"Mini" micro-cartelism

mmc.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract MicroCartelBidding {
    address public owner; // The owner of the bidding contract
    address[] public cartelMembers; // Addresses of cartel members
    uint public highestBid; // Highest bid amount
    
    constructor() {
        owner = msg.sender;
    }
    
    modifier onlyOwner() {
        require(msg.sender == owner, "Only owner can perform this action");
        _;
    }
    
    modifier onlyCartelMember() {
        bool isCartelMember = false;
        for (uint i = 0; i < cartelMembers.length; i++) {
            if (cartelMembers[i] == msg.sender) {
                isCartelMember = true;
                break;
            }
        }
        require(isCartelMember, "Only cartel members can perform this action");
        _;
    }
    
    // Function to join the cartel (only owner can invite members)
    function joinCartel(address _member) public onlyOwner {
        cartelMembers.push(_member);
    }
    
    // Function for cartel members to place unlimited bids
    function placeBid() public payable onlyCartelMember {
        // The highest bid is always set to the maximum amount sent
        highestBid = msg.value;
    }
    
    // Function for cartel members to withdraw their bids
    function withdrawBid() public onlyCartelMember {
        // Implement logic to refund the bidder
        // Note: In this scenario, cartel members can freely withdraw bids.
    }
    
    // Function to end the bidding and transfer all funds to the owner
    function endBidding() public onlyOwner {
        // Transfer all funds to the owner
        payable(owner).transfer(address(this).balance);
    }
    
    // Function to check the current highest bid
    function getCurrentHighestBid() public view returns (uint) {
        return highestBid;
    }
}