本文介绍了PathKey库的结构体定义及其方法，特别是getPoolAndSwapDirection函数的实现。内容详尽，涵盖了结构体字段含义及如何计算交易池和方向的逻辑，是对Uniswap v4相关概念的深入理解。
PathKey Library
结构体定义
PathKey
struct PathKey {
Currency intermediateCurrency;
uint24 fee;
int24 tickSpacing;
IHooks hooks;
bytes hookData;
}
intermediateCurrency：中间代币fee：手续费tickSpacing：池子 tick 间隔hooks：Hooks 合约hookData：Hooks 数据
方法定义
getPoolAndSwapDirection
根据输入代币和中间代币信息，计算交易池子和交易方向。
/// @notice Get the pool and swap direction for a given PathKey
/// @param params the given PathKey
/// @param currencyIn the input currency
/// @return poolKey the pool key of the swap
/// @return zeroForOne the direction of the swap, true if currency0 is being swapped for currency1
function getPoolAndSwapDirection(PathKey calldata params, Currency currencyIn)
internal
pure
returns (PoolKey memory poolKey, bool zeroForOne)
{
Currency currencyOut = params.intermediateCurrency;
(Currency currency0, Currency currency1) =
currencyIn < currencyOut ? (currencyIn, currencyOut) : (currencyOut, currencyIn);
zeroForOne = currencyIn == currency0;
poolKey = PoolKey(currency0, currency1, params.fee, params.tickSpacing, params.hooks);
}
在 PoolKey 中介绍了 PoolKey 结构体，Uniswap v4 通过 currency0、currency1、fee、tickSpacing、hooks 来唯一标识一个池子，其中，currency0 地址小于 currency1 地址。
因此，在 getPoolAndSwapDirection 中确定交易池子时，首先排序 currency0 和 currency1，结合 fee、tickSpacing、hooks，得到 poolKey。
根据 currencyIn 是否等于 currency0，确定交易方向 zeroForOne，因为此时 currency0 即 token0。
