// SPDX-License-Identifier: GPL-2.0-or-later
pragma solidity =0.7.6;
pragma abicoder v2;

import '../interfaces/IOracleSlippage.sol';

import '@pollum-io/v3-periphery/contracts/base/PeripheryImmutableState.sol';
import '@pollum-io/v3-periphery/contracts/base/BlockTimestamp.sol';
import '@pollum-io/v3-periphery/contracts/libraries/Path.sol';
import '@pollum-io/v3-periphery/contracts/libraries/PoolAddress.sol';
import '@pollum-io/v3-core/contracts/interfaces/IPegasysV3Pool.sol';
import '@pollum-io/v3-periphery/contracts/libraries/OracleLibrary.sol';

abstract contract OracleSlippage is IOracleSlippage, PeripheryImmutableState, BlockTimestamp {
    using Path for bytes;

    /// @dev Returns the tick as of the beginning of the current block, and as of right now, for the given pool.
    function getBlockStartingAndCurrentTick(
        IPegasysV3Pool pool
    ) internal view returns (int24 blockStartingTick, int24 currentTick) {
        uint16 observationIndex;
        uint16 observationCardinality;
        (, currentTick, observationIndex, observationCardinality, , , ) = pool.slot0();

        // 2 observations are needed to reliably calculate the block starting tick
        require(observationCardinality > 1, 'NEO');

        // If the latest observation occurred in the past, then no tick-changing trades have happened in this block
        // therefore the tick in `slot0` is the same as at the beginning of the current block.
        // We don't need to check if this observation is initialized - it is guaranteed to be.
        (uint32 observationTimestamp, int56 tickCumulative, , ) = pool.observations(observationIndex);
        if (observationTimestamp != uint32(_blockTimestamp())) {
            blockStartingTick = currentTick;
        } else {
            uint256 prevIndex = (uint256(observationIndex) + observationCardinality - 1) % observationCardinality;
            (uint32 prevObservationTimestamp, int56 prevTickCumulative, , bool prevInitialized) = pool.observations(
                prevIndex
            );

            require(prevInitialized, 'ONI');

            uint32 delta = observationTimestamp - prevObservationTimestamp;
            blockStartingTick = int24((tickCumulative - prevTickCumulative) / delta);
        }
    }

    /// @dev Virtual function to get pool addresses that can be overridden in tests.
    function getPoolAddress(
        address tokenA,
        address tokenB,
        uint24 fee
    ) internal view virtual returns (IPegasysV3Pool pool) {
        pool = IPegasysV3Pool(PoolAddress.computeAddress(factory, PoolAddress.getPoolKey(tokenA, tokenB, fee)));
    }

    /// @dev Returns the synthetic time-weighted average tick as of secondsAgo, as well as the current tick,
    /// for the given path. Returned synthetic ticks always represent tokenOut/tokenIn prices,
    /// meaning lower ticks are worse.
    function getSyntheticTicks(
        bytes memory path,
        uint32 secondsAgo
    ) internal view returns (int256 syntheticAverageTick, int256 syntheticCurrentTick) {
        bool lowerTicksAreWorse;

        uint256 numPools = path.numPools();
        address previousTokenIn;
        for (uint256 i = 0; i < numPools; i++) {
            // this assumes the path is sorted in swap order
            (address tokenIn, address tokenOut, uint24 fee) = path.decodeFirstPool();
            IPegasysV3Pool pool = getPoolAddress(tokenIn, tokenOut, fee);

            // get the average and current ticks for the current pool
            int256 averageTick;
            int256 currentTick;
            if (secondsAgo == 0) {
                // we optimize for the secondsAgo == 0 case, i.e. since the beginning of the block
                (averageTick, currentTick) = getBlockStartingAndCurrentTick(pool);
            } else {
                (averageTick, ) = OracleLibrary.consult(address(pool), secondsAgo);
                (, currentTick, , , , , ) = IPegasysV3Pool(pool).slot0();
            }

            if (i == numPools - 1) {
                // if we're here, this is the last pool in the path, meaning tokenOut represents the
                // destination token. so, if tokenIn < tokenOut, then tokenIn is token0 of the last pool,
                // meaning the current running ticks are going to represent tokenOut/tokenIn prices.
                // so, the lower these prices get, the worse of a price the swap will get
                lowerTicksAreWorse = tokenIn < tokenOut;
            } else {
                // if we're here, we need to iterate over the next pool in the path
                path = path.skipToken();
                previousTokenIn = tokenIn;
            }

            // accumulate the ticks derived from the current pool into the running synthetic ticks,
            // ensuring that intermediate tokens "cancel out"
            bool add = (i == 0) || (previousTokenIn < tokenIn ? tokenIn < tokenOut : tokenOut < tokenIn);
            if (add) {
                syntheticAverageTick += averageTick;
                syntheticCurrentTick += currentTick;
            } else {
                syntheticAverageTick -= averageTick;
                syntheticCurrentTick -= currentTick;
            }
        }

        // flip the sign of the ticks if necessary, to ensure that the lower ticks are always worse
        if (!lowerTicksAreWorse) {
            syntheticAverageTick *= -1;
            syntheticCurrentTick *= -1;
        }
    }

    /// @dev Cast a int256 to a int24, revert on overflow or underflow
    function toInt24(int256 y) private pure returns (int24 z) {
        require((z = int24(y)) == y);
    }

    /// @dev For each passed path, fetches the synthetic time-weighted average tick as of secondsAgo,
    /// as well as the current tick. Then, synthetic ticks from all paths are subjected to a weighted
    /// average, where the weights are the fraction of the total input amount allocated to each path.
    /// Returned synthetic ticks always represent tokenOut/tokenIn prices, meaning lower ticks are worse.
    /// Paths must all start and end in the same token.
    function getSyntheticTicks(
        bytes[] memory paths,
        uint128[] memory amounts,
        uint32 secondsAgo
    ) internal view returns (int256 averageSyntheticAverageTick, int256 averageSyntheticCurrentTick) {
        require(paths.length == amounts.length);

        OracleLibrary.WeightedTickData[] memory weightedSyntheticAverageTicks = new OracleLibrary.WeightedTickData[](
            paths.length
        );
        OracleLibrary.WeightedTickData[] memory weightedSyntheticCurrentTicks = new OracleLibrary.WeightedTickData[](
            paths.length
        );

        for (uint256 i = 0; i < paths.length; i++) {
            (int256 syntheticAverageTick, int256 syntheticCurrentTick) = getSyntheticTicks(paths[i], secondsAgo);
            weightedSyntheticAverageTicks[i].tick = toInt24(syntheticAverageTick);
            weightedSyntheticCurrentTicks[i].tick = toInt24(syntheticCurrentTick);
            weightedSyntheticAverageTicks[i].weight = amounts[i];
            weightedSyntheticCurrentTicks[i].weight = amounts[i];
        }

        averageSyntheticAverageTick = OracleLibrary.getWeightedArithmeticMeanTick(weightedSyntheticAverageTicks);
        averageSyntheticCurrentTick = OracleLibrary.getWeightedArithmeticMeanTick(weightedSyntheticCurrentTicks);
    }

    /// @inheritdoc IOracleSlippage
    function checkOracleSlippage(
        bytes memory path,
        uint24 maximumTickDivergence,
        uint32 secondsAgo
    ) external view override {
        (int256 syntheticAverageTick, int256 syntheticCurrentTick) = getSyntheticTicks(path, secondsAgo);
        require(syntheticAverageTick - syntheticCurrentTick < maximumTickDivergence, 'TD');
    }

    /// @inheritdoc IOracleSlippage
    function checkOracleSlippage(
        bytes[] memory paths,
        uint128[] memory amounts,
        uint24 maximumTickDivergence,
        uint32 secondsAgo
    ) external view override {
        (int256 averageSyntheticAverageTick, int256 averageSyntheticCurrentTick) = getSyntheticTicks(
            paths,
            amounts,
            secondsAgo
        );
        require(averageSyntheticAverageTick - averageSyntheticCurrentTick < maximumTickDivergence, 'TD');
    }
}