// File: contracts/BrewlabsTwapOracle.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "./libs/Babylonian.sol";
import "./libs/FixedPoint.sol";
import "./libs/UniswapV2OracleLibrary.sol";
import "./libs/IUniPair.sol";
import "./libs/Epoch.sol";

// fixed window oracle that recomputes the average price for the entire period once every period
// note that the price average is only guaranteed to be over at least 1 period, but may be over a longer period
contract BrewlabsTwapOracle is Epoch {
    using FixedPoint for *;

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

    // uniswap
    address public token0;
    address public token1;
    IUniswapV2Pair public pair;

    // oracle
    uint32 public blockTimestampLast;
    uint256 public price0CumulativeLast;
    uint256 public price1CumulativeLast;
    FixedPoint.uq112x112 public price0Average;
    FixedPoint.uq112x112 public price1Average;

    event Updated(uint256 price0CumulativeLast, uint256 price1CumulativeLast);

    /* ========== CONSTRUCTOR ========== */
    constructor(IUniswapV2Pair _pair, uint256 _period, uint256 _startTime) Epoch(_period, _startTime, 0) {
        pair = _pair;
        token0 = pair.token0();
        token1 = pair.token1();
        price0CumulativeLast = pair.price0CumulativeLast(); // fetch the current accumulated price value (1 / 0)
        price1CumulativeLast = pair.price1CumulativeLast(); // fetch the current accumulated price value (0 / 1)
        uint112 reserve0;
        uint112 reserve1;
        (reserve0, reserve1, blockTimestampLast) = pair.getReserves();
        require(reserve0 != 0 && reserve1 != 0, "BrewlabsTwapOracle: NO_RESERVES"); // ensure that there's liquidity in the pair
    }

    /* ========== MUTABLE FUNCTIONS ========== */

    /**
     * @dev Updates 1-day EMA price from Uniswap.
     */
    function update() external checkEpoch {
        (uint256 price0Cumulative, uint256 price1Cumulative, uint32 blockTimestamp) =
            UniswapV2OracleLibrary.currentCumulativePrices(address(pair));
        uint32 timeElapsed = blockTimestamp - blockTimestampLast; // overflow is desired

        if (timeElapsed == 0) {
            // prevent divided by zero
            return;
        }

        // overflow is desired, casting never truncates
        // cumulative price is in (uq112x112 price * seconds) units so we simply wrap it after division by time elapsed
        price0Average = FixedPoint.uq112x112(uint224((price0Cumulative - price0CumulativeLast) / timeElapsed));
        price1Average = FixedPoint.uq112x112(uint224((price1Cumulative - price1CumulativeLast) / timeElapsed));

        price0CumulativeLast = price0Cumulative;
        price1CumulativeLast = price1Cumulative;
        blockTimestampLast = blockTimestamp;

        emit Updated(price0Cumulative, price1Cumulative);
    }

    // note this will always return 0 before update has been called successfully for the first time.
    function consult(address _token, uint256 _amountIn) external view returns (uint144 amountOut) {
        if (_token == token0) {
            amountOut = price0Average.mul(_amountIn).decode144();
        } else {
            require(_token == token1, "BrewlabsTwapOracle: INVALID_TOKEN");
            amountOut = price1Average.mul(_amountIn).decode144();
        }
    }

    function twap(address _token, uint256 _amountIn) external view returns (uint144 _amountOut) {
        (uint256 price0Cumulative, uint256 price1Cumulative, uint32 blockTimestamp) =
            UniswapV2OracleLibrary.currentCumulativePrices(address(pair));
        uint32 timeElapsed = blockTimestamp - blockTimestampLast; // overflow is desired
        if (_token == token0) {
            if (timeElapsed == 0) {
                _amountOut = price0Average.mul(_amountIn).decode144();
            } else {
                _amountOut = FixedPoint.uq112x112(uint224((price0Cumulative - price0CumulativeLast) / timeElapsed)).mul(
                    _amountIn
                ).decode144();
            }
        } else if (_token == token1) {
            if (timeElapsed == 0) {
                _amountOut = price1Average.mul(_amountIn).decode144();
            } else {
                _amountOut = FixedPoint.uq112x112(uint224((price1Cumulative - price1CumulativeLast) / timeElapsed)).mul(
                    _amountIn
                ).decode144();
            }
        }
    }
}

// File: contracts/libs/Babylonian.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

library Babylonian {
    function sqrt(uint256 y) internal pure returns (uint256 z) {
        if (y > 3) {
            z = y;
            uint256 x = y / 2 + 1;
            while (x < z) {
                z = x;
                x = (y / x + x) / 2;
            }
        } else if (y != 0) {
            z = 1;
        }
        // else z = 0
    }
}

// File: contracts/libs/FixedPoint.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "./Babylonian.sol";

// a library for handling binary fixed point numbers (https://en.wikipedia.org/wiki/Q_(number_format))
library FixedPoint {
    // range: [0, 2**112 - 1]
    // resolution: 1 / 2**112
    struct uq112x112 {
        uint224 _x;
    }

    // range: [0, 2**144 - 1]
    // resolution: 1 / 2**112
    struct uq144x112 {
        uint256 _x;
    }

    uint8 private constant RESOLUTION = 112;
    uint256 private constant Q112 = uint256(1) << RESOLUTION;
    uint256 private constant Q224 = Q112 << RESOLUTION;

    // encode a uint112 as a UQ112x112
    function encode(uint112 x) internal pure returns (uq112x112 memory) {
        return uq112x112(uint224(x) << RESOLUTION);
    }

    // encodes a uint144 as a UQ144x112
    function encode144(uint144 x) internal pure returns (uq144x112 memory) {
        return uq144x112(uint256(x) << RESOLUTION);
    }

    // divide a UQ112x112 by a uint112, returning a UQ112x112
    function div(uq112x112 memory self, uint112 x) internal pure returns (uq112x112 memory) {
        require(x != 0, "FixedPoint: DIV_BY_ZERO");
        return uq112x112(self._x / uint224(x));
    }

    // multiply a UQ112x112 by a uint, returning a UQ144x112
    // reverts on overflow
    function mul(uq112x112 memory self, uint256 y) internal pure returns (uq144x112 memory) {
        uint256 z;
        require(y == 0 || (z = uint256(self._x) * y) / y == uint256(self._x), "FixedPoint: MULTIPLICATION_OVERFLOW");
        return uq144x112(z);
    }

    // returns a UQ112x112 which represents the ratio of the numerator to the denominator
    // equivalent to encode(numerator).div(denominator)
    function fraction(uint112 numerator, uint112 denominator) internal pure returns (uq112x112 memory) {
        require(denominator > 0, "FixedPoint: DIV_BY_ZERO");
        return uq112x112((uint224(numerator) << RESOLUTION) / denominator);
    }

    // decode a UQ112x112 into a uint112 by truncating after the radix point
    function decode(uq112x112 memory self) internal pure returns (uint112) {
        return uint112(self._x >> RESOLUTION);
    }

    // decode a UQ144x112 into a uint144 by truncating after the radix point
    function decode144(uq144x112 memory self) internal pure returns (uint144) {
        return uint144(self._x >> RESOLUTION);
    }

    // take the reciprocal of a UQ112x112
    function reciprocal(uq112x112 memory self) internal pure returns (uq112x112 memory) {
        require(self._x != 0, "FixedPoint: ZERO_RECIPROCAL");
        return uq112x112(uint224(Q224 / self._x));
    }

    // square root of a UQ112x112
    function sqrt(uq112x112 memory self) internal pure returns (uq112x112 memory) {
        return uq112x112(uint224(Babylonian.sqrt(uint256(self._x)) << 56));
    }
}

// File: contracts/libs/UniswapV2OracleLibrary.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "./FixedPoint.sol";
import "./IUniswapV2Pair.sol";

// library with helper methods for oracles that are concerned with computing average prices
library UniswapV2OracleLibrary {
    using FixedPoint for *;

    // helper function that returns the current block timestamp within the range of uint32, i.e. [0, 2**32 - 1]
    function currentBlockTimestamp() internal view returns (uint32) {
        return uint32(block.timestamp % 2 ** 32);
    }

    // produces the cumulative price using counterfactuals to save gas and avoid a call to sync.
    function currentCumulativePrices(address pair)
        internal
        view
        returns (uint256 price0Cumulative, uint256 price1Cumulative, uint32 blockTimestamp)
    {
        blockTimestamp = currentBlockTimestamp();
        price0Cumulative = IUniswapV2Pair(pair).price0CumulativeLast();
        price1Cumulative = IUniswapV2Pair(pair).price1CumulativeLast();

        // if time has elapsed since the last update on the pair, mock the accumulated price values
        (uint112 reserve0, uint112 reserve1, uint32 blockTimestampLast) = IUniswapV2Pair(pair).getReserves();
        if (blockTimestampLast != blockTimestamp) {
            // subtraction overflow is desired
            uint32 timeElapsed = blockTimestamp - blockTimestampLast;
            // addition overflow is desired
            // counterfactual
            price0Cumulative += uint256(FixedPoint.fraction(reserve1, reserve0)._x) * timeElapsed;
            // counterfactual
            price1Cumulative += uint256(FixedPoint.fraction(reserve0, reserve1)._x) * timeElapsed;
        }
    }
}

// File: contracts/libs/IUniPair.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

interface IUniPair {
    function token0() external view returns (address);
    function token1() external view returns (address);

    function getReserves() external view returns (uint112 _reserve0, uint112 _reserve1, uint32 _blockTimestampLast);
}

// File: contracts/libs/Epoch.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/access/Ownable.sol";

contract Epoch is Ownable {
    uint256 private period;
    uint256 private startTime;
    uint256 private lastEpochTime;
    uint256 private epoch;

    /* ========== CONSTRUCTOR ========== */

    constructor(uint256 _period, uint256 _startTime, uint256 _startEpoch) {
        period = _period;
        startTime = _startTime;
        epoch = _startEpoch;
        lastEpochTime = startTime - period;
    }

    /* ========== Modifier ========== */

    modifier checkStartTime() {
        require(block.timestamp >= startTime, "Epoch: not started yet");

        _;
    }

    modifier checkEpoch() {
        uint256 _nextEpochPoint = nextEpochPoint();
        if (block.timestamp < _nextEpochPoint) {
            require(msg.sender == owner(), "Epoch: only operator allowed for pre-epoch");
            _;
        } else {
            _;

            for (;;) {
                lastEpochTime = _nextEpochPoint;
                ++epoch;
                _nextEpochPoint = nextEpochPoint();
                if (block.timestamp < _nextEpochPoint) break;
            }
        }
    }

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

    function getCurrentEpoch() public view returns (uint256) {
        return epoch;
    }

    function getPeriod() public view returns (uint256) {
        return period;
    }

    function getStartTime() public view returns (uint256) {
        return startTime;
    }

    function getLastEpochTime() public view returns (uint256) {
        return lastEpochTime;
    }

    function nextEpochPoint() public view returns (uint256) {
        return lastEpochTime + period;
    }

    /* ========== GOVERNANCE ========== */

    function setPeriod(uint256 _period) external onlyOwner {
        require(_period >= 1 hours && _period <= 48 hours, "_period: out of range");
        period = _period;
    }

    function setEpoch(uint256 _epoch) external onlyOwner {
        epoch = _epoch;
    }
}

// File: contracts/libs/IUniswapV2Pair.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

interface IUniswapV2Pair {
    function token0() external view returns (address);

    function token1() external view returns (address);

    function getReserves() external view returns (uint112 _reserve0, uint112 _reserve1, uint32 _blockTimestampLast);

    function price0CumulativeLast() external view returns (uint256);
    function price1CumulativeLast() external view returns (uint256);
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (access/Ownable.sol)

pragma solidity ^0.8.0;

import "../utils/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() {
        _transferOwnership(_msgSender());
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual 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 {
        _transferOwnership(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");
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)

pragma solidity ^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 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) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}