Apply and mint interest

contracts/src/ActivePool.sol

@@ -4,12 +4,15 @@ pragma solidity 0.8.18;
 
 import "openzeppelin-contracts/contracts/token/ERC20/utils/SafeERC20.sol";
 
+import './Interfaces/IActivePool.sol';
+import './Interfaces/IBoldToken.sol';
+import "./Interfaces/IInterestRouter.sol";
 import "./Dependencies/Ownable.sol";
 import "./Dependencies/CheckContract.sol";
 import './Interfaces/IDefaultPool.sol';
 import './Interfaces/IActivePool.sol';
 
-// import "forge-std/console.sol";
+//import "forge-std/console2.sol";
 
 /*
  * The Active Pool holds the ETH collateral and Bold debt (but not Bold tokens) for all active troves.
@@ -28,8 +31,31 @@ contract ActivePool is Ownable, CheckContract, IActivePool {
     address public troveManagerAddress;
     address public stabilityPoolAddress;
     address public defaultPoolAddress;
+
+    IBoldToken boldToken;
+
+    IInterestRouter public interestRouter;
+
+    uint256 constant public SECONDS_IN_ONE_YEAR = 31536000; // 60 * 60 * 24 * 365,
+
     uint256 internal ETHBalance;  // deposited ether tracker
-    uint256 internal boldDebt;
+
+    // Sum of individual recorded Trove debts. Updated only at individual Trove operations.
+    // "G" in the spec.
+    uint256 internal recordedDebtSum;
+
+    // Aggregate recorded debt tracker. Updated whenever a Trove's debt is touched AND whenever the aggregate pending interest is minted.
+    // "D" in the spec.
+    uint256 public aggRecordedDebt;
+
+    /* Sum of individual recorded Trove debts weighted by their respective chosen interest rates.
+    * Updated at individual Trove operations.
+    * "S" in the spec.
+    */
+    uint256 public aggWeightedDebtSum;
+
+    // Last time at which the aggregate recorded debt and weighted sum were updated
+    uint256 public lastAggUpdateTime;
 
     // --- Events ---
 
@@ -38,21 +64,24 @@ contract ActivePool is Ownable, CheckContract, IActivePool {
     event EtherSent(address _to, uint _amount);
     event BorrowerOperationsAddressChanged(address _newBorrowerOperationsAddress);
     event TroveManagerAddressChanged(address _newTroveManagerAddress);
-    event ActivePoolBoldDebtUpdated(uint _boldDebt);
+    event ActivePoolBoldDebtUpdated(uint _recordedDebtSum);
     event ActivePoolETHBalanceUpdated(uint _ETHBalance);
 
     constructor(address _ETHAddress) {
         checkContract(_ETHAddress);
         ETH = IERC20(_ETHAddress);
     }
 
+
     // --- Contract setters ---
 
     function setAddresses(
         address _borrowerOperationsAddress,
         address _troveManagerAddress,
         address _stabilityPoolAddress,
-        address _defaultPoolAddress
+        address _defaultPoolAddress,
+        address _boldTokenAddress,
+        address _interestRouterAddress
     )
         external
         onlyOwner
@@ -61,11 +90,15 @@ contract ActivePool is Ownable, CheckContract, IActivePool {
         checkContract(_troveManagerAddress);
         checkContract(_stabilityPoolAddress);
         checkContract(_defaultPoolAddress);
+        checkContract(_boldTokenAddress);
+        checkContract(_interestRouterAddress);
 
         borrowerOperationsAddress = _borrowerOperationsAddress;
         troveManagerAddress = _troveManagerAddress;
         stabilityPoolAddress = _stabilityPoolAddress;
         defaultPoolAddress = _defaultPoolAddress;
+        boldToken = IBoldToken(_boldTokenAddress);
+        interestRouter = IInterestRouter(_interestRouterAddress);
 
         emit BorrowerOperationsAddressChanged(_borrowerOperationsAddress);
         emit TroveManagerAddressChanged(_troveManagerAddress);
@@ -89,8 +122,17 @@ contract ActivePool is Ownable, CheckContract, IActivePool {
         return ETHBalance;
     }
 
-    function getBoldDebt() external view override returns (uint) {
-        return boldDebt;
+    function getRecordedDebtSum() external view override returns (uint) {
+        return recordedDebtSum;
+    }
+
+    function calcPendingAggInterest() public view returns (uint256) {
+        return aggWeightedDebtSum * (block.timestamp - lastAggUpdateTime) / SECONDS_IN_ONE_YEAR / 1e18;
+    }
+
+    // Returns sum of agg.recorded debt plus agg. pending interest. Excludes pending redist. gains.
+    function getTotalActiveDebt() public view returns (uint256) {
+        return aggRecordedDebt + calcPendingAggInterest();
     }
 
     // --- Pool functionality ---
@@ -131,16 +173,54 @@ contract ActivePool is Ownable, CheckContract, IActivePool {
         emit ActivePoolETHBalanceUpdated(newETHBalance);
     }
 
-    function increaseBoldDebt(uint _amount) external override {
+    function increaseRecordedDebtSum(uint _amount) external override {
+        _requireCallerIsBOorTroveM();
+        uint256 newRecordedDebtSum = recordedDebtSum + _amount;
+        recordedDebtSum  = newRecordedDebtSum;
+        emit ActivePoolBoldDebtUpdated(newRecordedDebtSum);
+    }
+
+    function decreaseRecordedDebtSum(uint _amount) external override {
+        _requireCallerIsBOorTroveMorSP();
+        uint256 newRecordedDebtSum = recordedDebtSum - _amount;
+
+        recordedDebtSum = newRecordedDebtSum;
+
+        emit ActivePoolBoldDebtUpdated(newRecordedDebtSum);
+    }
+
+    function changeAggWeightedDebtSum(uint256 _oldWeightedRecordedTroveDebt, uint256 _newTroveWeightedRecordedTroveDebt) external {
         _requireCallerIsBOorTroveM();
-        boldDebt  = boldDebt + _amount;
-        emit ActivePoolBoldDebtUpdated(boldDebt);
+        // Do the arithmetic in 2 steps here to avoid overflow from the decrease
+        uint256 newAggWeightedDebtSum = aggWeightedDebtSum + _newTroveWeightedRecordedTroveDebt; // 1 SLOAD
+        newAggWeightedDebtSum -= _oldWeightedRecordedTroveDebt;
+        aggWeightedDebtSum = newAggWeightedDebtSum; // 1 SSTORE
     }
 
-    function decreaseBoldDebt(uint _amount) external override {
+    // --- Aggregate interest operations ---
+
+    // This function is called inside all state-changing user ops: borrower ops, liquidations, redemptions and SP deposits/withdrawals.
+    // Some user ops trigger debt changes to Trove(s), in which case _troveDebtChange will be non-zero.
+    // The aggregate recorded debt is incremented by the aggregate pending interest, plus the net Trove debt change.
+    // The net Trove debt change consists of the sum of a) any debt issued/repaid and b) any redistribution debt gain applied in the encapsulating operation.
+    // It does *not* include the Trove's individual accrued interest - this gets accounted for in the aggregate accrued interest.
+    // The net Trove debt change could be positive or negative in a repayment (depending on whether its redistribution gain or repayment amount is larger),
+    // so this function accepts both the increase and the decrease to avoid using (and converting to/from) signed ints.
+    function mintAggInterest(uint256 _troveDebtIncrease, uint256 _troveDebtDecrease) public {
         _requireCallerIsBOorTroveMorSP();
-        boldDebt = boldDebt - _amount;
-        emit ActivePoolBoldDebtUpdated(boldDebt);
+        uint256 aggInterest = calcPendingAggInterest();
+        // Mint the new BOLD interest to a mock interest router that would split it and send it onward to SP, LP staking, etc.
+        // TODO: implement interest routing and SP Bold reward tracking
+        if (aggInterest > 0) {boldToken.mint(address(interestRouter), aggInterest);}
+
+        // Do the arithmetic in 2 steps here to avoid overflow from the decrease
+        uint256 newAggRecordedDebt = aggRecordedDebt + aggInterest + _troveDebtIncrease; // 1 SLOAD
+        newAggRecordedDebt -=_troveDebtDecrease;
+        aggRecordedDebt = newAggRecordedDebt; // 1 SSTORE
+        // assert(aggRecordedDebt >= 0) // This should never be negative. If all redistribution gians and all aggregate interest was applied
+        // and all Trove debts were repaid, it should become 0.
+
+        lastAggUpdateTime = block.timestamp;
     }
 
     // --- 'require' functions ---

contracts/src/BoldToken.sol

@@ -56,7 +56,9 @@ contract BoldToken is CheckContract, IBoldToken {
     address public immutable troveManagerAddress;
     address public immutable stabilityPoolAddress;
     address public immutable borrowerOperationsAddress;
+    address public immutable activePoolAddress;
 
+
     // --- Events ---
     event TroveManagerAddressChanged(address _troveManagerAddress);
     event StabilityPoolAddressChanged(address _newStabilityPoolAddress);
@@ -66,11 +68,13 @@ contract BoldToken is CheckContract, IBoldToken {
     ( 
         address _troveManagerAddress,
         address _stabilityPoolAddress,
-        address _borrowerOperationsAddress
+        address _borrowerOperationsAddress,
+        address _activePoolAddress
     ) {
         checkContract(_troveManagerAddress);
         checkContract(_stabilityPoolAddress);
         checkContract(_borrowerOperationsAddress);
+        checkContract(_activePoolAddress);
 
         troveManagerAddress = _troveManagerAddress;
         emit TroveManagerAddressChanged(_troveManagerAddress);
@@ -80,6 +84,8 @@ contract BoldToken is CheckContract, IBoldToken {
 
         borrowerOperationsAddress = _borrowerOperationsAddress;        
         emit BorrowerOperationsAddressChanged(_borrowerOperationsAddress);
+
+        activePoolAddress = _activePoolAddress;
 
         bytes32 hashedName = keccak256(bytes(_NAME));
         bytes32 hashedVersion = keccak256(bytes(_VERSION));
@@ -95,7 +101,7 @@ contract BoldToken is CheckContract, IBoldToken {
     // --- Functions for intra-Liquity calls ---
 
     function mint(address _account, uint256 _amount) external override {
-        _requireCallerIsBorrowerOperations();
+        _requireCallerIsBOorAP();
         _mint(_account, _amount);
     }
 
@@ -258,8 +264,10 @@ contract BoldToken is CheckContract, IBoldToken {
         );
     }
 
-    function _requireCallerIsBorrowerOperations() internal view {
-        require(msg.sender == borrowerOperationsAddress, "BoldToken: Caller is not BorrowerOperations");
+    function _requireCallerIsBOorAP() internal view {
+        require(msg.sender == borrowerOperationsAddress ||
+            msg.sender == activePoolAddress,
+            "BoldToken: Caller is not BO or AP");
     }
 
     function _requireCallerIsBOorTroveMorSP() internal view {