ERC-7720: Deferred Token Transfer

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    // Event emitted when tokens are withdrawn.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    // - _unlockTime: Time after which the tokens can be withdrawn.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            bool withdrawn
        );
}

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        uint40 unlockTime; // Time after which the tokens can be withdrawn.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        bool withdrawn;     // Flag indicating if the tokens have been withdrawn.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
        );
    }
}