Estrategias Anti-Ballenas para proteger tu Token
Tags: blockchain, solidity, ethereum, web3
Published: 2022-01-27 15:33:01

---
title: Estrategias Anti-Ballenas para proteger tu Token
published: true
description: 
tags: blockchain, solidity, ethereum, web3
cover_image: https://dev-to-uploads.s3.amazonaws.com/uploads/articles/1ns4936vrh2foouwkpl1.png
---

¿Cómo protegemos un lanzamiento de un token con fuertes inversionistas iniciales? Cuando realizamos una presale de token ERC-20, usualmente el precio que se dá a los inversionistas mayoritarios es menor al del precio en el lanzamiento público al momento de proveer liquidez en un DEX. Por eso es muy importante acompañar el presale con un contrato de timelock. Esto no solo suavisará los primeros momentos del token en el mercado sino que también te dará control al momento de proveer liquidez en los DEXes. En este video veremos cómo crear un contrato con Timelocks para estrategias de Vesting.

## Dependencias

Para este tutorial ocuparás [NodeJs](https://nodejs.org/es/) que recomiendo descargarlo en Linux via [NVM](https://github.com/nvm-sh/nvm#installing-and-updating), y finalmente [Metamask](https://metamask.io/) con fondos de Rinkeby Testnet que puedes conseguir desde el [Faucet](https://faucet.rinkeby.io/).

## 1. Lanza el smart contract

Primero lanzaremos un contrato de un token ERC20 como ejemplo.

```solidity
// SPDX-License-Identifier: MIT
pragma solidity 0.8.11;

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

contract MyERC20 is ERC20 {
  constructor () ERC20("My Token", "TKN") {
    _mint(msg.sender, 1000000 ether);
  }
}
```

Luego lanzamos el contrato del Timelock, recuerda reemplalzar el la dirección `0x0000000000000000000000000000000000000000` por la del token recién lanzado.

```solidity
// SPDX-License-Identifier: MIT

pragma solidity 0.8.11;

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

contract TokenTimelock is Ownable {
  ERC20 public token;
  uint public ENTRY_PRICE = 0.1 ether;
  uint public AMOUNT_PER_UNLOCK = 10 ether;
  uint public UNLOCK_COUNT = 3;

  mapping(uint8 => uint256) public unlock_time;
  mapping(address => bool) public is_beneficiary;
  mapping(address => mapping(uint => bool)) public beneficiary_has_claimed;

  constructor()
  {
    token = ERC20(0x0000000000000000000000000000000000000000);

    unlock_time[0] = 1642052293;
    unlock_time[1] = 1642052293;
    unlock_time[2] = 1642052293;
  }
  
  function claim(uint8 unlock_number) public {
    require(unlock_number < UNLOCK_COUNT, "Must be below unlock count.");
    require(block.timestamp >= unlock_time[unlock_number], "Must have reached unlock time.");
    require(is_beneficiary[msg.sender], "Beneficiary must has bought.");
    require(beneficiary_has_claimed[msg.sender][unlock_number] == false, "Beneficiary should not have claimed.");

    beneficiary_has_claimed[msg.sender][unlock_number] = true;

    token.transfer(msg.sender, AMOUNT_PER_UNLOCK);
  }

  function buy() public payable
  {
    require(msg.value == ENTRY_PRICE, "Must pay the entry price.");
    is_beneficiary[msg.sender] = true;
  }

  function withdraw() public
  {
    (bool sent, bytes memory data) = address(owner()).call{value: address(this).balance}("");
    require(sent, "Failed to send Ether");
    data;
  }
}
```

## 2. Construye el frontend

Estos son los archivos que necesitas para tener un frontend funcional:
1. El archivo HTML `index.html`
2. El archivo Javascript que te permite comunicarte con web3 en este caso yo lo llamé `blockchain_stuff.js`
3. El Json ABI que puedes obtener desde remix `ContractABI.json`

`index.html`
```html
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
</head>
<body>
  <p id="web3_message"></p>
  <input type="button" value="Buy" onclick="buy()"></input>
  <div id="claim_buttons"></div>
  <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/web3/1.3.5/web3.min.js"></script>
  <script type="text/javascript" src="blockchain_stuff.js"></script>
</body>
</html>
```

`blockchain_stuff.js`
```js
const NETWORK_ID = 4
const CONTRACT_ADDRESS = "0x03E59E35BC96060D0a4565Ebd307a3102d5627e1"
const JSON_CONTRACT_ABI_PATH = "./ContractABI.json"
var contract
var accounts
var web3
var ENTRY_PRICE

function metamaskReloadCallback() {
  window.ethereum.on('accountsChanged', (accounts) => {
    document.getElementById("web3_message").textContent="Se cambió el account, refrescando...";
    window.location.reload()
  })
  window.ethereum.on('networkChanged', (accounts) => {
    document.getElementById("web3_message").textContent="Se el network, refrescando...";
    window.location.reload()
  })
}

const getWeb3 = async () => {
  return new Promise((resolve, reject) => {
    if(document.readyState=="complete")
    {
      if (window.ethereum) {
        const web3 = new Web3(window.ethereum)
        window.location.reload()
        resolve(web3)
      } else {
        reject("must install MetaMask")
        document.getElementById("web3_message").textContent="Error: Porfavor conéctate a Metamask";
      }
    }else
    {
      window.addEventListener("load", async () => {
        if (window.ethereum) {
          const web3 = new Web3(window.ethereum)
          resolve(web3)
        } else {
          reject("must install MetaMask")
          document.getElementById("web3_message").textContent="Error: Please install Metamask";
        }
      });
    }
  });
};

const getContract = async (web3) => {
  const response = await fetch(JSON_CONTRACT_ABI_PATH);
  const data = await response.json();
  
  const netId = await web3.eth.net.getId();
  contract = new web3.eth.Contract(
    data,
    CONTRACT_ADDRESS
    );
  return contract
}

async function loadDapp() {
  metamaskReloadCallback()
  document.getElementById("web3_message").textContent="Please connect to Metamask"
  var awaitWeb3 = async function () {
    web3 = await getWeb3()
    web3.eth.net.getId((err, netId) => {
      if (netId == NETWORK_ID) {
        var awaitContract = async function () {
          contract = await getContract(web3);
          await window.ethereum.request({ method: "eth_requestAccounts" })
          accounts = await web3.eth.getAccounts()
          document.getElementById("web3_message").textContent="You are connected to Metamask"
          onContractInitCallback()
        };
        awaitContract();
      } else {
        document.getElementById("web3_message").textContent="Please connect to Rinkeby";
      }
    });
  };
  awaitWeb3();
}

const onContractInitCallback = async () => {
  AMOUNT_PER_UNLOCK = await contract.methods.AMOUNT_PER_UNLOCK().call()
  UNLOCK_COUNT = await contract.methods.UNLOCK_COUNT().call()
  ENTRY_PRICE = await contract.methods.ENTRY_PRICE().call()
  user_is_beneficiary = await contract.methods.is_beneficiary(accounts[0]).call()

  var parent = document.getElementById("claim_buttons")
  if(user_is_beneficiary)
  {
    for(i=0; i<UNLOCK_COUNT; i++)
    {
      var unlock_h = document.createElement("h3")
      unlock_h.innerHTML = "Unlock #" + (i+1)
      parent.appendChild(unlock_h)

      user_has_claimed = await contract.methods.beneficiary_has_claimed(accounts[0],i).call()
      if(!user_has_claimed)
      {
        timestamp = await contract.methods.unlock_time(i).call()
        current_time = Math.round(Date.now() / 1000)
        if(parseInt(timestamp) < current_time)
        {
          if(parseInt(timestamp) != 0)
          {
            var btn = document.createElement("button")
            btn.innerHTML = "Claim!"
            btn.unlock_number = i
            btn.onclick = function (e, e, x) {
              claim(this.unlock_number)
            }
            parent.appendChild(btn)
            parent.appendChild(document.createElement("br"))
          }else
          {
            claimed_p = document.createElement("p")
            claimed_p.innerHTML = "This timelock is still not set"
            parent.appendChild(claimed_p)
          }
        }else
        {
          claimed_p = document.createElement("p")
          claimed_p.innerHTML = "Please claim " + web3.utils.fromWei(AMOUNT_PER_UNLOCK) + " tokens on " + new Date(timestamp * 1000)
          parent.appendChild(claimed_p)
        }
      }else
      {
        claimed_p = document.createElement("p")
        claimed_p.innerHTML = "Claimed"
        parent.appendChild(claimed_p)
      }
    }
  }else
  {
    claimed_p = document.createElement("p")
    claimed_p.innerHTML = "No timelocks found for this account"
    parent.appendChild(claimed_p)
  }
}


//// PUBLIC FUNCTIONS ////

/*
await claim(3)
*/
const claim = async (unlock_number) => {
  const result = await contract.methods.claim(unlock_number)
  .send({ from: accounts[0], gas: 0, value: 0 })
  .on('transactionHash', function(hash){
    document.getElementById("web3_message").textContent="Claiming...";
  })
  .on('receipt', function(receipt){
    document.getElementById("web3_message").textContent="Success.";    })
  .catch((revertReason) => {
    console.log("ERROR! Transaction reverted: " + revertReason.receipt.transactionHash)
  });
}

/*
await buy()
*/
const buy = async (unlock_number) => {
  const result = await contract.methods.buy()
  .send({ from: accounts[0], gas: 0, value: ENTRY_PRICE })
  .on('transactionHash', function(hash){
    document.getElementById("web3_message").textContent="Buying...";
  })
  .on('receipt', function(receipt){
    document.getElementById("web3_message").textContent="Success.";    })
  .catch((revertReason) => {
    console.log("ERROR! Transaction reverted: " + revertReason.receipt.transactionHash)
  });
}

/*
await withdraw()
*/
const withdraw = async (unlock_number) => {
  const result = await contract.methods.withdraw()
  .send({ from: accounts[0], gas: 0, value: 0 })
  .on('transactionHash', function(hash){
    document.getElementById("web3_message").textContent="Withdrawing...";
  })
  .on('receipt', function(receipt){
    document.getElementById("web3_message").textContent="Success.";    })
  .catch((revertReason) => {
    console.log("ERROR! Transaction reverted: " + revertReason.receipt.transactionHash)
  });
}

loadDapp()
```

## 3. Probar la dapp

Instalamos un servidor local.

```bash
npm i -g lite-server
```

Y lo lanzamos.

```bash
lite-server
```

Ahora podemos interactuar con la dapp en nuestro browser en `localhost:3000`.

## Bono: Timelock editable y con whitelist

```solidity
// SPDX-License-Identifier: MIT

pragma solidity 0.8.11;

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

contract TokenTimelock is Ownable {
  ERC20 public token;
  uint public ENTRY_PRICE;
  uint public AMOUNT_PER_UNLOCK;
  uint public UNLOCK_COUNT;

  mapping(uint8 => uint256) public unlock_time;
  mapping(address => bool) public is_beneficiary;
  mapping(address => mapping(uint => bool)) public beneficiary_has_claimed;

  mapping(address => bool) public whitelist;

  constructor()
  {
    token = ERC20(0x0000000000000000000000000000000000000000);
  }
  
  function claim(uint8 unlock_number) public {
    require(unlock_number < UNLOCK_COUNT, "Must be below unlock count.");
    require(block.timestamp >= unlock_time[unlock_number], "Must have reached unlock time.");
    require(is_beneficiary[msg.sender], "Beneficiary must has bought.");
    require(beneficiary_has_claimed[msg.sender][unlock_number] == false, "Beneficiary should not have claimed.");
    require(whitelist[msg.sender],"Sender must be whitelisted");

    beneficiary_has_claimed[msg.sender][unlock_number] = true;

    token.transfer(msg.sender, AMOUNT_PER_UNLOCK);
  }

  function buy() public payable
  {
    require(msg.value == ENTRY_PRICE, "Must pay the entry price.");
    is_beneficiary[msg.sender] = true;
  }

  function withdraw() public
  {
    (bool sent, bytes memory data) = address(owner()).call{value: address(this).balance}("");
    require(sent, "Failed to send Ether");
    data;
  }

  // Admin functions

  function setEntryPrice(uint entry_price) public onlyOwner
  {
    ENTRY_PRICE = entry_price;
  }

  function setAmountPerUnlock(uint amount_per_unlock) public onlyOwner
  {
    AMOUNT_PER_UNLOCK = amount_per_unlock;
  }

  function setUnlockCount(uint unlock_count) public onlyOwner
  {
    UNLOCK_COUNT = unlock_count;
  }

  function setUnlockTimes(uint[] memory unlock_times) public onlyOwner
  {
    setEntryPrice(unlock_times.length);
    for(uint8 i; i<unlock_times.length; i++)
    {
      unlock_time[i] = unlock_times[i];
    }
  }

  function editWhitelist(address[] memory addresses, bool value) public onlyOwner {
    for(uint i; i < addresses.length; i++){
      whitelist[addresses[i]] = value;
    }
  }
}
```

**¡Gracias por ver este tutorial!**

Sígueme en dev.to y en [Youtube](https://www.youtube.com/channel/UCNRB4tgwp09z4391JRjEsRA) para todo lo relacionado al desarrollo en Blockchain en Español.