Example of extending Account implementation (#10)

* feat: example contract demonstrating Account extension

* review feedback

packages/contracts/contracts/ERC721SafeTransferAccount.sol

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+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.23;
+
+import { Account } from './Account.sol';
+import "@openzeppelin/contracts/token/ERC721/IERC721Receiver.sol";
+
+contract ERC721SafeTransferAccount is Account, IERC721Receiver {
+    constructor(Account.PublicKey memory publicKey) Account(publicKey) {}
+
+    function onERC721Received(address, address, uint256, bytes calldata) external pure override returns (bytes4) {
+		return IERC721Receiver.onERC721Received.selector;
+	}
+}

packages/contracts/contracts/ERC721SafeTransferAccountFactory.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.23;
+
+import {ERC721SafeTransferAccount} from "./ERC721SafeTransferAccount.sol";
+
+contract ERC721SafeTransferAccountFactory {
+    struct User {
+        uint256 id;
+        ERC721SafeTransferAccount.PublicKey publicKey;
+        address account;
+    }
+
+    mapping(uint256 => User) users;
+
+    event UserCreated(uint256 userId, ERC721SafeTransferAccount.PublicKey publicKey, address account);
+
+    function getUser(uint256 id) public view returns (User memory) {
+        return users[id];
+    }
+
+    function createUser(uint256 id, ERC721SafeTransferAccount.PublicKey memory publicKey) public {
+        ERC721SafeTransferAccount account = new ERC721SafeTransferAccount(publicKey);
+        users[id] = User(id, publicKey, address(account));
+        emit UserCreated(id, publicKey, address(account));
+    }
+}

packages/contracts/ignition/modules/ERC721SafeTransferAccount.ts

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+import { buildModule } from '@nomicfoundation/hardhat-ignition/modules';
+import hre from 'hardhat';
+
+export default buildModule('ERC721SafeTransferAccount', (m) => {
+  // bytecode of contract available at https://github.com/daimo-eth/p256-verifier/tree/master
+  const p256PrecompileBytecode =
+    '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';
+
+  // deploy precompile code at the expected predetermined address
+  void hre.network.provider.send('hardhat_setCode', ['0xc2b78104907F722DABAc4C69f826a522B2754De4', p256PrecompileBytecode]);
+  const accountFactory = m.contract('ERC721SafeTransferAccountFactory');
+  const erc721 = m.contract('GenericERC721');
+
+  return { accountFactory, erc721 };
+});

packages/contracts/test/ERC721SafeTransferAccount.ts

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+import type { HardhatEthersSigner } from '@nomicfoundation/hardhat-ethers/signers';
+import { expect } from 'chai';
+import type { Contract, TransactionResponse } from 'ethers';
+import { ethers, ignition } from 'hardhat';
+import ERC721SafeTransferAccountModule from '../ignition/modules/ERC721SafeTransferAccount';
+import { ERC721SafeTransferAccountFactory__factory } from '../typechain-types';
+import { createKeypair } from './utils';
+
+describe('ERC721SafeTransferAccount', () => {
+  const deployFixture = async () => {
+    const [signer, otherAccount] = await ethers.getSigners();
+    const { accountFactory, erc721 } = await ignition.deploy(ERC721SafeTransferAccountModule);
+
+    return { signer, otherAccount, accountFactory, erc721 };
+  };
+
+  let signer: HardhatEthersSigner, otherAccount: HardhatEthersSigner, accountFactory: Contract, erc721: Contract;
+
+  beforeEach(async () => {
+    ({ signer, otherAccount, accountFactory, erc721 } = await deployFixture());
+  });
+
+  describe('accepting ERC721.safeTransferFrom', () => {
+    it('should successfully receive tokens transferred with safeTransferFrom', async () => {
+      await erc721.mint(otherAccount.address);
+
+      const { x, y } = createKeypair();
+
+      const tx: TransactionResponse = await accountFactory.createUser(1n, { x, y });
+      const receipt = await tx.wait();
+      expect(receipt).to.not.be.null;
+      const iface = ethers.Interface.from(ERC721SafeTransferAccountFactory__factory.abi);
+      const userCreated = iface.parseLog(receipt!.logs[0]);
+      const account = userCreated!.args[2];
+
+      // Transfer the token using safeTransferFrom
+      await (erc721.connect(otherAccount) as Contract).safeTransferFrom(otherAccount.address, account, 1n);
+
+      // Verify that accountFactory now owns the token
+      const newOwner = await erc721.ownerOf(1n);
+      expect(newOwner).to.equal(account);
+    });
+  });
+});