feat: Pool support pool burn and collect (#116)

demo-contract/contracts/wtfswap/Pool.sol

@@ -8,6 +8,7 @@ import "./libraries/SqrtPriceMath.sol";
 import "./libraries/TickMath.sol";
 import "./libraries/LiquidityMath.sol";
 import "./libraries/LowGasSafeMath.sol";
+import "./libraries/TransferHelper.sol";
 
 import "./interfaces/IPool.sol";
 import "./interfaces/IFactory.sol";
@@ -143,24 +144,49 @@ contract Pool is IPool {
     function collect(
         address recipient
     ) external override returns (uint128 amount0, uint128 amount1) {
-        // 获取当前用户的 position，TODO recipient 应该改为 msg.sender
-        Position storage position = positions[recipient];
-        // TODO 把钱退给用户 recipient
-        // 修改 position 中的信息
-        position.tokensOwed0 -= amount0;
-        position.tokensOwed1 -= amount1;
+        // 获取当前用户的 position
+        Position storage position = positions[msg.sender];
+        // 把钱退给用户 recipient，只支持全部退还
+        amount0 = position.tokensOwed0;
+        amount1 = position.tokensOwed1;
+
+        if (amount0 > 0) {
+            position.tokensOwed0 -= amount0;
+            TransferHelper.safeTransfer(token0, recipient, amount0);
+        }
+        if (amount1 > 0) {
+            position.tokensOwed1 -= amount1;
+            TransferHelper.safeTransfer(token1, recipient, amount1);
+        }
+
+        emit Collect(msg.sender, recipient, amount0, amount1);
     }
 
     function burn(
         uint128 amount
     ) external override returns (uint256 amount0, uint256 amount1) {
         // 修改 positions 中的信息
-        positions[msg.sender].liquidity -= amount;
+        (int256 amount0Int, int256 amount1Int) = _modifyPosition(
+            ModifyPositionParams({
+                owner: msg.sender,
+                liquidityDelta: -int256(int128(amount)).toInt128()
+            })
+        );
         // 获取燃烧后的 amount0 和 amount1
-        // TODO 当前先写个假的
-        (amount0, amount1) = (amount / 2, amount / 2);
-        positions[msg.sender].tokensOwed0 += amount0;
-        positions[msg.sender].tokensOwed1 += amount1;
+        amount0 = uint256(-amount0Int);
+        amount1 = uint256(-amount1Int);
+
+        if (amount0 > 0 || amount1 > 0) {
+            (
+                positions[msg.sender].tokensOwed0,
+                positions[msg.sender].tokensOwed1
+            ) = (
+                positions[msg.sender].tokensOwed0 + uint128(amount0),
+                positions[msg.sender].tokensOwed1 + uint128(amount1)
+            );
+        }
+
+        emit Burn(msg.sender, amount, amount0, amount1);
     }
 
     function swap(

demo-contract/contracts/wtfswap/interfaces/IPool.sol

@@ -20,8 +20,8 @@ interface ISwapCallback {
 interface IPool {
     struct Position {
         uint128 liquidity;
-        uint256 tokensOwed0;
-        uint256 tokensOwed1;
+        uint128 tokensOwed0;
+        uint128 tokensOwed1;
     }
 
     function factory() external view returns (address);

demo-contract/contracts/wtfswap/libraries/TransferHelper.sol

@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+pragma solidity >=0.6.0;
+
+import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
+
+/// @title TransferHelper
+/// @notice Contains helper methods for interacting with ERC20 tokens that do not consistently return true/false
+library TransferHelper {
+    /// @notice Transfers tokens from msg.sender to a recipient
+    /// @dev Calls transfer on token contract, errors with TF if transfer fails
+    /// @param token The contract address of the token which will be transferred
+    /// @param to The recipient of the transfer
+    /// @param value The value of the transfer
+    function safeTransfer(address token, address to, uint256 value) internal {
+        (bool success, bytes memory data) = token.call(
+            abi.encodeWithSelector(IERC20.transfer.selector, to, value)
+        );
+        require(
+            success && (data.length == 0 || abi.decode(data, (bool))),
+            "TF"
+        );
+    }
+}