contract Multiownable {

    // VARIABLES

    uint256 public ownersGeneration;
    uint256 public howManyOwnersDecide;
    address[] public owners;
    bytes32[] public allOperations;
    address internal insideCallSender;
    uint256 internal insideCallCount;

    // Reverse lookup tables for owners and allOperations
    mapping(address => uint) public ownersIndices; // Starts from 1
    mapping(bytes32 => uint) public allOperationsIndicies;

    // Owners voting mask per operations
    mapping(bytes32 => uint256) public votesMaskByOperation;
    mapping(bytes32 => uint256) public votesCountByOperation;

    // EVENTS

    event OwnershipTransferred(address[] previousOwners, uint howManyOwnersDecide, address[] newOwners, uint newHowManyOwnersDecide);
    event OperationCreated(bytes32 operation, uint howMany, uint ownersCount, address proposer);
    event OperationUpvoted(bytes32 operation, uint votes, uint howMany, uint ownersCount, address upvoter);
    event OperationPerformed(bytes32 operation, uint howMany, uint ownersCount, address performer);
    event OperationDownvoted(bytes32 operation, uint votes, uint ownersCount,  address downvoter);
    event OperationCancelled(bytes32 operation, address lastCanceller);
    
    // ACCESSORS

    function isOwner(address wallet) public view returns(bool) {
        return ownersIndices[wallet] > 0;
    }

    function ownersCount() public view returns(uint) {
        return owners.length;
    }

    function allOperationsCount() public view returns(uint) {
        return allOperations.length;
    }

    // MODIFIERS

    /**
    * @dev Allows to perform method by any of the owners
    */
    modifier onlyAnyOwner {
        if (checkHowManyOwners(1)) {
            bool update = (insideCallSender == address(0));
            if (update) {
                insideCallSender = msg.sender;
                insideCallCount = 1;
            }
            _;
            if (update) {
                insideCallSender = address(0);
                insideCallCount = 0;
            }
        }
    }

    /**
    * @dev Allows to perform method only after many owners call it with the same arguments
    */
    modifier onlyManyOwners {
        if (checkHowManyOwners(howManyOwnersDecide)) {
            bool update = (insideCallSender == address(0));
            if (update) {
                insideCallSender = msg.sender;
                insideCallCount = howManyOwnersDecide;
            }
            _;
            if (update) {
                insideCallSender = address(0);
                insideCallCount = 0;
            }
        }
    }

    /**
    * @dev Allows to perform method only after all owners call it with the same arguments
    */
    modifier onlyAllOwners {
        if (checkHowManyOwners(owners.length)) {
            bool update = (insideCallSender == address(0));
            if (update) {
                insideCallSender = msg.sender;
                insideCallCount = owners.length;
            }
            _;
            if (update) {
                insideCallSender = address(0);
                insideCallCount = 0;
            }
        }
    }

    /**
    * @dev Allows to perform method only after some owners call it with the same arguments
    */
    modifier onlySomeOwners(uint howMany) {
        require(howMany > 0, "onlySomeOwners: howMany argument is zero");
        require(howMany <= owners.length, "onlySomeOwners: howMany argument exceeds the number of owners");
        
        if (checkHowManyOwners(howMany)) {
            bool update = (insideCallSender == address(0));
            if (update) {
                insideCallSender = msg.sender;
                insideCallCount = howMany;
            }
            _;
            if (update) {
                insideCallSender = address(0);
                insideCallCount = 0;
            }
        }
    }

    // CONSTRUCTOR

    constructor() public {
        owners.push(msg.sender);
        ownersIndices[msg.sender] = 1;
        howManyOwnersDecide = 1;
    }

    // INTERNAL METHODS

    /**
     * @dev onlyManyOwners modifier helper
     */
    function checkHowManyOwners(uint howMany) internal returns(bool) {
        if (insideCallSender == msg.sender) {
            require(howMany <= insideCallCount, "checkHowManyOwners: nested owners modifier check require more owners");
            return true;
        }

        uint ownerIndex = ownersIndices[msg.sender] - 1;
        require(ownerIndex < owners.length, "checkHowManyOwners: msg.sender is not an owner");
        bytes32 operation = keccak256(abi.encodePacked(msg.data, ownersGeneration));

        require((votesMaskByOperation[operation] & (2 ** ownerIndex)) == 0, "checkHowManyOwners: owner already voted for the operation");
        votesMaskByOperation[operation] |= (2 ** ownerIndex);
        uint operationVotesCount = votesCountByOperation[operation] + 1;
        votesCountByOperation[operation] = operationVotesCount;
        if (operationVotesCount == 1) {
            allOperationsIndicies[operation] = allOperations.length;
            allOperations.push(operation);
            emit OperationCreated(operation, howMany, owners.length, msg.sender);
        }
        emit OperationUpvoted(operation, operationVotesCount, howMany, owners.length, msg.sender);

        // If enough owners confirmed the same operation
        if (votesCountByOperation[operation] == howMany) {
            deleteOperation(operation);
            emit OperationPerformed(operation, howMany, owners.length, msg.sender);
            return true;
        }

        return false;
    }

    /**
    * @dev Used to delete cancelled or performed operation
    * @param operation defines which operation to delete
    */
    function deleteOperation(bytes32 operation) internal {
        uint index = allOperationsIndicies[operation];
        if (index < allOperations.length - 1) { // Not last
            allOperations[index] = allOperations[allOperations.length - 1];
            allOperationsIndicies[allOperations[index]] = index;
        }
        //allOperations.length-1
        allOperations.push(allOperations[allOperations.length-1]);

        delete votesMaskByOperation[operation];
        delete votesCountByOperation[operation];
        delete allOperationsIndicies[operation];
    }

    // PUBLIC METHODS

    /**
    * @dev Allows owners to change their mind by cacnelling votesMaskByOperation operations
    * @param operation defines which operation to delete
    */
    function cancelPending(bytes32 operation) public onlyAnyOwner {
        uint ownerIndex = ownersIndices[msg.sender] - 1;
        require((votesMaskByOperation[operation] & (2 ** ownerIndex)) != 0, "cancelPending: operation not found for this user");
        votesMaskByOperation[operation] &= ~(2 ** ownerIndex);
        uint operationVotesCount = votesCountByOperation[operation] - 1;
        votesCountByOperation[operation] = operationVotesCount;
        emit OperationDownvoted(operation, operationVotesCount, owners.length, msg.sender);
        if (operationVotesCount == 0) {
            deleteOperation(operation);
            emit OperationCancelled(operation, msg.sender);
        }
    }

    /**
    * @dev Allows owners to change ownership
    * @param newOwners defines array of addresses of new owners
    */
    function transferOwnership(address[] memory newOwners) public {
        transferOwnershipWithHowMany(newOwners, newOwners.length);
    }

    /**
    * @dev Allows owners to change ownership
    * @param newOwners defines array of addresses of new owners
    * @param newHowManyOwnersDecide defines how many owners can decide
    */
    function transferOwnershipWithHowMany(address[] memory newOwners, uint256 newHowManyOwnersDecide) public onlyManyOwners {
        require(newOwners.length > 0, "transferOwnershipWithHowMany: owners array is empty");
        require(newOwners.length <= 256, "transferOwnershipWithHowMany: owners count is greater then 256");
        require(newHowManyOwnersDecide > 0, "transferOwnershipWithHowMany: newHowManyOwnersDecide equal to 0");
        require(newHowManyOwnersDecide <= newOwners.length, "transferOwnershipWithHowMany: newHowManyOwnersDecide exceeds the number of owners");

        // Reset owners reverse lookup table
        for (uint j = 0; j < owners.length; j++) {
            delete ownersIndices[owners[j]];
        }
        for (uint i = 0; i < newOwners.length; i++) {
            require(newOwners[i] != address(0), "transferOwnershipWithHowMany: owners array contains zero");
            require(ownersIndices[newOwners[i]] == 0, "transferOwnershipWithHowMany: owners array contains duplicates");
            ownersIndices[newOwners[i]] = i + 1;
        }
        
        emit OwnershipTransferred(owners, howManyOwnersDecide, newOwners, newHowManyOwnersDecide);
        owners = newOwners;
        howManyOwnersDecide = newHowManyOwnersDecide;
        // allOperations.length = 0;
        allOperations.push(allOperations[0]);
        ownersGeneration++;
    }

}
function isOwner(address wallet) public view returns(bool) {
    return ownersIndices[wallet] > 0;
}

// ACCESSORS