Dutch auction

dutch_auction/.env.example

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+ALCHEMY_API_KEY=
+ROPSTEN_PRIVATE_KEY=

dutch_auction/.gitignore

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+node_modules
+.env
+
+#Hardhat files
+cache
+artifacts
+dist
+typechain

dutch_auction/.prettierrc

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+{
+  "overrides": [
+    {
+      "files": "*.sol",
+      "options": {
+        "printWidth": 120,
+        "tabWidth": 4,
+        "useTabs": false,
+        "singleQuote": false,
+        "bracketSpacing": false,
+        "explicitTypes": "always",
+        "semi": true
+      }
+    },
+    {
+      "files": "*.ts",
+      "options": {
+        "printWidth": 120
+      }
+    }
+  ]
+}

dutch_auction/contracts/DutchAuction.sol

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+pragma solidity ^0.8.7;
+
+import "@openzeppelin/contracts/access/Ownable.sol";
+import "@openzeppelin/contracts/token/ERC721/IERC721.sol";
+
+contract DutchAuction is Ownable {
+    IERC721 public immutable nft;
+    uint256 public immutable tokenId;
+
+    uint256 public immutable startPrice;
+    uint256 public immutable endPrice;
+
+    uint256 public immutable startTime;
+    uint256 public immutable endTime;
+
+    address public buyer; // address of buyer
+    uint256 public saleMoney; // price at which the nft sold
+    uint256 public buyersChange; // in case buyer sends more money than actual price
+
+    modifier onlyBuyer() {
+        require(msg.sender == buyer, "sender is not buyer");
+        _;
+    }
+
+    modifier ongoingSale() {
+        require(block.timestamp >= startTime, "sale didnt start yet");
+        require(block.timestamp <= endTime, "sale already ended");
+        _;
+    }
+
+    constructor(
+        address _nft,
+        uint256 _tokenId,
+        uint256 _startPrice,
+        uint256 _endPrice,
+        uint256 _startTime,
+        uint256 _endTime
+    ) {
+        require(_nft != address(0), "nft zero address");
+        require(_startPrice > 0, "start price must be positive");
+        require(_endPrice > 0, "end price must be positive");
+        require(_startPrice > _endPrice, "start price must be > end price");
+        require(_startTime >= block.timestamp, "must start in the future");
+        require(_endTime > _startTime, "end time must be > start time");
+
+        nft = IERC721(_nft);
+        tokenId = _tokenId;
+        startPrice = _startPrice;
+        endPrice = _endPrice;
+        startTime = _startTime;
+        endTime = _endTime;
+    }
+
+    function buy() external payable ongoingSale {
+        require(buyer == address(0), "already sold");
+
+        require(msg.value >= currentPrice(), "not enough ether");
+
+        saleMoney = currentPrice();
+        buyersChange = msg.value - saleMoney;
+        buyer = msg.sender;
+
+        nft.transferFrom(address(this), msg.sender, tokenId);
+    }
+
+    function withdrawPayment() external onlyOwner {
+        require(buyer != address(0), "token not sold yet");
+        require(saleMoney > 0, "already withdrew");
+
+        uint256 _saleMoney = saleMoney;
+        saleMoney = 0;
+        payable(owner()).transfer(_saleMoney);
+    }
+
+    function retrieveUnsoldToken() external onlyOwner {
+        require(buyer == address(0), "token was sold");
+        require(block.timestamp > endTime, "sale still in progress");
+        require(nft.ownerOf(tokenId) == address(this), "contract doesnt have the token anymore");
+
+        nft.transferFrom(address(this), owner(), tokenId);
+    }
+
+    function withdrawChange() external onlyBuyer {
+        require(buyersChange > 0, "nothing to withdraw");
+
+        uint256 _buyersChange = buyersChange;
+        buyersChange = 0;
+
+        payable(msg.sender).transfer(_buyersChange);
+    }
+
+    function currentPrice() public view ongoingSale returns (uint256) {
+        uint256 elapsed = block.timestamp - startTime;
+        uint256 duration = endTime - startTime;
+
+        uint256 priceDelta = startPrice - endPrice;
+
+        uint256 discount = (priceDelta * elapsed) / duration;
+        return startPrice - discount;
+    }
+}

dutch_auction/contracts/TestNFT.sol

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+pragma solidity ^0.8.7;
+
+import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
+
+contract TestNFT is ERC721("", "") {
+    function mint(address to, uint256 tokenId) public {
+        _mint(to, tokenId);
+    }
+}

dutch_auction/hardhat.config.ts

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+import { config as dotenvConfig } from "dotenv";
+import "@typechain/hardhat";
+import "@nomiclabs/hardhat-ethers";
+import "@nomiclabs/hardhat-waffle";
+import "@nomiclabs/hardhat-etherscan";
+import "solidity-coverage";
+import "hardhat-gas-reporter";
+import { HardhatUserConfig } from "hardhat/types/config";
+
+dotenvConfig();
+
+const gasPrice = parseInt(process.env.GAS_PRICE || "1000000000");
+
+const config: HardhatUserConfig = {
+  solidity: {
+    compilers: [
+      {
+        version: "0.8.10",
+        settings: {
+          optimizer: {
+            enabled: true,
+            runs: 200,
+          },
+        },
+      },
+    ],
+  },
+  networks: {
+    hardhat: {
+      initialBaseFeePerGas: 0,
+    },
+    rinkeby: {
+      url: process.env.RINKEBY_URL || "",
+      accounts:
+        process.env.PRIVATE_KEY !== undefined ? [process.env.PRIVATE_KEY] : [],
+      gasPrice,
+    },
+    mainnet: {
+      url: process.env.MAINNET_URL || "",
+      accounts:
+        process.env.PRIVATE_KEY !== undefined ? [process.env.PRIVATE_KEY] : [],
+      gasPrice,
+    },
+  },
+  gasReporter: {
+    enabled: process.env.REPORT_GAS !== undefined,
+    currency: "USD",
+    gasPrice: 120,
+    coinmarketcap: process.env.COINMARKETCAP_API_KEY,
+  },
+  etherscan: {
+    apiKey: process.env.ETHERSCAN_API_KEY,
+  },
+};
+
+export default config;