// SPDX-License-Identifier: MIT

pragma solidity >=0.5.0;

import "../../core/interfaces/ISomaSwapPair.sol";
import "../../libraries/FixedPoint.sol";

// library with helper methods for oracles that are concerned with computing average prices
library SomaSwapOracleLibrary {
    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) {
        // slither-disable-next-line weak-prng
        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 = ISomaSwapPair(pair).price0CumulativeLast();
        price1Cumulative = ISomaSwapPair(pair).price1CumulativeLast();

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