# Hook Logic

### Overview

When deploying a new pool, you (or the pool creator) pass a `Permissions` struct that tells the core AMM contract which lifecycle callbacks your hook should receive. This is a security and gas-optimization feature: the core only calls hooks for which the corresponding flag is `true`.

Only hooks that set the appropriate flags can be registered for a pool.

```solidity
struct Permissions {
    bool beforeInitialize;
    bool afterInitialize;
    bool beforeAddLiquidity;
    bool afterAddLiquidity;
    bool beforeRemoveLiquidity;
    bool afterRemoveLiquidity;
    bool beforeSwap;
    bool afterSwap;
    bool beforeDonate;
    bool afterDonate;
    bool beforeSwapReturnDelta;
    bool afterSwapReturnDelta;
    bool afterAddLiquidityReturnDelta;
    bool afterRemoveLiquidityReturnDelta;
}
```

### Permission Flags

<figure><img src="/files/roR56DKEYVCTQXCIgJyo" alt=""><figcaption></figcaption></figure>

#### Pool Lifecycle

* `beforeInitialize` — Called before a pool is created. Useful for validating parameters, setting initial state, or enforcing custom deployment rules.
* `afterInitialize` — Called immediately after pool creation. Good for one-time setup inside the hook (e.g., initializing oracle data, whitelists, etc.).

#### Liquidity Operations

* `beforeAddLiquidity` — Runs before liquidity is added. Common uses: position validation, fees, dynamic range checks, or KYC-style restrictions.
* `afterAddLiquidity` — Runs after liquidity is successfully added. Useful for post-mint accounting, reward distribution, or updating external contracts.
* `beforeRemoveLiquidity` — Runs before liquidity is removed. Can be used for withdrawal fees, cooldowns, or position lock checks.
* `afterRemoveLiquidity` — Runs after liquidity removal. Useful for cleanup or emitting events to external systems.

#### Swaps (Trading)

* `beforeSwap` — Executed before every swap. Most powerful hook for:
  * Dynamic fees
  * Price limits / circuit breakers
  * MEV protection (e.g., order flow auctions)
  * Custom routing or intent-based logic
* `afterSwap` — Executed after a swap completes. Ideal for:
  * Post-trade rewards
  * Oracle updates
  * TWAP calculations
  * Protocol fee logic

#### Donate

* `beforeDonate` — Called before a donate operation (adding tokens to the pool without minting LP tokens).
* `afterDonate` — Called after a successful donate.

#### Return Delta Flags (Advanced)

These flags allow your hook to return a delta (positive or negative token amount adjustment) that modifies the core operation. They enable very powerful custom accounting.

* `beforeSwapReturnDelta` — Hook can return a delta on input/output amounts before the swap executes.
* `afterSwapReturnDelta` — Hook can return a delta after the swap (e.g., to take a custom fee in output tokens).
* `afterAddLiquidityReturnDelta` — Hook can adjust the amount of liquidity minted or tokens required.
* `afterRemoveLiquidityReturnDelta` — Hook can adjust the tokens returned to the user on withdrawal.

Note: Return-delta hooks usually require the corresponding `before`/`after` flag to also be enabled.

#### Example Usage

```rust
// When creating a pool
let permissions = Permissions {
    beforeSwap: true,
    afterSwap: true,
    afterAddLiquidityReturnDelta: true,
    // ... other flags
    ..Default::default()
};

create_pool(token0, token1, fee, tickSpacing, hook_address, permissions);
```


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