contract UniswapPairOracle {
    using FixedPoint for *;
    
    address owner_address;
    address timelock_address;

    uint public PERIOD = 3600; // 1 hour TWAP (time-weighted average price)
    uint public CONSULT_LENIENCY = 120; // Used for being able to consult past the period end
    bool public ALLOW_STALE_CONSULTS = false; // If false, consult() will fail if the TWAP is stale

    IUniswapV2Pair public immutable 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;

    modifier onlyByOwnerOrGovernance() {
        require(msg.sender == owner_address || msg.sender == timelock_address, "You are not an owner or the governance timelock");
        _;
    }

    constructor(address factory, address tokenA, address tokenB, address _owner_address, address _timelock_address) public {
        IUniswapV2Pair _pair = IUniswapV2Pair(UniswapV2Library.pairFor(factory, tokenA, tokenB));
        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, 'UniswapPairOracle: NO_RESERVES'); // Ensure that there's liquidity in the pair

        owner_address = _owner_address;
        timelock_address = _timelock_address;
    }

    function setOwner(address _owner_address) external onlyByOwnerOrGovernance {
        owner_address = _owner_address;
    }

    function setTimelock(address _timelock_address) external onlyByOwnerOrGovernance {
        timelock_address = _timelock_address;
    }

    function setPeriod(uint _period) external onlyByOwnerOrGovernance {
        PERIOD = _period;
    }

    function setConsultLeniency(uint _consult_leniency) external onlyByOwnerOrGovernance {
        CONSULT_LENIENCY = _consult_leniency;
    }

    function setAllowStaleConsults(bool _allow_stale_consults) external onlyByOwnerOrGovernance {
        ALLOW_STALE_CONSULTS = _allow_stale_consults;
    }

    // Check if update() can be called instead of wasting gas calling it
    function canUpdate() public view returns (bool) {
        uint32 blockTimestamp = UniswapV2OracleLibrary.currentBlockTimestamp();
        uint32 timeElapsed = blockTimestamp - blockTimestampLast; // Overflow is desired
        return (timeElapsed >= PERIOD);
    }

    function update() external {
        (uint price0Cumulative, uint price1Cumulative, uint32 blockTimestamp) =
            UniswapV2OracleLibrary.currentCumulativePrices(address(pair));
        uint32 timeElapsed = blockTimestamp - blockTimestampLast; // Overflow is desired

        // Ensure that at least one full period has passed since the last update
        require(timeElapsed >= PERIOD, 'UniswapPairOracle: PERIOD_NOT_ELAPSED');

        // 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;
    }

    // Note this will always return 0 before update has been called successfully for the first time.
    function consult(address token, uint amountIn) external view returns (uint amountOut) {
        uint32 blockTimestamp = UniswapV2OracleLibrary.currentBlockTimestamp();
        uint32 timeElapsed = blockTimestamp - blockTimestampLast; // Overflow is desired

        // Ensure that the price is not stale
        require((timeElapsed < (PERIOD + CONSULT_LENIENCY)) || ALLOW_STALE_CONSULTS, 'UniswapPairOracle: PRICE_IS_STALE_NEED_TO_CALL_UPDATE');

        if (token == token0) {
            amountOut = price0Average.mul(amountIn).decode144();
        } else {
            require(token == token1, 'UniswapPairOracle: INVALID_TOKEN');
            amountOut = price1Average.mul(amountIn).decode144();
        }
    }
}
// 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
function canUpdate() public view returns (bool) {
    uint32 blockTimestamp = UniswapV2OracleLibrary.currentBlockTimestamp();
    uint32 timeElapsed = blockTimestamp - blockTimestampLast; // Overflow is desired
    return (timeElapsed >= PERIOD);
}

// Check if update() can be called instead of wasting gas calling it