(circles): introduce event DiscountCost

src/circles/Circles.sol

@@ -74,8 +74,6 @@ contract Circles is ERC1155 {
         DiscountedBalances(_inflation_day_zero)
     {}
 
-    // External functions
-
     // Public functions
 
     /**

src/circles/DiscountedBalances.sol

@@ -13,6 +13,10 @@ contract DiscountedBalances is Demurrage {
      */
     mapping(uint256 => mapping(address => DiscountedBalance)) public discountedBalances;
 
+    // Events
+
+    event DiscountCost(address indexed account, uint256 indexed id, uint256 discountCost);
+
     // Constructor
 
     /**
@@ -30,10 +34,30 @@ contract DiscountedBalances is Demurrage {
      * @param _account Address of the account to calculate the balance of
      * @param _id Circles identifier for which to calculate the balance
      * @param _day Day since inflation_day_zero to calculate the balance for
+     * @return balance_ The discounted balance of the account for the Circles identifier
+     * @return discountCost_ The discount cost of the demurrage of the balance since the last update
      */
-    function balanceOfOnDay(address _account, uint256 _id, uint64 _day) public view returns (uint256) {
+    function balanceOfOnDay(address _account, uint256 _id, uint64 _day)
+        public
+        view
+        returns (uint256 balance_, uint256 discountCost_)
+    {
         DiscountedBalance memory discountedBalance = discountedBalances[_id][_account];
-        return _calculateDiscountedBalance(discountedBalance.balance, _day - discountedBalance.lastUpdatedDay);
+        if (_day < discountedBalance.lastUpdatedDay) {
+            // DiscountedBalances: day is before last updated day
+            revert CirclesERC1155DayBeforeLastUpdatedDay(_account, _id, _day, discountedBalance.lastUpdatedDay, 0);
+        }
+        uint256 dayDifference;
+        unchecked {
+            dayDifference = _day - discountedBalance.lastUpdatedDay;
+        }
+        // Calculate the discounted balance
+        balance_ = _calculateDiscountedBalance(discountedBalance.balance, dayDifference);
+        // Calculate the discount cost; this can be unchecked as cost is strict positive
+        unchecked {
+            discountCost_ = discountedBalance.balance - balance_;
+        }
+        return (balance_, discountCost_);
     }
 
     // Internal functions
@@ -74,8 +98,22 @@ contract DiscountedBalances is Demurrage {
      */
     function _discountAndAddToBalance(address _account, uint256 _id, uint256 _value, uint64 _day) internal {
         DiscountedBalance storage discountedBalance = discountedBalances[_id][_account];
-        uint256 discountedBalanceValue =
-            _calculateDiscountedBalance(discountedBalance.balance, _day - discountedBalance.lastUpdatedDay);
+        if (_day < discountedBalance.lastUpdatedDay) {
+            // DiscountedBalances: day is before last updated day
+            revert CirclesERC1155DayBeforeLastUpdatedDay(_account, _id, _day, discountedBalance.lastUpdatedDay, 1);
+        }
+        uint256 dayDifference;
+        unchecked {
+            dayDifference = _day - discountedBalance.lastUpdatedDay;
+        }
+        uint256 discountedBalanceValue = _calculateDiscountedBalance(discountedBalance.balance, dayDifference);
+        // Calculate the discount cost; this can be unchecked as cost is strict positive
+        unchecked {
+            uint256 discountCost_ = discountedBalance.balance - discountedBalanceValue;
+            if (discountCost_ > 0) {
+                emit DiscountCost(_account, _id, discountCost_);
+            }
+        }
         uint256 newBalance = discountedBalanceValue + _value;
         if (newBalance > MAX_VALUE) {
             // DiscountedBalances: balance exceeds maximum value

src/circles/ERC1155.sol

@@ -32,10 +32,6 @@ abstract contract ERC1155 is DiscountedBalances, Context, ERC165, IERC1155, IERC
     // Used as the URI for all token types by relying on ID substitution, e.g. https://token-cdn-domain/{id}.json
     string private _uri;
 
-    // Events
-
-    event ConvertInflation(uint256 inflationValue, uint256 demurrageValue, uint64 day);
-
     // Constructor
 
     /**
@@ -73,7 +69,8 @@ abstract contract ERC1155 is DiscountedBalances, Context, ERC165, IERC1155, IERC
      * @dev See {IERC1155-balanceOf}.
      */
     function balanceOf(address _account, uint256 _id) public view returns (uint256) {
-        return balanceOfOnDay(_account, _id, day(block.timestamp));
+        (uint256 balance,) = balanceOfOnDay(_account, _id, day(block.timestamp));
+        return balance;
     }
 
     /**
@@ -93,7 +90,7 @@ abstract contract ERC1155 is DiscountedBalances, Context, ERC165, IERC1155, IERC
         uint256[] memory batchBalances = new uint256[](_accounts.length);
 
         for (uint256 i = 0; i < _accounts.length; ++i) {
-            batchBalances[i] = balanceOfOnDay(_accounts.unsafeMemoryAccess(i), _ids.unsafeMemoryAccess(i), today);
+            (batchBalances[i],) = balanceOfOnDay(_accounts.unsafeMemoryAccess(i), _ids.unsafeMemoryAccess(i), today);
         }
 
         return batchBalances;
@@ -171,10 +168,13 @@ abstract contract ERC1155 is DiscountedBalances, Context, ERC165, IERC1155, IERC
             uint256 value = values.unsafeMemoryAccess(i);
 
             if (from != address(0)) {
-                uint256 fromBalance = balanceOfOnDay(from, id, today);
+                (uint256 fromBalance, uint256 discountCost) = balanceOfOnDay(from, id, today);
                 if (fromBalance < value) {
                     revert ERC1155InsufficientBalance(from, fromBalance, value, id);
                 }
+                if (discountCost > 0) {
+                    emit DiscountCost(from, id, discountCost);
+                }
                 unchecked {
                     // Overflow not possible: value <= fromBalance
                     _updateBalance(from, id, fromBalance - value, today);

src/errors/Errors.sol

@@ -39,6 +39,10 @@ interface ICirclesERC1155Errors {
     error CirclesERC1155MintBlocked(address human, address mintV1Status);
 
     error CirclesERC1155AmountExceedsMaxUint190(address account, uint256 circlesId, uint256 amount, uint8 code);
+
+    error CirclesERC1155DayBeforeLastUpdatedDay(
+        address account, uint256 circlesId, uint64 day, uint64 lastUpdatedDay, uint8 code
+    );
 }
 
 interface ICirclesErrors {

test/circles/Circles.t.sol

@@ -66,7 +66,7 @@ contract CirclesTest is Test, TimeCirclesSetup, Approximation {
             previousEndPeriod = endPeriod;
 
             // Generate a pseudo-random number between 1 and 4
-            uint256 hoursSkip = uint256(keccak256(abi.encodePacked(block.timestamp, i, uint256(0)))) % 4 + 1;
+            uint256 hoursSkip = uint256(keccak256(abi.encodePacked(block.timestamp, i, uint256(0)))) % 34 + 1;
             uint256 secondsSkip = uint256(keccak256(abi.encodePacked(block.timestamp, i, uint256(1)))) % 3600;
 
             // Simulate passing of time variable windows of time (1-5 hours)
@@ -98,23 +98,17 @@ contract CirclesTest is Test, TimeCirclesSetup, Approximation {
             assertEq(balance, expectedIssuance);
         }
 
+        skipTime(26 hours);
+
         // send 5 CRC from alice to bob
         uint256 aliceBalance = circles.balanceOf(addresses[0], circlesIdentifiers[0]);
         uint256 bobBalance = circles.balanceOf(addresses[1], circlesIdentifiers[0]);
-        // uint256 aliceInflationaryBalance = circles.inflationaryBalanceOf(addresses[0], circlesIdentifiers[0]);
-        // uint256 bobInflationaryBalance = circles.inflationaryBalanceOf(addresses[1], circlesIdentifiers[0]);
         vm.prank(addresses[0]);
         circles.safeTransferFrom(addresses[0], addresses[1], circlesIdentifiers[0], 5 * CRC, "");
         uint256 aliceBalanceAfter = circles.balanceOf(addresses[0], circlesIdentifiers[0]);
         uint256 bobBalanceAfter = circles.balanceOf(addresses[1], circlesIdentifiers[0]);
-        // uint256 aliceInflationaryBalanceAfter = circles.inflationaryBalanceOf(addresses[0], circlesIdentifiers[0]);
-        // uint256 bobInflationaryBalanceAfter = circles.inflationaryBalanceOf(addresses[1], circlesIdentifiers[0]);
         assertEq(aliceBalance - 5 * CRC, aliceBalanceAfter);
         assertEq(bobBalance + 5 * CRC, bobBalanceAfter);
-        // assertEq(
-        //     aliceInflationaryBalance - aliceInflationaryBalanceAfter,
-        //     bobInflationaryBalanceAfter - bobInflationaryBalance
-        // );
     }
 
     // Private functions

test/hub/PathTransferHub.t.sol

@@ -71,6 +71,9 @@ contract HubPathTransferTest is Test, TimeCirclesSetup, HumanRegistration, Appro
         // first four avatars have a linear bi-directional trust
         uint256 M = N;
 
+        // induce demurrage for the path transfer of the balances
+        skipTime(2 days);
+
         // Flow matrix for transferring Circles from Alice to David
         // with indication of which Circles are being sent
         //       A     B     C     D