contract MultiSig {

    // ============ Events ============

    event Confirmation(address indexed sender, uint256 indexed transactionId);
    event Revocation(address indexed sender, uint256 indexed transactionId);
    event Submission(uint256 indexed transactionId);
    event Execution(uint256 indexed transactionId);
    event ExecutionFailure(uint256 indexed transactionId);
    event OwnerAddition(address indexed owner);
    event OwnerRemoval(address indexed owner);
    event RequirementChange(uint256 required);

    // ============ Constants ============

    uint256 constant public MAX_OWNER_COUNT = 50;
    address constant ADDRESS_ZERO = address(0x0);

    // ============ Storage ============

    mapping (uint256 => Transaction) public transactions;
    mapping (uint256 => mapping (address => bool)) public confirmations;
    mapping (address => bool) public isOwner;
    address[] public owners;
    uint256 public required;
    uint256 public transactionCount;

    // ============ Structs ============

    struct Transaction {
        address destination;
        uint256 value;
        bytes data;
        bool executed;
    }

    // ============ Modifiers ============

    modifier onlyWallet() {
        /* solium-disable-next-line error-reason */
        require(msg.sender == address(this));
        _;
    }

    modifier ownerDoesNotExist(
        address owner
    ) {
        /* solium-disable-next-line error-reason */
        require(!isOwner[owner]);
        _;
    }

    modifier ownerExists(
        address owner
    ) {
        /* solium-disable-next-line error-reason */
        require(isOwner[owner]);
        _;
    }

    modifier transactionExists(
        uint256 transactionId
    ) {
        /* solium-disable-next-line error-reason */
        require(transactions[transactionId].destination != ADDRESS_ZERO);
        _;
    }

    modifier confirmed(
        uint256 transactionId,
        address owner
    ) {
        /* solium-disable-next-line error-reason */
        require(confirmations[transactionId][owner]);
        _;
    }

    modifier notConfirmed(
        uint256 transactionId,
        address owner
    ) {
        /* solium-disable-next-line error-reason */
        require(!confirmations[transactionId][owner]);
        _;
    }

    modifier notExecuted(
        uint256 transactionId
    ) {
        /* solium-disable-next-line error-reason */
        require(!transactions[transactionId].executed);
        _;
    }

    modifier notNull(
        address _address
    ) {
        /* solium-disable-next-line error-reason */
        require(_address != ADDRESS_ZERO);
        _;
    }

    modifier validRequirement(
        uint256 ownerCount,
        uint256 _required
    ) {
        /* solium-disable-next-line error-reason */
        require(
            ownerCount <= MAX_OWNER_COUNT
            && _required <= ownerCount
            && _required != 0
            && ownerCount != 0
        );
        _;
    }

    // ============ Constructor ============

    /**
     * Contract constructor sets initial owners and required number of confirmations.
     *
     * @param  _owners    List of initial owners.
     * @param  _required  Number of required confirmations.
     */
    constructor(
        address[] memory _owners,
        uint256 _required
    )
        public
        validRequirement(_owners.length, _required)
    {
        for (uint256 i = 0; i < _owners.length; i++) {
            /* solium-disable-next-line error-reason */
            require(!isOwner[_owners[i]] && _owners[i] != ADDRESS_ZERO);
            isOwner[_owners[i]] = true;
        }
        owners = _owners;
        required = _required;
    }

    // ============ Wallet-Only Functions ============

    /**
     * Allows to add a new owner. Transaction has to be sent by wallet.
     *
     * @param  owner  Address of new owner.
     */
    function addOwner(
        address owner
    )
        public
        onlyWallet
        ownerDoesNotExist(owner)
        notNull(owner)
        validRequirement(owners.length + 1, required)
    {
        isOwner[owner] = true;
        owners.push(owner);
        emit OwnerAddition(owner);
    }

    /**
     * Allows to remove an owner. Transaction has to be sent by wallet.
     *
     * @param  owner  Address of owner.
     */
    function removeOwner(
        address owner
    )
        public
        onlyWallet
        ownerExists(owner)
    {
        isOwner[owner] = false;
        for (uint256 i = 0; i < owners.length - 1; i++) {
            if (owners[i] == owner) {
                owners[i] = owners[owners.length - 1];
                break;
            }
        }
        owners.length -= 1;
        if (required > owners.length) {
            changeRequirement(owners.length);
        }
        emit OwnerRemoval(owner);
    }

    /**
     * Allows to replace an owner with a new owner. Transaction has to be sent by wallet.
     *
     * @param  owner     Address of owner to be replaced.
     * @param  newOwner  Address of new owner.
     */
    function replaceOwner(
        address owner,
        address newOwner
    )
        public
        onlyWallet
        ownerExists(owner)
        ownerDoesNotExist(newOwner)
        notNull(newOwner)
    {
        for (uint256 i = 0; i < owners.length; i++) {
            if (owners[i] == owner) {
                owners[i] = newOwner;
                break;
            }
        }
        isOwner[owner] = false;
        isOwner[newOwner] = true;
        emit OwnerRemoval(owner);
        emit OwnerAddition(newOwner);
    }

    /**
     * Allows to change the number of required confirmations. Transaction has to be sent by wallet.
     *
     * @param  _required  Number of required confirmations.
     */
    function changeRequirement(
        uint256 _required
    )
        public
        onlyWallet
        validRequirement(owners.length, _required)
    {
        required = _required;
        emit RequirementChange(_required);
    }

    // ============ Owner Functions ============

    /**
     * Allows an owner to submit and confirm a transaction.
     *
     * @param  destination  Transaction target address.
     * @param  value        Transaction ether value.
     * @param  data         Transaction data payload.
     * @return              Transaction ID.
     */
    function submitTransaction(
        address destination,
        uint256 value,
        bytes memory data
    )
        public
        returns (uint256)
    {
        uint256 transactionId = addTransaction(destination, value, data);
        confirmTransaction(transactionId);
        return transactionId;
    }

    /**
     * Allows an owner to confirm a transaction.
     *
     * @param  transactionId  Transaction ID.
     */
    function confirmTransaction(
        uint256 transactionId
    )
        public
        ownerExists(msg.sender)
        transactionExists(transactionId)
        notConfirmed(transactionId, msg.sender)
    {
        confirmations[transactionId][msg.sender] = true;
        emit Confirmation(msg.sender, transactionId);
        executeTransaction(transactionId);
    }

    /**
     * Allows an owner to revoke a confirmation for a transaction.
     *
     * @param  transactionId  Transaction ID.
     */
    function revokeConfirmation(
        uint256 transactionId
    )
        public
        ownerExists(msg.sender)
        confirmed(transactionId, msg.sender)
        notExecuted(transactionId)
    {
        confirmations[transactionId][msg.sender] = false;
        emit Revocation(msg.sender, transactionId);
    }

    /**
     * Allows an owner to execute a confirmed transaction.
     *
     * @param  transactionId  Transaction ID.
     */
    function executeTransaction(
        uint256 transactionId
    )
        public
        ownerExists(msg.sender)
        confirmed(transactionId, msg.sender)
        notExecuted(transactionId)
    {
        if (isConfirmed(transactionId)) {
            Transaction storage txn = transactions[transactionId];
            txn.executed = true;
            if (externalCall(
                txn.destination,
                txn.value,
                txn.data.length,
                txn.data)
            ) {
                emit Execution(transactionId);
            } else {
                emit ExecutionFailure(transactionId);
                txn.executed = false;
            }
        }
    }

    // ============ Getter Functions ============

    /**
     * Returns the confirmation status of a transaction.
     *
     * @param  transactionId  Transaction ID.
     * @return                Confirmation status.
     */
    function isConfirmed(
        uint256 transactionId
    )
        public
        view
        returns (bool)
    {
        uint256 count = 0;
        for (uint256 i = 0; i < owners.length; i++) {
            if (confirmations[transactionId][owners[i]]) {
                count += 1;
            }
            if (count == required) {
                return true;
            }
        }
    }

    /**
     * Returns number of confirmations of a transaction.
     *
     * @param  transactionId  Transaction ID.
     * @return                Number of confirmations.
     */
    function getConfirmationCount(
        uint256 transactionId
    )
        public
        view
        returns (uint256)
    {
        uint256 count = 0;
        for (uint256 i = 0; i < owners.length; i++) {
            if (confirmations[transactionId][owners[i]]) {
                count += 1;
            }
        }
        return count;
    }

    /**
     * Returns total number of transactions after filers are applied.
     *
     * @param  pending   Include pending transactions.
     * @param  executed  Include executed transactions.
     * @return           Total number of transactions after filters are applied.
     */
    function getTransactionCount(
        bool pending,
        bool executed
    )
        public
        view
        returns (uint256)
    {
        uint256 count = 0;
        for (uint256 i = 0; i < transactionCount; i++) {
            if (
                pending && !transactions[i].executed
                || executed && transactions[i].executed
            ) {
                count += 1;
            }
        }
        return count;
    }

    /**
     * Returns array of owners.
     *
     * @return  Array of owner addresses.
     */
    function getOwners()
        public
        view
        returns (address[] memory)
    {
        return owners;
    }

    /**
     * Returns array with owner addresses, which confirmed transaction.
     *
     * @param  transactionId  Transaction ID.
     * @return                Array of owner addresses.
     */
    function getConfirmations(
        uint256 transactionId
    )
        public
        view
        returns (address[] memory)
    {
        address[] memory confirmationsTemp = new address[](owners.length);
        uint256 count = 0;
        uint256 i;
        for (i = 0; i < owners.length; i++) {
            if (confirmations[transactionId][owners[i]]) {
                confirmationsTemp[count] = owners[i];
                count += 1;
            }
        }
        address[] memory _confirmations = new address[](count);
        for (i = 0; i < count; i++) {
            _confirmations[i] = confirmationsTemp[i];
        }
        return _confirmations;
    }

    /**
     * Returns list of transaction IDs in defined range.
     *
     * @param  from      Index start position of transaction array.
     * @param  to        Index end position of transaction array.
     * @param  pending   Include pending transactions.
     * @param  executed  Include executed transactions.
     * @return           Array of transaction IDs.
     */
    function getTransactionIds(
        uint256 from,
        uint256 to,
        bool pending,
        bool executed
    )
        public
        view
        returns (uint256[] memory)
    {
        uint256[] memory transactionIdsTemp = new uint256[](transactionCount);
        uint256 count = 0;
        uint256 i;
        for (i = 0; i < transactionCount; i++) {
            if (
                pending && !transactions[i].executed
                || executed && transactions[i].executed
            ) {
                transactionIdsTemp[count] = i;
                count += 1;
            }
        }
        uint256[] memory _transactionIds = new uint256[](to - from);
        for (i = from; i < to; i++) {
            _transactionIds[i - from] = transactionIdsTemp[i];
        }
        return _transactionIds;
    }

    // ============ Helper Functions ============

    // call has been separated into its own function in order to take advantage
    // of the Solidity's code generator to produce a loop that copies tx.data into memory.
    function externalCall(
        address destination,
        uint256 value,
        uint256 dataLength,
        bytes memory data
    )
        internal
        returns (bool)
    {
        bool result;
        /* solium-disable-next-line security/no-inline-assembly */
        assembly {
            let x := mload(0x40)   // "Allocate" memory for output (0x40 is where "free memory" pointer is stored by convention)
            let d := add(data, 32) // First 32 bytes are the padded length of data, so exclude that
            result := call(
                sub(gas, 34710),   // 34710 is the value that solidity is currently emitting
                                   // It includes callGas (700) + callVeryLow (3, to pay for SUB) + callValueTransferGas (9000) +
                                   // callNewAccountGas (25000, in case the destination address does not exist and needs creating)
                destination,
                value,
                d,
                dataLength,        // Size of the input (in bytes) - this is what fixes the padding problem
                x,
                0                  // Output is ignored, therefore the output size is zero
            )
        }
        return result;
    }

    /**
     * Adds a new transaction to the transaction mapping, if transaction does not exist yet.
     *
     * @param  destination  Transaction target address.
     * @param  value        Transaction ether value.
     * @param  data         Transaction data payload.
     * @return              Transaction ID.
     */
    function addTransaction(
        address destination,
        uint256 value,
        bytes memory data
    )
        internal
        notNull(destination)
        returns (uint256)
    {
        uint256 transactionId = transactionCount;
        transactions[transactionId] = Transaction({
            destination: destination,
            value: value,
            data: data,
            executed: false
        });
        transactionCount += 1;
        emit Submission(transactionId);
        return transactionId;
    }
}
/**
 * @title MultiSig
 * @author dYdX
 *
 * Multi-Signature Wallet.
 * Allows multiple parties to agree on transactions before execution.
 * Adapted from Stefan George's MultiSigWallet contract.
 *
 * Logic Changes:
 *  - Removed the fallback function
 *  - Ensure newOwner is notNull
 *
 * Syntax Changes:
 *  - Update Solidity syntax for 0.5.X: use `emit` keyword (events), use `view` keyword (functions)
 *  - Add braces to all `if` and `for` statements
 *  - Remove named return variables
 *  - Add space before and after comparison operators
 *  - Add ADDRESS_ZERO as a constant
 *  - uint => uint256
 *  - external_call => externalCall
 */
function removeOwner(
        address owner
    )
        public
        onlyWallet
        ownerExists(owner)
    {
        isOwner[owner] = false;
        for (uint256 i = 0; i < owners.length - 1; i++) {
            if (owners[i] == owner) {
                owners[i] = owners[owners.length - 1];
                break;
            }
        }
        owners.length -= 1;
        if (required > owners.length) {
            changeRequirement(owners.length);
        }
        emit OwnerRemoval(owner);
    }
/**
 * Allows to remove an owner. Transaction has to be sent by wallet.
 *
 * @param  owner  Address of owner.
 */