KlimaLPBonds_v4.sol

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

interface IOwnable {
    function policy() external view returns (address);

    function renounceManagement() external;

    function pushManagement( address newOwner_ ) external;

    function pullManagement() external;
}

contract Ownable is IOwnable {

    address internal _owner;
    address internal _newOwner;

    event OwnershipPushed(address indexed previousOwner, address indexed newOwner);
    event OwnershipPulled(address indexed previousOwner, address indexed newOwner);

    constructor () {
        _owner = msg.sender;
        emit OwnershipPushed( address(0), _owner );
    }

    function policy() public view override returns (address) {
        return _owner;
    }

    modifier onlyPolicy() {
        require( _owner == msg.sender, "Ownable: caller is not the owner" );
        _;
    }

    function renounceManagement() public virtual override onlyPolicy() {
        emit OwnershipPushed( _owner, address(0) );
        _owner = address(0);
    }

    function pushManagement( address newOwner_ ) public virtual override onlyPolicy() {
        require( newOwner_ != address(0), "Ownable: new owner is the zero address");
        emit OwnershipPushed( _owner, newOwner_ );
        _newOwner = newOwner_;
    }

    function pullManagement() public virtual override {
        require( msg.sender == _newOwner, "Ownable: must be new owner to pull");
        emit OwnershipPulled( _owner, _newOwner );
        _owner = _newOwner;
    }
}

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;
        }
    }
}

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);

    }
}

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);
}

abstract contract ERC20 is IERC20 {

    using SafeMath for uint256;

    // TODO comment actual hash value.
    bytes32 constant private ERC20TOKEN_ERC1820_INTERFACE_ID = keccak256( "ERC20Token" );

    mapping (address => uint256) internal _balances;

    mapping (address => mapping (address => uint256)) internal _allowances;

    uint256 internal _totalSupply;

    string internal _name;

    string internal _symbol;

    uint8 internal _decimals;

    constructor (string memory name_, string memory symbol_, uint8 decimals_) {
        _name = name_;
        _symbol = symbol_;
        _decimals = decimals_;
    }

    function name() public view returns (string memory) {
        return _name;
    }

    function symbol() public view returns (string memory) {
        return _symbol;
    }

    function decimals() public view override returns (uint8) {
        return _decimals;
    }

    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account) public view virtual override returns (uint256) {
        return _balances[account];
    }

    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(msg.sender, recipient, amount);
        return true;
    }

    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(msg.sender, spender, amount);
        return true;
    }

    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, msg.sender, _allowances[sender][msg.sender].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(msg.sender, spender, _allowances[msg.sender][spender].add(addedValue));
        return true;
    }

    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(msg.sender, spender, _allowances[msg.sender][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    function _transfer(address sender, address recipient, uint256 amount) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    function _mint(address account_, uint256 ammount_) internal virtual {
        require(account_ != address(0), "ERC20: mint to the zero address");
        _beforeTokenTransfer(address( this ), account_, ammount_);
        _totalSupply = _totalSupply.add(ammount_);
        _balances[account_] = _balances[account_].add(ammount_);
        emit Transfer(address( this ), account_, ammount_);
    }

    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    function _beforeTokenTransfer( address from_, address to_, uint256 amount_ ) internal virtual { }
}

interface IERC2612Permit {

    function permit(
        address owner,
        address spender,
        uint256 amount,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external;

    function nonces(address owner) external view returns (uint256);
}

library Counters {
    using SafeMath for uint256;

    struct Counter {

        uint256 _value; // default: 0
    }

    function current(Counter storage counter) internal view returns (uint256) {
        return counter._value;
    }

    function increment(Counter storage counter) internal {
        counter._value += 1;
    }

    function decrement(Counter storage counter) internal {
        counter._value = counter._value.sub(1);
    }
}

abstract contract ERC20Permit is ERC20, IERC2612Permit {
    using Counters for Counters.Counter;

    mapping(address => Counters.Counter) private _nonces;

    // keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");
    bytes32 public constant PERMIT_TYPEHASH = 0x6e71edae12b1b97f4d1f60370fef10105fa2faae0126114a169c64845d6126c9;

    bytes32 public DOMAIN_SEPARATOR;

    constructor() {
        uint256 chainID;
        assembly {
            chainID := chainid()
        }

        DOMAIN_SEPARATOR = keccak256(
            abi.encode(
                keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
                keccak256(bytes(name())),
                keccak256(bytes("1")), // Version
                chainID,
                address(this)
            )
        );
    }

    function permit(
        address owner,
        address spender,
        uint256 amount,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) public virtual override {
        require(block.timestamp <= deadline, "Permit: expired deadline");

        bytes32 hashStruct =
        keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, amount, _nonces[owner].current(), deadline));

        bytes32 _hash = keccak256(abi.encodePacked(uint16(0x1901), DOMAIN_SEPARATOR, hashStruct));

        address signer = ecrecover(_hash, v, r, s);
        require(signer != address(0) && signer == owner, "ZeroSwapPermit: Invalid signature");

        _nonces[owner].increment();
        _approve(owner, spender, amount);
    }

    function nonces(address owner) public view override returns (uint256) {
        return _nonces[owner].current();
    }
}

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");
        }
    }
}

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);
    }
}

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));
        }
    }
}

interface ITreasury {
    function deposit( uint _amount, address _token, uint _profit ) external returns ( bool );
    function valueOf( address _token, uint _amount ) external view returns ( uint value_ );
}

interface IBondCalculator {
    function valuation( address _LP, uint _amount ) external view returns ( uint );
    function markdown( address _LP ) external view returns ( uint );
}

interface IStaking {
    function stake( uint _amount, address _recipient ) external returns ( bool );
}

interface IStakingHelper {
    function stake( uint _amount, address _recipient ) external;
}

contract KlimaBondDepository is Ownable {

    using FixedPoint for *;
    using SafeERC20 for IERC20;
    using SafeMath for uint;




    /* ======== EVENTS ======== */

    event BondCreated( uint deposit, uint indexed payout, uint indexed expires, uint indexed priceInUSD );
    event BondRedeemed( address indexed recipient, uint payout, uint remaining );
    event BondPriceChanged( uint indexed priceInUSD, uint indexed internalPrice, uint indexed debtRatio );
    event ControlVariableAdjustment( uint initialBCV, uint newBCV, uint adjustment, bool addition );




    /* ======== STATE VARIABLES ======== */

    address public immutable KLIMA; // token given as payment for bond
    address public immutable principle; // token used to create bond
    address public immutable treasury; // mints KLIMA when receives principle
    address public immutable DAO; // receives profit share from bond

    bool public immutable isLiquidityBond; // LP and Reserve bonds are treated slightly different
    address public immutable bondCalculator; // calculates value of LP tokens

    address public staking; // to auto-stake payout
    address public stakingHelper; // to stake and claim if no staking warmup
    bool public useHelper;

    Terms public terms; // stores terms for new bonds
    Adjust public adjustment; // stores adjustment to BCV data

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

    uint public totalDebt; // total value of outstanding bonds; used for pricing
    uint public lastDecay; // reference block for debt decay




    /* ======== STRUCTS ======== */

    // Info for creating new bonds
    struct Terms {
        uint controlVariable; // scaling variable for price
        uint vestingTerm; // in blocks
        uint minimumPrice; // vs principle value
        uint maxPayout; // in thousandths of a %. i.e. 500 = 0.5%
        uint fee; // as % of bond payout, in hundreths. ( 500 = 5% = 0.05 for every 1 paid)
        uint maxDebt; // 9 decimal debt ratio, max % total supply created as debt
    }

    // Info for bond holder
    struct Bond {
        uint payout; // KLIMA remaining to be paid
        uint vesting; // Blocks left to vest
        uint lastBlock; // Last interaction
        uint pricePaid; // In BCT, for front end viewing
    }

    // 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
    }

    /* ======== INITIALIZATION ======== */

    constructor (
        address _KLIMA,
        address _principle,
        address _treasury,
        address _DAO,
        address _bondCalculator
    ) {
        require( _KLIMA != address(0) );
        KLIMA = _KLIMA;
        require( _principle != address(0) );
        principle = _principle;
        require( _treasury != address(0) );
        treasury = _treasury;
        require( _DAO != address(0) );
        DAO = _DAO;
        // bondCalculator should be address(0) if not LP bond
        bondCalculator = _bondCalculator;
        isLiquidityBond = ( _bondCalculator != address(0) );
    }

    /**
     *  @notice initializes bond parameters
     *  @param _controlVariable uint
     *  @param _vestingTerm uint
     *  @param _minimumPrice uint
     *  @param _maxPayout uint
     *  @param _fee uint
     *  @param _maxDebt uint
     *  @param _initialDebt uint
     */
    function initializeBondTerms(
        uint _controlVariable,
        uint _vestingTerm,
        uint _minimumPrice,
        uint _maxPayout,
        uint _fee,
        uint _maxDebt,
        uint _initialDebt
    ) external onlyPolicy() {
        require( terms.controlVariable == 0, "Bonds must be initialized from 0" );
        terms = Terms ({
        controlVariable: _controlVariable,
        vestingTerm: _vestingTerm,
        minimumPrice: _minimumPrice,
        maxPayout: _maxPayout,
        fee: _fee,
        maxDebt: _maxDebt
        });
        totalDebt = _initialDebt;
        lastDecay = block.number;
    }
    /* ======== POLICY FUNCTIONS ======== */

    enum PARAMETER { VESTING, PAYOUT, FEE, 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.FEE ) { // 2
            require( _input <= 10000, "DAO fee cannot exceed payout" );
            terms.fee = _input;
        } else if ( _parameter == PARAMETER.DEBT ) { // 3
            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( 25 ).div( 1000 ), "Increment too large" );

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

    /**
     *  @notice set contract for auto stake
     *  @param _staking address
     *  @param _helper bool
     */
    function setStaking( address _staking, bool _helper ) external onlyPolicy() {
        require( _staking != address(0) );
        if ( _helper ) {
            useHelper = true;
            stakingHelper = _staking;
        } else {
            useHelper = false;
            staking = _staking;
        }
    }

    /* ======== 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();
        require( totalDebt <= terms.maxDebt, "Max capacity reached" );

        uint priceInUSD = bondPriceInUSD(); // Stored in bond info
        uint nativePrice = _bondPrice();

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

        uint value = ITreasury( treasury ).valueOf( principle, _amount );
        uint payout = payoutFor( value ); // payout to bonder is computed

        require( payout >= 10000000, "Bond too small" ); // must be > 0.01 KLIMA ( underflow protection )
        require( payout <= maxPayout(), "Bond too large"); // size protection because there is no slippage

        // profits are calculated
        uint fee = payout.mul( terms.fee ).div( 10000 );
        uint profit = value.sub( payout ).sub( fee );

        /**
            principle is transferred in
            approved and
            deposited into the treasury, returning (_amount - profit) KLIMA
         */
        IERC20( principle ).safeTransferFrom( msg.sender, address(this), _amount );
        IERC20( principle ).approve( address( treasury ), _amount );
        ITreasury( treasury ).deposit( _amount, principle, profit );

        if ( fee != 0 ) { // fee is transferred to dao 
            IERC20( KLIMA ).safeTransfer( DAO, fee );
        }

        // total debt is increased
        totalDebt = totalDebt.add( value );

        // depositor info is stored
        bondInfo[ _depositor ] = Bond({
        payout: bondInfo[ _depositor ].payout.add( payout ),
        vesting: terms.vestingTerm,
        lastBlock: block.number,
        pricePaid: priceInUSD
        });

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

        adjust(); // control variable is adjusted
        return payout;
    }

    /** 
     *  @notice redeem bond for user
     *  @param _recipient address
     *  @param _stake bool
     *  @return uint
     */
    function redeem( address _recipient, bool _stake ) external returns ( uint ) {
        Bond memory info = bondInfo[ _recipient ];
        uint percentVested = percentVestedFor( _recipient ); // (blocks since last interaction / vesting term remaining)

        if ( percentVested >= 10000 ) { // if fully vested
            delete bondInfo[ _recipient ]; // delete user info
            emit BondRedeemed( _recipient, info.payout, 0 ); // emit bond data
            return stakeOrSend( _recipient, _stake, info.payout ); // pay user everything due

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

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

            emit BondRedeemed( _recipient, payout, bondInfo[ _recipient ].payout );
            return stakeOrSend( _recipient, _stake, payout );
        }
    }




    /* ======== INTERNAL HELPER FUNCTIONS ======== */

    /**
     *  @notice allow user to stake payout automatically
     *  @param _stake bool
     *  @param _amount uint
     *  @return uint
     */
    function stakeOrSend( address _recipient, bool _stake, uint _amount ) internal returns ( uint ) {
        if ( !_stake ) { // if user does not want to stake
            IERC20( KLIMA ).transfer( _recipient, _amount ); // send payout
        } else { // if user wants to stake
            if ( useHelper ) { // use if staking warmup is 0
                IERC20( KLIMA ).approve( stakingHelper, _amount );
                IStakingHelper( stakingHelper ).stake( _amount, _recipient );
            } else {
                IERC20( KLIMA ).approve( staking, _amount );
                IStaking( staking ).stake( _amount, _recipient );
            }
        }
        return _amount;
    }

    /**
     *  @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;
    }




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

    /**
     *  @notice determine maximum bond size
     *  @return uint
     */
    function maxPayout() public view returns ( uint ) {
        return IERC20( KLIMA ).totalSupply().mul( terms.maxPayout ).div( 100000 );
    }

    /**
     *  @notice calculate interest due for new bond
     *  @param _value uint
     *  @return uint
     */
    function payoutFor( uint _value ) public view returns ( uint ) {
        return FixedPoint.fraction( _value, bondPrice() ).decode112with18().div( 1e16 );
    }


    /**
     *  @notice calculate current bond premium
     *  @return price_ uint
     */
    function bondPrice() public view returns ( uint price_ ) {
        price_ = terms.controlVariable.mul( debtRatio() ).add( 1000000000 ).div( 1e7 );
        if ( price_ < terms.minimumPrice ) {
            price_ = terms.minimumPrice;
        }
    }

    /**
     *  @notice calculate current bond price and remove floor if above
     *  @return price_ uint
     */
    function _bondPrice() internal returns ( uint price_ ) {
        price_ = terms.controlVariable.mul( debtRatio() ).add( 1000000000 ).div( 1e7 );
        if ( price_ < terms.minimumPrice ) {
            price_ = terms.minimumPrice;
        } else if ( terms.minimumPrice != 0 ) {
            terms.minimumPrice = 0;
        }
    }

    /**
     *  @notice converts bond price to BCT value
     *  @return price_ uint
     */
    function bondPriceInUSD() public view returns ( uint price_ ) {
        if( isLiquidityBond ) {
            price_ = bondPrice().mul( IBondCalculator( bondCalculator ).markdown( principle ) ).div( 100 );
        } else {
            price_ = bondPrice().mul( 10 ** IERC20( principle ).decimals() ).div( 100 );
        }
    }


    /**
     *  @notice calculate current ratio of debt to KLIMA supply
     *  @return debtRatio_ uint
     */
    function debtRatio() public view returns ( uint debtRatio_ ) {
        uint supply = IERC20( KLIMA ).totalSupply();
        debtRatio_ = FixedPoint.fraction(
            currentDebt().mul( 1e9 ),
            supply
        ).decode112with18().div( 1e18 );
    }

    /**
     *  @notice debt ratio in same terms for reserve or liquidity bonds
     *  @return uint
     */
    function standardizedDebtRatio() external view returns ( uint ) {
        if ( isLiquidityBond ) {
            return debtRatio().mul( IBondCalculator( bondCalculator ).markdown( principle ) ).div( 1e9 );
        } else {
            return debtRatio();
        }
    }

    /**
     *  @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 KLIMA 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 );
        }
    }

    /* ======= AUXILLIARY ======= */

    /**
     *  @notice allow anyone to send lost tokens (excluding principle or KLIMA) to the DAO
     *  @return bool
     */
    function recoverLostToken( address _token ) external returns ( bool ) {
        require( _token != KLIMA );
        require( _token != principle );
        IERC20( _token ).safeTransfer( DAO, IERC20( _token ).balanceOf( address(this) ) );
        return true;
    }
}