Cómo implementar Staking en Solidity

 pragma solidity ^ 0.5 .0 ; import "openzeppelin-solidity/contracts/token/ERC20/ERC20.sol" ; import "openzeppelin-solidity/contracts/math/SafeMath.sol" ; import "openzeppelin-solidity/contracts/ownership/Ownable.sol" ; /** * @title Staking Token (STK) * @author Alberto Cuesta Canada * @notice Implements a basic ERC20 staking token with incentive distribution. */ contract StakingToken is ERC20, Ownable { using SafeMath for uint256; /** * @notice The constructor for the Staking Token. * @param _owner The address to receive all tokens on construction. * @param _supply The amount of tokens to mint on construction. */ constructor (address _owner, uint256 _supply) public { _mint(_owner, _supply); }

 /** * @notice We usually require to know who are all the stakeholders. */ address[] internal stakeholders;

 /** * @notice A method to check if an address is a stakeholder. * @param _address The address to verify. * @return bool, uint256 Whether the address is a stakeholder, * and if so its position in the stakeholders array. */ function isStakeholder ( address _address ) public view returns ( bool, uint256 ) { for (uint256 s = 0 ; s < stakeholders.length; s += 1 ){ if (_address == stakeholders[s]) return ( true , s); } return ( false , 0 ); } /** * @notice A method to add a stakeholder. * @param _stakeholder The stakeholder to add. */ function addStakeholder ( address _stakeholder ) public { (bool _isStakeholder, ) = isStakeholder(_stakeholder); if (!_isStakeholder) stakeholders.push(_stakeholder); } /** * @notice A method to remove a stakeholder. * @param _stakeholder The stakeholder to remove. */ function removeStakeholder ( address _stakeholder ) public { (bool _isStakeholder, uint256 s) = isStakeholder(_stakeholder); if (_isStakeholder){ stakeholders[s] = stakeholders[stakeholders.length - 1 ]; stakeholders.pop(); } }

 /** * @notice The stakes for each stakeholder. */ mapping( address => uint256) internal stakes;

 /** * @notice A method to retrieve the stake for a stakeholder. * @param _stakeholder The stakeholder to retrieve the stake for. * @return uint256 The amount of wei staked. */ function stakeOf ( address _stakeholder ) public view returns ( uint256 ) { return stakes[_stakeholder]; } /** * @notice A method to the aggregated stakes from all stakeholders. * @return uint256 The aggregated stakes from all stakeholders. */ function totalStakes ( ) public view returns ( uint256 ) { uint256 _totalStakes = 0 ; for (uint256 s = 0 ; s < stakeholders.length; s += 1 ){ _totalStakes = _totalStakes.add(stakes[stakeholders[s]]); } return _totalStakes; }

 /** * @notice A method for a stakeholder to create a stake. * @param _stake The size of the stake to be created. */ function createStake ( uint256 _stake ) public { _burn(msg.sender, _stake); if (stakes[msg.sender] == 0 ) addStakeholder(msg.sender); stakes[msg.sender] = stakes[msg.sender].add(_stake); } /** * @notice A method for a stakeholder to remove a stake. * @param _stake The size of the stake to be removed. */ function removeStake ( uint256 _stake ) public { stakes[msg.sender] = stakes[msg.sender].sub(_stake); if (stakes[msg.sender] == 0 ) removeStakeholder(msg.sender); _mint(msg.sender, _stake); }

 /** * @notice The accumulated rewards for each stakeholder. */ mapping( address => uint256) internal rewards; /** * @notice A method to allow a stakeholder to check his rewards. * @param _stakeholder The stakeholder to check rewards for. */ function rewardOf ( address _stakeholder ) public view returns ( uint256 ) { return rewards[_stakeholder]; } /** * @notice A method to the aggregated rewards from all stakeholders. * @return uint256 The aggregated rewards from all stakeholders. */ function totalRewards ( ) public view returns ( uint256 ) { uint256 _totalRewards = 0 ; for (uint256 s = 0 ; s < stakeholders.length; s += 1 ){ _totalRewards = _totalRewards.add(rewards[stakeholders[s]]); } return _totalRewards; }

 /** * @notice A simple method that calculates the rewards for each stakeholder. * @param _stakeholder The stakeholder to calculate rewards for. */ function calculateReward ( address _stakeholder ) public view returns ( uint256 ) { return stakes[_stakeholder] / 100 ; } /** * @notice A method to distribute rewards to all stakeholders. */ function distributeRewards ( ) public onlyOwner { for (uint256 s = 0 ; s < stakeholders.length; s += 1 ){ address stakeholder = stakeholders[s]; uint256 reward = calculateReward(stakeholder); rewards[stakeholder] = rewards[stakeholder].add(reward); } } /** * @notice A method to allow a stakeholder to withdraw his rewards. */ function withdrawReward ( ) public { uint256 reward = rewards[msg.sender]; rewards[msg.sender] = 0 ; _mint(msg.sender, reward); }

 contract( 'StakingToken' , (accounts) => { let stakingToken; const manyTokens = BigNumber( 10 ).pow( 18 ).multipliedBy( 1000 ); const owner = accounts[ 0 ]; const user = accounts[ 1 ]; before( async () => { stakingToken = await StakingToken.deployed(); }); describe( 'Staking' , () => { beforeEach( async () => { stakingToken = await StakingToken.new( owner, manyTokens.toString( 10 ) ); });

 it( 'createStake creates a stake.' , async () => { await stakingToken.transfer(user, 3 , { from : owner }); await stakingToken.createStake( 1 , { from : user }); assert.equal( await stakingToken.balanceOf(user), 2 ); assert.equal( await stakingToken.stakeOf(user), 1 ); assert.equal( await stakingToken.totalSupply(), manyTokens.minus( 1 ).toString( 10 ), ); assert.equal( await stakingToken.totalStakes(), 1 ); });

 it( 'rewards are distributed.' , async () => { await stakingToken.transfer(user, 100 , { from : owner }); await stakingToken.createStake( 100 , { from : user }); await stakingToken.distributeRewards({ from : owner }); assert.equal( await stakingToken.rewardOf(user), 1 ); assert.equal( await stakingToken.totalRewards(), 1 ); });

 it( 'rewards can be withdrawn.' , async () => { await stakingToken.transfer(user, 100 , { from : owner }); await stakingToken.createStake( 100 , { from : user }); await stakingToken.distributeRewards({ from : owner }); await stakingToken.withdrawReward({ from : user }); const initialSupply = manyTokens; const existingStakes = 100 ; const mintedAndWithdrawn = 1 ; assert.equal( await stakingToken.balanceOf(user), 1 ); assert.equal( await stakingToken.stakeOf(user), 100 ); assert.equal( await stakingToken.rewardOf(user), 0 ); assert.equal( await stakingToken.totalSupply(), initialSupply .minus(existingStakes) .plus(mintedAndWithdrawn) .toString( 10 ) ); assert.equal( await stakingToken.totalStakes(), 100 ); assert.equal( await stakingToken.totalRewards(), 0 ); });