Merge pull request #31 from ronin-chain/feature/statistic

feat: return collected fees of a position & auto burn when the liquidity is empty and no tokens owed

src/periphery/NonfungiblePositionManager.sol

@@ -51,6 +51,11 @@ contract NonfungiblePositionManager is
     uint128 tokensOwed1;
   }
 
+  struct CollectedFees {
+    uint256 token0;
+    uint256 token1;
+  }
+
   /// @dev IDs of pools assigned by this contract
   mapping(address => uint80) private _poolIds;
 
@@ -60,6 +65,9 @@ contract NonfungiblePositionManager is
   /// @dev The token ID position data
   mapping(uint256 => Position) private _positions;
 
+  /// @dev How many tokens are collected by the position, as of the last colection
+  mapping(uint256 => CollectedFees) private _collectedFees;
+
   /// @dev The ID of the next token that will be minted. Skips 0
   uint176 private _nextId = 1;
   /// @dev The ID of the next pool that is used for the first time. Skips 0
@@ -114,6 +122,11 @@ contract NonfungiblePositionManager is
     );
   }
 
+  function collectedFees(uint256 tokenId) external view override returns (uint256 token0, uint256 token1) {
+    CollectedFees memory fees = _collectedFees[tokenId];
+    return (fees.token0, fees.token1);
+  }
+
   /// @dev Caches a pool key
   function cachePoolKey(address pool, PoolAddress.PoolKey memory poolKey) private returns (uint80 poolId) {
     poolId = _poolIds[pool];
@@ -333,10 +346,20 @@ contract NonfungiblePositionManager is
     // the actual amounts collected are returned
     (amount0, amount1) = pool.collect(recipient, position.tickLower, position.tickUpper, amount0Collect, amount1Collect);
 
+    CollectedFees storage fees = _collectedFees[params.tokenId];
+    fees.token0 += amount0;
+    fees.token1 += amount1;
+
     // sometimes there will be a few less wei than expected due to rounding down in core, but we just subtract the full amount expected
     // instead of the actual amount so we can burn the token
     (position.tokensOwed0, position.tokensOwed1) = (tokensOwed0 - amount0Collect, tokensOwed1 - amount1Collect);
 
+    // if there's no liquidity and no tokens owed, burn the position
+    if (position.liquidity == 0 && tokensOwed0 == amount0Collect && tokensOwed1 == amount1Collect) {
+      delete _positions[params.tokenId];
+      _burn(params.tokenId);
+    }
+
     emit Collect(params.tokenId, recipient, amount0Collect, amount1Collect);
   }
 

src/periphery/interfaces/INonfungiblePositionManager.sol

@@ -76,6 +76,12 @@ interface INonfungiblePositionManager is
       uint128 tokensOwed1
     );
 
+  /// @notice Returns the collected fees for a given token ID
+  /// @param tokenId The ID of the token for which fees are collected
+  /// @return token0 The amount of token0 collected
+  /// @return token1 The amount of token1 collected
+  function collectedFees(uint256 tokenId) external view returns (uint256 token0, uint256 token1);
+
   struct MintParams {
     address token0;
     address token1;