Web3系列教程之入门篇---13. 像 Uniswap 一样建立自己的去中心化交易所

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

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npx hardhat

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npm install --save-dev @nomicfoundation/hardhat-toolbox

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 npm install @openzeppelin/contracts

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

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

contract Exchange is ERC20 {
}

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// 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, because 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;
    }
}

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

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/**
* @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;
}

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/** 
* @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);
}

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/** 
* @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);
}

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// 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, because 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 should 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);
    }
}

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  npm install dotenv

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// 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"

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

module.exports = { CRYPTO_DEV_TOKEN_CONTRACT_ADDRESS };

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  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);
    });

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require("@nomicfoundation/hardhat-toolbox");
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],
    },
  },
};

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npx hardhat compile

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

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

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  npx create-next-app@latest

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cd my-app
npm run dev

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  npm install web3modal

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npm i ethers

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.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;
  }
}

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export const TOKEN_CONTRACT_ABI = "ABI-CRYPTO-DEV-TOKEN-CONTRACT";
export const TOKEN_CONTRACT_ADDRESS =
  "ADDRESS-OF-CRYPTO-DEV-TOKEN-CONTRACT";
export const EXCHANGE_CONTRACT_ABI = "ABI-EXCHANGE-CONTRACT";
export const EXCHANGE_CONTRACT_ADDRESS = "ADDRESS-EXCHANGE-CONTRACT";

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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);
  }
};

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

/**
 * 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
 */
export const addLiquidity = async (
  signer,
  addCDAmountWei,
  addEtherAmountWei
) => {
  try {
    // create a new instance of the token contract
    const tokenContract = new Contract(
      TOKEN_CONTRACT_ADDRESS,
      TOKEN_CONTRACT_ABI,
      signer
    );
    // create a new instance of the exchange contract
    const exchangeContract = new Contract(
      EXCHANGE_CONTRACT_ADDRESS,
      EXCHANGE_CONTRACT_ABI,
      signer
    );
    // Because CD tokens are an ERC20, user would need to give the contract allowance
    // to take the required number CD tokens out of his contract
    let tx = await tokenContract.approve(
      EXCHANGE_CONTRACT_ADDRESS,
      addCDAmountWei.toString()
    );
    await tx.wait();
    // After the contract has the approval, add the ether and cd tokens in the liquidity
    tx = await exchangeContract.addLiquidity(addCDAmountWei, {
      value: addEtherAmountWei,
    });
    await tx.wait();
  } catch (err) {
    console.error(err);
  }
};

/**
 * calculateCD calculates the CD tokens that need to be added to the liquidity
 * given `_addEtherAmountWei` amount of ether
 */
export const calculateCD = async (
  _addEther = "0",
  etherBalanceContract,
  cdTokenReserve
) => {
  // `_addEther` is a string, we need to convert it to a Bignumber before we can do our calculations
  // We do that using the `parseEther` function from `ethers.js`
  const _addEtherAmountWei = utils.parseEther(_addEther);

  // Ratio needs to be maintained when we add liquidty.
  // We need to let the user know for a specific amount of ether how many `CD` tokens
  // He can add so that the price impact is not large
  // The ratio we follow is (amount of Crypto Dev tokens to be added) / (Crypto Dev tokens balance) = (Eth that would be added) / (Eth reserve in the contract)
  // So by maths we get (amount of Crypto Dev tokens to be added) = (Eth that would be added * Crypto Dev tokens balance) / (Eth reserve in the contract)

  const cryptoDevTokenAmount = _addEtherAmountWei
    .mul(cdTokenReserve)
    .div(etherBalanceContract);
  return cryptoDevTokenAmount;
};

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import { Contract, providers, utils, BigNumber } from "ethers";
import { EXCHANGE_CONTRACT_ABI, EXCHANGE_CONTRACT_ADDRESS } from "../constants";

/**
* removeLiquidity: Removes the `removeLPTokensWei` amount of LP tokens from
* liquidity and also the calculated amount of `ether` and `CD` tokens
*/
export const removeLiquidity = async (signer, removeLPTokensWei) => {
  // Create a new instance of the exchange contract
  const exchangeContract = new Contract(
    EXCHANGE_CONTRACT_ADDRESS,
    EXCHANGE_CONTRACT_ABI,
    signer
  );
  const tx = await exchangeContract.removeLiquidity(removeLPTokensWei);
  await tx.wait();
};

/**
* getTokensAfterRemove: Calculates the amount of `Eth` and `CD` tokens
* that would be returned back to user after he removes `removeLPTokenWei` amount
* of LP tokens from the contract
*/
export const getTokensAfterRemove = async (
  provider,
  removeLPTokenWei,
  _ethBalance,
  cryptoDevTokenReserve
) => {
  try {
    // Create a new instance of the exchange contract
    const exchangeContract = new Contract(
      EXCHANGE_CONTRACT_ADDRESS,
      EXCHANGE_CONTRACT_ABI,
      provider
    );
    // Get the total supply of `Crypto Dev` LP tokens
    const _totalSupply = await exchangeContract.totalSupply();
    // Here we are using the BigNumber methods of multiplication and division
    // The amount of Eth that would be sent back to the user after he withdraws the LP token
    // is calculated based on a ratio,
    // Ratio is -> (amount of Eth that would be sent back to the user / Eth reserve) = (LP tokens withdrawn) / (total supply of LP tokens)
    // By some maths we get -> (amount of Eth that would be sent back to the user) = (Eth Reserve * LP tokens withdrawn) / (total supply of LP tokens)
    // Similarly we also maintain a ratio for the `CD` tokens, so here in our case
    // Ratio is -> (amount of CD tokens sent back to the user / CD Token reserve) = (LP tokens withdrawn) / (total supply of LP tokens)
    // Then (amount of CD tokens sent back to the user) = (CD token reserve * LP tokens withdrawn) / (total supply of LP tokens)
    const _removeEther = _ethBalance.mul(removeLPTokenWei).div(_totalSupply);
    const _removeCD = cryptoDevTokenReserve
      .mul(removeLPTokenWei)
      .div(_totalSupply);
    return {
      _removeEther,
      _removeCD,
    };
  } catch (err) {
    console.error(err);
  }
};

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

/*
    getAmountOfTokensReceivedFromSwap:  Returns the number of Eth/Crypto Dev tokens that can be received 
    when the user swaps `_swapAmountWei` amount of Eth/Crypto Dev tokens.
*/
export const getAmountOfTokensReceivedFromSwap = async (
  _swapAmountWei,
  provider,
  ethSelected,
  ethBalance,
  reservedCD
) => {
  // Create a new instance of the exchange contract
  const exchangeContract = new Contract(
    EXCHANGE_CONTRACT_ADDRESS,
    EXCHANGE_CONTRACT_ABI,
    provider
  );
  let amountOfTokens;
  // If `Eth` is selected this means our input value is `Eth` which means our input amount would be
  // `_swapAmountWei`, the input reserve would be the `ethBalance` of the contract and output reserve
  // would be the `Crypto Dev` token reserve
  if (ethSelected) {
    amountOfTokens = await exchangeContract.getAmountOfTokens(
      _swapAmountWei,
      ethBalance,
      reservedCD
    );
  } else {
    // If `Eth` is not selected this means our input value is `Crypto Dev` tokens which means our input amount would be
    // `_swapAmountWei`, the input reserve would be the `Crypto Dev` token reserve of the contract and output reserve
    // would be the `ethBalance`
    amountOfTokens = await exchangeContract.getAmountOfTokens(
      _swapAmountWei,
      reservedCD,
      ethBalance
    );
  }

  return amountOfTokens;
};

/*
  swapTokens: Swaps `swapAmountWei` of Eth/Crypto Dev tokens with `tokenToBeReceivedAfterSwap` amount of Eth/Crypto Dev tokens.
*/
export const swapTokens = async (
  signer,
  swapAmountWei,
  tokenToBeReceivedAfterSwap,
  ethSelected
) => {
  // Create a new instance of the exchange contract
  const exchangeContract = new Contract(
    EXCHANGE_CONTRACT_ADDRESS,
    EXCHANGE_CONTRACT_ABI,
    signer
  );
  const tokenContract = new Contract(
    TOKEN_CONTRACT_ADDRESS,
    TOKEN_CONTRACT_ABI,
    signer
  );
  let tx;
  // If Eth is selected call the `ethToCryptoDevToken` function else
  // call the `cryptoDevTokenToEth` function from the contract
  // As you can see you need to pass the `swapAmount` as a value to the function because
  // it is the ether we are paying to the contract, instead of a value we are passing to the function
  if (ethSelected) {
    tx = await exchangeContract.ethToCryptoDevToken(
      tokenToBeReceivedAfterSwap,
      {
        value: swapAmountWei,
      }
    );
  } else {
    // User has to approve `swapAmountWei` for the contract because `Crypto Dev` token
    // is an ERC20
    tx = await tokenContract.approve(
      EXCHANGE_CONTRACT_ADDRESS,
      swapAmountWei.toString()
    );
    await tx.wait();
    // call cryptoDevTokenToEth function which would take in `swapAmountWei` of `Crypto Dev` tokens and would
    // send back `tokenToBeReceivedAfterSwap` amount of `Eth` to the user
    tx = await exchangeContract.cryptoDevTokenToEth(
      swapAmountWei,
      tokenToBeReceivedAfterSwap
    );
  }
  await tx.wait();
};

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