// File: openzeppelin-solidity/contracts/access/Roles.sol

pragma solidity ^0.5.0;

/**
 * @title Roles
 * @dev Library for managing addresses assigned to a Role.
 */
library Roles {
    struct Role {
        mapping (address => bool) bearer;
    }

    /**
     * @dev give an account access to this role
     */
    function add(Role storage role, address account) internal {
        require(account != address(0));
        require(!has(role, account));

        role.bearer[account] = true;
    }

    /**
     * @dev remove an account's access to this role
     */
    function remove(Role storage role, address account) internal {
        require(account != address(0));
        require(has(role, account));

        role.bearer[account] = false;
    }

    /**
     * @dev check if an account has this role
     * @return bool
     */
    function has(Role storage role, address account) internal view returns (bool) {
        require(account != address(0));
        return role.bearer[account];
    }
}

// File: openzeppelin-solidity/contracts/access/roles/SignerRole.sol

pragma solidity ^0.5.0;


contract SignerRole {
    using Roles for Roles.Role;

    event SignerAdded(address indexed account);
    event SignerRemoved(address indexed account);

    Roles.Role private _signers;

    constructor () internal {
        _addSigner(msg.sender);
    }

    modifier onlySigner() {
        require(isSigner(msg.sender));
        _;
    }

    function isSigner(address account) public view returns (bool) {
        return _signers.has(account);
    }

    function addSigner(address account) public onlySigner {
        _addSigner(account);
    }

    function renounceSigner() public {
        _removeSigner(msg.sender);
    }

    function _addSigner(address account) internal {
        _signers.add(account);
        emit SignerAdded(account);
    }

    function _removeSigner(address account) internal {
        _signers.remove(account);
        emit SignerRemoved(account);
    }
}

// File: openzeppelin-solidity/contracts/cryptography/ECDSA.sol

pragma solidity ^0.5.0;

/**
 * @title Elliptic curve signature operations
 * @dev Based on https://gist.github.com/axic/5b33912c6f61ae6fd96d6c4a47afde6d
 * TODO Remove this library once solidity supports passing a signature to ecrecover.
 * See https://github.com/ethereum/solidity/issues/864
 */

library ECDSA {
    /**
     * @dev Recover signer address from a message by using their signature
     * @param hash bytes32 message, the hash is the signed message. What is recovered is the signer address.
     * @param signature bytes signature, the signature is generated using web3.eth.sign()
     */
    function recover(bytes32 hash, bytes memory signature) internal pure returns (address) {
        bytes32 r;
        bytes32 s;
        uint8 v;

        // Check the signature length
        if (signature.length != 65) {
            return (address(0));
        }

        // Divide the signature in r, s and v variables
        // ecrecover takes the signature parameters, and the only way to get them
        // currently is to use assembly.
        // solhint-disable-next-line no-inline-assembly
        assembly {
            r := mload(add(signature, 0x20))
            s := mload(add(signature, 0x40))
            v := byte(0, mload(add(signature, 0x60)))
        }

        // Version of signature should be 27 or 28, but 0 and 1 are also possible versions
        if (v < 27) {
            v += 27;
        }

        // If the version is correct return the signer address
        if (v != 27 && v != 28) {
            return (address(0));
        } else {
            return ecrecover(hash, v, r, s);
        }
    }

    /**
     * toEthSignedMessageHash
     * @dev prefix a bytes32 value with "\x19Ethereum Signed Message:"
     * and hash the result
     */
    function toEthSignedMessageHash(bytes32 hash) internal pure returns (bytes32) {
        // 32 is the length in bytes of hash,
        // enforced by the type signature above
        return keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n32", hash));
    }
}

// File: openzeppelin-solidity/contracts/drafts/SignatureBouncer.sol

pragma solidity ^0.5.0;



/**
 * @title SignatureBouncer
 * @author PhABC, Shrugs and aflesher
 * @dev SignatureBouncer allows users to submit a signature as a permission to
 * do an action.
 * If the signature is from one of the authorized signer addresses, the
 * signature is valid.
 * Note that SignatureBouncer offers no protection against replay attacks, users
 * must add this themselves!
 *
 * Signer addresses can be individual servers signing grants or different
 * users within a decentralized club that have permission to invite other
 * members. This technique is useful for whitelists and airdrops; instead of
 * putting all valid addresses on-chain, simply sign a grant of the form
 * keccak256(abi.encodePacked(`:contractAddress` + `:granteeAddress`)) using a
 * valid signer address.
 * Then restrict access to your crowdsale/whitelist/airdrop using the
 * `onlyValidSignature` modifier (or implement your own using _isValidSignature).
 * In addition to `onlyValidSignature`, `onlyValidSignatureAndMethod` and
 * `onlyValidSignatureAndData` can be used to restrict access to only a given
 * method or a given method with given parameters respectively.
 * See the tests in SignatureBouncer.test.js for specific usage examples.
 *
 * @notice A method that uses the `onlyValidSignatureAndData` modifier must make
 * the _signature parameter the "last" parameter. You cannot sign a message that
 * has its own signature in it so the last 128 bytes of msg.data (which
 * represents the length of the _signature data and the _signaature data itself)
 * is ignored when validating. Also non fixed sized parameters make constructing
 * the data in the signature much more complex.
 * See https://ethereum.stackexchange.com/a/50616 for more details.
 */
contract SignatureBouncer is SignerRole {
    using ECDSA for bytes32;

    // Function selectors are 4 bytes long, as documented in
    // https://solidity.readthedocs.io/en/v0.4.24/abi-spec.html#function-selector
    uint256 private constant _METHOD_ID_SIZE = 4;
    // Signature size is 65 bytes (tightly packed v + r + s), but gets padded to 96 bytes
    uint256 private constant _SIGNATURE_SIZE = 96;

    constructor () internal {
        // solhint-disable-previous-line no-empty-blocks
    }

    /**
     * @dev requires that a valid signature of a signer was provided
     */
    modifier onlyValidSignature(bytes memory signature) {
        require(_isValidSignature(msg.sender, signature));
        _;
    }

    /**
     * @dev requires that a valid signature with a specifed method of a signer was provided
     */
    modifier onlyValidSignatureAndMethod(bytes memory signature) {
        require(_isValidSignatureAndMethod(msg.sender, signature));
        _;
    }

    /**
     * @dev requires that a valid signature with a specifed method and params of a signer was provided
     */
    modifier onlyValidSignatureAndData(bytes memory signature) {
        require(_isValidSignatureAndData(msg.sender, signature));
        _;
    }

    /**
     * @dev is the signature of `this + sender` from a signer?
     * @return bool
     */
    function _isValidSignature(address account, bytes memory signature) internal view returns (bool) {
        return _isValidDataHash(keccak256(abi.encodePacked(address(this), account)), signature);
    }

    /**
     * @dev is the signature of `this + sender + methodId` from a signer?
     * @return bool
     */
    function _isValidSignatureAndMethod(address account, bytes memory signature) internal view returns (bool) {
        bytes memory data = new bytes(_METHOD_ID_SIZE);
        for (uint i = 0; i < data.length; i++) {
            data[i] = msg.data[i];
        }
        return _isValidDataHash(keccak256(abi.encodePacked(address(this), account, data)), signature);
    }

    /**
        * @dev is the signature of `this + sender + methodId + params(s)` from a signer?
        * @notice the signature parameter of the method being validated must be the "last" parameter
        * @return bool
        */
    function _isValidSignatureAndData(address account, bytes memory signature) internal view returns (bool) {
        require(msg.data.length > _SIGNATURE_SIZE);

        bytes memory data = new bytes(msg.data.length - _SIGNATURE_SIZE);
        for (uint i = 0; i < data.length; i++) {
            data[i] = msg.data[i];
        }

        return _isValidDataHash(keccak256(abi.encodePacked(address(this), account, data)), signature);
    }

    /**
     * @dev internal function to convert a hash to an eth signed message
     * and then recover the signature and check it against the signer role
     * @return bool
     */
    function _isValidDataHash(bytes32 hash, bytes memory signature) internal view returns (bool) {
        address signer = hash.toEthSignedMessageHash().recover(signature);

        return signer != address(0) && isSigner(signer);
    }
}

// File: openzeppelin-solidity/contracts/token/ERC20/IERC20.sol

pragma solidity ^0.5.0;

/**
 * @title ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/20
 */
interface IERC20 {
    function transfer(address to, uint256 value) external returns (bool);

    function approve(address spender, uint256 value) external returns (bool);

    function transferFrom(address from, address to, uint256 value) external returns (bool);

    function totalSupply() external view returns (uint256);

    function balanceOf(address who) external view returns (uint256);

    function allowance(address owner, address spender) external view returns (uint256);

    event Transfer(address indexed from, address indexed to, uint256 value);

    event Approval(address indexed owner, address indexed spender, uint256 value);
}

// File: openzeppelin-solidity/contracts/math/SafeMath.sol

pragma solidity ^0.5.0;

/**
 * @title SafeMath
 * @dev Unsigned math operations with safety checks that revert on error
 */
library SafeMath {
    /**
    * @dev Multiplies two unsigned integers, reverts on overflow.
    */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b);

        return c;
    }

    /**
    * @dev Integer division of two unsigned integers truncating the quotient, reverts on division by zero.
    */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
    * @dev Subtracts two unsigned integers, reverts on overflow (i.e. if subtrahend is greater than minuend).
    */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a);
        uint256 c = a - b;

        return c;
    }

    /**
    * @dev Adds two unsigned integers, reverts on overflow.
    */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a);

        return c;
    }

    /**
    * @dev Divides two unsigned integers and returns the remainder (unsigned integer modulo),
    * reverts when dividing by zero.
    */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b != 0);
        return a % b;
    }
}

// File: openzeppelin-solidity/contracts/token/ERC20/ERC20.sol

pragma solidity ^0.5.0;



/**
 * @title Standard ERC20 token
 *
 * @dev Implementation of the basic standard token.
 * https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md
 * Originally based on code by FirstBlood:
 * https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
 *
 * This implementation emits additional Approval events, allowing applications to reconstruct the allowance status for
 * all accounts just by listening to said events. Note that this isn't required by the specification, and other
 * compliant implementations may not do it.
 */
contract ERC20 is IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowed;

    uint256 private _totalSupply;

    /**
    * @dev Total number of tokens in existence
    */
    function totalSupply() public view returns (uint256) {
        return _totalSupply;
    }

    /**
    * @dev Gets the balance of the specified address.
    * @param owner The address to query the balance of.
    * @return An uint256 representing the amount owned by the passed address.
    */
    function balanceOf(address owner) public view returns (uint256) {
        return _balances[owner];
    }

    /**
     * @dev Function to check the amount of tokens that an owner allowed to a spender.
     * @param owner address The address which owns the funds.
     * @param spender address The address which will spend the funds.
     * @return A uint256 specifying the amount of tokens still available for the spender.
     */
    function allowance(address owner, address spender) public view returns (uint256) {
        return _allowed[owner][spender];
    }

    /**
    * @dev Transfer token for a specified address
    * @param to The address to transfer to.
    * @param value The amount to be transferred.
    */
    function transfer(address to, uint256 value) public returns (bool) {
        _transfer(msg.sender, to, value);
        return true;
    }

    /**
     * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
     * Beware that changing an allowance with this method brings the risk that someone may use both the old
     * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
     * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     * @param spender The address which will spend the funds.
     * @param value The amount of tokens to be spent.
     */
    function approve(address spender, uint256 value) public returns (bool) {
        require(spender != address(0));

        _allowed[msg.sender][spender] = value;
        emit Approval(msg.sender, spender, value);
        return true;
    }

    /**
     * @dev Transfer tokens from one address to another.
     * Note that while this function emits an Approval event, this is not required as per the specification,
     * and other compliant implementations may not emit the event.
     * @param from address The address which you want to send tokens from
     * @param to address The address which you want to transfer to
     * @param value uint256 the amount of tokens to be transferred
     */
    function transferFrom(address from, address to, uint256 value) public returns (bool) {
        _allowed[from][msg.sender] = _allowed[from][msg.sender].sub(value);
        _transfer(from, to, value);
        emit Approval(from, msg.sender, _allowed[from][msg.sender]);
        return true;
    }

    /**
     * @dev Increase the amount of tokens that an owner allowed to a spender.
     * approve should be called when allowed_[_spender] == 0. To increment
     * allowed value is better to use this function to avoid 2 calls (and wait until
     * the first transaction is mined)
     * From MonolithDAO Token.sol
     * Emits an Approval event.
     * @param spender The address which will spend the funds.
     * @param addedValue The amount of tokens to increase the allowance by.
     */
    function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
        require(spender != address(0));

        _allowed[msg.sender][spender] = _allowed[msg.sender][spender].add(addedValue);
        emit Approval(msg.sender, spender, _allowed[msg.sender][spender]);
        return true;
    }

    /**
     * @dev Decrease the amount of tokens that an owner allowed to a spender.
     * approve should be called when allowed_[_spender] == 0. To decrement
     * allowed value is better to use this function to avoid 2 calls (and wait until
     * the first transaction is mined)
     * From MonolithDAO Token.sol
     * Emits an Approval event.
     * @param spender The address which will spend the funds.
     * @param subtractedValue The amount of tokens to decrease the allowance by.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
        require(spender != address(0));

        _allowed[msg.sender][spender] = _allowed[msg.sender][spender].sub(subtractedValue);
        emit Approval(msg.sender, spender, _allowed[msg.sender][spender]);
        return true;
    }

    /**
    * @dev Transfer token for a specified addresses
    * @param from The address to transfer from.
    * @param to The address to transfer to.
    * @param value The amount to be transferred.
    */
    function _transfer(address from, address to, uint256 value) internal {
        require(to != address(0));

        _balances[from] = _balances[from].sub(value);
        _balances[to] = _balances[to].add(value);
        emit Transfer(from, to, value);
    }

    /**
     * @dev Internal function that mints an amount of the token and assigns it to
     * an account. This encapsulates the modification of balances such that the
     * proper events are emitted.
     * @param account The account that will receive the created tokens.
     * @param value The amount that will be created.
     */
    function _mint(address account, uint256 value) internal {
        require(account != address(0));

        _totalSupply = _totalSupply.add(value);
        _balances[account] = _balances[account].add(value);
        emit Transfer(address(0), account, value);
    }

    /**
     * @dev Internal function that burns an amount of the token of a given
     * account.
     * @param account The account whose tokens will be burnt.
     * @param value The amount that will be burnt.
     */
    function _burn(address account, uint256 value) internal {
        require(account != address(0));

        _totalSupply = _totalSupply.sub(value);
        _balances[account] = _balances[account].sub(value);
        emit Transfer(account, address(0), value);
    }

    /**
     * @dev Internal function that burns an amount of the token of a given
     * account, deducting from the sender's allowance for said account. Uses the
     * internal burn function.
     * Emits an Approval event (reflecting the reduced allowance).
     * @param account The account whose tokens will be burnt.
     * @param value The amount that will be burnt.
     */
    function _burnFrom(address account, uint256 value) internal {
        _allowed[account][msg.sender] = _allowed[account][msg.sender].sub(value);
        _burn(account, value);
        emit Approval(account, msg.sender, _allowed[account][msg.sender]);
    }
}

// File: openzeppelin-solidity/contracts/token/ERC20/ERC20Burnable.sol

pragma solidity ^0.5.0;


/**
 * @title Burnable Token
 * @dev Token that can be irreversibly burned (destroyed).
 */
contract ERC20Burnable is ERC20 {
    /**
     * @dev Burns a specific amount of tokens.
     * @param value The amount of token to be burned.
     */
    function burn(uint256 value) public {
        _burn(msg.sender, value);
    }

    /**
     * @dev Burns a specific amount of tokens from the target address and decrements allowance
     * @param from address The address which you want to send tokens from
     * @param value uint256 The amount of token to be burned
     */
    function burnFrom(address from, uint256 value) public {
        _burnFrom(from, value);
    }
}

// File: openzeppelin-solidity/contracts/token/ERC20/SafeERC20.sol

pragma solidity ^0.5.0;



/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure.
 * To use this library you can add a `using SafeERC20 for ERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        require(token.transfer(to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        require(token.transferFrom(from, to, value));
    }

    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        require((value == 0) || (token.allowance(address(this), spender) == 0));
        require(token.approve(spender, value));
    }

    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        require(token.approve(spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value);
        require(token.approve(spender, newAllowance));
    }
}

// File: openzeppelin-solidity/contracts/ownership/Ownable.sol

pragma solidity ^0.5.0;

/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions".
 */
contract Ownable {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev The Ownable constructor sets the original `owner` of the contract to the sender
     * account.
     */
    constructor () internal {
        _owner = msg.sender;
        emit OwnershipTransferred(address(0), _owner);
    }

    /**
     * @return the address of the owner.
     */
    function owner() public view returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(isOwner());
        _;
    }

    /**
     * @return true if `msg.sender` is the owner of the contract.
     */
    function isOwner() public view returns (bool) {
        return msg.sender == _owner;
    }

    /**
     * @dev Allows the current owner to relinquish control of the contract.
     * @notice Renouncing to ownership will leave the contract without an owner.
     * It will not be possible to call the functions with the `onlyOwner`
     * modifier anymore.
     */
    function renounceOwnership() public onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Allows the current owner to transfer control of the contract to a newOwner.
     * @param newOwner The address to transfer ownership to.
     */
    function transferOwnership(address newOwner) public onlyOwner {
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers control of the contract to a newOwner.
     * @param newOwner The address to transfer ownership to.
     */
    function _transferOwnership(address newOwner) internal {
        require(newOwner != address(0));
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: contracts/misc/DutchAuction.sol

pragma solidity ^0.5.0;






/// @title Dutch auction contract - distribution of XRT tokens using an auction.
/// @author Stefan George - <stefan.george@consensys.net>
/// @author Airalab - <research@aira.life> 
contract DutchAuction is SignatureBouncer, Ownable {
    using SafeERC20 for ERC20Burnable;

    /*
     *  Events
     */
    event BidSubmission(address indexed sender, uint256 amount);

    /*
     *  Constants
     */
    uint constant public WAITING_PERIOD = 0; // 1 days;

    /*
     *  Storage
     */
    ERC20Burnable public token;
    address public ambix;
    address payable public wallet;
    uint public maxTokenSold;
    uint public ceiling;
    uint public priceFactor;
    uint public startBlock;
    uint public endTime;
    uint public totalReceived;
    uint public finalPrice;
    mapping (address => uint) public bids;
    Stages public stage;

    /*
     *  Enums
     */
    enum Stages {
        AuctionDeployed,
        AuctionSetUp,
        AuctionStarted,
        AuctionEnded,
        TradingStarted
    }

    /*
     *  Modifiers
     */
    modifier atStage(Stages _stage) {
        // Contract on stage
        require(stage == _stage);
        _;
    }

    modifier isValidPayload() {
        require(msg.data.length == 4 || msg.data.length == 164);
        _;
    }

    modifier timedTransitions() {
        if (stage == Stages.AuctionStarted && calcTokenPrice() <= calcStopPrice())
            finalizeAuction();
        if (stage == Stages.AuctionEnded && now > endTime + WAITING_PERIOD)
            stage = Stages.TradingStarted;
        _;
    }

    /*
     *  Public functions
     */
    /// @dev Contract constructor function sets owner.
    /// @param _wallet Multisig wallet.
    /// @param _maxTokenSold Auction token balance.
    /// @param _ceiling Auction ceiling.
    /// @param _priceFactor Auction price factor.
    constructor(address payable _wallet, uint _maxTokenSold, uint _ceiling, uint _priceFactor)
        public
    {
        require(_wallet != address(0) && _ceiling > 0 && _priceFactor > 0);

        wallet = _wallet;
        maxTokenSold = _maxTokenSold;
        ceiling = _ceiling;
        priceFactor = _priceFactor;
        stage = Stages.AuctionDeployed;
    }

    /// @dev Setup function sets external contracts' addresses.
    /// @param _token Token address.
    /// @param _ambix Distillation cube address.
    function setup(ERC20Burnable _token, address _ambix)
        public
        onlyOwner
        atStage(Stages.AuctionDeployed)
    {
        // Validate argument
        require(_token != ERC20Burnable(0) && _ambix != address(0));

        token = _token;
        ambix = _ambix;

        // Validate token balance
        require(token.balanceOf(address(this)) == maxTokenSold);

        stage = Stages.AuctionSetUp;
    }

    /// @dev Starts auction and sets startBlock.
    function startAuction()
        public
        onlyOwner
        atStage(Stages.AuctionSetUp)
    {
        stage = Stages.AuctionStarted;
        startBlock = block.number;
    }

    /// @dev Calculates current token price.
    /// @return Returns token price.
    function calcCurrentTokenPrice()
        public
        timedTransitions
        returns (uint)
    {
        if (stage == Stages.AuctionEnded || stage == Stages.TradingStarted)
            return finalPrice;
        return calcTokenPrice();
    }

    /// @dev Returns correct stage, even if a function with timedTransitions modifier has not yet been called yet.
    /// @return Returns current auction stage.
    function updateStage()
        public
        timedTransitions
        returns (Stages)
    {
        return stage;
    }

    /// @dev Allows to send a bid to the auction.
    /// @param signature KYC approvement
    function bid(bytes calldata signature)
        external
        payable
        isValidPayload
        timedTransitions
        atStage(Stages.AuctionStarted)
        onlyValidSignature(signature)
        returns (uint amount)
    {
        require(msg.value > 0);
        amount = msg.value;

        address payable receiver = msg.sender;

        // Prevent that more than 90% of tokens are sold. Only relevant if cap not reached.
        uint maxWei = maxTokenSold * calcTokenPrice() / 10**9 - totalReceived;
        uint maxWeiBasedOnTotalReceived = ceiling - totalReceived;
        if (maxWeiBasedOnTotalReceived < maxWei)
            maxWei = maxWeiBasedOnTotalReceived;

        // Only invest maximum possible amount.
        if (amount > maxWei) {
            amount = maxWei;
            // Send change back to receiver address.
            receiver.transfer(msg.value - amount);
        }

        // Forward funding to ether wallet
        (bool success,) = wallet.call.value(amount)("");
        require(success);

        bids[receiver] += amount;
        totalReceived += amount;
        emit BidSubmission(receiver, amount);

        // Finalize auction when maxWei reached
        if (amount == maxWei)
            finalizeAuction();
    }

    /// @dev Claims tokens for bidder after auction.
    function claimTokens()
        public
        isValidPayload
        timedTransitions
        atStage(Stages.TradingStarted)
    {
        address receiver = msg.sender;
        uint tokenCount = bids[receiver] * 10**9 / finalPrice;
        bids[receiver] = 0;
        token.safeTransfer(receiver, tokenCount);
    }

    /// @dev Calculates stop price.
    /// @return Returns stop price.
    function calcStopPrice()
        view
        public
        returns (uint)
    {
        return totalReceived * 10**9 / maxTokenSold + 1;
    }

    /// @dev Calculates token price.
    /// @return Returns token price.
    function calcTokenPrice()
        view
        public
        returns (uint)
    {
        return priceFactor * 10**18 / (block.number - startBlock + 7500) + 1;
    }

    /*
     *  Private functions
     */
    function finalizeAuction()
        private
    {
        stage = Stages.AuctionEnded;
        finalPrice = totalReceived == ceiling ? calcTokenPrice() : calcStopPrice();
        uint soldTokens = totalReceived * 10**9 / finalPrice;

        if (totalReceived == ceiling) {
            // Auction contract transfers all unsold tokens to Ambix contract
            token.safeTransfer(ambix, maxTokenSold - soldTokens);
        } else {
            // Auction contract burn all unsold tokens
            token.burn(maxTokenSold - soldTokens);
        }

        endTime = now;
    }
}