Price feed governable addition

solidity/contracts/external/IMedianizer.sol

@@ -7,4 +7,10 @@ interface IMedianizer {
     /// @dev May revert if caller not whitelisted.
     /// @return Price (USD) with 18 decimal places.
     function read() external view returns (uint256);
+
+    /// @notice Get the current price and check if the price feed is active
+    /// @dev May revert if caller not whitelisted.
+    /// @return Price (USD) with 18 decimal places.
+    /// @return true if price is > 0, else returns false
+    function peek() external view returns (uint256, bool);
 }

solidity/contracts/interfaces/IBTCETHPriceFeed.sol

@@ -1,8 +1,12 @@
 pragma solidity ^0.5.10;
+import "../external/IMedianizer.sol";
 
 interface IBTCETHPriceFeed {
     /// @notice Get the current price of bitcoin in ether.
     /// @dev This does not account for any 'Flippening' event.
     /// @return The price of one satoshi in wei.
     function getPrice() external view returns (uint256);
+
+    /// @notice add a new BTC/ETH meidanizer to the internal btcEthFeeds array
+    function addBtcEthFeed(IMedianizer _btcEthFeed) external;
 }

solidity/contracts/price-feed/BTCETHPriceFeed.sol

@@ -11,27 +11,25 @@ contract BTCETHPriceFeed is Ownable, IBTCETHPriceFeed {
     using SafeMath for uint256;
 
     bool private _initialized = false;
+    address internal tbtcSystemAddress;
 
-    IMedianizer btcPriceFeed;
-    IMedianizer ethPriceFeed;
+    IMedianizer[] private btcEthFeeds;
 
     constructor() public {
     // solium-disable-previous-line no-empty-blocks
     }
 
     /// @notice Initialises the addresses of the BTC/USD and ETH/USD price feeds.
-    /// @param _BTCUSDPriceFeed The BTC/USD price feed address.
-    /// @param _ETHUSDPriceFeed The ETH/USD price feed address.
+    /// @param _BTCETHPriceFeed The BTC/USD price feed address.
     function initialize(
-        address _BTCUSDPriceFeed,
-        address _ETHUSDPriceFeed
+        address _tbtcSystemAddress,
+        IMedianizer _BTCETHPriceFeed
     )
         external onlyOwner
     {
         require(!_initialized, "Already initialized.");
-
-        btcPriceFeed = IMedianizer(_BTCUSDPriceFeed);
-        ethPriceFeed = IMedianizer(_ETHUSDPriceFeed);
+        tbtcSystemAddress = _tbtcSystemAddress;
+        btcEthFeeds.push(_BTCETHPriceFeed);
         _initialized = true;
     }
 
@@ -41,17 +39,49 @@ contract BTCETHPriceFeed is Ownable, IBTCETHPriceFeed {
     function getPrice()
         external view returns (uint256)
     {
+        bool btcEthActive;
+        uint256 btcEth;
+
+        for(uint i = 0; i < btcEthFeeds.length; i++){
+            (btcEth, btcEthActive) = btcEthFeeds[i].peek();
+            if(btcEthActive) {
+                break;
+            }
+        }
+
+        require(btcEthActive, "Price feed offline");
+
         // We typecast down to uint128, because the first 128 bits of
         // the medianizer oracle value is unrelated to the price.
-        uint256 btcUsd = uint256(uint128(btcPriceFeed.read()));
-        uint256 ethUsd = uint256(uint128(ethPriceFeed.read()));
-        // The price is a ratio of bitcoin to ether is expressed as:
-        //  x btc : y eth
-        // Bitcoin has 10 decimal places, ether has 18. Normalising the units, we have:
-        //  x * 10^8 : y * 10^18
-        // Simplfying down, we can express it as:
-        //  x : y * 10^10
-        // Due to order-of-ops, we can move the multiplication to get some more precision.
-        return btcUsd.mul(10**10).div(ethUsd);
+        return uint256(uint128(btcEth));
+    }
+
+    /// @notice Get the first active Medianizer contract from the btcEthFeeds array.
+    /// @return The address of the first Active Medianizer. address(0) if none found
+    function getWorkingBtcEthFeed() external view returns (address){
+        bool btcEthActive;
+
+        for(uint i = 0; i < btcEthFeeds.length; i++){
+            (, btcEthActive) = btcEthFeeds[i].peek();
+            if(btcEthActive) {
+                return address(btcEthFeeds[i]);
+            }
+        }
+        return address(0);
+    }
+
+    /// @notice Add _btcEthFeed to internal btcEthFeeds array.
+    /// @dev IMedianizer must be active in order to add.
+    function addBtcEthFeed(IMedianizer _btcEthFeed) external onlyTbtcSystem {
+        bool btcEthActive;
+        (, btcEthActive) = _btcEthFeed.peek();
+        require(btcEthActive, "Cannot add inactive feed");
+        btcEthFeeds.push(_btcEthFeed);
+    }
+
+    /// @notice Function modifier ensures modified function is only called by tbtcSystemAddress.
+    modifier onlyTbtcSystem(){
+        require(msg.sender == tbtcSystemAddress, "Caller must be tbtcSystem contract");
+        _;
     }
 }

solidity/contracts/price-feed/MockMedianizer.sol

@@ -16,15 +16,15 @@ contract MockMedianizer is Ownable, IMedianizer {
         return value;
     }
 
+    function peek() external view returns (uint256, bool) {
+        return (value, value > 0);
+    }
+
     function setValue(uint256 _value) external onlyOwner{
         value = _value;
     }
 }
 
-contract BTCUSDPriceFeed is MockMedianizer {
-    // solium-disable-previous-line no-empty-blocks
-}
-
-contract ETHUSDPriceFeed is MockMedianizer {
+contract BTCETHPriceFeedMock is MockMedianizer {
     // solium-disable-previous-line no-empty-blocks
 }

solidity/contracts/system/TBTCSystem.sol

@@ -8,6 +8,7 @@ import {VendingMachine} from "./VendingMachine.sol";
 import {DepositFactory} from "../proxy/DepositFactory.sol";
 
 import {IRelay} from "@summa-tx/relay-sol/contracts/Relay.sol";
+import "../external/IMedianizer.sol";
 
 import {ITBTCSystem} from "../interfaces/ITBTCSystem.sol";
 import {IBTCETHPriceFeed} from "../interfaces/IBTCETHPriceFeed.sol";
@@ -27,6 +28,7 @@ contract TBTCSystem is Ownable, ITBTCSystem, DepositLog {
 
     using SafeMath for uint256;
 
+    event BtcEthPriceFeedAdditionStarted(address _priceFeed, uint256 _timestamp);
     event LotSizesUpdateStarted(uint64[] _lotSizes, uint256 _timestamp);
     event SignerFeeDivisorUpdateStarted(uint16 _signerFeeDivisor, uint256 _timestamp);
     event CollateralizationThresholdsUpdateStarted(
@@ -36,6 +38,7 @@ contract TBTCSystem is Ownable, ITBTCSystem, DepositLog {
         uint256 _timestamp
     );
 
+    event BtcEthPriceFeedAdded(address _priceFeed);
     event LotSizesUpdated(uint64[] _lotSizes);
     event AllowNewDepositsUpdated(bool _allowNewDeposits);
     event SignerFeeDivisorUpdated(uint16 _signerFeeDivisor);
@@ -45,6 +48,7 @@ contract TBTCSystem is Ownable, ITBTCSystem, DepositLog {
         uint16 _severelyUndercollateralizedThresholdPercent
     );
 
+
     bool _initialized = false;
     uint256 pausedTimestamp;
     uint256 constant pausedDuration = 10 days;
@@ -73,6 +77,11 @@ contract TBTCSystem is Ownable, ITBTCSystem, DepositLog {
     uint16 private newUndercollateralizedThresholdPercent;
     uint16 private newSeverelyUndercollateralizedThresholdPercent;
 
+    // price feed
+    uint256 priceFeedGovernanceTimeDelay = 90 days;
+    uint256 appendBtcEthFeedTimer;
+    IMedianizer nextBtcEthFeed;
+
     constructor(address _priceFeed, address _relay) public {
         priceFeed = IBTCETHPriceFeed(_priceFeed);
         relay = IRelay(_relay);
@@ -351,6 +360,10 @@ contract TBTCSystem is Ownable, ITBTCSystem, DepositLog {
         return governanceTimeDelay;
     }
 
+    function getPriceFeedGovernanceTimeDelay() public view returns (uint256) {
+        return priceFeedGovernanceTimeDelay;
+    }
+
     // Price Feed
 
     /// @notice Get the price of one satoshi in wei.
@@ -369,6 +382,23 @@ contract TBTCSystem is Ownable, ITBTCSystem, DepositLog {
         return price;
     }
 
+    /// @notice Initialize the addition of a new BTC/ETH price feed contract to the priecFeed.
+    /// @dev `FinalizeAddBtcEthFeed` must be called to finalize.
+    function initializeAddBtcEthFeed(IMedianizer _btcEthFeed) external {
+        nextBtcEthFeed = _btcEthFeed;
+        appendBtcEthFeedTimer = block.timestamp + priceFeedGovernanceTimeDelay;
+        emit BtcEthPriceFeedAdditionStarted(address(_btcEthFeed), block.timestamp);
+    }
+
+    /// @notice Finish adding a new price feed contract to the priceFeed.
+    /// @dev `InitializeAddBtcEthFeed` must be called first, once `appendBtcEthFeedTimer`
+    ///       has passed, this function can be called to append a new price feed.
+    function finalizeAddBtcEthFeed() external {
+        require(block.timestamp > appendBtcEthFeedTimer, "Timeout not yet elapsed");
+        priceFeed.addBtcEthFeed(nextBtcEthFeed);
+        emit BtcEthPriceFeedAdded(address(nextBtcEthFeed));
+    }
+
     // Difficulty Oracle
     // TODO: This is a workaround. It will be replaced by tbtc-difficulty-oracle.
     function fetchRelayCurrentDifficulty() external view returns (uint256) {

solidity/contracts/test/price-feed/MockMedianizer.sol

@@ -6,7 +6,7 @@ import "../../../contracts/external/IMedianizer.sol";
 /// @notice A mock implementation of a medianizer price oracle
 /// @dev This is used in the Keep testnets only. Mainnet uses the MakerDAO medianizer.
 contract MockMedianizer is Ownable, IMedianizer {
-    uint256 private value;
+    uint128 private value;
 
     constructor() public {
     // solium-disable-previous-line no-empty-blocks
@@ -16,7 +16,11 @@ contract MockMedianizer is Ownable, IMedianizer {
         return value;
     }
 
-    function setValue(uint256 _value) external onlyOwner {
+    function peek() external view returns (uint256, bool) {
+        return (value, value > 0);
+    }
+
+    function setValue(uint128 _value) external onlyOwner {
         value = _value;
     }
 }

solidity/migrations/2_deploy_contracts.js

@@ -18,9 +18,7 @@ const Deposit = artifacts.require("Deposit")
 const VendingMachine = artifacts.require("VendingMachine")
 
 // price feed
-const BTCETHPriceFeed = artifacts.require("BTCETHPriceFeed")
-const BTCUSDPriceFeed = artifacts.require("BTCUSDPriceFeed")
-const ETHUSDPriceFeed = artifacts.require("ETHUSDPriceFeed")
+const MockBTCETHPriceFeed = artifacts.require("BTCETHPriceFeedMock")
 const prices = require("./prices")
 
 const MockRelay = artifacts.require("MockRelay")
@@ -83,18 +81,13 @@ module.exports = (deployer, network, accounts) => {
     let difficultyRelay
     // price feeds
     if (network !== "mainnet") {
-      // On mainnet, we use the MakerDAO-deployed price feeds.
+      // On mainnet, we use the MakerDAO-deployed price feed.
       // See: https://github.com/makerdao/oracles-v2#live-mainnet-oracles
       // Otherwise, we deploy our own mock price feeds, which are simpler
       // to maintain.
-      await deployer.deploy(BTCUSDPriceFeed)
-      await deployer.deploy(ETHUSDPriceFeed)
-
-      const btcPriceFeed = await BTCUSDPriceFeed.deployed()
-      const ethPriceFeed = await ETHUSDPriceFeed.deployed()
-
-      await btcPriceFeed.setValue(web3.utils.toWei(prices.BTCUSD))
-      await ethPriceFeed.setValue(web3.utils.toWei(prices.ETHUSD))
+      await deployer.deploy(MockBTCETHPriceFeed)
+      const btcEthPriceFeed = await MockBTCETHPriceFeed.deployed()
+      await btcEthPriceFeed.setValue(prices.BTCETH)
 
       // On mainnet, we use the Summa-provided relay; see
       // https://github.com/summa-tx/relays . On testnet, we use a local mock.

solidity/migrations/3_initialize.js

@@ -1,8 +1,7 @@
 const TBTCSystem = artifacts.require("TBTCSystem")
 
 const BTCETHPriceFeed = artifacts.require("BTCETHPriceFeed")
-const MockBTCUSDPriceFeed = artifacts.require("BTCUSDPriceFeed")
-const MockETHUSDPriceFeed = artifacts.require("ETHUSDPriceFeed")
+const MockBTCETHPriceFeed = artifacts.require("BTCETHPriceFeedMock")
 
 const DepositFactory = artifacts.require("DepositFactory")
 const Deposit = artifacts.require("Deposit")
@@ -11,11 +10,7 @@ const TBTCDepositToken = artifacts.require("TBTCDepositToken")
 const FeeRebateToken = artifacts.require("FeeRebateToken")
 const VendingMachine = artifacts.require("VendingMachine")
 
-const {
-  BondedECDSAKeepVendorAddress,
-  BTCUSDPriceFeed,
-  ETHUSDPriceFeed,
-} = require("./externals")
+const {BondedECDSAKeepVendorAddress, BTCETHMedianizer} = require("./externals")
 
 module.exports = async function(deployer, network) {
   // Don't enact this setup during unit testing.
@@ -57,14 +52,13 @@ module.exports = async function(deployer, network) {
   const btcEthPriceFeed = await BTCETHPriceFeed.deployed()
   if (network === "mainnet") {
     // Inject mainnet price feeds.
-    await btcEthPriceFeed.initialize(BTCUSDPriceFeed, ETHUSDPriceFeed)
+    await btcEthPriceFeed.initialize(tbtcSystem.address, BTCETHMedianizer)
   } else {
     // Inject mock price feeds.
-    const mockBtcPriceFeed = await MockBTCUSDPriceFeed.deployed()
-    const mockEthPriceFeed = await MockETHUSDPriceFeed.deployed()
+    const mockBtcEthPriceFeed = await MockBTCETHPriceFeed.deployed()
     await btcEthPriceFeed.initialize(
-      mockBtcPriceFeed.address,
-      mockEthPriceFeed.address,
+      tbtcSystem.address,
+      mockBtcEthPriceFeed.address,
     )
   }
 }

solidity/migrations/externals.js

@@ -5,11 +5,9 @@ const BondedECDSAKeepVendorAddress = "0xZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
 // Medianized price feeds.
 // These are deployed and maintained by Maker.
 // See: https://github.com/makerdao/oracles-v2#live-mainnet-oracles
-const BTCUSDPriceFeed = "0xe0F30cb149fAADC7247E953746Be9BbBB6B5751f"
-const ETHUSDPriceFeed = "0x64de91f5a373cd4c28de3600cb34c7c6ce410c85"
+const BTCETHMedianizer = "0xABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE"
 
 module.exports = {
   BondedECDSAKeepVendorAddress,
-  BTCUSDPriceFeed,
-  ETHUSDPriceFeed,
+  BTCETHMedianizer,
 }

solidity/migrations/prices.json

@@ -1,4 +1,3 @@
 {
-    "BTCUSD": "7152.55",
-    "ETHUSD": "142.28"
+    "BTCETH": "502709446162"
 }