// File: /home/bugman/Projects/idle/idle-governance/contracts/PriceOracleV2.sol



pragma solidity 0.6.12;

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/math/SafeMath.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

import "./interfaces/IdleToken.sol";
import "./interfaces/CERC20.sol";
import "./interfaces/AToken.sol";
import "./interfaces/Comptroller.sol";
import "./interfaces/ChainLinkOracle.sol";
import "./interfaces/IAaveIncentivesController.sol";

contract PriceOracleV2 is Ownable {
  using SafeMath for uint256;

  uint256 constant private ONE_18 = 10**18;
  address constant public WETH = 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2;
  address constant public COMP = 0xc00e94Cb662C3520282E6f5717214004A7f26888;
  address constant public WBTC = 0x2260FAC5E5542a773Aa44fBCfeDf7C193bc2C599;
  address constant public DAI = 0x6B175474E89094C44Da98b954EedeAC495271d0F;
  address constant public SUSD = 0x57Ab1ec28D129707052df4dF418D58a2D46d5f51;
  address constant public TUSD = 0x0000000000085d4780B73119b644AE5ecd22b376;
  address constant public USDC = 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48;
  address constant public USDT = 0xdAC17F958D2ee523a2206206994597C13D831ec7;
  address public constant stkAAVE = address(0x4da27a545c0c5B758a6BA100e3a049001de870f5);

  uint256 public blocksPerYear = 2371428; // -> blocks per year with ~13.3s block time
  uint256 public constant secondsPerYear = 31536000;
  // underlying -> chainlink feed see https://docs.chain.link/docs/reference-contracts
  mapping (address => address) public priceFeedsUSD;
  mapping (address => address) public priceFeedsETH;

  constructor() public {
    // USD feeds
    priceFeedsUSD[WETH] = 0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419; // WETH
    priceFeedsUSD[COMP] = 0xdbd020CAeF83eFd542f4De03e3cF0C28A4428bd5; // COMP
    priceFeedsUSD[WBTC] = 0xF4030086522a5bEEa4988F8cA5B36dbC97BeE88c; // wBTC
    priceFeedsUSD[DAI] = 0xAed0c38402a5d19df6E4c03F4E2DceD6e29c1ee9; // DAI
    priceFeedsUSD[stkAAVE] = 0x547a514d5e3769680Ce22B2361c10Ea13619e8a9; // AAVE

    // ETH feeds
    priceFeedsETH[WBTC] = 0xdeb288F737066589598e9214E782fa5A8eD689e8; // wBTC
    priceFeedsETH[DAI] = 0x773616E4d11A78F511299002da57A0a94577F1f4; // DAI
    priceFeedsETH[SUSD] = 0x8e0b7e6062272B5eF4524250bFFF8e5Bd3497757; // SUSD
    priceFeedsETH[TUSD] = 0x3886BA987236181D98F2401c507Fb8BeA7871dF2; // TUSD
    priceFeedsETH[USDC] = 0x986b5E1e1755e3C2440e960477f25201B0a8bbD4; // USDC
    priceFeedsETH[USDT] = 0xEe9F2375b4bdF6387aa8265dD4FB8F16512A1d46; // USDT
    priceFeedsETH[stkAAVE] = 0x6Df09E975c830ECae5bd4eD9d90f3A95a4f88012; // AAVE
  }

  /// @notice get price in USD for an asset
  function getPriceUSD(address _asset) public view returns (uint256) {
    return _getPriceUSD(_asset); // 1e18
  }
  /// @notice get price in ETH for an asset
  function getPriceETH(address _asset) public view returns (uint256) {
    return _getPriceETH(_asset); // 1e18
  }
  /// @notice get price in a specific token for an asset
  function getPriceToken(address _asset, address _token) public view returns (uint256) {
    return _getPriceToken(_asset, _token); // 1e(_token.decimals())
  }
  /// @notice get price for the underlying token of an idleToken
  function getUnderlyingPrice(address _idleToken) external view returns (uint256) {
    return getPriceUSD(IdleToken(_idleToken).token()); // 1e18
  }
  /// @notice get COMP additional apr for a specific cToken market
  function getCompApr(address _cToken, address _token) external view returns (uint256) {
    CERC20 _ctoken = CERC20(_cToken);
    uint256 compSpeeds = Comptroller(_ctoken.comptroller()).compSpeeds(_cToken);
    uint256 cTokenNAV = _ctoken.exchangeRateStored().mul(IERC20(_cToken).totalSupply()).div(ONE_18);
    // how much costs 1COMP in token (1e(_token.decimals()))
    uint256 compUnderlyingPrice = getPriceToken(COMP, _token);
    // mul(100) needed to have a result in the format 4.4e18
    return compSpeeds.mul(compUnderlyingPrice).mul(blocksPerYear).mul(100).div(cTokenNAV);
  }

  /// @notice get AAVE additional apr for a specific aToken market
  function getStkAaveApr(address _aToken, address _token) external view returns (uint256) {
    IAaveIncentivesController _ctrl = IAaveIncentivesController(AToken(_aToken).getIncentivesController());
    (,uint256 aavePerSec,) = _ctrl.getAssetData(_aToken);
    uint256 aTokenNAV = IERC20(_aToken).totalSupply();
    // how much costs 1AAVE in token (1e(_token.decimals()))
    uint256 aaveUnderlyingPrice = getPriceToken(stkAAVE, _token);
    // mul(100) needed to have a result in the format 4.4e18
    return aavePerSec.mul(aaveUnderlyingPrice).mul(secondsPerYear).mul(100).div(aTokenNAV);
  }

  // #### internal
  function _getPriceUSD(address _asset) internal view returns (uint256 price) {
    if (priceFeedsUSD[_asset] != address(0)) {
      price = ChainLinkOracle(priceFeedsUSD[_asset]).latestAnswer().mul(10**10); // scale it to 1e18
    } else if (priceFeedsETH[_asset] != address(0)) {
      price = ChainLinkOracle(priceFeedsETH[_asset]).latestAnswer();
      price = price.mul(ChainLinkOracle(priceFeedsUSD[WETH]).latestAnswer().mul(10**10)).div(ONE_18);
    }
  }
  function _getPriceETH(address _asset) internal view returns (uint256 price) {
    if (priceFeedsETH[_asset] != address(0)) {
      price = ChainLinkOracle(priceFeedsETH[_asset]).latestAnswer();
    }
  }
  function _getPriceToken(address _asset, address _token) internal view returns (uint256 price) {
    uint256 assetUSD = getPriceUSD(_asset);
    uint256 tokenUSD = getPriceUSD(_token);
    if (tokenUSD == 0) {
      return price;
    }
    return assetUSD.mul(10**(uint256(ERC20(_token).decimals()))).div(tokenUSD); // 1e(tokenDecimals)
  }

  // #### onlyOwner
  function setBlocksPerYear(uint256 _blocksPerYear) external onlyOwner {
    blocksPerYear = _blocksPerYear;
  }
  // _feed can be address(0) which means disabled
  function updateFeedETH(address _asset, address _feed) external onlyOwner {
    priceFeedsETH[_asset] = _feed;
  }
  function updateFeedUSD(address _asset, address _feed) external onlyOwner {
    priceFeedsUSD[_asset] = _feed;
  }
}

// File: /home/bugman/Projects/idle/idle-governance/contracts/interfaces/AToken.sol



pragma solidity 0.6.12;

interface AToken {
  function getIncentivesController() external view returns (address);
  function redeem(uint256 amount) external;
  function burn(address user, address receiverOfUnderlying, uint256 amount, uint256 index) external;
}

// File: /home/bugman/Projects/idle/idle-governance/contracts/interfaces/CERC20.sol



pragma solidity 0.6.12;

interface CERC20 {
  function comptroller() external view returns (address);
  function exchangeRateStored() external view returns (uint256);
}

// File: /home/bugman/Projects/idle/idle-governance/contracts/interfaces/ChainLinkOracle.sol



pragma solidity 0.6.12;

interface ChainLinkOracle {
  function latestAnswer() external view returns (uint256);
}

// File: /home/bugman/Projects/idle/idle-governance/contracts/interfaces/Comptroller.sol



pragma solidity 0.6.12;

interface Comptroller {
  function claimComp(address) external;
  function compSpeeds(address _cToken) external view returns (uint256);
  function claimComp(address[] calldata holders, address[] calldata cTokens, bool borrowers, bool suppliers) external;
}

// File: /home/bugman/Projects/idle/idle-governance/contracts/interfaces/IAaveIncentivesController.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.6.12;
interface IAaveIncentivesController {
  /**
   * @dev Claims reward for an user, on all the assets of the lending pool, accumulating the pending rewards
   * @param amount Amount of rewards to claim
   * @param to Address that will be receiving the rewards
   * @return Rewards claimed
   **/
  function claimRewards(
    address[] calldata assets,
    uint256 amount,
    address to
  ) external returns (uint256);

  /**
   * @dev returns the unclaimed rewards of the user
   * @param user the address of the user
   * @return the unclaimed user rewards
   */
  function getUserUnclaimedRewards(address user) external view returns (uint256);
  function getAssetData(address asset) external view returns (uint256, uint256, uint256);
}

// File: /home/bugman/Projects/idle/idle-governance/contracts/interfaces/IdleToken.sol



pragma solidity 0.6.12;

interface IdleToken {
  function totalSupply() external view returns (uint256);
  function tokenPrice() external view returns (uint256 price);
  function token() external view returns (address);
  function getAvgAPR() external view returns (uint256 apr);
  function balanceOf(address) external view returns (uint256 apr);
  function getAPRs() external view returns (address[] memory addresses, uint256[] memory aprs);
  function mintIdleToken(uint256 _amount, bool _skipRebalance, address _referral) external returns (uint256 mintedTokens);
  function redeemIdleToken(uint256 _amount) external returns (uint256 redeemedTokens);
  function redeemInterestBearingTokens(uint256 _amount) external;
  function rebalance() external returns (bool);
}

// File: @openzeppelin/contracts/GSN/Context.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

// File: @openzeppelin/contracts/access/Ownable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../GSN/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(_owner == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: @openzeppelin/contracts/math/SafeMath.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot 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-contracts/pull/522
        if (a == 0) {
            return 0;
        }

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

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

// File: @openzeppelin/contracts/token/ERC20/ERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../../GSN/Context.sol";
import "./IERC20.sol";
import "../../math/SafeMath.sol";

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) private _balances;

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

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    /**
     * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
     * a default value of 18.
     *
     * To select a different value for {decimals}, use {_setupDecimals}.
     *
     * All three of these values are immutable: they can only be set once during
     * construction.
     */
    constructor (string memory name_, string memory symbol_) public {
        _name = name_;
        _symbol = symbol_;
        _decimals = 18;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
     * called.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view returns (uint8) {
        return _decimals;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20}.
     *
     * Requirements:
     *
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    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);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

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

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    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);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    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);
    }

    /**
     * @dev Sets {decimals} to a value other than the default one of 18.
     *
     * WARNING: This function should only be called from the constructor. Most
     * applications that interact with token contracts will not expect
     * {decimals} to ever change, and may work incorrectly if it does.
     */
    function _setupDecimals(uint8 decimals_) internal {
        _decimals = decimals_;
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}