# `GmxHelper` Exercises `GmxHelper` is a contract that interacts with GMX to manage position size and fees. You need to complete the implementation of the `GmxHelper.sol` contract. ## Task 1: Implement `getSizeDeltaUsd` ```solidity function getSizeDeltaUsd( // Long token price from Chainlink (1e8 = 1 USD) uint256 longTokenPrice, // Current position size uint256 sizeInUsd, // Current collateral amount locked in the position uint256 collateralAmount, // Long token amount to add or remove uint256 longTokenAmount, // True for market increase bool isIncrease ) internal view returns (uint256 sizeDeltaUsd) {} ``` This function calculates the change in position size needed so that the new position size is the current collateral price times the new collateral amount. Return `0` if `sizeDeltaUsd` is less than `0`. ## Task 2: Implement `createIncreaseShortPositionOrder` ```solidity function createIncreaseShortPositionOrder( // Execution fee to send to the order vault uint256 executionFee, // Long token amount to add to the current position uint256 longTokenAmount ) internal returns (bytes32 orderKey) {} ``` This function creates a market increase order for a short position. ### Task 2.1: Calculate the position size delta Call `getSizeDeltaUsd` to calculate the delta for the next position size. > Hint: > > - Get `sizeInUsd` and `collateralAmount` from the current `position` ### Task 2.2: Create market increase order Call `exchangeRouter` to create a market increase order for a short position. ## Task 3: Implement `createDecreaseShortPositionOrder` ```solidity function createDecreaseShortPositionOrder( // Execution fee to send to the order vault uint256 executionFee, // Long token amount to remove from the current position uint256 longTokenAmount, // Receiver of long token address receiver, // Callback contract used to handle withdrawal from the vault address callbackContract, // Max gas to send to the callback contract uint256 callbackGasLimit ) internal returns (bytes32 orderKey) {} ``` This function creates a market decrease order for a short position. ### Task 3.1: Calculate the position size delta Call `getSizeDeltaUsd` to calculate the delta for the next position size. ### Task 3.2: Create market decrease order Call `exchangeRouter` to create a market decrease order for a short position. > Hints: > > - Set `receiver`, `callbackContract` and `callbackGasLimit` from the inputs. > - Set `decreasePositionSwapType` to `Order.DecreasePositionSwapType.SwapPnlTokenToCollateralToken` ## Task 4: Implement `cancelOrder` ```solidity function cancelOrder(bytes32 orderKey) internal {} ``` This function cancels an order. > Hint: > > - Call `exchangeRouter.cancelOrder` ## Task 5: Implement `claimFundingFees` ```solidity function claimFundingFees() internal {} ``` This function claims funding fees. > Hint: > > - You only need to claim funding fees for the long token since this is the only collateral used by this contract.