feat: add LibCollateralOracle skeleton

To be used by LibUbiquityPool to fetch collateral token prices

packages/contracts/src/dollar/interfaces/AggregatorV3Interface.sol

@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: MIT
+// ChainLink price feed interface
+// @dev Original implementation https://github.com/smartcontractkit/chainlink/blob/master/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol
+
+pragma solidity 0.8.19;
+
+interface AggregatorV3Interface {
+    function decimals() external view returns (uint8);
+
+    function description() external view returns (string memory);
+
+    function version() external view returns (uint256);
+
+    function getRoundData(
+        uint80 _roundId
+    )
+        external
+        view
+        returns (
+            uint80 roundId,
+            int256 answer,
+            uint256 startedAt,
+            uint256 updatedAt,
+            uint80 answeredInRound
+        );
+
+    function latestRoundData()
+        external
+        view
+        returns (
+            uint80 roundId,
+            int256 answer,
+            uint256 startedAt,
+            uint256 updatedAt,
+            uint80 answeredInRound
+        );
+}

packages/contracts/src/dollar/interfaces/ICollateralOracle.sol

@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.19;
+
+/**
+ * @notice Collateral Oracle interface
+ * @notice Returns price quotes for all registered collaterals
+ */
+
+interface ICollateralOracle {
+    /**
+     * @notice Updates the following state variables for each of the collaterals to the latest values
+     * - collateral token / 3CRV LP quote
+     * - cumulative prices
+     * - update timestamp
+     */
+    function update() external;
+
+    /**
+     * @notice Returns the quote for the provided `token` address
+     * @param token Token address
+     * @return amountOut Token price
+     */
+    function consult(address token) external view returns (uint256 amountOut);
+}

packages/contracts/src/dollar/libraries/LibCollateralOracle.sol

@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.19;
+
+import {IMetaPool} from "../../dollar/interfaces/IMetaPool.sol";
+import {AggregatorV3Interface} from "../../dollar/interfaces/AggregatorV3Interface.sol";
+import {LibAppStorage} from "./LibAppStorage.sol";
+
+/**
+ * @notice Library used for Collateral price oracles
+ * @dev Initially supports ChainLink price feeds
+ * @dev This library may combine in the future different price feeds and Curve Metapool TWAPs
+ * @dev List of available collateral tokens and their price is stored in LibUbiquityPool
+ */
+library LibCollateralOracle {
+    /// @notice Struct used as a storage for this library
+    struct CollateralOracleStorage {
+        mapping(address => AggregatorV3Interface) priceFeeds;
+    }
+
+    /// @notice Emitted when collateral token price was updated
+    event CollateralPriceUpdated(address token, uint256 price);
+
+    /// @notice Storage slot used to store data for this library
+    bytes32 constant COLLATERAL_ORACLE_STORAGE_POSITION =
+        bytes32(
+            uint256(keccak256("diamond.standard.collateral.oracle.storage")) - 1
+        );
+
+    /**
+     * @notice Returns struct used as a storage for this library
+     * @return ds Struct used as a storage
+     */
+    function collateralOracleStorage()
+        internal
+        pure
+        returns (collateralOracleStorage storage ds)
+    {
+        bytes32 position = COLLATERAL_ORACLE_STORAGE_POSITION;
+        assembly {
+            ds.slot := position
+        }
+    }
+
+    /**
+     * @notice Updates all registered collateral prices from ChainLink
+     */
+    function update() internal {}
+
+    /**
+     * @notice Returns the quote for the provided `token` address
+     * @param token Token address
+     * @return amountOut Token price vs 3CRV LP
+     */
+    function consult(address token) internal view returns (uint256) {}
+}

packages/contracts/src/dollar/libraries/LibUbiquityPool.sol

@@ -10,6 +10,7 @@ import {IERC20Ubiquity} from "../interfaces/IERC20Ubiquity.sol";
 import {UBIQUITY_POOL_PRICE_PRECISION} from "./Constants.sol";
 import {LibAppStorage} from "./LibAppStorage.sol";
 import {LibTWAPOracle} from "./LibTWAPOracle.sol";
+import {LibCollateralOracle} from "./LibCollateralOracle.sol";
 
 /**
  * @notice Ubiquity pool library