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// SPDX-License-Identifier: MIT

pragma solidity ^0.7.6;

import { Math } from "@openzeppelin/contracts/math/Math.sol";
import { SafeMath } from "@openzeppelin/contracts/math/SafeMath.sol";

import { ITwapOracle } from "../../price-oracle/interfaces/ITwapOracle.sol";
import { ICurvePoolOracle } from "../../interfaces/ICurvePoolOracle.sol";
import { IFxPriceOracle } from "../interfaces/IFxPriceOracle.sol";

// solhint-disable var-name-mixedcase

contract FxETHTwapOracle is IFxPriceOracle {
  using SafeMath for uint256;

  /*************
   * Constants *
   *************/

  /// @dev The precison use to calculation.
  uint256 private constant PRECISION = 1e18;

  /// @notice The address of chainlink stETH/USD twap oracle.
  address public immutable chainlinkStETHTwapOracle;

  /// @notice The address of chainlink ETH/USD twap oracle.
  address public immutable chainlinkETHTwapOracle;

  /// @notice The address of curve ETH/stETH pool.
  address public immutable curvePool;

  /***********
   * Structs *
   ***********/

  struct CachedPrice {
    uint256 ETH_USDPrice;
    uint256 stETH_USDPrice;
    uint256 stETH_ETHPrice;
  }

  /***************
   * Constructor *
   ***************/

  constructor(
    address _chainlinkStETHTwapOracle,
    address _chainlinkETHTwapOracle,
    address _curvePool
  ) {
    chainlinkStETHTwapOracle = _chainlinkStETHTwapOracle;
    chainlinkETHTwapOracle = _chainlinkETHTwapOracle;
    curvePool = _curvePool;
  }

  /*************************
   * Public View Functions *
   *************************/

  /// @inheritdoc IFxPriceOracle
  function getPrice()
    external
    view
    override
    returns (
      bool _isValid,
      uint256 _safePrice,
      uint256 _minUnsafePrice,
      uint256 _maxUnsafePrice
    )
  {
    CachedPrice memory _cached = _fetchPrice();

    _isValid = _isPriceValid(_cached);
    _safePrice = _cached.stETH_USDPrice;
    _minUnsafePrice = Math.min(_cached.ETH_USDPrice, _cached.stETH_USDPrice);
    _maxUnsafePrice = Math.max(_cached.ETH_USDPrice, _cached.stETH_USDPrice);

    if (_cached.stETH_ETHPrice != 0) {
      uint256 _curveStETHPrice = _cached.ETH_USDPrice.mul(_cached.stETH_ETHPrice) / PRECISION;
      if (_curveStETHPrice < _minUnsafePrice) {
        _minUnsafePrice = _curveStETHPrice;
      }
      if (_curveStETHPrice > _maxUnsafePrice) {
        _maxUnsafePrice = _curveStETHPrice;
      }
    }
  }

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

  function _fetchPrice() internal view returns (CachedPrice memory _cached) {
    _cached.ETH_USDPrice = ITwapOracle(chainlinkETHTwapOracle).getTwap(block.timestamp);
    _cached.stETH_USDPrice = ITwapOracle(chainlinkStETHTwapOracle).getTwap(block.timestamp);

    if (curvePool != address(0)) {
      _cached.stETH_ETHPrice = ICurvePoolOracle(curvePool).ema_price();
    }
  }

  function _isPriceValid(CachedPrice memory _cached) internal pure returns (bool) {
    uint256 priceDiff;
    if (_cached.ETH_USDPrice > _cached.stETH_USDPrice) {
      priceDiff = _cached.ETH_USDPrice - _cached.stETH_USDPrice;
    } else {
      priceDiff = _cached.stETH_USDPrice - _cached.ETH_USDPrice;
    }

    // |eth_usd_price - steth_usd_price| / steth_usd_price < 1%
    if (priceDiff * 100 >= _cached.stETH_USDPrice) return false;

    if (_cached.stETH_ETHPrice > 0) {
      return 0.99 ether <= _cached.stETH_ETHPrice && _cached.stETH_ETHPrice <= 1.01 ether;
    } else {
      return true;
    }
  }
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

/**
 * @dev Standard math utilities missing in the Solidity language.
 */
library Math {
    /**
     * @dev Returns the largest of two numbers.
     */
    function max(uint256 a, uint256 b) internal pure returns (uint256) {
        return a >= b ? a : b;
    }

    /**
     * @dev Returns the smallest of two numbers.
     */
    function min(uint256 a, uint256 b) internal pure returns (uint256) {
        return a < b ? a : b;
    }

    /**
     * @dev Returns the average of two numbers. The result is rounded towards
     * zero.
     */
    function average(uint256 a, uint256 b) internal pure returns (uint256) {
        // (a + b) / 2 can overflow, so we distribute
        return (a / 2) + (b / 2) + ((a % 2 + b % 2) / 2);
    }
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

/**
 * @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, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b > a) return (false, 0);
        return (true, a - b);
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, 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 (true, 0);
        uint256 c = a * b;
        if (c / a != b) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a / b);
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a % b);
    }

    /**
     * @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) {
        require(b <= a, "SafeMath: subtraction overflow");
        return a - b;
    }

    /**
     * @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) {
        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, reverting 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) {
        require(b > 0, "SafeMath: division by zero");
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting 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) {
        require(b > 0, "SafeMath: modulo by zero");
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * 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);
        return a - b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * 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);
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * 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;
    }
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.7.6;

interface IFxPriceOracle {
  /// @notice Return the oracle price with 18 decimal places.
  /// @return isValid Whether the oracle is valid.
  /// @return safePrice The safe oracle price when the oracle is valid.
  /// @return minUnsafePrice The minimum unsafe oracle price when the oracle is invalid.
  /// @return maxUnsafePrice The maximum unsafe oracle price when the oracle is invalid.
  function getPrice()
    external
    view
    returns (
      bool isValid,
      uint256 safePrice,
      uint256 minUnsafePrice,
      uint256 maxUnsafePrice
    );
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.7.6;

// solhint-disable func-name-mixedcase

interface ICurvePoolOracle {
  function last_price() external view returns (uint256);

  function ema_price() external view returns (uint256);

  function ma_exp_time() external view returns (uint256);

  function ma_last_time() external view returns (uint256);
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.7.6;

interface ITwapOracle {
  /// @notice Return TWAP with 18 decimal places in the epoch ending at the specified timestamp.
  ///         Zero is returned if TWAP in the epoch is not available.
  /// @param timestamp End Timestamp in seconds of the epoch
  /// @return TWAP (18 decimal places) in the epoch, or zero if not available
  function getTwap(uint256 timestamp) external view returns (uint256);

  /// @notice Return the latest price with 18 decimal places.
  function getLatest() external view returns (uint256);
}

{
  "optimizer": {
    "enabled": true,
    "runs": 200
  },
  "outputSelection": {
    "*": {
      "*": [
        "evm.bytecode",
        "evm.deployedBytecode",
        "devdoc",
        "userdoc",
        "metadata",
        "abi"
      ]
    }
  },
  "libraries": {}
}

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[{"inputs":[{"internalType":"address","name":"_chainlinkStETHTwapOracle","type":"address"},{"internalType":"address","name":"_chainlinkETHTwapOracle","type":"address"},{"internalType":"address","name":"_curvePool","type":"address"}],"stateMutability":"nonpayable","type":"constructor"},{"inputs":[],"name":"chainlinkETHTwapOracle","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"chainlinkStETHTwapOracle","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"curvePool","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"getPrice","outputs":[{"internalType":"bool","name":"_isValid","type":"bool"},{"internalType":"uint256","name":"_safePrice","type":"uint256"},{"internalType":"uint256","name":"_minUnsafePrice","type":"uint256"},{"internalType":"uint256","name":"_maxUnsafePrice","type":"uint256"}],"stateMutability":"view","type":"function"}]

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000000000000000000000000d24ac180e6769fd5f624e7605b93084171074a77000000000000000000000000460b3cde57dfba90dbed02fd83d3990a92da123000000000000000000000000021e27a5e5513d6e65c4f830167390997aa84843a

-----Decoded View---------------
Arg [0] : _chainlinkStETHTwapOracle (address): 0xD24AC180e6769Fd5F624e7605B93084171074A77
Arg [1] : _chainlinkETHTwapOracle (address): 0x460B3CdE57DfbA90DBed02fd83d3990a92DA1230
Arg [2] : _curvePool (address): 0x21E27a5E5513D6e65C4f830167390997aA84843a

-----Encoded View---------------
3 Constructor Arguments found :
Arg [0] : 000000000000000000000000d24ac180e6769fd5f624e7605b93084171074a77
Arg [1] : 000000000000000000000000460b3cde57dfba90dbed02fd83d3990a92da1230
Arg [2] : 00000000000000000000000021e27a5e5513d6e65c4f830167390997aa84843a