// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity ^0.8.0;

import "../../core/libraries/math/PMath.sol";
import "../../interfaces/IPMarket.sol";

// This library can & should be integrated directly for optimal gas usage.
// If you prefer not to integrate it directly, the PendlePtOracle contract (a pre-deployed version of this contract) can
// be used.
library PendlePYOracleLib {
    using PMath for uint256;
    using PMath for int256;

    /**
     * This function returns the twap rate PT/Asset on market, but take into account the current rate of SY
     *  This is to account for special cases where underlying asset becomes insolvent and has decreasing exchangeRate
     * @param market market to get rate from
     * @param duration twap duration
     */
    function getPtToAssetRate(IPMarket market, uint32 duration) internal view returns (uint256) {
        (uint256 syIndex, uint256 pyIndex) = getSYandPYIndexCurrent(market);
        if (syIndex >= pyIndex) {
            return getPtToAssetRateRaw(market, duration);
        } else {
            return (getPtToAssetRateRaw(market, duration) * syIndex) / pyIndex;
        }
    }

    /**
     * This function returns the twap rate YT/Asset on market, but take into account the current rate of SY
     *  This is to account for special cases where underlying asset becomes insolvent and has decreasing exchangeRate
     * @param market market to get rate from
     * @param duration twap duration
     */
    function getYtToAssetRate(IPMarket market, uint32 duration) internal view returns (uint256) {
        (uint256 syIndex, uint256 pyIndex) = getSYandPYIndexCurrent(market);
        if (syIndex >= pyIndex) {
            return getYtToAssetRateRaw(market, duration);
        } else {
            return (getYtToAssetRateRaw(market, duration) * syIndex) / pyIndex;
        }
    }

    /// @notice Similar to getPtToAsset but returns the rate in SY instead
    function getPtToSyRate(IPMarket market, uint32 duration) internal view returns (uint256) {
        (uint256 syIndex, uint256 pyIndex) = getSYandPYIndexCurrent(market);
        if (syIndex >= pyIndex) {
            return getPtToAssetRateRaw(market, duration).divDown(syIndex);
        } else {
            return getPtToAssetRateRaw(market, duration).divDown(pyIndex);
        }
    }

    /// @notice Similar to getPtToAsset but returns the rate in SY instead
    function getYtToSyRate(IPMarket market, uint32 duration) internal view returns (uint256) {
        (uint256 syIndex, uint256 pyIndex) = getSYandPYIndexCurrent(market);
        if (syIndex >= pyIndex) {
            return getYtToAssetRateRaw(market, duration).divDown(syIndex);
        } else {
            return getYtToAssetRateRaw(market, duration).divDown(pyIndex);
        }
    }

    /// @notice returns the raw rate without taking into account whether SY is solvent
    function getPtToAssetRateRaw(IPMarket market, uint32 duration) internal view returns (uint256) {
        uint256 expiry = market.expiry();

        if (expiry <= block.timestamp) {
            return PMath.ONE;
        } else {
            uint256 lnImpliedRate = getMarketLnImpliedRate(market, duration);
            uint256 timeToExpiry = expiry - block.timestamp;
            uint256 assetToPtRate = MarketMathCore._getExchangeRateFromImpliedRate(lnImpliedRate, timeToExpiry).Uint();
            return PMath.ONE.divDown(assetToPtRate);
        }
    }

    /// @notice returns the raw rate without taking into account whether SY is solvent
    function getYtToAssetRateRaw(IPMarket market, uint32 duration) internal view returns (uint256) {
        return PMath.ONE - getPtToAssetRateRaw(market, duration);
    }

    function getSYandPYIndexCurrent(IPMarket market) internal view returns (uint256 syIndex, uint256 pyIndex) {
        (IStandardizedYield SY,, IPYieldToken YT) = market.readTokens();

        syIndex = SY.exchangeRate();
        uint256 pyIndexStored = YT.pyIndexStored();

        if (YT.doCacheIndexSameBlock() && YT.pyIndexLastUpdatedBlock() == block.number) {
            pyIndex = pyIndexStored;
        } else {
            pyIndex = PMath.max(syIndex, pyIndexStored);
        }
    }

    function getMarketLnImpliedRate(IPMarket market, uint32 duration) internal view returns (uint256) {
        if (duration == 0) {
            (,, uint96 lnImpliedRate,,,) = IPMarket(market)._storage();
            return uint256(lnImpliedRate);
        }

        uint32[] memory durations = new uint32[](2);
        durations[0] = duration;

        uint216[] memory lnImpliedRateCumulative = market.observe(durations);
        return (lnImpliedRateCumulative[1] - lnImpliedRateCumulative[0]) / duration;
    }
}