LoveLetter-open.sol

contract LoveLetter {
    ...

    function open(uint256 id) external returns (string memory message) {
        require(receivers[id] == msg.sender, "Not receiver");
        require(!letters[id].opened, "Already opened");
        message = letters[id].message;
        letters[id].opened = true;
        uint256 amount = letters[id].etherAmount;
        console.log("[open]", id, amount);
        if (amount > 0) {
            payable(msg.sender).transfer(amount);
        }
        emit Opened(senders[id], msg.sender, id, amount);
    }
    
    ...
}