Add caveat to connector balance checking

contracts/savings/SavingsContract.sol

@@ -42,6 +42,7 @@ contract SavingsContract is
 
     event AutomaticInterestCollectionSwitched(bool automationEnabled);
 
+    // Connector poking
     event PokerUpdated(address poker);
 
     event FractionUpdated(uint256 fraction);
@@ -54,6 +55,7 @@ contract SavingsContract is
     // Rate between 'savings credits' and underlying
     // e.g. 1 credit (1e17) mulTruncate(exchangeRate) = underlying, starts at 10:1
     // exchangeRate increases over time
+    uint256 private constant startingRate = 1e17;
     uint256 public exchangeRate;
 
     // Underlying asset is underlying
@@ -99,7 +101,7 @@ contract SavingsContract is
 
         fraction = 2e17;
         automateInterestCollection = true;
-        exchangeRate = 1e17;
+        exchangeRate = startingRate;
     }
 
     /** @dev Only the savings managaer (pulled from Nexus) can execute this */
@@ -167,8 +169,8 @@ contract SavingsContract is
         external
         returns (uint256 creditsIssued)
     {
-        require(exchangeRate == 1e17, "Can only use this method before streaming begins");
-        return _deposit(_underlying, _beneficiary, true);
+        require(exchangeRate == startingRate, "Can only use this method before streaming begins");
+        return _deposit(_underlying, _beneficiary, false);
     }
 
     /**
@@ -183,7 +185,7 @@ contract SavingsContract is
         external
         returns (uint256 creditsIssued)
     {
-        return _deposit(_underlying, msg.sender, false);
+        return _deposit(_underlying, msg.sender, true);
     }
 
     /**
@@ -199,21 +201,21 @@ contract SavingsContract is
         external
         returns (uint256 creditsIssued)
     {
-        return _deposit(_underlying, _beneficiary, false);
+        return _deposit(_underlying, _beneficiary, true);
     }
 
     /**
      * @dev Internally deposit the _underlying from the sender and credit the beneficiary with new imUSD
      */
-    function _deposit(uint256 _underlying, address _beneficiary, bool _skipCollection)
+    function _deposit(uint256 _underlying, address _beneficiary, bool _collectInterest)
         internal
         returns (uint256 creditsIssued)
     {
         require(_underlying > 0, "Must deposit something");
 
         // Collect recent interest generated by basket and update exchange rate
         IERC20 mAsset = underlying;
-        if(!_skipCollection){
+        if(_collectInterest){
             ISavingsManager(_savingsManager()).collectAndDistributeInterest(address(mAsset));
         }
 
@@ -474,7 +476,7 @@ contract SavingsContract is
 
         // check total collateralisation of credits
         CachedData memory data = _cacheData();
-        // use rawBalance as the liquidity in the connector is not written off
+        // use rawBalance as the remaining liquidity in the connector is now written off
         _refreshExchangeRate(data.rawBalance, data.totalCredits, true);
 
         emit EmergencyUpdate();
@@ -501,24 +503,32 @@ contract SavingsContract is
             // 2. Check and verify new connector balance
             uint256 lastBalance_ = lastBalance;
             uint256 connectorBalance = connector_.checkBalance();
-            // Always expect the collateral in the connector to increase in value
+            //      Always expect the collateral in the connector to increase in value
             require(connectorBalance >= lastBalance_, "Invalid yield");
             if(connectorBalance > 0){
-                // Validate the collection by ensuring that the APY is not ridiculous (forked from SavingsManager)
+                //  Validate the collection by ensuring that the APY is not ridiculous (forked from SavingsManager)
                 _validateCollection(lastBalance_, connectorBalance.sub(lastBalance_), timeSinceLastPoke);
             }
 
             // 3. Level the assets to Fraction (connector) & 100-fraction (raw)
             uint256 realSum = _data.rawBalance.add(connectorBalance);
             uint256 ideal = realSum.mulTruncate(_data.fraction);
+            //     If there is not enough mAsset in the connector, then deposit
             if(ideal > connectorBalance){
                 uint256 deposit = ideal.sub(connectorBalance);
                 underlying.approve(address(connector_), deposit);
                 connector_.deposit(deposit);
-            } else {
-                connector_.withdraw(connectorBalance.sub(ideal));
             }
-            // TODO - check balance here again and update exchange rate accordingly
+            //     Else withdraw, if there is too much mAsset in the connector
+            else if(connectorBalance > ideal) {
+                // If fraction == 0, then withdraw everything
+                if(ideal == 0){
+                    connector_.withdrawAll();
+                } else {
+                    connector_.withdraw(connectorBalance.sub(ideal));
+                }
+            }
+            //     Else ideal == connectorBalance (e.g. 0), do nothing
 
             // 4i. Refresh exchange rate and emit event
             lastBalance = ideal;

contracts/savings/peripheral/Connector_yVault_mUSD.sol

@@ -58,6 +58,12 @@ contract Connector_yVault_mUSD is IConnector {
         IERC20(mUSD).transfer(save, _amt);
     }
 
+    function withdrawAll(uint256 _amt) external onlySave {
+        // getBalanceOf shares
+        // withdraw all
+        // send all to save
+    }
+
     function checkBalance() external view returns (uint256) {
         // TODO - if using meta pool LP token, account for coordinated flash loan scenario
         uint256 sharePrice = IyVault(yVault).getPricePerFullShare();

contracts/savings/peripheral/Connector_yVault_mUSD3Pool.sol

@@ -75,14 +75,20 @@ contract Connector_yVault_mUSD3Pool is IConnector {
         IERC20(mUSD).transfer(save, _amt);
     }
 
+    function withdrawAll(uint256 _amt) external onlySave {
+        // getBalanceOf shares
+        // withdraw all
+        // send all to save
+    }
+
     // Steps:
     //  - Get total mUSD3Pool balance held in yVault
     //    - Get yVault share balance
     //    - Get yVault share to mUSD3Pool ratio
     //  - Get exchange rate between mUSD3Pool LP and mUSD (virtual price?)
     // To consider: if using virtual price, and mUSD is initially traded at a discount,
-    // then depositing 10k mUSD is likely to net a virtual amount of 9.97k or so. Somehow
-    // need to make 
+    // then depositing 10k mUSD is likely to net a virtual amount of 9.97k or so. Can either take
+    // a deficit to begin with, or track the amount of units deposited
     function checkBalance() external view returns (uint256) {
         // TODO - if using meta pool LP token, account for coordinated flash loan scenario
         uint256 sharePrice = IyVault(yVault).getPricePerFullShare();

contracts/savings/peripheral/IConnector.sol

@@ -2,7 +2,31 @@ pragma solidity 0.5.16;
 
 
 interface IConnector {
-  function deposit(uint256) external;
-  function withdraw(uint256) external;
+
+  /**
+   * @notice Deposits the mAsset into the connector
+   * @param _amount Units of mAsset to receive and deposit
+   */
+  function deposit(uint256 _amount) external;
+
+  /**
+   * @notice Withdraws a specific amount of mAsset from the connector
+   * @param _amount Units of mAsset to withdraw
+   */
+  function withdraw(uint256 _amount) external;
+
+  /**
+   * @notice Withdraws all mAsset from the connector
+   */
+  function withdrawAll() external;
+
+  /**
+   * @notice Returns the available balance in the connector. In connections
+   * where there is likely to be an initial dip in value due to conservative
+   * exchange rates (e.g. with Curves `get_virtual_price`), it should return
+   * max(deposited, balance) to avoid temporary negative yield. Any negative yield
+   * should be corrected during a withdrawal or over time.
+   * @return Balance of mAsset in the connector
+   */
   function checkBalance() external view returns (uint256);
 }

test/masset/TestMassetCache.spec.ts

@@ -465,12 +465,12 @@ contract("Masset - Cache", async (accounts) => {
             await massetDetails.mAsset.approve(systemMachine.savingsContract.address, new BN(1), {
                 from: sa.default,
             });
-            await systemMachine.savingsContract.depositSavings(new BN(1), {
+            await systemMachine.savingsContract.methods["depositSavings(uint256)"](new BN(1), {
                 from: sa.default,
             });
             await assertSwap(massetDetails, bAssets[1], bAssets[2], new BN(1), true);
             await massetDetails.mAsset.approve(systemMachine.savingsContract.address, new BN(1));
-            await systemMachine.savingsContract.depositSavings(new BN(1));
+            await systemMachine.savingsContract.methods["depositSavings(uint256)"](new BN(1));
         };
         it("should exec with 0%", async () => {
             await massetDetails.mAsset.setCacheSize(0, {
@@ -707,7 +707,7 @@ contract("Masset - Cache", async (accounts) => {
             await massetDetails.mAsset.approve(systemMachine.savingsContract.address, new BN(1), {
                 from: sa.default,
             });
-            await systemMachine.savingsContract.depositSavings(new BN(1), {
+            await systemMachine.savingsContract.methods["depositSavings(uint256)"](new BN(1), {
                 from: sa.default,
             });
             const compositionAfter = await massetMachine.getBasketComposition(massetDetails);
@@ -722,7 +722,7 @@ contract("Masset - Cache", async (accounts) => {
             await massetDetails.mAsset.approve(systemMachine.savingsContract.address, new BN(1), {
                 from: sa.default,
             });
-            await systemMachine.savingsContract.depositSavings(new BN(1), {
+            await systemMachine.savingsContract.methods["depositSavings(uint256)"](new BN(1), {
                 from: sa.default,
             });
 

test/savings/TestSavingsContract.spec.ts

@@ -53,7 +53,7 @@ contract("SavingsContract", async (accounts) => {
     const TEN_EXACT = new BN(10).mul(fullScale);
     const ONE_EXACT = fullScale;
     const initialMint = new BN(1000000000);
-    const initialExchangeRate = fullScale.divn(10);
+    const initialExchangeRate = simpleToExactAmount(1, 17);
 
     let systemMachine: SystemMachine;
     let massetDetails: MassetDetails;

yarn.lock

@@ -4860,7 +4860,7 @@ inherits@2.0.3:
   resolved "https://registry.yarnpkg.com/inherits/-/inherits-2.0.3.tgz#633c2c83e3da42a502f52466022480f4208261de"
   integrity sha1-Yzwsg+PaQqUC9SRmAiSA9CCCYd4=
 
-ini@^1.3.4, ini@^1.3.5, ini@~1.3.0:
+ini@^1.3.5:
   version "1.3.8"
   resolved "https://registry.yarnpkg.com/ini/-/ini-1.3.8.tgz#a29da425b48806f34767a4efce397269af28432c"
   integrity sha512-JV/yugV2uzW5iMRSiZAyDtQd+nxtUnjeLt0acNdw98kKLrvuRVyB80tsREOE7yvGVgalhZ6RNXCmEHkUKBKxew==