// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract SecureVault {
    mapping(address => uint256) public balances;
    
    event Deposited(address indexed user, uint256 amount);
    event Withdrawn(address indexed user, uint256 amount);

    // Checks-Effects-Interactions Pattern prevents Reentrancy
    function withdraw() external {
        uint256 amount = balances[msg.sender];
        require(amount > 0, "Insufficient funds");

        // Effect: Update state BEFORE sending ether
        balances[msg.sender] = 0;

        // Interaction: Send ether
        (bool success, ) = msg.sender.call{value: amount}("");
        require(success, "Transfer failed");

        emit Withdrawn(msg.sender, amount);
    }
    
    receive() external payable {
        balances[msg.sender] += msg.value;
        emit Deposited(msg.sender, msg.value);
    }
}