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

import {IUniswapV2Pair} from '@uniswap/v2-core/contracts/interfaces/IUniswapV2Pair.sol';

/// @title Uniswap v2 Helper Library
/// @notice Calculates the recipient address for a command
library UniswapV2Library {
    error InvalidReserves();
    error InvalidPath();

    /// @notice Calculates the v2 address for a pair without making any external calls
    /// @param factory The address of the v2 factory
    /// @param initCodeHash The hash of the pair initcode
    /// @param tokenA One of the tokens in the pair
    /// @param tokenB The other token in the pair
    /// @return pair The resultant v2 pair address
    function pairFor(address factory, bytes32 initCodeHash, address tokenA, address tokenB)
        internal
        pure
        returns (address pair)
    {
        (address token0, address token1) = sortTokens(tokenA, tokenB);
        pair = pairForPreSorted(factory, initCodeHash, token0, token1);
    }

    /// @notice Calculates the v2 address for a pair and the pair's token0
    /// @param factory The address of the v2 factory
    /// @param initCodeHash The hash of the pair initcode
    /// @param tokenA One of the tokens in the pair
    /// @param tokenB The other token in the pair
    /// @return pair The resultant v2 pair address
    /// @return token0 The token considered token0 in this pair
    function pairAndToken0For(address factory, bytes32 initCodeHash, address tokenA, address tokenB)
        internal
        pure
        returns (address pair, address token0)
    {
        address token1;
        (token0, token1) = sortTokens(tokenA, tokenB);
        pair = pairForPreSorted(factory, initCodeHash, token0, token1);
    }

    /// @notice Calculates the v2 address for a pair assuming the input tokens are pre-sorted
    /// @param factory The address of the v2 factory
    /// @param initCodeHash The hash of the pair initcode
    /// @param token0 The pair's token0
    /// @param token1 The pair's token1
    /// @return pair The resultant v2 pair address
    function pairForPreSorted(address factory, bytes32 initCodeHash, address token0, address token1)
        private
        pure
        returns (address pair)
    {
        pair = address(
            uint160(
                uint256(
                    keccak256(
                        abi.encodePacked(hex'ff', factory, keccak256(abi.encodePacked(token0, token1)), initCodeHash)
                    )
                )
            )
        );
    }

    /// @notice Calculates the v2 address for a pair and fetches the reserves for each token
    /// @param factory The address of the v2 factory
    /// @param initCodeHash The hash of the pair initcode
    /// @param tokenA One of the tokens in the pair
    /// @param tokenB The other token in the pair
    /// @return pair The resultant v2 pair address
    /// @return reserveA The reserves for tokenA
    /// @return reserveB The reserves for tokenB
    function pairAndReservesFor(address factory, bytes32 initCodeHash, address tokenA, address tokenB)
        private
        view
        returns (address pair, uint256 reserveA, uint256 reserveB)
    {
        address token0;
        (pair, token0) = pairAndToken0For(factory, initCodeHash, tokenA, tokenB);
        (uint256 reserve0, uint256 reserve1,) = IUniswapV2Pair(pair).getReserves();
        (reserveA, reserveB) = tokenA == token0 ? (reserve0, reserve1) : (reserve1, reserve0);
    }

    /// @notice Given an input asset amount returns the maximum output amount of the other asset
    /// @param amountIn The token input amount
    /// @param reserveIn The reserves available of the input token
    /// @param reserveOut The reserves available of the output token
    /// @return amountOut The output amount of the output token
    function getAmountOut(uint256 amountIn, uint256 reserveIn, uint256 reserveOut)
        internal
        pure
        returns (uint256 amountOut)
    {
        if (reserveIn == 0 || reserveOut == 0) revert InvalidReserves();
        uint256 amountInWithFee = amountIn * 997;
        uint256 numerator = amountInWithFee * reserveOut;
        uint256 denominator = reserveIn * 1000 + amountInWithFee;
        amountOut = numerator / denominator;
    }

    /// @notice Returns the input amount needed for a desired output amount in a single-hop trade
    /// @param amountOut The desired output amount
    /// @param reserveIn The reserves available of the input token
    /// @param reserveOut The reserves available of the output token
    /// @return amountIn The input amount of the input token
    function getAmountIn(uint256 amountOut, uint256 reserveIn, uint256 reserveOut)
        internal
        pure
        returns (uint256 amountIn)
    {
        if (reserveIn == 0 || reserveOut == 0) revert InvalidReserves();
        uint256 numerator = reserveIn * amountOut * 1000;
        uint256 denominator = (reserveOut - amountOut) * 997;
        amountIn = (numerator / denominator) + 1;
    }

    /// @notice Returns the input amount needed for a desired output amount in a multi-hop trade
    /// @param factory The address of the v2 factory
    /// @param initCodeHash The hash of the pair initcode
    /// @param amountOut The desired output amount
    /// @param path The path of the multi-hop trade
    /// @return amount The input amount of the input token
    /// @return pair The first pair in the trade
    function getAmountInMultihop(address factory, bytes32 initCodeHash, uint256 amountOut, address[] memory path)
        internal
        view
        returns (uint256 amount, address pair)
    {
        if (path.length < 2) revert InvalidPath();
        amount = amountOut;
        for (uint256 i = path.length - 1; i > 0; i--) {
            uint256 reserveIn;
            uint256 reserveOut;

            (pair, reserveIn, reserveOut) = pairAndReservesFor(factory, initCodeHash, path[i - 1], path[i]);
            amount = getAmountIn(amount, reserveIn, reserveOut);
        }
    }

    /// @notice Sorts two tokens to return token0 and token1
    /// @param tokenA The first token to sort
    /// @param tokenB The other token to sort
    /// @return token0 The smaller token by address value
    /// @return token1 The larger token by address value
    function sortTokens(address tokenA, address tokenB) internal pure returns (address token0, address token1) {
        (token0, token1) = tokenA < tokenB ? (tokenA, tokenB) : (tokenB, tokenA);
    }
}