contract DebtIssuanceModule is ModuleBase, ReentrancyGuard {

    /* ============ Structs ============ */

    // NOTE: moduleIssuanceHooks uses address[] for compatibility with AddressArrayUtils library
    struct IssuanceSettings {
        uint256 maxManagerFee;                          // Max issue/redeem fee defined on instantiation
        uint256 managerIssueFee;                        // Current manager issuance fees in precise units (10^16 = 1%)
        uint256 managerRedeemFee;                       // Current manager redeem fees in precise units (10^16 = 1%)
        address feeRecipient;                           // Address that receives all manager issue and redeem fees
        IManagerIssuanceHook managerIssuanceHook;       // Instance of manager defined hook, can hold arbitrary logic
        address[] moduleIssuanceHooks;                  // Array of modules that are registered with this module
        mapping(address => bool) isModuleHook;          // Mapping of modules to if they've registered a hook
    }

    /* ============ Events ============ */

    event SetTokenIssued(
        ISetToken indexed _setToken,
        address indexed _issuer,
        address indexed _to,
        address _hookContract,
        uint256 _quantity,
        uint256 _managerFee,
        uint256 _protocolFee
    );
    event SetTokenRedeemed(
        ISetToken indexed _setToken,
        address indexed _redeemer,
        address indexed _to,
        uint256 _quantity,
        uint256 _managerFee,
        uint256 _protocolFee
    );
    event FeeRecipientUpdated(ISetToken indexed _setToken, address _newFeeRecipient);
    event IssueFeeUpdated(ISetToken indexed _setToken, uint256 _newIssueFee);
    event RedeemFeeUpdated(ISetToken indexed _setToken, uint256 _newRedeemFee);

    /* ============ Constants ============ */

    uint256 private constant ISSUANCE_MODULE_PROTOCOL_FEE_SPLIT_INDEX = 0;

    /* ============ State ============ */

    mapping(ISetToken => IssuanceSettings) public issuanceSettings;

    /* ============ Constructor ============ */

    constructor(IController _controller) public ModuleBase(_controller) {}

    /* ============ External Functions ============ */

    /**
     * Deposits components to the SetToken, replicates any external module component positions and mints 
     * the SetToken. If the token has a debt position all collateral will be transferred in first then debt
     * will be returned to the minting address. If specified, a fee will be charged on issuance.
     *
     * @param _setToken         Instance of the SetToken to issue
     * @param _quantity         Quantity of SetToken to issue
     * @param _to               Address to mint SetToken to
     */
    function issue(
        ISetToken _setToken,
        uint256 _quantity,
        address _to
    )
        external
        virtual
        nonReentrant
        onlyValidAndInitializedSet(_setToken)
    {
        require(_quantity > 0, "Issue quantity must be > 0");

        address hookContract = _callManagerPreIssueHooks(_setToken, _quantity, msg.sender, _to);

        _callModulePreIssueHooks(_setToken, _quantity);

        (
            uint256 quantityWithFees,
            uint256 managerFee,
            uint256 protocolFee
        ) = calculateTotalFees(_setToken, _quantity, true);

        (
            address[] memory components,
            uint256[] memory equityUnits,
            uint256[] memory debtUnits
        ) = _calculateRequiredComponentIssuanceUnits(_setToken, quantityWithFees, true);

        _resolveEquityPositions(_setToken, quantityWithFees, _to, true, components, equityUnits);
        _resolveDebtPositions(_setToken, quantityWithFees, true, components, debtUnits);
        _resolveFees(_setToken, managerFee, protocolFee);

        _setToken.mint(_to, _quantity);

        emit SetTokenIssued(
            _setToken,
            msg.sender,
            _to,
            hookContract,
            _quantity,
            managerFee,
            protocolFee
        );
    }

    /**
     * Returns components from the SetToken, unwinds any external module component positions and burns the SetToken.
     * If the token has debt positions, the module transfers in the required debt amounts from the caller and uses
     * those funds to repay the debts on behalf of the SetToken. All debt will be paid down first then equity positions
     * will be returned to the minting address. If specified, a fee will be charged on redeem.
     *
     * @param _setToken         Instance of the SetToken to redeem
     * @param _quantity         Quantity of SetToken to redeem
     * @param _to               Address to send collateral to
     */
    function redeem(
        ISetToken _setToken,
        uint256 _quantity,
        address _to
    )
        external
        virtual        
        nonReentrant
        onlyValidAndInitializedSet(_setToken)
    {
        require(_quantity > 0, "Redeem quantity must be > 0");

        _callModulePreRedeemHooks(_setToken, _quantity);

        // Place burn after pre-redeem hooks because burning tokens may lead to false accounting of synced positions
        _setToken.burn(msg.sender, _quantity);

        (
            uint256 quantityNetFees,
            uint256 managerFee,
            uint256 protocolFee
        ) = calculateTotalFees(_setToken, _quantity, false);

        (
            address[] memory components,
            uint256[] memory equityUnits,
            uint256[] memory debtUnits
        ) = _calculateRequiredComponentIssuanceUnits(_setToken, quantityNetFees, false);

        _resolveDebtPositions(_setToken, quantityNetFees, false, components, debtUnits);
        _resolveEquityPositions(_setToken, quantityNetFees, _to, false, components, equityUnits);
        _resolveFees(_setToken, managerFee, protocolFee);

        emit SetTokenRedeemed(
            _setToken,
            msg.sender,
            _to,
            _quantity,
            managerFee,
            protocolFee
        );
    }

    /**
     * MANAGER ONLY: Updates address receiving issue/redeem fees for a given SetToken.
     *
     * @param _setToken             Instance of the SetToken to update fee recipient
     * @param _newFeeRecipient      New fee recipient address
     */
    function updateFeeRecipient(
        ISetToken _setToken,
        address _newFeeRecipient
    )
        external
        onlyManagerAndValidSet(_setToken)
    {
        require(_newFeeRecipient != address(0), "Fee Recipient must be non-zero address.");
        require(_newFeeRecipient != issuanceSettings[_setToken].feeRecipient, "Same fee recipient passed");

        issuanceSettings[_setToken].feeRecipient = _newFeeRecipient;

        emit FeeRecipientUpdated(_setToken, _newFeeRecipient);
    }

    /**
     * MANAGER ONLY: Updates issue fee for passed SetToken
     *
     * @param _setToken             Instance of the SetToken to update issue fee
     * @param _newIssueFee          New fee amount in preciseUnits (1% = 10^16)
     */
    function updateIssueFee(
        ISetToken _setToken,
        uint256 _newIssueFee
    )
        external
        onlyManagerAndValidSet(_setToken)
    {
        require(_newIssueFee <= issuanceSettings[_setToken].maxManagerFee, "Issue fee can't exceed maximum");
        require(_newIssueFee != issuanceSettings[_setToken].managerIssueFee, "Same issue fee passed");

        issuanceSettings[_setToken].managerIssueFee = _newIssueFee;

        emit IssueFeeUpdated(_setToken, _newIssueFee);
    }

    /**
     * MANAGER ONLY: Updates redeem fee for passed SetToken
     *
     * @param _setToken             Instance of the SetToken to update redeem fee
     * @param _newRedeemFee         New fee amount in preciseUnits (1% = 10^16)
     */
    function updateRedeemFee(
        ISetToken _setToken,
        uint256 _newRedeemFee
    )
        external
        onlyManagerAndValidSet(_setToken)
    {
        require(_newRedeemFee <= issuanceSettings[_setToken].maxManagerFee, "Redeem fee can't exceed maximum");
        require(_newRedeemFee != issuanceSettings[_setToken].managerRedeemFee, "Same redeem fee passed");

        issuanceSettings[_setToken].managerRedeemFee = _newRedeemFee;

        emit RedeemFeeUpdated(_setToken, _newRedeemFee);
    }

    /**
     * MODULE ONLY: Adds calling module to array of modules that require they be called before component hooks are
     * called. Can be used to sync debt positions before issuance.
     *
     * @param _setToken             Instance of the SetToken to issue
     */
    function registerToIssuanceModule(ISetToken _setToken) external onlyModule(_setToken) onlyValidAndInitializedSet(_setToken) {
        require(!issuanceSettings[_setToken].isModuleHook[msg.sender], "Module already registered.");
        issuanceSettings[_setToken].moduleIssuanceHooks.push(msg.sender);
        issuanceSettings[_setToken].isModuleHook[msg.sender] = true;
    }

    /**
     * MODULE ONLY: Removes calling module from array of modules that require they be called before component hooks are
     * called.
     *
     * @param _setToken             Instance of the SetToken to issue
     */
    function unregisterFromIssuanceModule(ISetToken _setToken) external onlyModule(_setToken) onlyValidAndInitializedSet(_setToken) {
        require(issuanceSettings[_setToken].isModuleHook[msg.sender], "Module not registered.");
        issuanceSettings[_setToken].moduleIssuanceHooks.removeStorage(msg.sender);
        issuanceSettings[_setToken].isModuleHook[msg.sender] = false;
    }

    /**
     * MANAGER ONLY: Initializes this module to the SetToken with issuance-related hooks and fee information. Only callable
     * by the SetToken's manager. Hook addresses are optional. Address(0) means that no hook will be called
     *
     * @param _setToken                     Instance of the SetToken to issue
     * @param _maxManagerFee                Maximum fee that can be charged on issue and redeem
     * @param _managerIssueFee              Fee to charge on issuance
     * @param _managerRedeemFee             Fee to charge on redemption
     * @param _feeRecipient                 Address to send fees to
     * @param _managerIssuanceHook          Instance of the Manager Contract with the Pre-Issuance Hook function
     */
    function initialize(
        ISetToken _setToken,
        uint256 _maxManagerFee,
        uint256 _managerIssueFee,
        uint256 _managerRedeemFee,
        address _feeRecipient,
        IManagerIssuanceHook _managerIssuanceHook
    )
        external
        onlySetManager(_setToken, msg.sender)
        onlyValidAndPendingSet(_setToken)
    {
        require(_managerIssueFee <= _maxManagerFee, "Issue fee can't exceed maximum fee");
        require(_managerRedeemFee <= _maxManagerFee, "Redeem fee can't exceed maximum fee");

        issuanceSettings[_setToken] = IssuanceSettings({
            maxManagerFee: _maxManagerFee,
            managerIssueFee: _managerIssueFee,
            managerRedeemFee: _managerRedeemFee,
            feeRecipient: _feeRecipient,
            managerIssuanceHook: _managerIssuanceHook,
            moduleIssuanceHooks: new address[](0)
        });

        _setToken.initializeModule();
    }

    /**
     * SET TOKEN ONLY: Allows removal of module (and deletion of state) if no other modules are registered.
     */
    function removeModule() external override {
        require(issuanceSettings[ISetToken(msg.sender)].moduleIssuanceHooks.length == 0, "Registered modules must be removed.");
        delete issuanceSettings[ISetToken(msg.sender)];
    }

    /* ============ External View Functions ============ */

    /**
     * Calculates the manager fee, protocol fee and resulting totalQuantity to use when calculating unit amounts. If fees are charged they
     * are added to the total issue quantity, for example 1% fee on 100 Sets means 101 Sets are minted by caller, the _to address receives
     * 100 and the feeRecipient receives 1. Conversely, on redemption the redeemer will only receive the collateral that collateralizes 99
     * Sets, while the additional Set is given to the feeRecipient.
     *
     * @param _setToken                 Instance of the SetToken to issue
     * @param _quantity                 Amount of SetToken issuer wants to receive/redeem
     * @param _isIssue                  If issuing or redeeming
     *
     * @return totalQuantity           Total amount of Sets to be issued/redeemed with fee adjustment
     * @return managerFee              Sets minted to the manager
     * @return protocolFee             Sets minted to the protocol
     */
    function calculateTotalFees(
        ISetToken _setToken,
        uint256 _quantity,
        bool _isIssue
    )
        public
        view
        returns (uint256 totalQuantity, uint256 managerFee, uint256 protocolFee)
    {
        IssuanceSettings memory setIssuanceSettings = issuanceSettings[_setToken];
        uint256 protocolFeeSplit = controller.getModuleFee(address(this), ISSUANCE_MODULE_PROTOCOL_FEE_SPLIT_INDEX);
        uint256 totalFeeRate = _isIssue ? setIssuanceSettings.managerIssueFee : setIssuanceSettings.managerRedeemFee;
        
        uint256 totalFee = totalFeeRate.preciseMul(_quantity);
        protocolFee = totalFee.preciseMul(protocolFeeSplit);
        managerFee = totalFee.sub(protocolFee);

        totalQuantity = _isIssue ? _quantity.add(totalFee) : _quantity.sub(totalFee);
    }

    /**
     * Calculates the amount of each component needed to collateralize passed issue quantity plus fees of Sets as well as amount of debt
     * that will be returned to caller. Values DO NOT take into account any updates from pre action manager or module hooks.
     *
     * @param _setToken         Instance of the SetToken to issue
     * @param _quantity         Amount of Sets to be issued
     *
     * @return address[]        Array of component addresses making up the Set
     * @return uint256[]        Array of equity notional amounts of each component, respectively, represented as uint256
     * @return uint256[]        Array of debt notional amounts of each component, respectively, represented as uint256
     */
    function getRequiredComponentIssuanceUnits(
        ISetToken _setToken,
        uint256 _quantity
    )
        external
        view
        returns (address[] memory, uint256[] memory, uint256[] memory)
    {
        (
            uint256 totalQuantity,,
        ) = calculateTotalFees(_setToken, _quantity, true);

        return _calculateRequiredComponentIssuanceUnits(_setToken, totalQuantity, true);
    }

    /**
     * Calculates the amount of each component will be returned on redemption net of fees as well as how much debt needs to be paid down to.
     * redeem. Values DO NOT take into account any updates from pre action manager or module hooks.
     *
     * @param _setToken         Instance of the SetToken to issue
     * @param _quantity         Amount of Sets to be redeemed
     *
     * @return address[]        Array of component addresses making up the Set
     * @return uint256[]        Array of equity notional amounts of each component, respectively, represented as uint256
     * @return uint256[]        Array of debt notional amounts of each component, respectively, represented as uint256
     */
    function getRequiredComponentRedemptionUnits(
        ISetToken _setToken,
        uint256 _quantity
    )
        external
        view
        returns (address[] memory, uint256[] memory, uint256[] memory)
    {
        (
            uint256 totalQuantity,,
        ) = calculateTotalFees(_setToken, _quantity, false);

        return _calculateRequiredComponentIssuanceUnits(_setToken, totalQuantity, false);
    }

    function getModuleIssuanceHooks(ISetToken _setToken) external view returns(address[] memory) {
        return issuanceSettings[_setToken].moduleIssuanceHooks;
    }

    function isModuleIssuanceHook(ISetToken _setToken, address _hook) external view returns(bool) {
        return issuanceSettings[_setToken].isModuleHook[_hook];
    }

    /* ============ Internal Functions ============ */

    /**
     * Calculates the amount of each component needed to collateralize passed issue quantity of Sets as well as amount of debt that will
     * be returned to caller. Can also be used to determine how much collateral will be returned on redemption as well as how much debt
     * needs to be paid down to redeem.
     *
     * @param _setToken         Instance of the SetToken to issue
     * @param _quantity         Amount of Sets to be issued/redeemed
     * @param _isIssue          Whether Sets are being issued or redeemed
     *
     * @return address[]        Array of component addresses making up the Set
     * @return uint256[]        Array of equity notional amounts of each component, respectively, represented as uint256
     * @return uint256[]        Array of debt notional amounts of each component, respectively, represented as uint256
     */
    function _calculateRequiredComponentIssuanceUnits(
        ISetToken _setToken,
        uint256 _quantity,
        bool _isIssue
    )
        internal
        view
        returns (address[] memory, uint256[] memory, uint256[] memory)
    {
        (
            address[] memory components,
            uint256[] memory equityUnits,
            uint256[] memory debtUnits
        ) = _getTotalIssuanceUnits(_setToken);

        uint256 componentsLength = components.length;
        uint256[] memory totalEquityUnits = new uint256[](componentsLength);
        uint256[] memory totalDebtUnits = new uint256[](componentsLength);
        for (uint256 i = 0; i < components.length; i++) {
            // Use preciseMulCeil to round up to ensure overcollateration when small issue quantities are provided
            // and preciseMul to round down to ensure overcollateration when small redeem quantities are provided
            totalEquityUnits[i] = _isIssue ?
                equityUnits[i].preciseMulCeil(_quantity) :
                equityUnits[i].preciseMul(_quantity);

            totalDebtUnits[i] = _isIssue ?
                debtUnits[i].preciseMul(_quantity) :
                debtUnits[i].preciseMulCeil(_quantity);
        }

        return (components, totalEquityUnits, totalDebtUnits);
    }

    /**
     * Sums total debt and equity units for each component, taking into account default and external positions.
     *
     * @param _setToken         Instance of the SetToken to issue
     *
     * @return address[]        Array of component addresses making up the Set
     * @return uint256[]        Array of equity unit amounts of each component, respectively, represented as uint256
     * @return uint256[]        Array of debt unit amounts of each component, respectively, represented as uint256
     */
    function _getTotalIssuanceUnits(
        ISetToken _setToken
    )
        internal
        view
        returns (address[] memory, uint256[] memory, uint256[] memory)
    {
        address[] memory components = _setToken.getComponents();
        uint256 componentsLength = components.length;

        uint256[] memory equityUnits = new uint256[](componentsLength);
        uint256[] memory debtUnits = new uint256[](componentsLength);

        for (uint256 i = 0; i < components.length; i++) {
            address component = components[i];
            int256 cumulativeEquity = _setToken.getDefaultPositionRealUnit(component);
            int256 cumulativeDebt = 0;
            address[] memory externalPositions = _setToken.getExternalPositionModules(component);

            if (externalPositions.length > 0) {
                for (uint256 j = 0; j < externalPositions.length; j++) { 
                    int256 externalPositionUnit = _setToken.getExternalPositionRealUnit(component, externalPositions[j]);

                    // If positionUnit <= 0 it will be "added" to debt position
                    if (externalPositionUnit > 0) {
                        cumulativeEquity = cumulativeEquity.add(externalPositionUnit);
                    } else {
                        cumulativeDebt = cumulativeDebt.add(externalPositionUnit);
                    }
                }
            }

            equityUnits[i] = cumulativeEquity.toUint256();
            debtUnits[i] = cumulativeDebt.mul(-1).toUint256();
        }

        return (components, equityUnits, debtUnits);
    }

    /**
     * Resolve equity positions associated with SetToken. On issuance, the total equity position for an asset (including default and external
     * positions) is transferred in. Then any external position hooks are called to transfer the external positions to their necessary place.
     * On redemption all external positions are recalled by the external position hook, then those position plus any default position are
     * transferred back to the _to address.
     */
    function _resolveEquityPositions(
        ISetToken _setToken,
        uint256 _quantity,
        address _to,
        bool _isIssue,
        address[] memory _components,
        uint256[] memory _componentEquityQuantities
    )
        internal
    {
        for (uint256 i = 0; i < _components.length; i++) {
            address component = _components[i];
            uint256 componentQuantity = _componentEquityQuantities[i];
            if (componentQuantity > 0) {
                if (_isIssue) {
                    transferFrom(
                        IERC20(component),
                        msg.sender,
                        address(_setToken),
                        componentQuantity
                    );

                    _executeExternalPositionHooks(_setToken, _quantity, IERC20(component), true, true);
                } else {
                    _executeExternalPositionHooks(_setToken, _quantity, IERC20(component), false, true);

                    _setToken.strictInvokeTransfer(
                        component,
                        _to,
                        componentQuantity
                    );
                }
            }
        }
    }

    /**
     * Resolve debt positions associated with SetToken. On issuance, debt positions are entered into by calling the external position hook. The
     * resulting debt is then returned to the calling address. On redemption, the module transfers in the required debt amount from the caller
     * and uses those funds to repay the debt on behalf of the SetToken.
     */
    function _resolveDebtPositions(
        ISetToken _setToken,
        uint256 _quantity,
        bool _isIssue,
        address[] memory _components,
        uint256[] memory _componentDebtQuantities
    )
        internal
    {
        for (uint256 i = 0; i < _components.length; i++) {
            address component = _components[i];
            uint256 componentQuantity = _componentDebtQuantities[i];
            if (componentQuantity > 0) {
                if (_isIssue) {
                    _executeExternalPositionHooks(_setToken, _quantity, IERC20(component), true, false);
                    _setToken.strictInvokeTransfer(
                        component,
                        msg.sender,
                        componentQuantity
                    );
                } else {
                    transferFrom(
                        IERC20(component),
                        msg.sender,
                        address(_setToken),
                        componentQuantity
                    );
                    _executeExternalPositionHooks(_setToken, _quantity, IERC20(component), false, false);
                }
            }
        }
    }

    /**
     * If any manager fees mints Sets to the defined feeRecipient. If protocol fee is enabled mints Sets to protocol
     * feeRecipient. 
     */
    function _resolveFees(ISetToken _setToken, uint256 managerFee, uint256 protocolFee) internal {
        if (managerFee > 0) {
            _setToken.mint(issuanceSettings[_setToken].feeRecipient, managerFee);

            // Protocol fee check is inside manager fee check because protocol fees are only collected on manager fees
            if (protocolFee > 0) {
                _setToken.mint(controller.feeRecipient(), protocolFee);
            }
        }
    }

    /**
     * If a pre-issue hook has been configured, call the external-protocol contract. Pre-issue hook logic
     * can contain arbitrary logic including validations, external function calls, etc.
     */
    function _callManagerPreIssueHooks(
        ISetToken _setToken,
        uint256 _quantity,
        address _caller,
        address _to
    )
        internal
        returns(address)
    {
        IManagerIssuanceHook preIssueHook = issuanceSettings[_setToken].managerIssuanceHook;
        if (address(preIssueHook) != address(0)) {
            preIssueHook.invokePreIssueHook(_setToken, _quantity, _caller, _to);
            return address(preIssueHook);
        }

        return address(0);
    }
    
    /**
     * Calls all modules that have registered with the DebtIssuanceModule that have a moduleIssueHook.
     */
    function _callModulePreIssueHooks(ISetToken _setToken, uint256 _quantity) internal {
        address[] memory issuanceHooks = issuanceSettings[_setToken].moduleIssuanceHooks;
        for (uint256 i = 0; i < issuanceHooks.length; i++) {
            IModuleIssuanceHook(issuanceHooks[i]).moduleIssueHook(_setToken, _quantity);
        }
    }

    /**
     * Calls all modules that have registered with the DebtIssuanceModule that have a moduleRedeemHook.
     */
    function _callModulePreRedeemHooks(ISetToken _setToken, uint256 _quantity) internal {
        address[] memory issuanceHooks = issuanceSettings[_setToken].moduleIssuanceHooks;
        for (uint256 i = 0; i < issuanceHooks.length; i++) {
            IModuleIssuanceHook(issuanceHooks[i]).moduleRedeemHook(_setToken, _quantity);
        }
    }

    /**
     * For each component's external module positions, calculate the total notional quantity, and 
     * call the module's issue hook or redeem hook.
     * Note: It is possible that these hooks can cause the states of other modules to change.
     * It can be problematic if the hook called an external function that called back into a module, resulting in state inconsistencies.
     */
    function _executeExternalPositionHooks(
        ISetToken _setToken,
        uint256 _setTokenQuantity,
        IERC20 _component,
        bool _isIssue,
        bool _isEquity
    )
        internal
    {
        address[] memory externalPositionModules = _setToken.getExternalPositionModules(address(_component));
        uint256 modulesLength = externalPositionModules.length;
        if (_isIssue) {
            for (uint256 i = 0; i < modulesLength; i++) {
                IModuleIssuanceHook(externalPositionModules[i]).componentIssueHook(_setToken, _setTokenQuantity, _component, _isEquity);
            }
        } else {
            for (uint256 i = 0; i < modulesLength; i++) {
                IModuleIssuanceHook(externalPositionModules[i]).componentRedeemHook(_setToken, _setTokenQuantity, _component, _isEquity);
            }
        }
    }
}
/**
 * @title DebtIssuanceModule
 * @author Set Protocol
 *
 * The DebtIssuanceModule is a module that enables users to issue and redeem SetTokens that contain default and all
 * external positions, including debt positions. Module hooks are added to allow for syncing of positions, and component
 * level hooks are added to ensure positions are replicated correctly. The manager can define arbitrary issuance logic
 * in the manager hook, as well as specify issue and redeem fees.
 */
function registerToIssuanceModule(ISetToken _setToken) external onlyModule(_setToken) onlyValidAndInitializedSet(_setToken) {
        require(!issuanceSettings[_setToken].isModuleHook[msg.sender], "Module already registered.");
        issuanceSettings[_setToken].moduleIssuanceHooks.push(msg.sender);
        issuanceSettings[_setToken].isModuleHook[msg.sender] = true;
    }
/**
 * MODULE ONLY: Adds calling module to array of modules that require they be called before component hooks are
 * called. Can be used to sync debt positions before issuance.
 *
 * @param _setToken             Instance of the SetToken to issue
 */