first commit

.github/workflows/test.yml

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+name: CI
+
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
+
+env:
+  FOUNDRY_PROFILE: ci
+
+jobs:
+  check:
+    strategy:
+      fail-fast: true
+
+    name: Foundry project
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: recursive
+
+      - name: Install Foundry
+        uses: foundry-rs/foundry-toolchain@v1
+        with:
+          version: nightly
+
+      - name: Show Forge version
+        run: |
+          forge --version
+
+      - name: Run Forge fmt
+        run: |
+          forge fmt --check
+        id: fmt
+
+      - name: Run Forge build
+        run: |
+          forge build --sizes
+        id: build
+
+      - name: Run Forge tests
+        run: |
+          forge test -vvv
+        id: test

.gitignore

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+# Compiler files
+cache/
+out/
+
+# Ignores development broadcast logs
+!/broadcast
+/broadcast/*/31337/
+/broadcast/**/dry-run/
+
+# Docs
+docs/
+
+# Dotenv file
+.env

.gitmodules

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+[submodule "lib/v4-periphery"]
+	path = lib/v4-periphery
+	url = https://github.com/uniswap/v4-periphery

README.md

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+## Foundry
+
+**Foundry is a blazing fast, portable and modular toolkit for Ethereum application development written in Rust.**
+
+Foundry consists of:
+
+-   **Forge**: Ethereum testing framework (like Truffle, Hardhat and DappTools).
+-   **Cast**: Swiss army knife for interacting with EVM smart contracts, sending transactions and getting chain data.
+-   **Anvil**: Local Ethereum node, akin to Ganache, Hardhat Network.
+-   **Chisel**: Fast, utilitarian, and verbose solidity REPL.
+
+## Documentation
+
+https://book.getfoundry.sh/
+
+## Usage
+
+### Build
+
+```shell
+$ forge build
+```
+
+### Test
+
+```shell
+$ forge test
+```
+
+### Format
+
+```shell
+$ forge fmt
+```
+
+### Gas Snapshots
+
+```shell
+$ forge snapshot
+```
+
+### Anvil
+
+```shell
+$ anvil
+```
+
+### Deploy
+
+```shell
+$ forge script script/Counter.s.sol:CounterScript --rpc-url <your_rpc_url> --private-key <your_private_key>
+```
+
+### Cast
+
+```shell
+$ cast <subcommand>
+```
+
+### Help
+
+```shell
+$ forge --help
+$ anvil --help
+$ cast --help
+```

foundry.toml

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+[profile.default]
+src = "src"
+out = "out"
+libs = ["lib"]
+
+# See more config options https://github.com/foundry-rs/foundry/blob/master/crates/config/README.md#all-options

remappings.txt

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+@ensdomains/=lib/v4-periphery/lib/v4-core/node_modules/@ensdomains/
+@openzeppelin/=lib/v4-periphery/lib/v4-core/lib/openzeppelin-contracts/
+@openzeppelin/contracts/=lib/v4-periphery/lib/v4-core/lib/openzeppelin-contracts/contracts/
+@uniswap/v4-core/=lib/v4-periphery/lib/v4-core/
+ds-test/=lib/v4-periphery/lib/v4-core/lib/forge-std/lib/ds-test/src/
+erc4626-tests/=lib/v4-periphery/lib/v4-core/lib/openzeppelin-contracts/lib/erc4626-tests/
+forge-gas-snapshot/=lib/v4-periphery/lib/permit2/lib/forge-gas-snapshot/src/
+forge-std/=lib/v4-periphery/lib/v4-core/lib/forge-std/src/
+hardhat/=lib/v4-periphery/lib/v4-core/node_modules/hardhat/
+openzeppelin-contracts/=lib/v4-periphery/lib/v4-core/lib/openzeppelin-contracts/
+permit2/=lib/v4-periphery/lib/permit2/
+solmate/=lib/v4-periphery/lib/v4-core/lib/solmate/
+v4-core/=lib/v4-periphery/lib/v4-core/src/
+v4-periphery/=lib/v4-periphery/

src/GasPriceHook.sol

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+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.0;
+
+import {BaseHook} from "v4-periphery/src/base/hooks/BaseHook.sol";
+import {ERC1155} from "@openzeppelin/contracts/token/ERC1155/ERC1155.sol";
+import {Hooks} from "v4-core/libraries/Hooks.sol";
+
+import {StateLibrary} from "v4-core/libraries/StateLibrary.sol";
+import {TickMath} from "v4-core/libraries/TickMath.sol";
+
+import {PoolId} from "v4-core/types/PoolId.sol";
+import {IPoolManager} from "v4-core/interfaces/IPoolManager.sol";
+
+import {PoolKey} from "v4-core/types/PoolKey.sol";
+
+import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
+import {ERC20} from "@openzeppelin/contracts/token/ERC20/ERC20.sol";
+
+import {BalanceDelta} from "v4-core/types/BalanceDelta.sol";
+
+import {CurrencyLibrary, Currency} from "v4-core/types/Currency.sol";
+
+import {FixedPointMathLib} from "solmate/src/utils/FixedPointMathLib.sol";
+import {BeforeSwapDelta, BeforeSwapDeltaLibrary} from "v4-core/types/BeforeSwapDelta.sol";
+import {LPFeeLibrary} from "v4-core/libraries/LPFeeLibrary.sol";
+
+contract GasPriceHook is BaseHook {
+    using LPFeeLibrary for uint24;
+
+    // keep track of the moving average gas price
+    uint128 movingAverageGasPrice;
+
+    // num of times the moving average is updated
+    // need this as the denominator to update it next time based on moving average formulae
+    uint104 public movingAverageGasPriceCount;
+
+    // default base fee that we'll charging
+    uint24 public constant BASE_FEE = 5000; // 0.5%
+
+    error MustUseDynamicFee();
+
+    constructor(IPoolManager _poolManager) BaseHook(_poolManager) {
+        updateMovingAverage();
+    }
+
+    function getHookPermissions()
+        public
+        pure
+        override
+        returns (Hooks.Permissions memory)
+    {
+        return
+            Hooks.Permissions({
+                beforeInitialize: true,
+                afterInitialize: false,
+                beforeAddLiquidity: false,
+                afterAddLiquidity: false,
+                beforeRemoveLiquidity: false,
+                afterRemoveLiquidity: false,
+                beforeSwap: true,
+                afterSwap: true,
+                beforeDonate: false,
+                afterDonate: false,
+                beforeSwapReturnDelta: false,
+                afterSwapReturnDelta: false,
+                afterAddLiquidityReturnDelta: false,
+                afterRemoveLiquidityReturnDelta: false
+            });
+    }
+
+    function beforeInitialize(
+        address,
+        PoolKey calldata key,
+        uint160
+    ) external pure override returns (bytes4) {
+        // `.isDynamicFee()` function comes from using
+        // the `SwapFeeLibrary` for `uint24`
+        if (!key.fee.isDynamicFee()) revert MustUseDynamicFee();
+        return this.beforeInitialize.selector;
+    }
+
+    function afterSwap(
+        address,
+        PoolKey calldata,
+        IPoolManager.SwapParams calldata,
+        BalanceDelta,
+        bytes calldata
+    ) external override returns (bytes4, int128) {
+        updateMovingAverage();
+        return (this.afterSwap.selector, 0);
+    }
+
+    function beforeSwap(
+        address,
+        PoolKey calldata,
+        IPoolManager.SwapParams calldata,
+        bytes calldata
+    )
+        external
+        view
+        override
+        onlyPoolManager
+        returns (bytes4, BeforeSwapDelta, uint24)
+    {
+        uint24 fee = getFee();
+
+        uint24 feeWithFlag = fee | LPFeeLibrary.OVERRIDE_FEE_FLAG;
+
+        return (
+            this.beforeSwap.selector,
+            BeforeSwapDeltaLibrary.ZERO_DELTA,
+            feeWithFlag
+        );
+    }
+
+    function getFee() internal view returns (uint24) {
+        uint128 gasPrice = uint128(tx.gasprice);
+
+        // if gasPrice > movingAverageGasPrice * 1.1 , the half the fees
+        if (gasPrice > (movingAverageGasPrice * 11) / 10) {
+            return BASE_FEE / 2;
+        }
+
+        // if gasPrice < movingAverageGasPrice * 0.9 , then double the fees
+        if (gasPrice < (movingAverageGasPrice * 9) / 10) {
+            return BASE_FEE * 2;
+        }
+
+        return BASE_FEE;
+    }
+
+    // updates moving average gas price
+    function updateMovingAverage() internal {
+        uint128 gasPrice = uint128(tx.gasprice);
+
+        // new average = ((old average * # of transactions Tracked) + Current gas price) / (# of transactions tracked + 1)
+        movingAverageGasPrice =
+            ((movingAverageGasPrice * movingAverageGasPriceCount) + gasPrice) /
+            (movingAverageGasPriceCount + 1);
+        movingAverageGasPriceCount++;
+    }
+}

test/GasPriceHook.t.sol

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+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.0;
+
+import {Test} from "forge-std/Test.sol";
+
+import {BaseHook} from "v4-periphery/src/base/hooks/BaseHook.sol";
+import {ERC1155} from "@openzeppelin/contracts/token/ERC1155/ERC1155.sol";
+import {Hooks} from "v4-core/libraries/Hooks.sol";
+import {LPFeeLibrary} from "v4-core/libraries/LPFeeLibrary.sol";
+import {StateLibrary} from "v4-core/libraries/StateLibrary.sol";
+import {TickMath} from "v4-core/libraries/TickMath.sol";
+
+import {PoolId} from "v4-core/types/PoolId.sol";
+import {IPoolManager} from "v4-core/interfaces/IPoolManager.sol";
+
+import {PoolKey} from "v4-core/types/PoolKey.sol";
+
+import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
+
+import {BalanceDelta} from "v4-core/types/BalanceDelta.sol";
+
+import {Currency} from "v4-core/types/Currency.sol";
+
+import {FixedPointMathLib} from "solmate/src/utils/FixedPointMathLib.sol";
+
+// uniswap-v4 test utils
+import {Deployers} from "@uniswap/v4-core/test/utils/Deployers.sol";
+import {PoolSwapTest} from "v4-core/test/PoolSwapTest.sol";
+import {MockERC20} from "solmate/src/test/utils/mocks/MockERC20.sol";
+
+import {GasPriceHook} from "src/GasPriceHook.sol";
+
+contract GasPriceHooktest is Test, Deployers {
+    using StateLibrary for IPoolManager;
+    using FixedPointMathLib for uint256;
+
+    GasPriceHook hook;
+
+    function setUp() public {
+        // Deploy v4 core contracts
+        deployFreshManagerAndRouters();
+
+        // Deploy two test tokens
+
+        deployMintAndApprove2Currencies();
+
+        // deploy the hook
+        uint160 flags = uint160(
+            Hooks.BEFORE_INITIALIZE_FLAG |
+                Hooks.BEFORE_SWAP_FLAG |
+                Hooks.AFTER_SWAP_FLAG
+        );
+        address hookAddress = address(flags);
+
+        // set gas price = 10 gwei and then deploy
+        vm.txGasPrice(10 gwei);
+
+        deployCodeTo("GasPriceHook", abi.encode(manager, ""), hookAddress);
+
+        // initialize hook
+        hook = GasPriceHook(hookAddress);
+
+        // initialize a pool
+        (key, ) = initPool(
+            currency0,
+            currency1,
+            hook,
+            LPFeeLibrary.DYNAMIC_FEE_FLAG,
+            SQRT_PRICE_1_1
+        );
+
+        // adding liquidity
+        modifyLiquidityRouter.modifyLiquidity(
+            key,
+            IPoolManager.ModifiyLiquidityParams({
+                tickLower: -60,
+                tickUpper: 60,
+                liquidityDelta: 100 ether,
+                salt: bytes32(0)
+            }),
+            ZERO_BYTES
+        );
+    }
+
+    function test_feeUpdatesWithGasPrice() public {
+        // setup swap params
+
+        // 1. swap with gasprice = 10 gwei
+
+        // 2. swap with gas price = 4 gwei
+        vm.txGasPrice(4 gwei);
+
+        // 3. swap with gas price = 12 gwei
+        vm.txGasPrice(12 gwei);
+
+        // assert
+    }
+
+
+}