Feat: Dromos escrow

src/escrows/DromosEscrow.sol

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+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.20;
+
+import {IERC20} from "openzeppelin-contracts/contracts/token/ERC20/IERC20.sol";
+import {SafeERC20} from "openzeppelin-contracts/contracts/token/ERC20/utils/SafeERC20.sol";
+
+/// @dev Interface reference: Aerodrome vAMM-WETH/USDC Pool Gauge on Base.
+/// https://basescan.org/address/0x519BBD1Dd8C6A94C46080E24f316c14Ee758C025#code
+interface IDromosGauge {
+    function stakingToken() external view returns (address);
+    function rewardToken() external view returns (address);
+    function balanceOf(address account) external view returns (uint256);
+    function deposit(uint256 amount) external;
+    function withdraw(uint256 amount) external;
+    function getReward(address account) external;
+}
+
+/**
+ * @title Dromos Escrow
+ * @notice Stakes a borrower's Solidly-like LP collateral in a Dromos-compatible gauge.
+ * @dev This contract is used as a proxy implementation. Each implementation supports one immutable gauge.
+ */
+contract DromosEscrow {
+    using SafeERC20 for IERC20;
+
+    error AlreadyInitialized();
+    error InvalidGauge();
+    error InvalidReceiver();
+    error OnlyBeneficiary();
+    error OnlyBeneficiaryOrAllowlist();
+    error OnlyMarket();
+    error UnsafeRewardToken();
+    error WrongCollateral();
+
+    IDromosGauge public immutable gauge;
+    IERC20 public immutable token;
+    IERC20 public immutable rewardToken;
+
+    address public market;
+    address public beneficiary;
+
+    mapping(address claimer => bool isAllowed) public allowlist;
+
+    event Claim(address indexed caller, address indexed receiver, uint256 amount);
+    event SetClaimer(address indexed claimer, bool isAllowed);
+
+    modifier onlyBeneficiary() {
+        if (msg.sender != beneficiary) revert OnlyBeneficiary();
+        _;
+    }
+
+    modifier onlyBeneficiaryOrAllowlist() {
+        if (msg.sender != beneficiary && !allowlist[msg.sender]) {
+            revert OnlyBeneficiaryOrAllowlist();
+        }
+        _;
+    }
+
+    constructor(address _gauge) {
+        if (_gauge.code.length == 0) revert InvalidGauge();
+
+        gauge = IDromosGauge(_gauge);
+
+        address _token = gauge.stakingToken();
+        address _rewardToken = gauge.rewardToken();
+        if (_token == address(0) || _rewardToken == address(0)) {
+            revert InvalidGauge();
+        }
+        if (_token == _rewardToken) revert UnsafeRewardToken();
+
+        token = IERC20(_token);
+        rewardToken = IERC20(_rewardToken);
+    }
+
+    /**
+     * @notice Initializes an escrow clone.
+     * @param _token The market's collateral token.
+     * @param _beneficiary The borrower entitled to the gauge emissions.
+     */
+    function initialize(IERC20 _token, address _beneficiary) external {
+        if (market != address(0)) revert AlreadyInitialized();
+        if (address(_token) != address(token)) revert WrongCollateral();
+
+        market = msg.sender;
+        beneficiary = _beneficiary;
+
+        token.forceApprove(address(gauge), type(uint256).max);
+    }
+
+    /**
+     * @notice Transfers collateral to a recipient, unstaking only the amount required.
+     * @dev Only the market may call this function. Gauge emissions are not claimed.
+     */
+    function pay(address recipient, uint256 amount) external {
+        if (msg.sender != market) revert OnlyMarket();
+
+        uint256 tokenBalance = token.balanceOf(address(this));
+        if (tokenBalance < amount) {
+            gauge.withdraw(amount - tokenBalance);
+        }
+
+        token.safeTransfer(recipient, amount);
+    }
+
+    /**
+     * @notice Returns the escrow's total unstaked and gauge-staked collateral.
+     */
+    function balance() external view returns (uint256) {
+        return token.balanceOf(address(this)) + gauge.balanceOf(address(this));
+    }
+
+    /**
+     * @notice Stakes all collateral currently held by the escrow.
+     * @dev Permissionless so direct collateral transfers can subsequently be staked.
+     */
+    function onDeposit() external {
+        uint256 tokenBalance = token.balanceOf(address(this));
+        if (tokenBalance == 0) return;
+
+        gauge.deposit(tokenBalance);
+    }
+
+    /**
+     * @notice Claims gauge emissions to the beneficiary.
+     */
+    function claim() external onlyBeneficiary {
+        _claim(beneficiary);
+    }
+
+    /**
+     * @notice Claims gauge emissions to a specified receiver.
+     * @dev Callable by the beneficiary or an allowlisted claimer.
+     */
+    function claimTo(address receiver) external onlyBeneficiaryOrAllowlist {
+        _claim(receiver);
+    }
+
+    /**
+     * @notice Allows or disallows an address to claim emissions on the beneficiary's behalf.
+     */
+    function setClaimer(address claimer, bool isAllowed) external onlyBeneficiary {
+        allowlist[claimer] = isAllowed;
+        emit SetClaimer(claimer, isAllowed);
+    }
+
+    function _claim(address receiver) internal {
+        if (receiver == address(0) || receiver == address(this)) {
+            revert InvalidReceiver();
+        }
+
+        gauge.getReward(address(this));
+
+        uint256 amount = rewardToken.balanceOf(address(this));
+        if (amount != 0) rewardToken.safeTransfer(receiver, amount);
+
+        emit Claim(msg.sender, receiver, amount);
+    }
+}