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//SWAP(supporting fee-on-transfer tokens)
//requires the initial amount to have already been sent to the first pair
//交易方法，支持转账扣手续费的代币
//需要先将amounts[0]的金额已经转到第一个pair地址(即path[0]+path[1]组成的pair)！
function _swapSupportingFeeOnTransferTokens(address[]memory path,address _to)internal virtual{
for(uint i;i<path.length-1;i++){
//得到进/出token地址
(address input,address output)=(path,path[i+1]);
//排序得到token0
(address token0,)=UniswapV2Library.sortTokens(input,output);
//获取pair
IUniswapV2Pair pair=IUniswapV2Pair(UniswapV2Library.pairFor(factory,input,output));
uint amountInput;//输入金额
uint amountOutput;//输入金额
{//scope to avoid stack too deep errors避免堆栈太深错误，用{}括部分临时变量
//或许两个币的储备量
(uint reserve0,uint reserve1,)=pair.getReserves();
//根据input,token0得出inToken的储备量,outToken的储备量
(uint reserveInput,uint reserveOutput)=input==token0?(reserve0,reserve1):(reserve1,reserve0);
//查询交易对的inToken余额，减掉最后记录的储备量，就是交易对实际获取到的inToken数量(TODO和_swap的区别就在这里，不是使用计算来的amounts[0]作为输入，而是通过查询pair余额再减去最后更新的储备量得到实际pair到账额！)
amountInput=IERC20(input).balanceOf(address(pair)).sub(reserveInput);
//通过实际得到的input量，计算实际会输出的output数量
amountOutput=UniswapV2Library.getAmountOut(amountInput,reserveInput,reserveOutput);
}
//根据token0，input得到amount0需要out,还是amount1是out,;注意其中之一一定是0，即入token的金额，不需要pair转出
(uint amount0Out,uint amount1Out)=input==token0?(uint(0),amountOutput):(amountOutput,uint(0));
//如果i小于path长度-2，就表示还需要继续交易，所以to是下一个交易对，如果一样就表示path结束了，to就是参数中的_to
address to=i<path.length-2?UniswapV2Library.pairFor(factory,output,path[i+2]):_to;
//调用pair的swap方法，其中一个out是0，另一个是要转出的金额，内部是转出输出量，并校验交易是否正确，更新储备量
pair.swap(amount0Out,amount1Out,to,new bytes(0));
}
}
/**
TODO带supportingFeeOnTransfer方法都是通过余额的方式计算输入/出
下面的三个方法，都是swapExactXXXForXX,而没有swapXXXForExactXX
如果是自己开发合约调用，可以随意选用哪个swap
在uniswap中，如果滑点改成49，会自动切换带supportingFeeOnTransfer的方法
还有些其他情况也会自动切，这个会前端的可以看看代码，什么情况下，前端会选择使用带supportingFeeOnTransfer的方法去交易
*/
//输入精确的token,换取另一个token，支持转账时扣手续费的token
function swapExactTokensForTokensSupportingFeeOnTransferTokens(
uint amountIn,//输入金额
uint amountOutMin,//最小输出金额，该金额只要够小，交易就一定可以成功
address[]calldata path,//交换路径
address to,
uint deadline
)external virtual override ensure(deadline){
//将输入金额转到第一个pair地址
TransferHelper.safeTransferFrom(
path[0],msg.sender,UniswapV2Library.pairFor(factory,path[0],path[1]),amountIn
);
//查询to用户当前最终输出token的余额
uint balanceBefore=IERC20(path[path.length-1]).balanceOf(to);
//调用内部交易方法
_swapSupportingFeeOnTransferTokens(path,to);
//通过查询余额的方式，校验交易前后的余额差，大于等于最小输出！
require(
IERC20(path[path.length-1]).balanceOf(to).sub(balanceBefore)>=amountOutMin,
'UniswapV2Router:INSUFFICIENT_OUTPUT_AMOUNT'
);
}
//输入精确eth换取另一个token
function swapExactETHForTokensSupportingFeeOnTransferTokens(
uint amountOutMin,
address[]calldata path,
address to,
uint deadline
)
external
virtual
override
payable
ensure(deadline)
{
require(path[0]==WETH,'UniswapV2Router:INVALID_PATH');
//将eth转成weth,并转给第一个pair地址
uint amountIn=msg.value;
IWETH(WETH).deposit{value:amountIn}();
assert(IWETH(WETH).transfer(UniswapV2Library.pairFor(factory,path[0],path[1]),amountIn));
//跟上面方法一样，通过查询余额的方式校验
uint balanceBefore=IERC20(path[path.length-1]).balanceOf(to);
_swapSupportingFeeOnTransferTokens(path,to);
require(
IERC20(path[path.length-1]).balanceOf(to).sub(balanceBefore)>=amountOutMin,
'UniswapV2Router:INSUFFICIENT_OUTPUT_AMOUNT'
);
}
//输入精确token换取输出eth,
function swapExactTokensForETHSupportingFeeOnTransferTokens(
uint amountIn,
uint amountOutMin,
address[]calldata path,
address to,
uint deadline
)
external
virtual
override
ensure(deadline)
{
require(path[path.length-1]==WETH,'UniswapV2Router:INVALID_PATH');
TransferHelper.safeTransferFrom(
path[0],msg.sender,UniswapV2Library.pairFor(factory,path[0],path[1]),amountIn
);
_swapSupportingFeeOnTransferTokens(path,address(this));
uint amountOut=IERC20(WETH).balanceOf(address(this));
require(amountOut>=amountOutMin,'UniswapV2Router:INSUFFICIENT_OUTPUT_AMOUNT');
IWETH(WETH).withdraw(amountOut);
TransferHelper.safeTransferETH(to,amountOut);
}
