Multisig.sol

// SPDX-License-Identifier: GPL-3.0
pragma solidity 0.8.7;

contract Multisig {
    uint256 minSignatures = 3;
    address private contractOwner;
    mapping(address => bool) private owners;
    struct Transaction {
        address to;
        uint256 amount;
        uint256 createdAt;
        uint256 sentAt;
        uint256 signatureCount;
        mapping(address => bool) signatures;
    }
    mapping(uint256 => Transaction) transactions;
    uint256[] public pendingTransactionIds;
    uint256 private currentTransactionId = 0;

    constructor() payable {
        contractOwner = msg.sender;
        owners[msg.sender] = true;
    }

    modifier isOwner() {
        require(owners[msg.sender], "You are not the owner");
        _;
    }

    function addOwner(address newOwner) public {
        require(contractOwner == msg.sender, "You are not the owner");
        owners[newOwner] = true;
    }

    function removeOwner(address addr) public isOwner() {
        require(contractOwner == msg.sender, "You are not the owner");
        owners[addr] = false;
    }

    function createTransaction(address to, uint256 amount) public isOwner() returns(uint256) {
        uint256 currentBalance = address(this).balance;
        require(amount <= currentBalance, "Account balance is not enough");

        uint256 transactionId = currentTransactionId;
        Transaction storage newTransaction = transactions[transactionId];
        newTransaction.to = to;
        newTransaction.amount = amount;
        newTransaction.createdAt = block.timestamp;
        newTransaction.sentAt = 0;
        newTransaction.signatureCount = 0;
        pendingTransactionIds.push(transactionId);

        currentTransactionId += 1;

        return transactionId;
    }

    function signTransaction(uint256 tranactionId) public isOwner() {
        Transaction storage currentTransaction = transactions[tranactionId];

        require(currentTransaction.sentAt == 0, "This transaction has executed");
        require(currentTransaction.signatures[msg.sender] == false, "You have signed the transaction");
        currentTransaction.signatures[msg.sender] = true;
        currentTransaction.signatureCount += 1;

        if (currentTransaction.signatureCount >= minSignatures) {
            payable(currentTransaction.to).transfer(currentTransaction.amount);
            currentTransaction.sentAt = block.timestamp;

            for (uint256 i=0; i<pendingTransactionIds.length; i++) {
                if (pendingTransactionIds[i] == tranactionId) {
                    delete pendingTransactionIds[i];
                    break;
                }
            }
        }
    }
}