(ethReserve);
            require(_amount >= cryptoDevTokenAmount, "Amount of tokens sent is less than the minimum tokens required");
            // transfer only (cryptoDevTokenAmount user can add) amount of `Crypto Dev tokens` from users account
            // to the contract
            cryptoDevToken.transferFrom(msg.sender, address(this), cryptoDevTokenAmount);
            // The amount of LP tokens that would be sent to the user should be propotional to the liquidity of
            // ether added by the user
            // Ratio here to be maintained is -> 
            // (lp tokens to be sent to the user (liquidity)/ totalSupply of LP tokens in contract) = (Eth sent by the user)/(Eth reserve in the contract)
            // by some maths -> liquidity =  (totalSupply of LP tokens in contract * (Eth sent by the user))/(Eth reserve in the contract)
            liquidity = (totalSupply() * msg.value)/ ethReserve;
            _mint(msg.sender, liquidity);
        }
         return liquidity;
    }

    /** 
    * @dev Returns the amount Eth/Crypto Dev tokens that would be returned to the user
    * in the swap
    */
    function removeLiquidity(uint _amount) public returns (uint , uint) {
        require(_amount > 0, "_amount should be greater than zero");
        uint ethReserve = address(this).balance;
        uint _totalSupply = totalSupply();
        // The amount of Eth that would be sent back to the user is based
        // on a ratio 
        // Ratio is -> (Eth sent back to the user/ Current Eth reserve)  
        // = (amount of LP tokens that user wants to withdraw) / (total supply of LP tokens)
        // Then by some maths -> (Eth sent back to the user) 
        // = (current Eth reserve * amount of LP tokens that user wants to withdraw) / (total supply of LP tokens)
        uint ethAmount = (ethReserve * _amount)/ _totalSupply;
        // The amount of Crypto Dev token that would be sent back to the user is based
        // on a ratio 
        // Ratio is -> (Crypto Dev sent back to the user) / (current Crypto Dev token reserve)
        // = (amount of LP tokens that user wants to withdraw) / (total supply of LP tokens)
        // Then by some maths -> (Crypto Dev sent back to the user) 
        // = (current Crypto Dev token reserve * amount of LP tokens that user wants to withdraw) / (total supply of LP tokens)
        uint cryptoDevTokenAmount = (getReserve() * _amount)/ _totalSupply;
        // Burn the sent `LP` tokens from the user's wallet because they are already sent to 
        // remove liquidity
        _burn(msg.sender, _amount);
        // Transfer `ethAmount` of Eth from user's wallet to the contract
        payable(msg.sender).transfer(ethAmount);
        // Transfer `cryptoDevTokenAmount` of `Crypto Dev` tokens from the user's wallet to the contract 
        ERC20(cryptoDevTokenAddress).transfer(msg.sender, cryptoDevTokenAmount);
        return (ethAmount, cryptoDevTokenAmount);
    }

    /** 
    * @dev Returns the amount Eth/Crypto Dev tokens that would be returned to the user
    * in the swap
    */
    function getAmountOfTokens(
        uint256 inputAmount,
        uint256 inputReserve,
        uint256 outputReserve
    ) public pure returns (uint256) {
        require(inputReserve > 0 && outputReserve > 0, "invalid reserves");
        // We are charging a fee of `1%`
        // Input amount with fee = (input amount - (1*(input amount)/100)) = ((input amount)*99)/100
        uint256 inputAmountWithFee = inputAmount * 99;
        // Because we need to follow the concept of `XY = K` curve
        // We need to make sure (x + Δx) * (y - Δy) = x * y
        // So the final formula is Δy = (y * Δx) / (x + Δx)
        // Δy in our case is `tokens to be received`
        // Δx = ((input amount)*99)/100, x = inputReserve, y = outputReserve
        // So by putting the values in the formulae you can get the numerator and denominator
        uint256 numerator = inputAmountWithFee * outputReserve;
        uint256 denominator = (inputReserve * 100) + inputAmountWithFee;
        return numerator / denominator;
    }

    /** 
    * @dev Swaps Eth for CryptoDev Tokens
    */
    function ethToCryptoDevToken(uint _minTokens) public payable {
        uint256 tokenReserve = getReserve();
        // call the `getAmountOfTokens` to get the amount of Crypto Dev tokens
        // that would be returned to the user after the swap
        // Notice that the `inputReserve` we are sending is equal to  
        // `address(this).balance - msg.value` instead of just `address(this).balance`
        // because `address(this).balance` already contains the `msg.value` user has sent in the given call
        // so we need to subtract it to get the actual input reserve
        uint256 tokensBought = getAmountOfTokens(
            msg.value,
            address(this).balance - msg.value,
            tokenReserve
        );

        require(tokensBought >= _minTokens, "insufficient output amount");
        // Transfer the `Crypto Dev` tokens to the user
        ERC20(cryptoDevTokenAddress).transfer(msg.sender, tokensBought);
    }


    /** 
    * @dev Swaps CryptoDev Tokens for Eth
    */
    function cryptoDevTokenToEth(uint _tokensSold, uint _minEth) public {
        uint256 tokenReserve = getReserve();
        // call the `getAmountOfTokens` to get the amount of Eth
        // that would be returned to the user after the swap
        uint256 ethBought = getAmountOfTokens(
            _tokensSold,
            tokenReserve,
            address(this).balance
        );
        require(ethBought >= _minEth, "insufficient output amount");
        // Transfer `Crypto Dev` tokens from the user's address to the contract
        ERC20(cryptoDevTokenAddress).transferFrom(
            msg.sender,
            address(this),
            _tokensSold
        );
        // send the `ethBought` to the user from the contract
        payable(msg.sender).transfer(ethBought);
    }
}

  npm install dotenv

  // Go to https://www.alchemyapi.io, sign up, create
  // a new App in its dashboard and select the network as Rinkeby, and replace "add-the-alchemy-key-url-here" with its key url
  ALCHEMY_API_KEY_URL="add-the-alchemy-key-url-here"

  // Replace this private key with your RINKEBY account private key
  // To export your private key from Metamask, open Metamask and
  // go to Account Details > Export Private Key
  // Be aware of NEVER putting real Ether into testing accounts
  RINKEBY_PRIVATE_KEY="add-the-rinkeby-private-key-here"

  const CRYPTO_DEV_TOKEN_CONTRACT_ADDRESS = "ADDRESS-OF-CRYPTO-DEV-TOKEN";

  module.exports = { CRYPTO_DEV_TOKEN_CONTRACT_ADDRESS };

  const { ethers } = require("hardhat");
  require("dotenv").config({ path: ".env" });
  const { CRYPTO_DEV_TOKEN_CONTRACT_ADDRESS } = require("../constants");

  async function main() {
    const cryptoDevTokenAddress = CRYPTO_DEV_TOKEN_CONTRACT_ADDRESS;
    /*
    A ContractFactory in ethers.js is an abstraction used to deploy new smart contracts,
    so exchangeContract here is a factory for instances of our Exchange contract.
    */
    const exchangeContract = await ethers.getContractFactory("Exchange");

    // here we deploy the contract
    const deployedExchangeContract = await exchangeContract.deploy(
      cryptoDevTokenAddress
    );
    await deployedExchangeContract.deployed();

    // print the address of the deployed contract
    console.log("Exchange Contract Address:", deployedExchangeContract.address);
  }

  // Call the main function and catch if there is any error
  main()
    .then(() => process.exit(0))
    .catch((error) => {
      console.error(error);
      process.exit(1);
    });

  require("@nomiclabs/hardhat-waffle");
  require("dotenv").config({ path: ".env" });

  const ALCHEMY_API_KEY_URL = process.env.ALCHEMY_API_KEY_URL;

  const RINKEBY_PRIVATE_KEY = process.env.RINKEBY_PRIVATE_KEY;

  module.exports = {
    solidity: "0.8.4",
    networks: {
      rinkeby: {
        url: ALCHEMY_API_KEY_URL,
        accounts: [RINKEBY_PRIVATE_KEY],
      },
    },
  };

  npx hardhat compile

   npx hardhat run scripts/deploy.js --network rinkeby

     - DeFi-Exchange
         - hardhat-tutorial
         - my-app

    npx create-next-app@latest

  cd my-app
  npm run dev

    npm install web3modal

  npm i ethers

  .main {
    min-height: 90vh;
    display: flex;
    flex-direction: row;
    justify-content: center;
    align-items: center;
    font-family: "Courier New", Courier, monospace;
  }

  .footer {
    display: flex;
    padding: 2rem 0;
    border-top: 1px solid #eaeaea;
    justify-content: center;
    align-items: center;
  }

  .image {
    width: 70%;
    height: 50%;
    margin-left: 20%;
  }

  .input {
    width: 200px;
    height: 100%;
    padding: 1%;
    margin: 2%;
    box-shadow: 0 0 15px 4px rgba(0, 0, 0, 0.06);
    border-radius: 10px;
  }

  .title {
    font-size: 2rem;
    margin: 2rem 0;
  }

  .description {
    line-height: 1;
    margin: 2%;
    font-size: 1.2rem;
  }

  .button {
    border-radius: 4px;
    background-color: purple;
    border: none;
    color: #ffffff;
    font-size: 15px;
    padding: 5px;
    width: 100px;
    cursor: pointer;
    margin: 2%;
  }

  .inputDiv {
    width: 200px;
    height: 100%;
    padding: 1%;
    margin: 2%;
    border: lightslategray;
    box-shadow: 0 0 15px 4px rgba(0, 0, 0, 0.06);
    border-radius: 10px;
  }
  .select {
    border-radius: 4px;
    font-size: 15px;
    padding: 5px;
    width: 175px;
    cursor: pointer;
    margin: 2%;
  }

  .button1 {
    border-radius: 4px;
    background-color: blue;
    border: none;
    color: #ffffff;
    font-size: 15px;
    padding: 5px;
    width: 100px;
    cursor: pointer;
    margin: 2%;
  }
  @media (max-width: 1000px) {
    .main {
      width: 100%;
      flex-direction: column;
      justify-content: center;
      align-items: center;
    }
  }

  import { Contract } from "ethers";
  import {
    EXCHANGE_CONTRACT_ABI,
    EXCHANGE_CONTRACT_ADDRESS,
    TOKEN_CONTRACT_ABI,
    TOKEN_CONTRACT_ADDRESS,
  } from "../constants";

  /**
   * getEtherBalance: Retrieves the ether balance of the user or the contract
   */
  export const getEtherBalance = async (
    provider,
    address,
    contract = false
  ) => {
    try {
      // If the caller has set the `contract` boolean to true, retrieve the balance of
      // ether in the `exchange contract`, if it is set to false, retrieve the balance
      // of the user's address
      if (contract) {
        const balance = await provider.getBalance(EXCHANGE_CONTRACT_ADDRESS);
        return balance;
      } else {
        const balance = await provider.getBalance(address);
        return balance;
      }
    } catch (err) {
      console.error(err);
      return 0;
    }
  };

  /**
   * getCDTokensBalance: Retrieves the Crypto Dev tokens in the account
   * of the provided `address`
   */
  export const getCDTokensBalance = async (provider, address) => {
    try {
      const tokenContract = new Contract(
        TOKEN_CONTRACT_ADDRESS,
        TOKEN_CONTRACT_ABI,
        provider
      );
      const balanceOfCryptoDevTokens = await tokenContract.balanceOf(address);
      return balanceOfCryptoDevTokens;
    } catch (err) {
      console.error(err);
    }
  };

  /**
   * getLPTokensBalance: Retrieves the amount of LP tokens in the account
   * of the provided `address`
   */
  export const getLPTokensBalance = async (provider, address) => {
    try {
      const exchangeContract = new Contract(
        EXCHANGE_CONTRACT_ADDRESS,
        EXCHANGE_CONTRACT_ABI,
        provider
      );
      const balanceOfLPTokens = await exchangeContract.balanceOf(address);
      return balanceOfLPTokens;
    } catch (err) {
      console.error(err);
    }
  };

  /**
   * getReserveOfCDTokens: Retrieves the amount of CD tokens in the
   * exchange contract address
   */
  export const getReserveOfCDTokens = async (provider) => {
    try {
      const exchangeContract = new Contract(
        EXCHANGE_CONTRACT_ADDRESS,
        EXCHANGE_CONTRACT_ABI,
        provider
      );
      const reserve = await exchangeContract.getReserve();
      return reserve;
    } catch (err) {
      console.error(err);
    }
  };

import { BigNumber, providers, utils } from "ethers";
import Head from "next/head";
import React, { useEffect, useRef, useState } from "react";
import Web3Modal from "web3modal";
import styles from "../styles/Home.module.css";
import { addLiquidity, calculateCD } from "../utils/addLiquidity";
import {
  getCDTokensBalance,
  getEtherBalance,
  getLPTokensBalance,
  getReserveOfCDTokens,
} from "../utils/getAmounts";
import {
  getTokensAfterRemove,
  removeLiquidity,
} from "../utils/removeLiquidity";
import { swapTokens, getAmountOfTokensReceivedFromSwap } from "../utils/swap";

export default function Home() {
  /** General state variables */
  // loading is set to true when the transaction is mining and set to false when
  // the transaction has mined
  const [loading, setLoading] = useState(false);
  // We have two tabs in this dapp, Liquidity Tab and Swap Tab. This variable
  // keeps track of which Tab the user is on. If it is set to true this means
  // that the user is on `liquidity` tab else he is on `swap` tab
  const [liquidityTab, setLiquidityTab] = useState(true);
  // This variable is the `0` number in form of a BigNumber
  const zero = BigNumber.from(0);
  /** Variables to keep track of amount */
  // `ethBalance` keeps track of the amount of Eth held by the user's account
  const [ethBalance, setEtherBalance] = useState(zero);
  // `reservedCD` keeps track of the Crypto Dev tokens Reserve balance in the Exchange contract
  const [reservedCD, setReservedCD] = useState(zero);
  // Keeps track of the ether balance in the contract
  const [etherBalanceContract, setEtherBalanceContract] = useState(zero);
  // cdBalance is the amount of `CD` tokens help by the users account
  const [cdBalance, setCDBalance] = useState(zero);
  // `lpBalance` is the amount of LP tokens held by the users account
  const [lpBalance, setLPBalance] = useState(zero);
  /** Variables to keep track of liquidity to be added or removed */
  // addEther is the amount of Ether that the user wants to add to the liquidity
  const [addEther, setAddEther] = useState(zero);
  // addCDTokens keeps track of the amount of CD tokens that the user wants to add to the liquidity
  // in case when there is no initial liquidity and after liquidity gets added it keeps track of the
  // CD tokens that the user can add given a certain amount of ether
  const [addCDTokens, setAddCDTokens] = useState(zero);
  // removeEther is the amount of `Ether` that would be sent back to the user based on a certain number of `LP` tokens
  const [removeEther, setRemoveEther] = useState(zero);
  // removeCD is the amount of `Crypto Dev` tokens that would be sent back to the user based on a certain number of `LP` tokens
  // that he wants to withdraw
  const [removeCD, setRemoveCD] = useState(zero);
  // amount of LP tokens that the user wants to remove from liquidity
  const [removeLPTokens, setRemoveLPTokens] = useState("0");
  /** Variables to keep track of swap functionality */
  // Amount that the user wants to swap
  const [swapAmount, setSwapAmount] = useState("");
  // This keeps track of the number of tokens that the user would receive after a swap completes
  const [tokenToBeReceivedAfterSwap, settokenToBeReceivedAfterSwap] = useState(
    zero
  );
  // Keeps track of whether  `Eth` or `Crypto Dev` token is selected. If `Eth` is selected it means that the user
  // wants to swap some `Eth` for some `Crypto Dev` tokens and vice versa if `Eth` is not selected
  const [ethSelected, setEthSelected] = useState(true);
  /** Wallet connection */
  // Create a reference to the Web3 Modal (used for connecting to Metamask) which persists as long as the page is open
  const web3ModalRef = useRef();
  // walletConnected keep track of whether the user's wallet is connected or not
  const [walletConnected, setWalletConnected] = useState(false);

  /**
   * getAmounts call various functions to retrive amounts for ethbalance,
   * LP tokens etc
   */
  const getAmounts = async () => {
    try {
      const provider = await getProviderOrSigner(false);
      const signer = await getProviderOrSigner(true);
      const address = await signer.getAddress();
      // get the amount of eth in the user's account
      const _ethBalance = await getEtherBalance(provider, address);
      // get the amount of `Crypto Dev` tokens held by the user
      const _cdBalance = await getCDTokensBalance(provider, address);
      // get the amount of `Crypto Dev` LP tokens held by the user
      const _lpBalance = await getLPTokensBalance(provider, address);
      // gets the amount of `CD` tokens that are present in the reserve of the `Exchange contract`
      const _reservedCD = await getReserveOfCDTokens(provider);
      // Get the ether reserves in the contract
      const _ethBalanceContract = await getEtherBalance(provider, null, true);
      setEtherBalance(_ethBalance);
      setCDBalance(_cdBalance);
      setLPBalance(_lpBalance);
      setReservedCD(_reservedCD);
      setReservedCD(_reservedCD);
      setEtherBalanceContract(_ethBalanceContract);
    } catch (err) {
      console.error(err);
    }
  };

  /**** SWAP FUNCTIONS ****/

  /**
   * swapTokens: Swaps  `swapAmountWei` of Eth/Crypto Dev tokens with `tokenToBeReceivedAfterSwap` amount of Eth/Crypto Dev tokens.
   */
  const _swapTokens = async () => {
    try {
      // Convert the amount entered by the user to a BigNumber using the `parseEther` library from `ethers.js`
      const swapAmountWei = utils.parseEther(swapAmount);
      // Check if the user entered zero
      // We are here using the `eq` method from BigNumber class in `ethers.js`
      if (!swapAmountWei.eq(zero)) {
        const signer = await getProviderOrSigner(true);
        setLoading(true);
        // Call the swapTokens function from the `utils` folder
        await swapTokens(
          signer,
          swapAmountWei,
          tokenToBeReceivedAfterSwap,
          ethSelected
        );
        setLoading(false);
        // Get all the updated amounts after the swap
        await getAmounts();
        setSwapAmount("");
      }
    } catch (err) {
      console.error(err);
      setLoading(false);
      setSwapAmount("");
    }
  };

  /**
   * _getAmountOfTokensReceivedFromSwap:  Returns the number of Eth/Crypto Dev tokens that can be received 
   * when the user swaps `_swapAmountWEI` amount of Eth/Crypto Dev tokens.
   */
  const _getAmountOfTokensReceivedFromSwap = async (_swapAmount) => {
    try {
      // Convert the amount entered by the user to a BigNumber using the `parseEther` library from `ethers.js`
      const _swapAmountWEI = utils.parseEther(_swapAmount.toString());
      // Check if the user entered zero
      // We are here using the `eq` method from BigNumber class in `ethers.js`
      if (!_swapAmountWEI.eq(zero)) {
        const provider = await getProviderOrSigner();
        // Get the amount of ether in the contract
        const _ethBalance = await getEtherBalance(provider, null, true);
        // Call the `getAmountOfTokensReceivedFromSwap` from the utils folder
        const amountOfTokens = await getAmountOfTokensReceivedFromSwap(
          _swapAmountWEI,
          provider,
          ethSelected,
          _ethBalance,
          reservedCD
        );
        settokenToBeReceivedAfterSwap(amountOfTokens);
      } else {
        settokenToBeReceivedAfterSwap(zero);
      }
    } catch (err) {
      console.error(err);
    }
  };

  /*** END ***/

  /**** ADD LIQUIDITY FUNCTIONS ****/

  /**
   * _addLiquidity helps add liquidity to the exchange,
   * If the user is adding initial liquidity, user decides the ether and CD tokens he wants to add
   * to the exchange. If he is adding the liquidity after the initial liquidity has already been added
   * then we calculate the crypto dev tokens he can add, given the Eth he wants to add by keeping the ratios
   * constant
   */
  const _addLiquidity = async () => {
    try {
      // Convert the ether amount entered by the user to Bignumber
      const addEtherWei = utils.parseEther(addEther.toString());
      // Check if the values are zero
      if (!addCDTokens.eq(zero) && !addEtherWei.eq(zero)) {
        const signer = await getProviderOrSigner(true);
        setLoading(true);
        // call the addLiquidity function from the utils folder
        await addLiquidity(signer, addCDTokens, addEtherWei);
        setLoading(false);
        // Reinitialize the CD tokens
        setAddCDTokens(zero);
        // Get amounts for all values after the liquidity has been added
        await getAmounts();
      } else {
        setAddCDTokens(zero);
      }
    } catch (err) {
      console.error(err);
      setLoading(false);
      setAddCDTokens(zero);
    }
  };

  /**** END ****/

  /**** REMOVE LIQUIDITY FUNCTIONS ****/

  /**
   * _removeLiquidity: Removes the `removeLPTokensWei` amount of LP tokens from
   * liquidity and also the calculated amount of `ether` and `CD` tokens
   */
  const _removeLiquidity = async () => {
    try {
      const signer = await getProviderOrSigner(true);
      // Convert the LP tokens entered by the user to a BigNumber
      const removeLPTokensWei = utils.parseEther(removeLPTokens);
      setLoading(true);
      // Call the removeLiquidity function from the `utils` folder
      await removeLiquidity(signer, removeLPTokensWei);
      setLoading(false);
      await getAmounts();
      setRemoveCD(zero);
      setRemoveEther(zero);
    } catch (err) {
      console.error(err);
      setLoading(false);
      setRemoveCD(zero);
      setRemoveEther(zero);
    }
  };

  /**
   * _getTokensAfterRemove: Calculates the amount of `Ether` and `CD` tokens
   * that would be returned back to user after he removes `removeLPTokenWei` amount
   * of LP tokens from the contract
   */
  const _getTokensAfterRemove = async (_removeLPTokens) => {
    try {
      const provider = await getProviderOrSigner();
      // Convert the LP tokens entered by the user to a BigNumber
      const removeLPTokenWei = utils.parseEther(_removeLPTokens);
      // Get the Eth reserves within the exchange contract
      const _ethBalance = await getEtherBalance(provider, null, true);
      // get the crypto dev token reserves from the contract
      const cryptoDevTokenReserve = await getReserveOfCDTokens(provider);
      // call the getTokensAfterRemove from the utils folder
      const { _removeEther, _removeCD } = await getTokensAfterRemove(
        provider,
        removeLPTokenWei,
        _ethBalance,
        cryptoDevTokenReserve
      );
      setRemoveEther(_removeEther);
      setRemoveCD(_removeCD);
    } catch (err) {
      console.error(err);
    }
  };

  /**** END ****/

  /**
   * connectWallet: Connects the MetaMask wallet
   */
  const connectWallet = async () => {
    try {
      // Get the provider from web3Modal, which in our case is MetaMask
      // When used for the first time, it prompts the user to connect their wallet
      await getProviderOrSigner();
      setWalletConnected(true);
    } catch (err) {
      console.error(err);
    }
  };

  /**
   * Returns a Provider or Signer object representing the Ethereum RPC with or
   * without the signing capabilities of Metamask attached
   *
   * A `Provider` is needed to interact with the blockchain - reading
   * transactions, reading balances, reading state, etc.
   *
   * A `Signer` is a special type of Provider used in case a `write` transaction
   * needs to be made to the blockchain, which involves the connected account
   * needing to make a digital signature to authorize the transaction being
   * sent. Metamask exposes a Signer API to allow your website to request
   * signatures from the user using Signer functions.
   *
   * @param {*} needSigner - True if you need the signer, default false
   * otherwise
   */
  const getProviderOrSigner = async (needSigner = false) => {
    // Connect to Metamask
    // Since we store `web3Modal` as a reference, we need to access the `current` value to get access to the underlying object
    const provider = await web3ModalRef.current.connect();
    const web3Provider = new providers.Web3Provider(provider);

    // If user is not connected to the Rinkeby network, let them know and throw an error
    const { chainId } = await web3Provider.getNetwork();
    if (chainId !== 4) {
      window.alert("Change the network to Rinkeby");
      throw new Error("Change network to Rinkeby");
    }

    if (needSigner) {
      const signer = web3Provider.getSigner();
      return signer;
    }
    return web3Provider;
  };

  // useEffects are used to react to changes in state of the website
  // The array at the end of function call represents what state changes will trigger this effect
  // In this case, whenever the value of `walletConnected` changes - this effect will be called
  useEffect(() => {
    // if wallet is not connected, create a new instance of Web3Modal and connect the MetaMask wallet
    if (!walletConnected) {
      // Assign the Web3Modal class to the reference object by setting it's `current` value
      // The `current` value is persisted throughout as long as this page is open
      web3ModalRef.current = new Web3Modal({
        network: "rinkeby",
        providerOptions: {},
        disableInjectedProvider: false,
      });
      connectWallet();
      getAmounts();
    }
  }, [walletConnected]);

  /*
      renderButton: Returns a button based on the state of the dapp
  */
  const renderButton = () => {
    // If wallet is not connected, return a button which allows them to connect their wllet
    if (!walletConnected) {
      return (
        <button onClick={connectWallet} className={styles.button}>
          Connect your wallet
        </button>
      );
    }

    // If we are currently waiting for something, return a loading button
    if (loading) {
      return <button className={styles.button}>Loading...</button>;
    }

    if (liquidityTab) {
      return (
        <div>
          <div className={styles.description}>
            You have:
            <br />
            {/* Convert the BigNumber to string using the formatEther function from ethers.js */}
            {utils.formatEther(cdBalance)} Crypto Dev Tokens
            <br />
            {utils.formatEther(ethBalance)} Ether
            <br />
            {utils.formatEther(lpBalance)} Crypto Dev LP tokens
          </div>
          <div>
            {/* If reserved CD is zero, render the state for liquidity zero where we ask the user
            how much initial liquidity he wants to add else just render the state where liquidity is not zero and
            we calculate based on the `Eth` amount specified by the user how much `CD` tokens can be added */}
            {utils.parseEther(reservedCD.toString()).eq(zero) ? (
              <div>
                <input
                  type="number"
                  placeholder="Amount of Ether"
                  onChange={(e) => setAddEther(e.target.value || "0")}
                  className={styles.input}
                />
                <input
                  type="number"
                  placeholder="Amount of CryptoDev tokens"
                  onChange={(e) =>
                    setAddCDTokens(
                      BigNumber.from(utils.parseEther(e.target.value || "0"))
                    )
                  }
                  className={styles.input}
                />
                <button className={styles.button1} onClick={_addLiquidity}>
                  Add
                </button>
              </div>
            ) : (
              <div>
                <input
                  type="number"
                  placeholder="Amount of Ether"
                  onChange={async (e) => {
                    setAddEther(e.target.value || "0");
                    // calculate the number of CD tokens that
                    // can be added given  `e.target.value` amount of Eth
                    const _addCDTokens = await calculateCD(
                      e.target.value || "0",
                      etherBalanceContract,
                      reservedCD
                    );
                    setAddCDTokens(_addCDTokens);
                  }}
                  className={styles.input}
                />
                <div className={styles.inputDiv}>
                  {/* Convert the BigNumber to string using the formatEther function from ethers.js */}
                  {`You will need ${utils.formatEther(addCDTokens)} Crypto Dev
                  Tokens`}
                </div>
                <button className={styles.button1} onClick={_addLiquidity}>
                  Add
                </button>
              </div>
            )}
            <div>
              <input
                type="number"
                placeholder="Amount of LP Tokens"
                onChange={async (e) => {
                  setRemoveLPTokens(e.target.value || "0");
                  // Calculate the amount of Ether and CD tokens that the user would receive
                  // After he removes `e.target.value` amount of `LP` tokens
                  await _getTokensAfterRemove(e.target.value || "0");
                }}
                className={styles.input}
              />
              <div className={styles.inputDiv}>
                {/* Convert the BigNumber to string using the formatEther function from ethers.js */}
                {`You will get ${utils.formatEther(removeCD)} Crypto
              Dev Tokens and ${utils.formatEther(removeEther)} Eth`}
              </div>
              <button className={styles.button1} onClick={_removeLiquidity}>
                Remove
              </button>
            </div>
          </div>
        </div>
      );
    } else {
      return (
        <div>
          <input
            type="number"
            placeholder="Amount"
            onChange={async (e) => {
              setSwapAmount(e.target.value || "");
              // Calculate the amount of tokens user would receive after the swap
              await _getAmountOfTokensReceivedFromSwap(e.target.value || "0");
            }}
            className={styles.input}
            value={swapAmount}
          />
          <select
            className={styles.select}
            name="dropdown"
            id="dropdown"
            onChange={async () => {
              setEthSelected(!ethSelected);
              // Initialize the values back to zero
              await _getAmountOfTokensReceivedFromSwap(0);
              setSwapAmount("");
            }}
          >
            <option value="eth">Ethereum</option>
            <option value="cryptoDevToken">Crypto Dev Token</option>
          </select>
          <br />
          <div className={styles.inputDiv}>
            {/* Convert the BigNumber to string using the formatEther function from ethers.js */}
            {ethSelected
              ? `You will get ${utils.formatEther(
                  tokenToBeReceivedAfterSwap
                )} Crypto Dev Tokens`
              : `You will get ${utils.formatEther(
                  tokenToBeReceivedAfterSwap
                )} Eth`}
          </div>
          <button className={styles.button1} onClick={_swapTokens}>
            Swap
          </button>
        </div>
      );
    }
  };

  return (
    <div>
      <Head>
        <title>Crypto Devs</title>
        <meta name="description" content="Whitelist-Dapp" />
        <link rel="icon" href="/favicon.ico" />
      </Head>
      <div className={styles.main}>
        <div>
          <h1 className={styles.title}>Welcome to Crypto Devs Exchange!</h1>
          <div className={styles.description}>
            Exchange Ethereum &#60;&#62; Crypto Dev Tokens
          </div>
          <div>
            <button
              className={styles.button}
              onClick={() => {
                setLiquidityTab(!liquidityTab);
              }}
            >
              Liquidity
            </button>
            <button
              className={styles.button}
              onClick={() => {
                setLiquidityTab(false);
              }}
            >
              Swap
            </button>
          </div>
          {renderButton()}
        </div>
        <div>
          <img className={styles.image} src="./cryptodev.svg" />
        </div>
      </div>

      <footer className={styles.footer}>
        Made with &#10084; by Crypto Devs
      </footer>
    </div>
  );
}

  npm run dev