//SPDX-License-Identifier: Unlicense
pragma solidity 0.8.10;

import "../interfaces/IPancakePair.sol";

import "./FixedPoint.sol";

/**
 * @notice We copied directly from https://github.com/Uniswap/v2-periphery/blob/master/contracts/libraries/UniswapV2OracleLibrary.sol
 * @notice We simply swapped IUniswapV2Pair for IPancakePair and removed warning messages
 * 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) {
        //solhint-disable-next-line not-rely-on-time
        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 = IPancakePair(pair).price0CumulativeLast();
        price1Cumulative = IPancakePair(pair).price1CumulativeLast();

        // if time has elapsed since the last update on the pair, mock the accumulated price values
        (
            uint112 reserve0,
            uint112 reserve1,
            uint32 blockTimestampLast
        ) = IPancakePair(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;
        }
    }
}