# Doppler Hooks

### Overview

Doppler Hooks, aka dhooks, are a set of callback functions that can be called during the lifecycle of "locked" pools initialized by the `DopplerHookInitializer` contract. 

Three main events will trigger these hooks:

* `initialization`: when a new pool is created
* `swap`: when a swap occurs in the pool
* `graduation`: when the pool reaches a certain price maturity

Additionally, pools associated with a Doppler Hook can have their LP fee updated by the associated timelock governance contract or a delegated address.

#### **A couple of things to note:**

* A pool initialized without a Doppler Hook can opt-in to use one later via the `setHook` function
* A pool initialized with a Doppler Hook can opt-out of using it later by setting the hook address to `address(0)`
* A pool can change its associated Doppler Hook to a different one at any time via the `setHook` function
* Doppler Hooks are approved by the protocol multisig
* A pool without a Doppler Hook cannot be initialized with a dynamic LP fee

#### Implementation

Here are the different callback functions available for the Doppler Hooks.

Note that they can be implemented selectively based on the use case:

| Callback Function                                                                                                                                                                | Triggered By                                                                                                                                                                                           |
| -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `onInitialization(address asset, PoolKey calldata key, bytes calldata data`                                                                                                      | <p>- <code>initialize()</code> if a <code>dopplerHook</code> address is set in the <code>InitData</code><br>- <code>setDopplerHook()</code> if a Doppler Hook is set after the pool initialization</p> |
| `onSwap(address sender, PoolKey calldata key, IPoolManager.SwapParams calldata params,BalanceDelta delta, bytes calldata data) returns (Currency feeCurrency, int128 hookDelta)` | `afterSwap` before each swap happening in the Uniswap V4 pool                                                                                                                                          |
| `onGraduation(address asset, PoolKey calldata key, bytes calldata data)`                                                                                                         | `graduate` if the graduation conditions are met (e.g. `farTick` reached)                                                                                                                               |