pragma solidity ^0.6.12;

import './interfaces/IUniswapV2Factory.sol';
import './interfaces/IUniswapV2Pair.sol';
import './interfaces/ILedgityPriceOracle.sol';
import '@uniswap/lib/contracts/libraries/FixedPoint.sol';
import './libraries/SafeMath.sol';
import './libraries/Ownable.sol';
import './libraries/UniswapV2OracleLibrary.sol';

// SPDX-License-Identifier: Unlicensed
contract LedgityPriceOracle is ILedgityPriceOracle, Ownable {
    using FixedPoint for *;
    uint public period = 12 hours;
    IUniswapV2Pair pair;
    address public immutable token0;
    address public immutable token1;
    uint    public price0CumulativeLast;
    uint    public price1CumulativeLast;
    uint32  public blockTimestampLast;
    FixedPoint.uq112x112 public price0Average;
    FixedPoint.uq112x112 public price1Average;

    constructor(address pair_) public {
        IUniswapV2Pair _pair = IUniswapV2Pair(pair_);
        pair = _pair;
        token0 = _pair.token0();
        token1 = _pair.token1();
        changePeriod(12 hours);
    }

    function update() external override {
        require(tryUpdate(), 'LedgityPriceOracle: PERIOD_NOT_ELAPSED');
    }

    function tryUpdate() public override returns (bool) {
        uint32 timeElapsed = UniswapV2OracleLibrary.currentBlockTimestamp() - blockTimestampLast;
        if (timeElapsed < period) {
            return false;
        }
        (uint price0Cumulative, uint price1Cumulative, uint32 blockTimestamp) = UniswapV2OracleLibrary.currentCumulativePrices(address(pair));
        price0Average = FixedPoint.uq112x112(uint224((price0Cumulative - price0CumulativeLast) / timeElapsed));
        price1Average = FixedPoint.uq112x112(uint224((price1Cumulative - price1CumulativeLast) / timeElapsed));
        price0CumulativeLast = price0Cumulative;
        price1CumulativeLast = price1Cumulative;
        blockTimestampLast = blockTimestamp;
        return true;
    }

    function consult(address token, uint amountIn) external view override returns (uint amountOut) {
        if (token == token0) {
            amountOut = price0Average.mul(amountIn).decode144();
        } else {
            require(token == token1, 'LedgityPriceOracle: INVALID_TOKEN');
            amountOut = price1Average.mul(amountIn).decode144();
        }
    }

    function changePeriod(uint256 _period) public onlyOwner {
        require(_period > 0, 'LedgityPriceOracle: INVALID_PERIOD');
        period = _period;
        price0CumulativeLast = pair.price0CumulativeLast();
        price1CumulativeLast = pair.price1CumulativeLast();
        uint112 reserve0;
        uint112 reserve1;
        (reserve0, reserve1, blockTimestampLast) = pair.getReserves();
        require(reserve0 != 0 && reserve1 != 0, 'LedgityPriceOracle: NO_RESERVES'); // ensure that there's liquidity in the pair
        price0Average = FixedPoint.encode(reserve1).divuq(FixedPoint.encode(reserve0));
        price1Average = FixedPoint.encode(reserve0).divuq(FixedPoint.encode(reserve1));
    }
}

pragma solidity ^0.6.12;

interface IUniswapV2Factory {
    event PairCreated(address indexed token0, address indexed token1, address pair, uint);

    function feeTo() external view returns (address);
    function feeToSetter() external view returns (address);

    function getPair(address tokenA, address tokenB) external view returns (address pair);
    function allPairs(uint) external view returns (address pair);
    function allPairsLength() external view returns (uint);

    function createPair(address tokenA, address tokenB) external returns (address pair);

    function setFeeTo(address) external;
    function setFeeToSetter(address) external;
}

pragma solidity ^0.6.12;

interface IUniswapV2Pair {
    event Approval(address indexed owner, address indexed spender, uint value);
    event Transfer(address indexed from, address indexed to, uint value);

    function name() external pure returns (string memory);
    function symbol() external pure returns (string memory);
    function decimals() external pure returns (uint8);
    function totalSupply() external view returns (uint);
    function balanceOf(address owner) external view returns (uint);
    function allowance(address owner, address spender) external view returns (uint);

    function approve(address spender, uint value) external returns (bool);
    function transfer(address to, uint value) external returns (bool);
    function transferFrom(address from, address to, uint value) external returns (bool);

    function DOMAIN_SEPARATOR() external view returns (bytes32);
    function PERMIT_TYPEHASH() external pure returns (bytes32);
    function nonces(address owner) external view returns (uint);

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

    event Mint(address indexed sender, uint amount0, uint amount1);
    event Burn(address indexed sender, uint amount0, uint amount1, address indexed to);
    event Swap(
        address indexed sender,
        uint amount0In,
        uint amount1In,
        uint amount0Out,
        uint amount1Out,
        address indexed to
    );
    event Sync(uint112 reserve0, uint112 reserve1);

    function MINIMUM_LIQUIDITY() external pure returns (uint);
    function factory() external view returns (address);
    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 (uint);
    function price1CumulativeLast() external view returns (uint);
    function kLast() external view returns (uint);

    function mint(address to) external returns (uint liquidity);
    function burn(address to) external returns (uint amount0, uint amount1);
    function swap(uint amount0Out, uint amount1Out, address to, bytes calldata data) external;
    function skim(address to) external;
    function sync() external;

    function initialize(address, address) external;
}

pragma solidity ^0.6.12;

interface ILedgityPriceOracle {
    /**
     * @dev Update average price.
     * @return `true` if update successful; `false` if period has not yet elapsed.
     */
    function tryUpdate() external returns (bool);

    /**
     * @dev Update average price. Reverts if period has not yet elapsed.
     */
    function update() external;

    /**
     * @dev Returns the price of tokens.
     */
    function consult(address token, uint amountIn) external view returns (uint amountOut);
}

// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity >=0.4.0;

import './FullMath.sol';
import './Babylonian.sol';
import './BitMath.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 public constant RESOLUTION = 112;
    uint256 public constant Q112 = 0x10000000000000000000000000000; // 2**112
    uint256 private constant Q224 = 0x100000000000000000000000000000000000000000000000000000000; // 2**224
    uint256 private constant LOWER_MASK = 0xffffffffffffffffffffffffffff; // decimal of UQ*x112 (lower 112 bits)

    // 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);
    }

    // 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);
    }

    // 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 = 0;
        require(y == 0 || (z = self._x * y) / y == self._x, 'FixedPoint::mul: overflow');
        return uq144x112(z);
    }

    // multiply a UQ112x112 by an int and decode, returning an int
    // reverts on overflow
    function muli(uq112x112 memory self, int256 y) internal pure returns (int256) {
        uint256 z = FullMath.mulDiv(self._x, uint256(y < 0 ? -y : y), Q112);
        require(z < 2**255, 'FixedPoint::muli: overflow');
        return y < 0 ? -int256(z) : int256(z);
    }

    // multiply a UQ112x112 by a UQ112x112, returning a UQ112x112
    // lossy
    function muluq(uq112x112 memory self, uq112x112 memory other) internal pure returns (uq112x112 memory) {
        if (self._x == 0 || other._x == 0) {
            return uq112x112(0);
        }
        uint112 upper_self = uint112(self._x >> RESOLUTION); // * 2^0
        uint112 lower_self = uint112(self._x & LOWER_MASK); // * 2^-112
        uint112 upper_other = uint112(other._x >> RESOLUTION); // * 2^0
        uint112 lower_other = uint112(other._x & LOWER_MASK); // * 2^-112

        // partial products
        uint224 upper = uint224(upper_self) * upper_other; // * 2^0
        uint224 lower = uint224(lower_self) * lower_other; // * 2^-224
        uint224 uppers_lowero = uint224(upper_self) * lower_other; // * 2^-112
        uint224 uppero_lowers = uint224(upper_other) * lower_self; // * 2^-112

        // so the bit shift does not overflow
        require(upper <= uint112(-1), 'FixedPoint::muluq: upper overflow');

        // this cannot exceed 256 bits, all values are 224 bits
        uint256 sum = uint256(upper << RESOLUTION) + uppers_lowero + uppero_lowers + (lower >> RESOLUTION);

        // so the cast does not overflow
        require(sum <= uint224(-1), 'FixedPoint::muluq: sum overflow');

        return uq112x112(uint224(sum));
    }

    // divide a UQ112x112 by a UQ112x112, returning a UQ112x112
    function divuq(uq112x112 memory self, uq112x112 memory other) internal pure returns (uq112x112 memory) {
        require(other._x > 0, 'FixedPoint::divuq: division by zero');
        if (self._x == other._x) {
            return uq112x112(uint224(Q112));
        }
        if (self._x <= uint144(-1)) {
            uint256 value = (uint256(self._x) << RESOLUTION) / other._x;
            require(value <= uint224(-1), 'FixedPoint::divuq: overflow');
            return uq112x112(uint224(value));
        }

        uint256 result = FullMath.mulDiv(Q112, self._x, other._x);
        require(result <= uint224(-1), 'FixedPoint::divuq: overflow');
        return uq112x112(uint224(result));
    }

    // returns a UQ112x112 which represents the ratio of the numerator to the denominator
    // can be lossy
    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));
        }
    }

    // take the reciprocal of a UQ112x112
    // reverts on overflow
    // lossy
    function reciprocal(uq112x112 memory self) internal pure returns (uq112x112 memory) {
        require(self._x != 0, 'FixedPoint::reciprocal: reciprocal of zero');
        require(self._x != 1, 'FixedPoint::reciprocal: overflow');
        return uq112x112(uint224(Q224 / self._x));
    }

    // square root of a UQ112x112
    // lossy between 0/1 and 40 bits
    function sqrt(uq112x112 memory self) internal pure returns (uq112x112 memory) {
        if (self._x <= uint144(-1)) {
            return uq112x112(uint224(Babylonian.sqrt(uint256(self._x) << 112)));
        }

        uint8 safeShiftBits = 255 - BitMath.mostSignificantBit(self._x);
        safeShiftBits -= safeShiftBits % 2;
        return uq112x112(uint224(Babylonian.sqrt(uint256(self._x) << safeShiftBits) << ((112 - safeShiftBits) / 2)));
    }
}

pragma solidity ^0.6.12;

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;
    }
}

pragma solidity ^0.6.12;

import "./Context.sol";


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 () public {
        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() external 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) external virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

pragma solidity >=0.5.0;

import '../interfaces/IUniswapV2Pair.sol';
import '@uniswap/lib/contracts/libraries/FixedPoint.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 (uint price0Cumulative, uint 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 += uint(FixedPoint.fraction(reserve1, reserve0)._x) * timeElapsed;
            // counterfactual
            price1Cumulative += uint(FixedPoint.fraction(reserve0, reserve1)._x) * timeElapsed;
        }
    }
}

// SPDX-License-Identifier: CC-BY-4.0
pragma solidity >=0.4.0;

// taken from https://medium.com/coinmonks/math-in-solidity-part-3-percents-and-proportions-4db014e080b1
// license is CC-BY-4.0
library FullMath {
    function fullMul(uint256 x, uint256 y) internal 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;

        if (h == 0) return l / d;

        require(h < d, 'FullMath: FULLDIV_OVERFLOW');
        return fullDiv(l, h, d);
    }
}

// SPDX-License-Identifier: GPL-3.0-or-later

pragma solidity >=0.4.0;

// computes square roots using the babylonian method
// https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Babylonian_method
library Babylonian {
    // credit for this implementation goes to
    // https://github.com/abdk-consulting/abdk-libraries-solidity/blob/master/ABDKMath64x64.sol#L687
    function sqrt(uint256 x) internal pure returns (uint256) {
        if (x == 0) return 0;
        // this block is equivalent to r = uint256(1) << (BitMath.mostSignificantBit(x) / 2);
        // however that code costs significantly more gas
        uint256 xx = x;
        uint256 r = 1;
        if (xx >= 0x100000000000000000000000000000000) {
            xx >>= 128;
            r <<= 64;
        }
        if (xx >= 0x10000000000000000) {
            xx >>= 64;
            r <<= 32;
        }
        if (xx >= 0x100000000) {
            xx >>= 32;
            r <<= 16;
        }
        if (xx >= 0x10000) {
            xx >>= 16;
            r <<= 8;
        }
        if (xx >= 0x100) {
            xx >>= 8;
            r <<= 4;
        }
        if (xx >= 0x10) {
            xx >>= 4;
            r <<= 2;
        }
        if (xx >= 0x8) {
            r <<= 1;
        }
        r = (r + x / r) >> 1;
        r = (r + x / r) >> 1;
        r = (r + x / r) >> 1;
        r = (r + x / r) >> 1;
        r = (r + x / r) >> 1;
        r = (r + x / r) >> 1;
        r = (r + x / r) >> 1; // Seven iterations should be enough
        uint256 r1 = x / r;
        return (r < r1 ? r : r1);
    }
}

// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity >=0.5.0;

library BitMath {
    // returns the 0 indexed position of the most significant bit of the input x
    // s.t. x >= 2**msb and x < 2**(msb+1)
    function mostSignificantBit(uint256 x) internal pure returns (uint8 r) {
        require(x > 0, 'BitMath::mostSignificantBit: zero');

        if (x >= 0x100000000000000000000000000000000) {
            x >>= 128;
            r += 128;
        }
        if (x >= 0x10000000000000000) {
            x >>= 64;
            r += 64;
        }
        if (x >= 0x100000000) {
            x >>= 32;
            r += 32;
        }
        if (x >= 0x10000) {
            x >>= 16;
            r += 16;
        }
        if (x >= 0x100) {
            x >>= 8;
            r += 8;
        }
        if (x >= 0x10) {
            x >>= 4;
            r += 4;
        }
        if (x >= 0x4) {
            x >>= 2;
            r += 2;
        }
        if (x >= 0x2) r += 1;
    }

    // returns the 0 indexed position of the least significant bit of the input x
    // s.t. (x & 2**lsb) != 0 and (x & (2**(lsb) - 1)) == 0)
    // i.e. the bit at the index is set and the mask of all lower bits is 0
    function leastSignificantBit(uint256 x) internal pure returns (uint8 r) {
        require(x > 0, 'BitMath::leastSignificantBit: zero');

        r = 255;
        if (x & uint128(-1) > 0) {
            r -= 128;
        } else {
            x >>= 128;
        }
        if (x & uint64(-1) > 0) {
            r -= 64;
        } else {
            x >>= 64;
        }
        if (x & uint32(-1) > 0) {
            r -= 32;
        } else {
            x >>= 32;
        }
        if (x & uint16(-1) > 0) {
            r -= 16;
        } else {
            x >>= 16;
        }
        if (x & uint8(-1) > 0) {
            r -= 8;
        } else {
            x >>= 8;
        }
        if (x & 0xf > 0) {
            r -= 4;
        } else {
            x >>= 4;
        }
        if (x & 0x3 > 0) {
            r -= 2;
        } else {
            x >>= 2;
        }
        if (x & 0x1 > 0) r -= 1;
    }
}

pragma solidity ^0.6.12;

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;
    }
}