feat: add support for contract calls through intent (#25)

* change contract logic

* add test

* format

* skip gas payment when target is zetachain

* add intent proxy deployment script

* fmt

* use transfer instead of approve

* remove try initiate

* add call support

* fix tests

* add example contract

* fmt

* fix file

* add initiateTransfer

* add fulfillTransfer

* add intent call tests

* support ciustom gas limit

* a few fix

* fix imports

* remove nonReentrant

* increase default gas limit

Author: lumtis

examples/CrossChainSwapper.sol

@@ -0,0 +1,168 @@
+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.26;
+
+import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
+import "@openzeppelin/contracts/access/Ownable.sol";
+import "../src/interfaces/IntentTarget.sol";
+
+// Uniswap V2 Router interface (partial)
+interface IUniswapV2Router {
+    function swapExactTokensForTokens(
+        uint256 amountIn,
+        uint256 amountOutMin,
+        address[] calldata path,
+        address to,
+        uint256 deadline
+    ) external returns (uint256[] memory amounts);
+}
+
+/**
+ * @title CrossChainSwapper
+ * @dev Example implementation of IntentTarget that performs token swaps
+ */
+contract CrossChainSwapper is IntentTarget, Ownable {
+    // Uniswap V2 Router address
+    address public uniswapRouter;
+
+    // Reward configuration
+    uint256 public rewardPercentage = 5; // 5% reward to fulfillers
+
+    /**
+     * @dev Constructor
+     * @param _uniswapRouter The Uniswap V2 Router address
+     */
+    constructor(address _uniswapRouter) Ownable(msg.sender) {
+        uniswapRouter = _uniswapRouter;
+    }
+
+    /**
+     * @dev Update the Uniswap router address
+     * @param _uniswapRouter The new router address
+     */
+    function setUniswapRouter(address _uniswapRouter) external onlyOwner {
+        uniswapRouter = _uniswapRouter;
+    }
+
+    /**
+     * @dev Set reward percentage for fulfillers
+     * @param _percentage New percentage (0-100)
+     */
+    function setRewardPercentage(uint256 _percentage) external onlyOwner {
+        require(_percentage <= 100, "Percentage must be between 0-100");
+        rewardPercentage = _percentage;
+    }
+
+    /**
+     * @dev Called by the protocol during intent fulfillment
+     * @param intentId The ID of the intent
+     * @param asset The ERC20 token address
+     * @param amount Amount transferred
+     * @param data Custom data for execution
+     */
+    function onFulfill(
+        bytes32 intentId,
+        address asset,
+        uint256 amount,
+        bytes calldata data
+    ) external override {
+        // Decode the swap parameters from the data field
+        (
+            address[] memory path,
+            uint256 minAmountOut,
+            uint256 deadline,
+            address receiver
+        ) = decodeSwapParams(data);
+
+        // Ensure the first token in the path matches the received asset
+        require(path[0] == asset, "Asset mismatch");
+
+        // Approve router to spend the tokens
+        IERC20(asset).approve(uniswapRouter, amount);
+
+        // Execute the swap on Uniswap
+        IUniswapV2Router(uniswapRouter).swapExactTokensForTokens(
+            amount,
+            minAmountOut,
+            path,
+            receiver,
+            deadline
+        );
+    }
+
+    /**
+     * @dev Called by the protocol during intent settlement
+     * @param intentId The ID of the intent
+     * @param asset The ERC20 token address
+     * @param amount Amount transferred
+     * @param data Custom data for execution
+     * @param fulfillmentIndex The fulfillment index for this intent
+     */
+    function onSettle(
+        bytes32 intentId,
+        address asset,
+        uint256 amount,
+        bytes calldata data,
+        bytes32 fulfillmentIndex
+    ) external override {
+        // This function is called when an intent is settled
+        // We can implement custom logic here, such as rewarding the fulfiller
+
+        // We could send a small reward to the fulfiller from this contract's balance
+        // This might be tokens previously sent to this contract for this purpose
+
+        // Example: get receiver address from the data
+        (, , , address receiver) = decodeSwapParams(data);
+
+        // Example: transfer a small reward from this contract to the fulfiller
+        // This assumes this contract holds some tokens for rewards
+        // In a real implementation, you might have a more sophisticated reward system
+
+        // Get fulfiller address from the Intent contract (passed as msg.sender)
+        address intentContract = msg.sender;
+
+        // Note: In a real implementation, you would have a way to get the fulfiller address
+        // For this example, we're just showing the concept
+        // Normally, you could call a view function on the Intent contract to get the fulfiller
+    }
+
+    /**
+     * @dev Helper function to decode swap parameters from the bytes data
+     * @param data The encoded swap parameters
+     * @return path Array of token addresses for the swap path
+     * @return minAmountOut Minimum output amount
+     * @return deadline Transaction deadline
+     * @return receiver Address that will receive the swapped tokens
+     */
+    function decodeSwapParams(
+        bytes memory data
+    )
+        internal
+        pure
+        returns (
+            address[] memory path,
+            uint256 minAmountOut,
+            uint256 deadline,
+            address receiver
+        )
+    {
+        // Decode the packed data
+        return abi.decode(data, (address[], uint256, uint256, address));
+    }
+
+    /**
+     * @dev Helper function to encode swap parameters
+     * @param path Array of token addresses for the swap path
+     * @param minAmountOut Minimum output amount
+     * @param deadline Transaction deadline
+     * @param receiver Address that will receive the swapped tokens
+     * @return The encoded parameters as bytes
+     */
+    function encodeSwapParams(
+        address[] memory path,
+        uint256 minAmountOut,
+        uint256 deadline,
+        address receiver
+    ) public pure returns (bytes memory) {
+        return abi.encode(path, minAmountOut, deadline, receiver);
+    }
+}