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| // SPDX-License-Identifier: MIT | ||
| pragma solidity ^0.8.0; | ||
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| import '@openzeppelin-07/utils/Address.sol'; | ||
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| contract GoodSamaritan { | ||
| Wallet public wallet; | ||
| Coin public coin; | ||
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| constructor() { | ||
| wallet = new Wallet(); | ||
| coin = new Coin(address(wallet)); | ||
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| wallet.setCoin(coin); | ||
| } | ||
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| function requestDonation() external returns (bool enoughBalance) { | ||
| // donate 10 coins to requester | ||
| try wallet.donate10(msg.sender) { | ||
| return true; | ||
| } catch (bytes memory err) { | ||
| if ( | ||
| keccak256(abi.encodeWithSignature('NotEnoughBalance()')) == | ||
| keccak256(err) | ||
| ) { | ||
| // send the coins left | ||
| wallet.transferRemainder(msg.sender); | ||
| return false; | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| contract Coin { | ||
| using Address for address; | ||
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| mapping(address => uint256) public balances; | ||
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| error InsufficientBalance(uint256 current, uint256 required); | ||
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| constructor(address wallet_) { | ||
| // one million coins for Good Samaritan initially | ||
| balances[wallet_] = 10 ** 6; | ||
| } | ||
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| function transfer(address dest_, uint256 amount_) external { | ||
| uint256 currentBalance = balances[msg.sender]; | ||
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| // transfer only occurs if balance is enough | ||
| if (amount_ <= currentBalance) { | ||
| balances[msg.sender] -= amount_; | ||
| balances[dest_] += amount_; | ||
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| if (dest_.isContract()) { | ||
| // notify contract | ||
| INotifyable(dest_).notify(amount_); | ||
| } | ||
| } else { | ||
| revert InsufficientBalance(currentBalance, amount_); | ||
| } | ||
| } | ||
| } | ||
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| contract Wallet { | ||
| // The owner of the wallet instance | ||
| address public owner; | ||
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| Coin public coin; | ||
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| error OnlyOwner(); | ||
| error NotEnoughBalance(); | ||
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| modifier onlyOwner() { | ||
| if (msg.sender != owner) { | ||
| revert OnlyOwner(); | ||
| } | ||
| _; | ||
| } | ||
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| constructor() { | ||
| owner = msg.sender; | ||
| } | ||
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| function donate10(address dest_) external onlyOwner { | ||
| // check balance left | ||
| if (coin.balances(address(this)) < 10) { | ||
| revert NotEnoughBalance(); | ||
| } else { | ||
| // donate 10 coins | ||
| coin.transfer(dest_, 10); | ||
| } | ||
| } | ||
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| function transferRemainder(address dest_) external onlyOwner { | ||
| // transfer balance left | ||
| coin.transfer(dest_, coin.balances(address(this))); | ||
| } | ||
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| function setCoin(Coin coin_) external onlyOwner { | ||
| coin = coin_; | ||
| } | ||
| } | ||
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| interface INotifyable { | ||
| function notify(uint256 amount) external; | ||
| } |