contract RelayerModule is Module {

    uint256 constant internal BLOCKBOUND = 10000;

    mapping (address => RelayerConfig) public relayer; 

    struct RelayerConfig {
        uint256 nonce;
        mapping (bytes32 => bool) executedTx;
    }

    event TransactionExecuted(address indexed wallet, bool indexed success, bytes32 signedHash);

    /**
     * @dev Throws if the call did not go through the execute() method.
     */
    modifier onlyExecute {
        require(msg.sender == address(this), "RM: must be called via execute()");
        _;
    }

    /* ***************** Abstract method ************************* */

    /**
    * @dev Gets the number of valid signatures that must be provided to execute a
    * specific relayed transaction.
    * @param _wallet The target wallet.
    * @param _data The data of the relayed transaction.
    * @return The number of required signatures.
    */
    function getRequiredSignatures(BaseWallet _wallet, bytes _data) internal view returns (uint256);

    /**
    * @dev Validates the signatures provided with a relayed transaction.
    * The method MUST throw if one or more signatures are not valid.
    * @param _wallet The target wallet.
    * @param _data The data of the relayed transaction.
    * @param _signHash The signed hash representing the relayed transaction.
    * @param _signatures The signatures as a concatenated byte array.
    */
    function validateSignatures(BaseWallet _wallet, bytes _data, bytes32 _signHash, bytes _signatures) internal view returns (bool);

    /* ************************************************************ */

    /**
    * @dev Executes a relayed transaction.
    * @param _wallet The target wallet.
    * @param _data The data for the relayed transaction
    * @param _nonce The nonce used to prevent replay attacks.
    * @param _signatures The signatures as a concatenated byte array.
    * @param _gasPrice The gas price to use for the gas refund.
    * @param _gasLimit The gas limit to use for the gas refund.
    */
    function execute(
        BaseWallet _wallet,
        bytes _data, 
        uint256 _nonce, 
        bytes _signatures, 
        uint256 _gasPrice,
        uint256 _gasLimit
    )
        external
        returns (bool success)
    {
        uint startGas = gasleft();
        bytes32 signHash = getSignHash(address(this), _wallet, 0, _data, _nonce, _gasPrice, _gasLimit);
        require(checkAndUpdateUniqueness(_wallet, _nonce, signHash), "RM: Duplicate request");
        require(verifyData(address(_wallet), _data), "RM: the wallet authorized is different then the target of the relayed data");
        uint256 requiredSignatures = getRequiredSignatures(_wallet, _data);
        if((requiredSignatures * 65) == _signatures.length) {
            if(verifyRefund(_wallet, _gasLimit, _gasPrice, requiredSignatures)) {
                if(requiredSignatures == 0 || validateSignatures(_wallet, _data, signHash, _signatures)) {
                    // solium-disable-next-line security/no-call-value
                    success = address(this).call(_data);
                    refund(_wallet, startGas - gasleft(), _gasPrice, _gasLimit, requiredSignatures, msg.sender);
                }
            }
        }
        emit TransactionExecuted(_wallet, success, signHash); 
    }

    /**
    * @dev Gets the current nonce for a wallet.
    * @param _wallet The target wallet.
    */
    function getNonce(BaseWallet _wallet) external view returns (uint256 nonce) {
        return relayer[_wallet].nonce;
    }

    /**
    * @dev Generates the signed hash of a relayed transaction according to ERC 1077.
    * @param _from The starting address for the relayed transaction (should be the module)
    * @param _to The destination address for the relayed transaction (should be the wallet)
    * @param _value The value for the relayed transaction
    * @param _data The data for the relayed transaction
    * @param _nonce The nonce used to prevent replay attacks.
    * @param _gasPrice The gas price to use for the gas refund.
    * @param _gasLimit The gas limit to use for the gas refund.
    */
    function getSignHash(
        address _from,
        address _to, 
        uint256 _value, 
        bytes _data, 
        uint256 _nonce,
        uint256 _gasPrice,
        uint256 _gasLimit
    ) 
        internal 
        pure
        returns (bytes32) 
    {
        return keccak256(
            abi.encodePacked(
                "\x19Ethereum Signed Message:\n32",
                keccak256(abi.encodePacked(byte(0x19), byte(0), _from, _to, _value, _data, _nonce, _gasPrice, _gasLimit))
        ));
    }

    /**
    * @dev Checks if the relayed transaction is unique.
    * @param _wallet The target wallet.
    * @param _nonce The nonce
    * @param _signHash The signed hash of the transaction
    */
    function checkAndUpdateUniqueness(BaseWallet _wallet, uint256 _nonce, bytes32 _signHash) internal returns (bool) {
        if(relayer[_wallet].executedTx[_signHash] == true) {
            return false;
        }
        relayer[_wallet].executedTx[_signHash] = true;
        return true;
    }

    /**
    * @dev Checks that a nonce has the correct format and is valid. 
    * It must be constructed as nonce = {block number}{timestamp} where each component is 16 bytes.
    * @param _wallet The target wallet.
    * @param _nonce The nonce
    */
    function checkAndUpdateNonce(BaseWallet _wallet, uint256 _nonce) internal returns (bool) {
        if(_nonce <= relayer[_wallet].nonce) {
            return false;
        }   
        uint256 nonceBlock = (_nonce & 0xffffffffffffffffffffffffffffffff00000000000000000000000000000000) >> 128;
        if(nonceBlock > block.number + BLOCKBOUND) {
            return false;
        }
        relayer[_wallet].nonce = _nonce;
        return true;    
    }

    /**
    * @dev Recovers the signer at a given position from a list of concatenated signatures.
    * @param _signedHash The signed hash
    * @param _signatures The concatenated signatures.
    * @param _index The index of the signature to recover.
    */
    function recoverSigner(bytes32 _signedHash, bytes _signatures, uint _index) internal pure returns (address) {
        uint8 v;
        bytes32 r;
        bytes32 s;
        // we jump 32 (0x20) as the first slot of bytes contains the length
        // we jump 65 (0x41) per signature
        // for v we load 32 bytes ending with v (the first 31 come from s) then apply a mask
        // solium-disable-next-line security/no-inline-assembly
        assembly {
            r := mload(add(_signatures, add(0x20,mul(0x41,_index))))
            s := mload(add(_signatures, add(0x40,mul(0x41,_index))))
            v := and(mload(add(_signatures, add(0x41,mul(0x41,_index)))), 0xff)
        }
        require(v == 27 || v == 28); 
        return ecrecover(_signedHash, v, r, s);
    }

    /**
    * @dev Refunds the gas used to the Relayer. 
    * For security reasons the default behavior is to not refund calls with 0 or 1 signatures. 
    * @param _wallet The target wallet.
    * @param _gasUsed The gas used.
    * @param _gasPrice The gas price for the refund.
    * @param _gasLimit The gas limit for the refund.
    * @param _signatures The number of signatures used in the call.
    * @param _relayer The address of the Relayer.
    */
    function refund(BaseWallet _wallet, uint _gasUsed, uint _gasPrice, uint _gasLimit, uint _signatures, address _relayer) internal {
        uint256 amount = 29292 + _gasUsed; // 21000 (transaction) + 7620 (execution of refund) + 672 to log the event + _gasUsed
        // only refund if gas price not null, more than 1 signatures, gas less than gasLimit
        if(_gasPrice > 0 && _signatures > 1 && amount <= _gasLimit) {
            if(_gasPrice > tx.gasprice) {
                amount = amount * tx.gasprice;
            }
            else {
                amount = amount * _gasPrice;
            }
            _wallet.invoke(_relayer, amount, "");
        }
    }

    /**
    * @dev Returns false if the refund is expected to fail.
    * @param _wallet The target wallet.
    * @param _gasUsed The expected gas used.
    * @param _gasPrice The expected gas price for the refund.
    */
    function verifyRefund(BaseWallet _wallet, uint _gasUsed, uint _gasPrice, uint _signatures) internal view returns (bool) {
        if(_gasPrice > 0 
            && _signatures > 1 
            && (address(_wallet).balance < _gasUsed * _gasPrice || _wallet.authorised(this) == false)) {
            return false;
        }
        return true;
    }

    /**
    * @dev Checks that the wallet address provided as the first parameter of the relayed data is the same
    * as the wallet passed as the input of the execute() method. 
    @return false if the addresses are different.
    */
    function verifyData(address _wallet, bytes _data) private pure returns (bool) {
        require(_data.length >= 36, "RM: Invalid dataWallet");
        address dataWallet;
        // solium-disable-next-line security/no-inline-assembly
        assembly {
            //_data = {length:32}{sig:4}{_wallet:32}{...}
            dataWallet := mload(add(_data, 0x24))
        }
        return dataWallet == _wallet;
    }

    /**
    * @dev Parses the data to extract the method signature. 
    */
    function functionPrefix(bytes _data) internal pure returns (bytes4 prefix) {
        require(_data.length >= 4, "RM: Invalid functionPrefix");
        // solium-disable-next-line security/no-inline-assembly
        assembly {
            prefix := mload(add(_data, 0x20))
        }
    }
}
/**
 * @title RelayerModule
 * @dev Base module containing logic to execute transactions signed by eth-less accounts and sent by a relayer. 
 * @author Julien Niset - <julien@argent.xyz>
 */
function checkAndUpdateUniqueness(BaseWallet _wallet, uint256 _nonce, bytes32 _signHash) internal returns (bool) {
        if(relayer[_wallet].executedTx[_signHash] == true) {
            return false;
        }
        relayer[_wallet].executedTx[_signHash] = true;
        return true;
    }
/**
 * @dev Checks if the relayed transaction is unique.
 * @param _wallet The target wallet.
 * @param _nonce The nonce
 * @param _signHash The signed hash of the transaction
 */