[ERC7720] ERC20トークンを設定したタイムスタンプ以降に引き出せる仕組みを理解しよう！

pragma solidity ^0.8.0;

interface ITokenTransfer {
    // Event emitted when a transfer is initiated.
    event Transfer(
        uint256 txnId,
        address indexed token,
        address indexed from,
        address indexed to,
        uint256 amount,
        uint40 unlockTime,
        bytes32 referenceNo
    );

    // Event emitted when tokens are withdrawn.
    event Withdraw(
        uint256 txnId,
        address indexed token,
        address indexed from,
        address indexed to,
        uint256 amount
    );

    // Function to initiate a token transfer.
    // Parameters:
    // - _token: Address of the ERC20 token contract.
    // - _from: Address of the sender.
    // - _to: Address of the recipient.
    // - _amount: Amount of tokens to be transferred.
    // - _unlockTime: Time after which the tokens can be withdrawn.
    // - _reference: Reference ID for the transaction.
    // Returns the transaction ID.
    function transferFrom(
        address _token,
        address _from,
        address _to,
        uint256 _amount,
        uint40 _unlockTime,
        bytes32 _reference
    ) external returns (uint256 txnId);

    // Function to withdraw tokens from a transaction.
    // Parameters:
    // - _txnId: ID of the transaction to withdraw from.
    function withdraw(uint256 _txnId) external;

    // Function to get transaction details.
    // Parameters:
    // - _txnId: ID of the transaction.
    // Returns the transaction details.
    function getTransaction(uint256 _txnId)
        external
        view
        returns (
            address token,
            address from,
            address to,
            uint256 amount,
            uint40 unlockTime,
            bytes32 referenceNo,
            bool withdrawn
    );
}

event Transfer(
    uint256 txnId,
    address indexed token,
    address indexed from,
    address indexed to,
    uint256 amount,
    uint40 unlockTime,
    bytes32 referenceNo
);

event Withdraw(
    uint256 txnId,
    address indexed token,
    address indexed from,
    address indexed to,
    uint256 amount
);

function transferFrom(
    address _token,
    address _from,
    address _to,
    uint256 _amount,
    uint40 _unlockTime,
    bytes32 _reference
) external returns (uint256 txnId);

function withdraw(uint256 _txnId) external;

function getTransaction(uint256 _txnId)
    external
    view
    returns (
        address token,
        address from,
        address to,
        uint256 amount,
        uint40 unlockTime,
        bytes32 referenceNo,
        bool withdrawn
);

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";

contract TokenTransfer {
    using SafeERC20 for IERC20;

    struct Transaction {
        address token;      // Address of the ERC20 token contract.
        address from;       // Address of the sender.
        address to;         // Address of the recipient.
        uint256 amount;     // Amount of tokens to be transferred.
        uint40 unlockTime; // Time after which the tokens can be withdrawn.
        bytes32 referenceNo;  // Reference ID for the transaction.
        bool withdrawn;     // Flag indicating if the tokens have been withdrawn.
    }

    // Mapping from transaction ID to Transaction structure.
    mapping(uint256 => Transaction) public transactions;

    // Variable to keep track of the next transaction ID.
    uint256 public lastTxnId = 0;

    // Event emitted when a transfer is initiated.
    event Transfer(
        uint256 txnId,
        address indexed token,
        address indexed from,
        address indexed to,
        uint256 amount,
        uint40 unlockTime,
        bytes32 referenceNo
    );

    // Event emitted when tokens are withdrawn.
    event Withdraw(
        uint256 txnId,
        address indexed token,
        address indexed from,
        address indexed to,
        uint256 amount
    );

    constructor() {}

    // Function to initiate a token transfer.
    // Parameters:
    // - _token: Address of the ERC20 token contract.
    // - _from: Address of the sender.
    // - _to: Address of the recipient.
    // - _amount: Amount of tokens to be transferred.
    // - _unlockTime: Time after which the tokens can be withdrawn.
    // - _reference: Reference ID for the transaction.
    // Returns the transaction ID.
    function transferFrom(
        address _token,
        address _from,
        address _to,
        uint256 _amount,
        uint40 _unlockTime,
        bytes32 _reference
    ) external returns (uint256 txnId) {
        require(_amount > 0, "Invalid transfer amount");

        // Transfer tokens from sender to this contract.
        IERC20(_token).safeTransferFrom(_from, address(this), _amount);

        lastTxnId++;

        // Store the transaction details.
        transactions[lastTxnId] = Transaction({
            token: _token,
            from: _from,
            to: _to,
            amount: _amount,
            unlockTime: _unlockTime,
            referenceNo: _reference,
            withdrawn: false
        });

        // Emit an event for the transaction creation.
        emit Transfer(lastTxnId, _token, _from, _to, _amount, _unlockTime, _reference);
        return lastTxnId;
    }

    // Function to withdraw tokens from a transaction.
    // Parameters:
    // - _txnId: ID of the transaction to withdraw from.
    function withdraw(uint256 _txnId) external {
        Transaction storage transaction = transactions[_txnId];
        require(transaction.amount > 0, "Invalid transaction ID");
        require(block.timestamp >= transaction.unlockTime, "Current time is before unlock time");
        // require(transaction.to == msg.sender, "Only the recipient can withdraw the tokens");
        require(!transaction.withdrawn, "Tokens already withdrawn");

        IERC20(transaction.token).safeTransfer(transaction.to, transaction.amount);

        transaction.withdrawn = true;

        // Emit an event for the token withdrawal.
        emit Withdraw(_txnId, transaction.token, transaction.from, transaction.to, transaction.amount);
    }

    // Function to get transaction details.
    // Parameters:
    // - _txnId: ID of the transaction.
    // Returns the transaction details.
    function getTransaction(uint256 _txnId)
        external
        view
        returns (
            address token,
            address from,
            address to,
            uint256 amount,
            uint40 unlockTime,
            bytes32 referenceNo,
            bool withdrawn
        )
    {
        Transaction storage transaction = transactions[_txnId];
        require(transaction.amount > 0, "Invalid transaction ID");

        return (
            transaction.token,
            transaction.from,
            transaction.to,
            transaction.amount,
            transaction.unlockTime,
            transaction.referenceNo,
            transaction.withdrawn
        );
    }
}