# `WithdrawCallback` Exercises `WithdrawCallback` is the contract that is called by GMX when the vault creates a order to withdraw WETH from the position managed by the strategy. The callback functions are all executed after GMX executes the order. One of the 3 functions below will be called first by GMX. - `afterOrderExecution` - `afterOrderCancellation` - `afterOrderFrozen` Afterwards execution fee refund is sent to `refundExecutionFee` You need to complete the implementation of the `WithdrawCallback.sol` contract. ## Task 1: Implement `refundExecutionFee` ```solidity function refundExecutionFee( // Order key bytes32 key, EventUtils.EventLogData memory eventData ) external payable onlyGmx {} ``` This function will refund execution fee to the account that created the order to withdraw. - Check that `refunds[key]` is not `address(0)`. `refunds` is a mapping from the order key to the account to refund execution fee to. - Delete `refunds` for `key`. - Send all ETH in this contract to the address stored in `refunds[key]`. ## Task 2: Implement `afterOrderExecution` ```solidity function afterOrderExecution( // Order key bytes32 key, Order.Props memory order, EventUtils.EventLogData memory eventData ) external onlyGmx {} ``` This function is called by GMX after an order is successfully executed. - Check that the order type is a market decrease. - Get the withdraw order from the vault by calling `getWithdrawOrder` - Set `refunds` for `key` to the account stored in the withdraw order - Remove the withdraw order by calling `vault.removeWithdrawOrder`. Burn all remaining shares of this user. - Transfer at most the amount of WETH stored in the withdraw order to the account that is associated with this withdraw order. Send remaining WETH to the vault. ## Task 3: Implement `afterOrderCancellation` ```solidity function afterOrderCancellation( // Order key bytes32 key, Order.Props memory order, EventUtils.EventLogData memory eventData ) external onlyGmx {} ``` This function is called by GMX after an order is cancelled. - Check that the order type is a market decrease. - Get the withdraw order from the vault by calling `getWithdrawOrder` - Set `refunds` for `key` to the account stored in the withdraw order. - Remove the withdraw order by calling `vault.removeWithdrawOrder`. Unlock the shares that are locked for this user. ## Task 4: Implement `afterOrderFrozen` ```solidity function afterOrderFrozen( // Order key bytes32 key, Order.Props memory order, EventUtils.EventLogData memory eventData ) external onlyGmx {} ``` This function is called by GMX after an order is frozen. - Check that the order type is a market decrease. - Get the withdraw order from the vault by calling `getWithdrawOrder` - Set `refunds` for `key` to the account stored in the withdraw order - Remove the withdraw order by calling `vault.removeWithdrawOrder`. Unlock the shares that are locked for this user. ## Test ```shell forge test --fork-url $FORK_URL --fork-block-number $FORK_BLOCK_NUM --match-path test/app/WithdrawCallback.test.sol -vvv ```