[TOB-SANDCLOCK-6] use Liquity USD/ETH oracle (chainlink + tellor backup)

src/interfaces/liquity/IPriceFeed.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: MIT
+pragma solidity >0.8.10;
+
+interface IPriceFeed {
+    // --- Events ---
+    event LastGoodPriceUpdated(uint256 _lastGoodPrice);
+
+    // --- Function ---
+    function fetchPrice() external returns (uint256);
+
+    function lastGoodPrice() external view returns (uint256);
+}

src/lib/Constants.sol

@@ -64,8 +64,8 @@ library Constants {
     address public constant CHAINLINK_USDC_ETH_PRICE_FEED = 0x986b5E1e1755e3C2440e960477f25201B0a8bbD4;
     // Chainlink pricefeed (stETH -> ETH)
     address public constant CHAINLINK_STETH_ETH_PRICE_FEED = 0x86392dC19c0b719886221c78AB11eb8Cf5c52812;
-    // Chainlink pricefeed (stETH -> USD)
-    address public constant CHAINLINK_LUSD_ETH_PRICE_FEED = 0x60c0b047133f696334a2b7f68af0b49d2F3D4F72;
+    // Liquity pricefeed (USD -> ETH) with Chainlink as primary and Tellor as backup.
+    address public constant LIQUITY_USD_ETH_PRICE_FEED = 0x4c517D4e2C851CA76d7eC94B805269Df0f2201De;
 
     // address of the Balancer vault contract
     address public constant BALANCER_VAULT = 0xBA12222222228d8Ba445958a75a0704d566BF2C8;

src/liquity/scLiquity.sol

@@ -7,7 +7,7 @@ import {FixedPointMathLib} from "solmate/utils/FixedPointMathLib.sol";
 
 import {Constants as C} from "../lib/Constants.sol";
 import {IStabilityPool} from "../interfaces/liquity/IStabilityPool.sol";
-import {IPriceFeed} from "../interfaces/chainlink/IPriceFeed.sol";
+import {IPriceFeed} from "../interfaces/liquity/IPriceFeed.sol";
 import {sc4626} from "../sc4626.sol";
 
 contract scLiquity is sc4626 {
@@ -23,7 +23,7 @@ contract scLiquity is sc4626 {
     uint256 public totalProfit;
 
     IStabilityPool public stabilityPool = IStabilityPool(C.LIQUITY_STABILITY_POOL);
-    IPriceFeed public lusd2eth = IPriceFeed(C.CHAINLINK_LUSD_ETH_PRICE_FEED);
+    IPriceFeed public usd2eth = IPriceFeed(C.LIQUITY_USD_ETH_PRICE_FEED);
     ERC20 public lqty = ERC20(C.LIQUITY_LQTY_TOKEN);
 
     // 0x swap router
@@ -46,8 +46,8 @@ contract scLiquity is sc4626 {
     function totalAssets() public view override returns (uint256 assets) {
         uint256 ethBalance = address(this).balance + stabilityPool.getDepositorETHGain(address(this));
 
-        // add eth balance in lusd terms using chainlink oracle
-        assets = ethBalance.mulWadDown(uint256(lusd2eth.latestAnswer()));
+        // add eth balance in lusd terms using liquity oracle
+        assets = ethBalance.mulWadDown(uint256(usd2eth.lastGoodPrice()));
 
         // add float
         assets += asset.balanceOf(address(this));

test/mocks/liquity/MockPriceFeed.sol

@@ -1,18 +1,22 @@
 // SPDX-License-Identifier: MIT
 pragma solidity >0.8.10;
 
-import {IPriceFeed} from "../../../src/interfaces/chainlink/IPriceFeed.sol";
+import {IPriceFeed} from "../../../src/interfaces/liquity/IPriceFeed.sol";
 
 contract MockPriceFeed is IPriceFeed {
     string public constant NAME = "PriceFeed";
 
-    int256 public lastGoodPrice;
+    uint256 public price;
 
-    function latestAnswer() external view override returns (int256) {
-        return lastGoodPrice;
+    function lastGoodPrice() external view override returns (uint256) {
+        return price;
     }
 
-    function setPrice(uint256 price) external {
-        lastGoodPrice = int256(price);
+    function fetchPrice() external view override returns (uint256) {
+        return price;
+    }
+
+    function setPrice(uint256 _price) external {
+        price = _price;
     }
 }

test/scLiquity.t.sol

@@ -21,7 +21,7 @@ contract MockVault is Vault {
         address _xrouter
     ) Vault(_admin, _keeper, _lusd) {
         stabilityPool = _stabilityPool;
-        lusd2eth = _priceFeed;
+        usd2eth = _priceFeed;
         lqty = _lqty;
         xrouter = _xrouter;
         asset.approve(address(stabilityPool), type(uint256).max);
@@ -37,17 +37,17 @@ contract SandclockLUSDTest is DSTestPlus {
     MockVault vault;
     MockStabilityPool stabilityPool;
     MockLiquityPriceFeed priceFeed;
-    MockPriceFeed lusd2eth;
+    MockPriceFeed usd2eth;
 
     function setUp() public {
         underlying = new MockERC20("Mock LUSD", "LUSD", 18);
         lqty = new MockERC20("Mock LQTY", "LQTY", 18);
         xrouter = new Mock0x();
         priceFeed = new MockLiquityPriceFeed();
         stabilityPool = new MockStabilityPool(address(underlying), address(lqty), address(priceFeed));
-        lusd2eth = new MockPriceFeed();
-        lusd2eth.setPrice(935490589304841);
-        vault = new MockVault(address(this), address(this), underlying, stabilityPool, lusd2eth, lqty, address(xrouter));
+        usd2eth = new MockPriceFeed();
+        usd2eth.setPrice(935490589304841);
+        vault = new MockVault(address(this), address(this), underlying, stabilityPool, usd2eth, lqty, address(xrouter));
         vault.grantRole(vault.KEEPER_ROLE(), address(this));
     }