/**
 *Submitted for verification at Etherscan.io on 2021-12-06
*/

pragma solidity 0.7.5;


library SafeMath {

    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        return c;
    }

    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }

    function sqrrt(uint256 a) internal pure returns (uint c) {
        if (a > 3) {
            c = a;
            uint b = add( div( a, 2), 1 );
            while (b < c) {
                c = b;
                b = div( add( div( a, b ), b), 2 );
            }
        } else if (a != 0) {
            c = 1;
        }
    }
}

pragma solidity 0.7.5;


library Address {

    function isContract(address account) internal view returns (bool) {

        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }

    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return _functionCallWithValue(target, data, 0, errorMessage);
    }

    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: value }(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function _functionCallWithValue(address target, bytes memory data, uint256 weiValue, string memory errorMessage) private returns (bytes memory) {
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: weiValue }(data);
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }

    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
        if (success) {
            return returndata;
        } else {
            if (returndata.length > 0) {

                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }

    function addressToString(address _address) internal pure returns(string memory) {
        bytes32 _bytes = bytes32(uint256(_address));
        bytes memory HEX = "0123456789abcdef";
        bytes memory _addr = new bytes(42);

        _addr[0] = '0';
        _addr[1] = 'x';

        for(uint256 i = 0; i < 20; i++) {
            _addr[2+i*2] = HEX[uint8(_bytes[i + 12] >> 4)];
            _addr[3+i*2] = HEX[uint8(_bytes[i + 12] & 0x0f)];
        }

        return string(_addr);

    }
}

pragma solidity 0.7.5;

interface IERC20 {
    function decimals() external view returns (uint8);

    function totalSupply() external view returns (uint256);

    function balanceOf(address account) external view returns (uint256);

    function transfer(address recipient, uint256 amount) external returns (bool);

    function allowance(address owner, address spender) external view returns (uint256);

    function approve(address spender, uint256 amount) external returns (bool);

    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    event Transfer(address indexed from, address indexed to, uint256 value);

    event Approval(address indexed owner, address indexed spender, uint256 value);
}

pragma solidity 0.7.5;


library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    function safeApprove(IERC20 token, address spender, uint256 value) internal {

        require((value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function _callOptionalReturn(IERC20 token, bytes memory data) private {

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) { // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}


// File contracts/libraries/FullMath.sol

pragma solidity 0.7.5;

library FullMath {
    function fullMul(uint256 x, uint256 y) private pure returns (uint256 l, uint256 h) {
        uint256 mm = mulmod(x, y, uint256(-1));
        l = x * y;
        h = mm - l;
        if (mm < l) h -= 1;
    }

    function fullDiv(
        uint256 l,
        uint256 h,
        uint256 d
    ) private pure returns (uint256) {
        uint256 pow2 = d & -d;
        d /= pow2;
        l /= pow2;
        l += h * ((-pow2) / pow2 + 1);
        uint256 r = 1;
        r *= 2 - d * r;
        r *= 2 - d * r;
        r *= 2 - d * r;
        r *= 2 - d * r;
        r *= 2 - d * r;
        r *= 2 - d * r;
        r *= 2 - d * r;
        r *= 2 - d * r;
        return l * r;
    }

    function mulDiv(
        uint256 x,
        uint256 y,
        uint256 d
    ) internal pure returns (uint256) {
        (uint256 l, uint256 h) = fullMul(x, y);
        uint256 mm = mulmod(x, y, d);
        if (mm > l) h -= 1;
        l -= mm;
        require(h < d, 'FullMath::mulDiv: overflow');
        return fullDiv(l, h, d);
    }
}


// File contracts/libraries/FixedPoint.sol

pragma solidity 0.7.5;

library Babylonian {

    function sqrt(uint256 x) internal pure returns (uint256) {
        if (x == 0) return 0;

        uint256 xx = x;
        uint256 r = 1;
        if (xx >= 0x100000000000000000000000000000000) {
            xx >>= 128;
            r <<= 64;
        }
        if (xx >= 0x10000000000000000) {
            xx >>= 64;
            r <<= 32;
        }
        if (xx >= 0x100000000) {
            xx >>= 32;
            r <<= 16;
        }
        if (xx >= 0x10000) {
            xx >>= 16;
            r <<= 8;
        }
        if (xx >= 0x100) {
            xx >>= 8;
            r <<= 4;
        }
        if (xx >= 0x10) {
            xx >>= 4;
            r <<= 2;
        }
        if (xx >= 0x8) {
            r <<= 1;
        }
        r = (r + x / r) >> 1;
        r = (r + x / r) >> 1;
        r = (r + x / r) >> 1;
        r = (r + x / r) >> 1;
        r = (r + x / r) >> 1;
        r = (r + x / r) >> 1;
        r = (r + x / r) >> 1; // Seven iterations should be enough
        uint256 r1 = x / r;
        return (r < r1 ? r : r1);
    }
}

library BitMath {

    function mostSignificantBit(uint256 x) internal pure returns (uint8 r) {
        require(x > 0, 'BitMath::mostSignificantBit: zero');

        if (x >= 0x100000000000000000000000000000000) {
            x >>= 128;
            r += 128;
        }
        if (x >= 0x10000000000000000) {
            x >>= 64;
            r += 64;
        }
        if (x >= 0x100000000) {
            x >>= 32;
            r += 32;
        }
        if (x >= 0x10000) {
            x >>= 16;
            r += 16;
        }
        if (x >= 0x100) {
            x >>= 8;
            r += 8;
        }
        if (x >= 0x10) {
            x >>= 4;
            r += 4;
        }
        if (x >= 0x4) {
            x >>= 2;
            r += 2;
        }
        if (x >= 0x2) r += 1;
    }
}


library FixedPoint {

    struct uq112x112 {
        uint224 _x;
    }

    struct uq144x112 {
        uint256 _x;
    }

    uint8 private constant RESOLUTION = 112;
    uint256 private constant Q112 = 0x10000000000000000000000000000;
    uint256 private constant Q224 = 0x100000000000000000000000000000000000000000000000000000000;
    uint256 private constant LOWER_MASK = 0xffffffffffffffffffffffffffff; // decimal of UQ*x112 (lower 112 bits)

    function decode(uq112x112 memory self) internal pure returns (uint112) {
        return uint112(self._x >> RESOLUTION);
    }

    function decode112with18(uq112x112 memory self) internal pure returns (uint) {

        return uint(self._x) / 5192296858534827;
    }

    function fraction(uint256 numerator, uint256 denominator) internal pure returns (uq112x112 memory) {
        require(denominator > 0, 'FixedPoint::fraction: division by zero');
        if (numerator == 0) return FixedPoint.uq112x112(0);

        if (numerator <= uint144(-1)) {
            uint256 result = (numerator << RESOLUTION) / denominator;
            require(result <= uint224(-1), 'FixedPoint::fraction: overflow');
            return uq112x112(uint224(result));
        } else {
            uint256 result = FullMath.mulDiv(numerator, Q112, denominator);
            require(result <= uint224(-1), 'FixedPoint::fraction: overflow');
            return uq112x112(uint224(result));
        }
    }
    
    // square root of a UQ112x112
    // lossy between 0/1 and 40 bits
    function sqrt(uq112x112 memory self) internal pure returns (uq112x112 memory) {
        if (self._x <= uint144(-1)) {
            return uq112x112(uint224(Babylonian.sqrt(uint256(self._x) << 112)));
        }

        uint8 safeShiftBits = 255 - BitMath.mostSignificantBit(self._x);
        safeShiftBits -= safeShiftBits % 2;
        return uq112x112(uint224(Babylonian.sqrt(uint256(self._x) << safeShiftBits) << ((112 - safeShiftBits) / 2)));
    }
}


// File contracts/interfaces/ITreasury.sol

pragma solidity 0.7.5;

interface ITreasury {
    function sendPayoutTokens(uint _amountPayoutToken) external;
    function valueOfToken( address _principalTokenAddress, uint _amount ) external view returns ( uint value_ );
    function payoutToken() external view returns (address);
}


// File contracts/types/Ownable.sol

pragma solidity 0.7.5;

contract Ownable {

    address public policy;

    constructor () {
        policy = msg.sender;
    }

    modifier onlyPolicy() {
        require( policy == msg.sender, "Ownable: caller is not the owner" );
        _;
    }
    
    function transferManagment(address _newOwner) external onlyPolicy() {
        require( _newOwner != address(0) );
        policy = _newOwner;
    }
}


// File contracts/OlympusProCustomBond.sol

// SPDX-License-Identifier: AGPL-3.0-or-later
pragma solidity 0.7.5;




contract CustomBond is Ownable {
    using FixedPoint for *;
    using SafeERC20 for IERC20;
    using SafeMath for uint;
    
    /* ======== EVENTS ======== */

    event BondCreated( uint deposit, uint payout, uint expires );
    event BondRedeemed( address recipient, uint payout, uint remaining );
    event BondPriceChanged( uint internalPrice, uint debtRatio );
    event ControlVariableAdjustment( uint initialBCV, uint newBCV, uint adjustment, bool addition );
    
    
     /* ======== STATE VARIABLES ======== */
    
    IERC20 immutable private payoutToken; // token paid for principal
    IERC20 immutable private principalToken; // inflow token
    ITreasury immutable private customTreasury; // pays for and receives principal
    address immutable private olympusDAO;
    address private olympusTreasury; // receives fee
    address immutable private subsidyRouter; // pays subsidy in OHM to custom treasury

    uint public totalPrincipalBonded;
    uint public totalPayoutGiven;
    uint public totalDebt; // total value of outstanding bonds; used for pricing
    uint public lastDecay; // reference block for debt decay
    uint private payoutSinceLastSubsidy; // principal accrued since subsidy paid
    
    Terms public terms; // stores terms for new bonds
    Adjust public adjustment; // stores adjustment to BCV data
    FeeTiers[] private feeTiers; // stores fee tiers

    bool immutable private feeInPayout;

    mapping( address => Bond ) public bondInfo; // stores bond information for depositors
    
    /* ======== STRUCTS ======== */

    struct FeeTiers {
        uint tierCeilings; // principal bonded till next tier
        uint fees; // in ten-thousandths (i.e. 33300 = 3.33%)
    }

    // Info for creating new bonds
    struct Terms {
        uint controlVariable; // scaling variable for price
        uint vestingTerm; // in blocks
        uint minimumPrice; // vs principal value
        uint maxPayout; // in thousandths of a %. i.e. 500 = 0.5%
        uint maxDebt; // payout token decimal debt ratio, max % total supply created as debt
    }

    // Info for bond holder
    struct Bond {
        uint payout; // payout token remaining to be paid
        uint vesting; // Blocks left to vest
        uint lastBlock; // Last interaction
        uint truePricePaid; // Price paid (principal tokens per payout token) in ten-millionths - 4000000 = 0.4
    }

    // Info for incremental adjustments to control variable 
    struct Adjust {
        bool add; // addition or subtraction
        uint rate; // increment
        uint target; // BCV when adjustment finished
        uint buffer; // minimum length (in blocks) between adjustments
        uint lastBlock; // block when last adjustment made
    }
    
    /* ======== CONSTRUCTOR ======== */

    constructor(
        address _customTreasury, 
        address _principalToken, 
        address _olympusTreasury,
        address _subsidyRouter, 
        address _initialOwner, 
        address _olympusDAO,
        uint[] memory _tierCeilings, 
        uint[] memory _fees,
        bool _feeInPayout
    ) {
        require( _customTreasury != address(0) );
        customTreasury = ITreasury( _customTreasury );
        payoutToken = IERC20( ITreasury(_customTreasury).payoutToken() );
        require( _principalToken != address(0) );
        principalToken = IERC20( _principalToken );
        require( _olympusTreasury != address(0) );
        olympusTreasury = _olympusTreasury;
        require( _subsidyRouter != address(0) );
        subsidyRouter = _subsidyRouter;
        require( _initialOwner != address(0) );
        policy = _initialOwner;
        require( _olympusDAO != address(0) );
        olympusDAO = _olympusDAO;
        require(_tierCeilings.length == _fees.length, "tier length and fee length not the same");

        for(uint i; i < _tierCeilings.length; i++) {
            feeTiers.push( FeeTiers({
                tierCeilings: _tierCeilings[i],
                fees: _fees[i]
            }));
        }

        feeInPayout = _feeInPayout;
    }

    /* ======== INITIALIZATION ======== */
    
    /**
     *  @notice initializes bond parameters
     *  @param _controlVariable uint
     *  @param _vestingTerm uint
     *  @param _minimumPrice uint
     *  @param _maxPayout uint
     *  @param _maxDebt uint
     *  @param _initialDebt uint
     */
    function initializeBond( 
        uint _controlVariable, 
        uint _vestingTerm,
        uint _minimumPrice,
        uint _maxPayout,
        uint _maxDebt,
        uint _initialDebt
    ) external onlyPolicy() {
        require( currentDebt() == 0, "Debt must be 0 for initialization" );
        terms = Terms ({
            controlVariable: _controlVariable,
            vestingTerm: _vestingTerm,
            minimumPrice: _minimumPrice,
            maxPayout: _maxPayout,
            maxDebt: _maxDebt
        });
        totalDebt = _initialDebt;
        lastDecay = block.number;
    }
    
    
    /* ======== POLICY FUNCTIONS ======== */

    enum PARAMETER { VESTING, PAYOUT, DEBT }
    /**
     *  @notice set parameters for new bonds
     *  @param _parameter PARAMETER
     *  @param _input uint
     */
    function setBondTerms ( PARAMETER _parameter, uint _input ) external onlyPolicy() {
        if ( _parameter == PARAMETER.VESTING ) { // 0
            require( _input >= 10000, "Vesting must be longer than 36 hours" );
            terms.vestingTerm = _input;
        } else if ( _parameter == PARAMETER.PAYOUT ) { // 1
            require( _input <= 1000, "Payout cannot be above 1 percent" );
            terms.maxPayout = _input;
        } else if ( _parameter == PARAMETER.DEBT ) { // 2
            terms.maxDebt = _input;
        }
    }

    /**
     *  @notice set control variable adjustment
     *  @param _addition bool
     *  @param _increment uint
     *  @param _target uint
     *  @param _buffer uint
     */
    function setAdjustment ( 
        bool _addition,
        uint _increment, 
        uint _target,
        uint _buffer 
    ) external onlyPolicy() {
        require( _increment <= terms.controlVariable.mul( 30 ).div( 1000 ), "Increment too large" );

        adjustment = Adjust({
            add: _addition,
            rate: _increment,
            target: _target,
            buffer: _buffer,
            lastBlock: block.number
        });
    }

    /**
     *  @notice change address of Olympus Treasury
     *  @param _olympusTreasury uint
     */
    function changeOlympusTreasury(address _olympusTreasury) external {
        require( msg.sender == olympusDAO, "Only Olympus DAO" );
        olympusTreasury = _olympusTreasury;
    }

    /**
     *  @notice subsidy controller checks payouts since last subsidy and resets counter
     *  @return payoutSinceLastSubsidy_ uint
     */
    function paySubsidy() external returns ( uint payoutSinceLastSubsidy_ ) {
        require( msg.sender == subsidyRouter, "Only subsidy controller" );

        payoutSinceLastSubsidy_ = payoutSinceLastSubsidy;
        payoutSinceLastSubsidy = 0;
    }
    
    /* ======== USER FUNCTIONS ======== */
    
    /**
     *  @notice deposit bond
     *  @param _amount uint
     *  @param _maxPrice uint
     *  @param _depositor address
     *  @return uint
     */
    function deposit(uint _amount, uint _maxPrice, address _depositor) external returns (uint) {
        require( _depositor != address(0), "Invalid address" );

        decayDebt();
        
        uint nativePrice = trueBondPrice();

        require( _maxPrice >= nativePrice, "Slippage limit: more than max price" ); // slippage protection

        uint value = customTreasury.valueOfToken( address(principalToken), _amount );

        uint payout;
        uint fee;

        if(feeInPayout) {
            (payout, fee) = payoutFor( value ); // payout and fee is computed
        } else {
            (payout, fee) = payoutFor( _amount ); // payout and fee is computed
            _amount = _amount.sub(fee);
        }

        require( payout >= 10 ** payoutToken.decimals() / 100, "Bond too small" ); // must be > 0.01 payout token ( underflow protection )
        require( payout <= maxPayout(), "Bond too large"); // size protection because there is no slippage
        
        // total debt is increased
        totalDebt = totalDebt.add( value );

        require( totalDebt <= terms.maxDebt, "Max capacity reached" );
                
        // depositor info is stored
        bondInfo[ _depositor ] = Bond({ 
            payout: bondInfo[ _depositor ].payout.add( payout ),
            vesting: terms.vestingTerm,
            lastBlock: block.number,
            truePricePaid: trueBondPrice()
        });

        totalPrincipalBonded = totalPrincipalBonded.add(_amount); // total bonded increased
        totalPayoutGiven = totalPayoutGiven.add(payout); // total payout increased
        payoutSinceLastSubsidy = payoutSinceLastSubsidy.add( payout ); // subsidy counter increased

        if(feeInPayout) {
            customTreasury.sendPayoutTokens( payout.add(fee) );
            if(fee != 0) { // if fee, send to Olympus treasury
                payoutToken.safeTransfer(olympusTreasury, fee);
            }
        } else {
            customTreasury.sendPayoutTokens( payout );
            if(fee != 0) { // if fee, send to Olympus treasury
                principalToken.safeTransferFrom( msg.sender, olympusTreasury, fee );
            }
        }

        principalToken.safeTransferFrom( msg.sender, address(customTreasury), _amount ); // transfer principal bonded to custom treasury

        // indexed events are emitted
        emit BondCreated( _amount, payout, block.number.add( terms.vestingTerm ) );
        emit BondPriceChanged( _bondPrice(), debtRatio() );

        adjust(); // control variable is adjusted
        return payout; 
    }
    
    /** 
     *  @notice redeem bond for user
     *  @return uint
     */ 
    function redeem(address _depositor) external returns (uint) {
        Bond memory info = bondInfo[ _depositor ];
        uint percentVested = percentVestedFor( _depositor ); // (blocks since last interaction / vesting term remaining)

        if ( percentVested >= 10000 ) { // if fully vested
            delete bondInfo[ _depositor ]; // delete user info
            emit BondRedeemed( _depositor, info.payout, 0 ); // emit bond data
            payoutToken.safeTransfer( _depositor, info.payout );
            return info.payout;

        } else { // if unfinished
            // calculate payout vested
            uint payout = info.payout.mul( percentVested ).div( 10000 );

            // store updated deposit info
            bondInfo[ _depositor ] = Bond({
                payout: info.payout.sub( payout ),
                vesting: info.vesting.sub( block.number.sub( info.lastBlock ) ),
                lastBlock: block.number,
                truePricePaid: info.truePricePaid
            });

            emit BondRedeemed( _depositor, payout, bondInfo[ _depositor ].payout );
            payoutToken.safeTransfer( _depositor, payout );
            return payout;
        }
        
    }
    
    /* ======== INTERNAL HELPER FUNCTIONS ======== */

    /**
     *  @notice makes incremental adjustment to control variable
     */
    function adjust() internal {
        uint blockCanAdjust = adjustment.lastBlock.add( adjustment.buffer );
        if( adjustment.rate != 0 && block.number >= blockCanAdjust ) {
            uint initial = terms.controlVariable;
            if ( adjustment.add ) {
                terms.controlVariable = terms.controlVariable.add( adjustment.rate );
                if ( terms.controlVariable >= adjustment.target ) {
                    adjustment.rate = 0;
                }
            } else {
                terms.controlVariable = terms.controlVariable.sub( adjustment.rate );
                if ( terms.controlVariable <= adjustment.target ) {
                    adjustment.rate = 0;
                }
            }
            adjustment.lastBlock = block.number;
            emit ControlVariableAdjustment( initial, terms.controlVariable, adjustment.rate, adjustment.add );
        }
    }

    /**
     *  @notice reduce total debt
     */
    function decayDebt() internal {
        totalDebt = totalDebt.sub( debtDecay() );
        lastDecay = block.number;
    }

    /**
     *  @notice calculate current bond price and remove floor if above
     *  @return price_ uint
     */
    function _bondPrice() internal returns ( uint price_ ) {
        price_ = terms.controlVariable.mul( debtRatio() ).div( 10 ** (uint256(payoutToken.decimals()).sub(5)) );
        if ( price_ < terms.minimumPrice ) {
            price_ = terms.minimumPrice;        
        } else if ( terms.minimumPrice != 0 ) {
            terms.minimumPrice = 0;
        }
    }


    /* ======== VIEW FUNCTIONS ======== */

    /**
     *  @notice calculate current bond premium
     *  @return price_ uint
     */
    function bondPrice() public view returns ( uint price_ ) {        
        price_ = terms.controlVariable.mul( debtRatio() ).div( 10 ** (uint256(payoutToken.decimals()).sub(5)) );
        if ( price_ < terms.minimumPrice ) {
            price_ = terms.minimumPrice;
        }
    }

    /**
     *  @notice calculate true bond price a user pays
     *  @return price_ uint
     */
    function trueBondPrice() public view returns ( uint price_ ) {
        price_ = bondPrice().add(bondPrice().mul( currentOlympusFee() ).div( 1e6 ) );
    }

    /**
     *  @notice determine maximum bond size
     *  @return uint
     */
    function maxPayout() public view returns ( uint ) {
        return payoutToken.totalSupply().mul( terms.maxPayout ).div( 100000 );
    }

    /**
     *  @notice calculate user's interest due for new bond, accounting for Olympus Fee. 
     If fee is in payout then takes in the already calcualted value. If fee is in principal token 
     than takes in the amount of principal being deposited and then calculautes the fee based on
     the amount of principal and not in terms of the payout token
     *  @param _value uint
     *  @return _payout uint
     *  @return _fee uint
     */
    function payoutFor( uint _value ) public view returns ( uint _payout, uint _fee) {
        if(feeInPayout) {
            uint total = FixedPoint.fraction( _value, bondPrice() ).decode112with18().div( 1e11 );
            _fee = total.mul( currentOlympusFee() ).div( 1e6 );
            _payout = total.sub(_fee);
        } else {
            _fee = _value.mul( currentOlympusFee() ).div( 1e6 );
            _payout = FixedPoint.fraction( customTreasury.valueOfToken(address(principalToken), _value.sub(_fee)), bondPrice() ).decode112with18().div( 1e11 );
        }
    }

    /**
     *  @notice calculate current ratio of debt to payout token supply
     *  @notice protocols using Olympus Pro should be careful when quickly adding large %s to total supply
     *  @return debtRatio_ uint
     */
    function debtRatio() public view returns ( uint debtRatio_ ) {   
        debtRatio_ = FixedPoint.fraction( 
            currentDebt().mul( 10 ** payoutToken.decimals() ), 
            payoutToken.totalSupply()
        ).decode112with18().div( 1e18 );
    }

    /**
     *  @notice calculate debt factoring in decay
     *  @return uint
     */
    function currentDebt() public view returns ( uint ) {
        return totalDebt.sub( debtDecay() );
    }

    /**
     *  @notice amount to decay total debt by
     *  @return decay_ uint
     */
    function debtDecay() public view returns ( uint decay_ ) {
        uint blocksSinceLast = block.number.sub( lastDecay );
        decay_ = totalDebt.mul( blocksSinceLast ).div( terms.vestingTerm );
        if ( decay_ > totalDebt ) {
            decay_ = totalDebt;
        }
    }

    /**
     *  @notice calculate how far into vesting a depositor is
     *  @param _depositor address
     *  @return percentVested_ uint
     */
    function percentVestedFor( address _depositor ) public view returns ( uint percentVested_ ) {
        Bond memory bond = bondInfo[ _depositor ];
        uint blocksSinceLast = block.number.sub( bond.lastBlock );
        uint vesting = bond.vesting;

        if ( vesting > 0 ) {
            percentVested_ = blocksSinceLast.mul( 10000 ).div( vesting );
        } else {
            percentVested_ = 0;
        }
    }

    /**
     *  @notice calculate amount of payout token available for claim by depositor
     *  @param _depositor address
     *  @return pendingPayout_ uint
     */
    function pendingPayoutFor( address _depositor ) external view returns ( uint pendingPayout_ ) {
        uint percentVested = percentVestedFor( _depositor );
        uint payout = bondInfo[ _depositor ].payout;

        if ( percentVested >= 10000 ) {
            pendingPayout_ = payout;
        } else {
            pendingPayout_ = payout.mul( percentVested ).div( 10000 );
        }
    }

    /**
     *  @notice current fee Olympus takes of each bond
     *  @return currentFee_ uint
     */
    function currentOlympusFee() public view returns( uint currentFee_ ) {
        uint tierLength = feeTiers.length;
        for(uint i; i < tierLength; i++) {
            if(totalPrincipalBonded < feeTiers[i].tierCeilings || i == tierLength - 1 ) {
                return feeTiers[i].fees;
            }
        }
    }
    
}