Add Launch Auction pricing contract

src/L2/LaunchAuctionPriceOracle.sol

@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ~0.8.17;
+
+import {FixedPointMathLib} from "solady/utils/FixedPointMathLib.sol";
+
+import {EDAPrice} from "src/lib/EDAPrice.sol";
+import {StablePriceOracle} from "src/L2/StablePriceOracle.sol";
+
+/// @title Launch Auction Price Oracle
+///
+/// @notice The mechanism by which names are auctioned upon Basenames public launch. The RegistrarController
+///     Passes the `launchTime` in place of expiry for all new names. The half life of this contract is hard-coded
+///     to 1 hour, accomplished by bitshifting the `endValue` and by passing this period into the exponential decay
+///     calculation.
+///
+///     Inspired by the `ExponentialPremiumPriceOracle` implemented by ENS:
+///     https://github.com/ensdomains/ens-contracts/blob/staging/contracts/ethregistrar/ExponentialPremiumPriceOracle.sol
+///
+/// @author Coinbase (https://github.com/base-org/usernames)
+contract LaunchAuctionPriceOracle is StablePriceOracle {
+    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
+    /*                          STORAGE                           */
+    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/
+    /// @notice Starting premium for the dutch auction.
+    uint256 public immutable startPremium;
+
+    /// @notice Ending value of the auction, calculated on construction.
+    uint256 public immutable endValue;
+
+    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
+    /*                          CONSTANTS                         */
+    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/
+
+    /// @notice The half-life of the premium price decay
+    uint256 constant SECONDS_IN_PERIOD = 1 hours;
+
+    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
+    /*                        IMPLEMENTATION                      */
+    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/
+
+    /// @notice Construction of the premium pricing oracle.
+    ///
+    /// @param rentPrices The base prices passed to construction of the StablePriceOracle.
+    /// @param startPremium_ The starting price for the dutch auction, denominated in wei.
+    /// @param totalDays    The total duration (in days) for the dutch auction.
+    constructor(uint256[] memory rentPrices, uint256 startPremium_, uint256 totalDays) StablePriceOracle(rentPrices) {
+        startPremium = startPremium_;
+        endValue = startPremium >> (totalDays * 24); // 1 hour halflife
+    }
+
+    /// @notice The internal method for calculating pricing premium
+    ///
+    /// @dev This method handles three cases:
+    ///     1. The name is not yet expired, premium = 0.
+    ///     2. The name is expired and in the auction window, premium = calculated decayed premium.
+    ///     3. The name is expired and outside of the auction window, premium = 0.
+    ///
+    /// @param expires Timestamp of when the name will expire.
+    ///
+    /// @return Price premium denominated in wei.
+    function _premium(string memory, uint256 expires, uint256) internal view override returns (uint256) {
+        if (expires > block.timestamp) {
+            return 0;
+        }
+        uint256 elapsed = block.timestamp - expires;
+        uint256 premium = decayedPremium(elapsed);
+        if (premium > endValue) {
+            return premium - endValue;
+        }
+        return 0;
+    }
+
+    /// @notice The mechanism for calculating the decayed premium.
+    ///
+    /// @param elapsed Seconds elapsed since the auction started.
+    ///
+    /// @return Dacayed price premium denominated in wei.
+    function decayedPremium(uint256 elapsed) public view returns (uint256) {
+        /// @dev 50% decay per period in wad format
+        uint256 perPeriodDecayPercentWad = FixedPointMathLib.WAD / 2;
+        uint256 premium = EDAPrice.currentPrice(startPremium, elapsed, SECONDS_IN_PERIOD, perPeriodDecayPercentWad);
+        return premium;
+    }
+}