// SPDX-License-Identifier: MIT

/*
MIT License

Copyright (c) 2018 requestnetwork
Copyright (c) 2018 Fragments, Inc.
Copyright (c) 2020 Rebased

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

*/

pragma solidity ^0.6.12;

/**
 * @title SafeMath
 * @dev Math operations with safety checks that revert on error
 */
library SafeMath {

  /**
  * @dev Multiplies two numbers, reverts on overflow.
  */
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
    // benefit is lost if 'b' is also tested.
    // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
    if (a == 0) {
      return 0;
    }

    uint256 c = a * b;
    require(c / a == b);

    return c;
  }

  /**
  * @dev Integer division of two numbers truncating the quotient, reverts on division by zero.
  */
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b > 0); // Solidity only automatically asserts when dividing by 0
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold

    return c;
  }

  /**
  * @dev Subtracts two numbers, reverts on overflow (i.e. if subtrahend is greater than minuend).
  */
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b <= a);
    uint256 c = a - b;

    return c;
  }

  /**
  * @dev Adds two numbers, reverts on overflow.
  */
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    require(c >= a);

    return c;
  }

  /**
  * @dev Divides two numbers and returns the remainder (unsigned integer modulo),
  * reverts when dividing by zero.
  */
  function mod(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b != 0);
    return a % b;
  }
}

library SafeMathInt {
    int256 private constant MIN_INT256 = int256(1) << 255;
    int256 private constant MAX_INT256 = ~(int256(1) << 255);

    /**
     * @dev Multiplies two int256 variables and fails on overflow.
     */
    function mul(int256 a, int256 b)
        internal
        pure
        returns (int256)
    {
        int256 c = a * b;

        // Detect overflow when multiplying MIN_INT256 with -1
        require(c != MIN_INT256 || (a & MIN_INT256) != (b & MIN_INT256));
        require((b == 0) || (c / b == a));
        return c;
    }

    /**
     * @dev Division of two int256 variables and fails on overflow.
     */
    function div(int256 a, int256 b)
        internal
        pure
        returns (int256)
    {
        // Prevent overflow when dividing MIN_INT256 by -1
        require(b != -1 || a != MIN_INT256);

        // Solidity already throws when dividing by 0.
        return a / b;
    }

    /**
     * @dev Subtracts two int256 variables and fails on overflow.
     */
    function sub(int256 a, int256 b)
        internal
        pure
        returns (int256)
    {
        int256 c = a - b;
        require((b >= 0 && c <= a) || (b < 0 && c > a));
        return c;
    }

    /**
     * @dev Adds two int256 variables and fails on overflow.
     */
    function add(int256 a, int256 b)
        internal
        pure
        returns (int256)
    {
        int256 c = a + b;
        require((b >= 0 && c >= a) || (b < 0 && c < a));
        return c;
    }

    /**
     * @dev Converts to absolute value, and fails on overflow.
     */
    function abs(int256 a)
        internal
        pure
        returns (int256)
    {
        require(a != MIN_INT256);
        return a < 0 ? -a : a;
    }
}

/**
 * @title Various utilities useful for uint256.
 */
library UInt256Lib {

    uint256 private constant MAX_INT256 = ~(uint256(1) << 255);

    /**
     * @dev Safely converts a uint256 to an int256.
     */
    function toInt256Safe(uint256 a)
        internal
        pure
        returns (int256)
    {
        require(a <= MAX_INT256);
        return int256(a);
    }
}

/**
 * @title ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/20
 */
interface IERC20 {

  function totalSupply() external view returns (uint256);

  function balanceOf(address who) external view returns (uint256);

  function allowance(address owner, address spender)
    external view returns (uint256);

  function transfer(address to, uint256 value) external returns (bool);

  function approve(address spender, uint256 value)
    external returns (bool);

  function transferFrom(address from, address to, uint256 value)
    external returns (bool);

  event Transfer(
    address indexed from,
    address indexed to,
    uint256 value
  );

  event Approval(
    address indexed owner,
    address indexed spender,
    uint256 value
  );
}

interface IRebased {
    function totalSupply() external view returns (uint256);
    function rebase(uint256 epoch, int256 supplyDelta) external returns (uint256);
}

interface IOracle {
    function getData() external view returns (uint256, bool);
}

/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions".
 */
contract Ownable {
  address private _owner;

  event OwnershipRenounced(address indexed previousOwner);
  
  event OwnershipTransferred(
    address indexed previousOwner,
    address indexed newOwner
  );


  /**
   * @dev The Ownable constructor sets the original `owner` of the contract to the sender
   * account.
   */
  constructor() public {
    _owner = msg.sender;
  }

  /**
   * @return the address of the owner.
   */
  function owner() public view returns(address) {
    return _owner;
  }

  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyOwner() {
    require(isOwner());
    _;
  }

  /**
   * @return true if `msg.sender` is the owner of the contract.
   */
  function isOwner() public view returns(bool) {
    return msg.sender == _owner;
  }

  /**
   * @dev Allows the current owner to relinquish control of the contract.
   * @notice Renouncing to ownership will leave the contract without an owner.
   * It will not be possible to call the functions with the `onlyOwner`
   * modifier anymore.
   */
  function renounceOwnership() public onlyOwner {
    emit OwnershipRenounced(_owner);
    _owner = address(0);
  }

  /**
   * @dev Allows the current owner to transfer control of the contract to a newOwner.
   * @param newOwner The address to transfer ownership to.
   */
  function transferOwnership(address newOwner) public onlyOwner {
    _transferOwnership(newOwner);
  }

  /**
   * @dev Transfers control of the contract to a newOwner.
   * @param newOwner The address to transfer ownership to.
   */
  function _transferOwnership(address newOwner) internal {
    require(newOwner != address(0));
    emit OwnershipTransferred(_owner, newOwner);
    _owner = newOwner;
  }
}

/**
 * @title Rebased Monetary Supply Policy
 * @dev This is a simplified version of the uFragments Ideal Money protocol a.k.a. Ampleforth.
 *      uFragments operates symmetrically on expansion and contraction. It will both split and
 *      combine coins to maintain a stable unit price.
 *
 *      This component regulates the token supply of the uFragments ERC20 token in response to
 *      market oracles.
 */
contract MonetaryPolicy is Ownable {
    using SafeMath for uint256;
    using SafeMathInt for int256;
    using UInt256Lib for uint256;

    event LogRebase(
        uint256 indexed epoch,
        uint256 exchangeRate,
        uint256 cpi,
        int256 requestedSupplyAdjustment,
        uint256 timestampSec
    );

    IRebased public rebased;

    // Provides the current CPI as a 20 decimal fixed point number.
    IOracle public cpiOracle;

    // Market oracle provides the token/USD exchange rate as an 18 decimal fixed point number.
    IOracle public marketOracle;

    // CPI value at the time of launch, as an 18 decimal fixed point number.
    uint256 private baseCpi;

    // If the current exchange rate is within this fractional distance from the target, no supply
    // update is performed. Fixed point number--same format as the rate.
    // (ie) abs(rate - targetRate) / targetRate < deviationThreshold, then no supply change.
    // DECIMALS Fixed point number.
    uint256 public deviationThreshold;

    // The rebase lag parameter, used to dampen the applied supply adjustment by 1 / rebaseLag
    // Check setRebaseLag comments for more details.
    // Natural number, no decimal places.
    uint256 public rebaseLag;

    // More than this much time must pass between rebase operations.
    uint256 public minRebaseTimeIntervalSec;

    // Block timestamp of last rebase operation
    uint256 public lastRebaseTimestampSec;

    // The number of rebase cycles since inception
    uint256 public epoch;

    uint256 private constant DECIMALS = 18;

    // Due to the expression in computeSupplyDelta(), MAX_RATE * MAX_SUPPLY must fit into an int256.
    // Both are 18 decimals fixed point numbers.
    uint256 private constant MAX_RATE = 10**6 * 10**DECIMALS;
    // MAX_SUPPLY = MAX_INT256 / MAX_RATE
    uint256 private constant MAX_SUPPLY = ~(uint256(1) << 255) / MAX_RATE;

    constructor(uint256 baseCpi_) public {
        deviationThreshold = 5 * 10 ** (DECIMALS-2);

        rebaseLag = 20;
        minRebaseTimeIntervalSec = 12 hours;
        lastRebaseTimestampSec = 0;
        epoch = 0;
        
        baseCpi = baseCpi_;
    }

    /**
     * @notice Returns true if at least minRebaseTimeIntervalSec seconds have passed since last rebase.
     *
     */
     
    function canRebase() public view returns (bool) {
        
        return (lastRebaseTimestampSec.add(minRebaseTimeIntervalSec) < now);
    }

    /**
     * @notice Initiates a new rebase operation, provided the minimum time period has elapsed.
     *
     */
     
    function rebase() external {

        require(canRebase(), "Insufficient time has passed since last rebase");
        lastRebaseTimestampSec = now;

        epoch = epoch.add(1);
        
        (uint256 cpi, uint256 exchangeRate, uint256 targetRate, int256 supplyDelta) = getRebaseValues();

        uint256 supplyAfterRebase = rebased.rebase(epoch, supplyDelta);
        assert(supplyAfterRebase <= MAX_SUPPLY);
        
        emit LogRebase(epoch, exchangeRate, cpi, supplyDelta, now);
    }
    
    /**
     * @notice Calculates the supplyDelta and returns the current set of values for the rebase
     *
     * @dev The supply adjustment equals (_totalSupply * DeviationFromTargetRate) / rebaseLag
     *      Where DeviationFromTargetRate is (MarketOracleRate - targetRate) / targetRate
     *      and targetRate is CpiOracleRate / baseCpi
     * 
     */    
    
    function getRebaseValues() public view returns (uint256, uint256, uint256, int256) {
        uint256 cpi;
        bool cpiValid;
        (cpi, cpiValid) = cpiOracle.getData();
        
        require(cpiValid);

        uint256 targetRate = cpi.mul(10 ** DECIMALS).div(baseCpi);

        uint256 exchangeRate;
        bool rateValid;
        
        (exchangeRate, rateValid) = marketOracle.getData();
        
        require(rateValid);

        if (exchangeRate > MAX_RATE) {
            exchangeRate = MAX_RATE;
        }

        int256 supplyDelta = computeSupplyDelta(exchangeRate, targetRate);

        // Apply the Dampening factor.
        supplyDelta = supplyDelta.div(rebaseLag.toInt256Safe());

        if (supplyDelta > 0 && rebased.totalSupply().add(uint256(supplyDelta)) > MAX_SUPPLY) {
            supplyDelta = (MAX_SUPPLY.sub(rebased.totalSupply())).toInt256Safe();
        }

       return (cpi, exchangeRate, targetRate, supplyDelta);
    }


    /**
     * @return Computes the total supply adjustment in response to the exchange rate
     *         and the targetRate.
     */
    function computeSupplyDelta(uint256 rate, uint256 targetRate)
        internal
        view
        returns (int256)
    {
        if (withinDeviationThreshold(rate, targetRate)) {
            return 0;
        }

        // supplyDelta = totalSupply * (rate - targetRate) / targetRate
        int256 targetRateSigned = targetRate.toInt256Safe();
        return rebased.totalSupply().toInt256Safe()
            .mul(rate.toInt256Safe().sub(targetRateSigned))
            .div(targetRateSigned);
    }

    /**
     * @param rate The current exchange rate, an 18 decimal fixed point number.
     * @param targetRate The target exchange rate, an 18 decimal fixed point number.
     * @return If the rate is within the deviation threshold from the target rate, returns true.
     *         Otherwise, returns false.
     */
    function withinDeviationThreshold(uint256 rate, uint256 targetRate)
        internal
        view
        returns (bool)
    {
        uint256 absoluteDeviationThreshold = targetRate.mul(deviationThreshold)
            .div(10 ** DECIMALS);

        return (rate >= targetRate && rate.sub(targetRate) < absoluteDeviationThreshold)
            || (rate < targetRate && targetRate.sub(rate) < absoluteDeviationThreshold);
    }
    
    /**
     * @notice Sets the reference to the Rebased token governed.
     *         Can only be called once during initialization.
     * 
     * @param rebased_ The address of the Rebased ERC20 token.
     */
    function setRebased(IRebased rebased_)
        external
        onlyOwner
    {
        require(rebased == IRebased(0)); 
        rebased = rebased_;    
    }
    
    /**
     * @notice Sets the reference to the CPI oracle.
     * @param cpiOracle_ The address of the cpi oracle contract.
     */
    function setCpiOracle(IOracle cpiOracle_)
        external
        onlyOwner
    {
        cpiOracle = cpiOracle_;
    }

    /**
     * @notice Sets the reference to the market oracle.
     * @param marketOracle_ The address of the market oracle contract.
     */
    function setMarketOracle(IOracle marketOracle_)
        external
        onlyOwner
    {
        marketOracle = marketOracle_;
    }

}