# Limit Order Exercises In this exercise, you'll learn how to write a limit order hooks contract. The starter code for this exercise is provided in [`foundry/src/exercises/LimitOrder.sol`](https://github.com/Cyfrin/defi-uniswap-v4/blob/main/foundry/src/exercises/LimitOrder.sol) Solution is in [`foundry/src/solutions/LimitOrder.sol`](https://github.com/Cyfrin/defi-uniswap-v4/blob/main/foundry/src/solutions/LimitOrder.sol) ## Task 1 - After initialize hook ```solidity function afterInitialize( address sender, PoolKey calldata key, uint160 sqrtPriceX96, int24 tick ) external onlyPoolManager returns (bytes4) { // Write your code here return this.afterInitialize.selector; } ``` - Store the current tick of the pool into the state variable `ticks`. ## Task 2 - Place a limit order ```solidity function place( PoolKey calldata key, int24 tickLower, bool zeroForOne, uint128 liquidity ) external payable setAction(ADD_LIQUIDITY) { // Write your code here } ``` This function places a limit order for `msg.sender`. - Revert if `tickLower` is not a multiple of the pool's tick spacing - Call `poolManager.unlock` and write code inside `unlockCallback` to add liquidity. - Liquidity must be added between `tickLower` and `tickLower + tickSpacing`. - Revert if liquidity is going to be added to the current tick. - Update `Bucket` stored in the current slot. - Call `getBucketId` to get the `Bucket` id. - Current slot for this bucket is stored in `slots[id]`. - Current `Bucket` is stored in `buckets[id][slots[id]]`. - Emit `Place` event ## Task 3 - Cancel a limit order ```solidity function cancel(PoolKey calldata key, int24 tickLower, bool zeroForOne) external setAction(REMOVE_LIQUIDITY) { // Write your code here } ``` This funciton cancels a limit order for `msg.sender`. - Revert if the `Bucket` to remove limit order from is `filled`. - Remove liquidity for `msg.sender` from the `Bucket`. - Call `poolManager.unlock` and write code inside `unlockCallback` to remove liquidity. - Removing liquidity, return fees that accrued to this position. - Allocate the fees to the `Bucket` if liquidity in it is greater than 0. - If liquidity in the `Bucket` is 0, give the fees to `msg.sender`. - Emit `Cancel` event ## Task 4 - Take swapped token ```solidity function take( PoolKey calldata key, int24 tickLower, bool zeroForOne, uint256 slot ) external { // Write your code here } ``` This function is called by `msg.sender` to withdraw the tokens that were swapped after their limit order was processed. - Revert if the `Bucket` is not `filled`. - Update `Bucket` - Send the approriate amount of `currency0` and `currency1` to `msg.sender`. - Emit `Take` event ## Task 5 - After swap hook ```solidity function afterSwap( address sender, PoolKey calldata key, SwapParams calldata params, BalanceDelta delta, bytes calldata hookData ) external onlyPoolManager setAction(REMOVE_LIQUIDITY) returns (bytes4, int128) { // Write your code here return (this.afterSwap.selector, 0); } ``` This hook is triggered after a swap and is responsible for removing liquidity from the processed `Bucket`s. - Find the range of ticks to remove liquidity. - This will range from the last stored tick (`ticks[key.toId()]`) to the current `tick`, both rounded down to a multiple of `tickSpacing` and then `+/-` `tickSpacing`. - Hint: Call `_getTickRange` - Remove liquidity from the tick range above. - Set `Bucket.filled` to `true`. - Store the amounts of `currency0` and `currency1` returned into the `Bucket`. - Emit `Fill` event. - Increment the slot for this bucket by 1. - Store the latest tick into `ticks[key.toId()]` ## Test 1. Find the value of `salt` needed to deploy the hooks contract at a valid address. ```shell forge test --match-path test/FindHookAddr.sol -vvv ``` 2. Export the salt printed to your terminal from executing the command in the previous step. ```shell export SALT=YOUR_SALT forge test --fork-url $FORK_URL --match-path test/LimitOrder.test.sol -vvv ```