refactor: sd as 18 decimals

test: update tests accordingly

benchmark/results/SablierFlow.md

@@ -2,15 +2,15 @@
 
 | Function                      | Gas Usage |
 | ----------------------------- | --------- |
-| `adjustRatePerSecond`         | 43628     |
+| `adjustRatePerSecond`         | 44149     |
 | `create`                      | 113659    |
 | `deposit`                     | 30035     |
 | `depositViaBroker`            | 21953     |
-| `pause`                       | 8983      |
-| `refund`                      | 11534     |
-| `restart`                     | 7031      |
-| `void (solvent stream)`       | 9517      |
-| `void (insolvent stream)`     | 36241     |
-| `withdraw (insolvent stream)` | 57034     |
-| `withdraw (solvent stream)`   | 39502     |
-| `withdrawMax`                 | 51379     |
+| `pause`                       | 9522      |
+| `refund`                      | 11894     |
+| `restart`                     | 7013      |
+| `void (solvent stream)`       | 10038     |
+| `void (insolvent stream)`     | 37438     |
+| `withdraw (insolvent stream)` | 57688     |
+| `withdraw (solvent stream)`   | 40156     |
+| `withdrawMax`                 | 51966     |

src/SablierFlow.sol

@@ -69,35 +69,35 @@ contract SablierFlow is
             return 0;
         }
 
+        uint8 tokenDecimals = _streams[streamId].tokenDecimals;
+        uint256 scaledBalance = Helpers.scaleAmount({ amount: balance, decimals: tokenDecimals });
+
         uint256 snapshotDebt = _streams[streamId].snapshotDebt;
 
         // If the stream has uncovered debt, return zero.
-        if (snapshotDebt + _ongoingDebtOf(streamId) > balance) {
+        if (snapshotDebt + _scaledOngoingDebtOf(streamId) > scaledBalance) {
             return 0;
         }
 
-        uint256 tokenDecimals = _streams[streamId].tokenDecimals;
-        uint256 solvencyAmount;
-
         // Depletion time is defined as the UNIX timestamp beyond which the total debt exceeds stream balance.
         // So we calculate it by solving: debt at depletion time = stream balance + 1. This ensures that we find the
         // lowest timestamp at which the debt exceeds the balance.
         // Safe to use unchecked because the calculations cannot overflow or underflow.
         unchecked {
-            if (tokenDecimals == 18) {
-                solvencyAmount = (balance - snapshotDebt + 1);
-            } else {
-                uint256 scaleFactor = (10 ** (18 - tokenDecimals));
-                solvencyAmount = (balance - snapshotDebt + 1) * scaleFactor;
-            }
+            uint256 solvencyAmount =
+                scaledBalance - snapshotDebt + Helpers.scaleAmount({ amount: 1, decimals: tokenDecimals });
             uint256 solvencyPeriod = solvencyAmount / _streams[streamId].ratePerSecond.unwrap();
-            return _streams[streamId].snapshotTime + solvencyPeriod;
+
+            depletionTime = _streams[streamId].snapshotTime + solvencyPeriod;
         }
     }
 
     /// @inheritdoc ISablierFlow
     function ongoingDebtOf(uint256 streamId) external view override notNull(streamId) returns (uint256 ongoingDebt) {
-        ongoingDebt = _ongoingDebtOf(streamId);
+        ongoingDebt = Helpers.descaleAmount({
+            amount: _scaledOngoingDebtOf(streamId),
+            decimals: _streams[streamId].tokenDecimals
+        });
     }
 
     /// @inheritdoc ISablierFlow
@@ -192,7 +192,7 @@ contract SablierFlow is
         // Log the adjustment.
         emit ISablierFlow.AdjustFlowStream({
             streamId: streamId,
-            totalDebt: _streams[streamId].snapshotDebt,
+            totalDebt: _totalDebtOf(streamId),
             oldRatePerSecond: oldRatePerSecond,
             newRatePerSecond: newRatePerSecond
         });
@@ -449,11 +449,11 @@ contract SablierFlow is
         return totalDebt.toUint128();
     }
 
-    /// @dev Calculates the ongoing debt accrued since last snapshot. Return 0 if the stream is paused or
-    /// `block.timestamp` is less than or equal to snapshot time.
-    function _ongoingDebtOf(uint256 streamId) internal view returns (uint256 ongoingDebt) {
-        uint40 blockTimestamp = uint40(block.timestamp);
-        uint40 snapshotTime = _streams[streamId].snapshotTime;
+    /// @dev Calculates the ongoing debt, as a 18-decimals fixed point number, accrued since last snapshot. Return 0 if
+    /// the stream is paused or `block.timestamp` is less than or equal to snapshot time.
+    function _scaledOngoingDebtOf(uint256 streamId) internal view returns (uint256) {
+        uint256 blockTimestamp = block.timestamp;
+        uint256 snapshotTime = _streams[streamId].snapshotTime;
 
         uint256 ratePerSecond = _streams[streamId].ratePerSecond.unwrap();
 
@@ -470,22 +470,8 @@ contract SablierFlow is
             elapsedTime = blockTimestamp - snapshotTime;
         }
 
-        // Calculate the ongoing debt accrued by multiplying the elapsed time by the rate per second.
-        uint256 scaledOngoingDebt = elapsedTime * ratePerSecond;
-
-        uint8 tokenDecimals = _streams[streamId].tokenDecimals;
-
-        // If the token decimals are 18, return the scaled ongoing debt and the `block.timestamp`.
-        if (tokenDecimals == 18) {
-            return scaledOngoingDebt;
-        }
-
-        // Safe to use unchecked because we use {SafeCast}.
-        unchecked {
-            uint256 scaleFactor = 10 ** (18 - tokenDecimals);
-            // Since debt is denoted in token decimals, descale the amount.
-            ongoingDebt = scaledOngoingDebt / scaleFactor;
-        }
+        // Calculate the scaled ongoing debt accrued by multiplying the elapsed time by the rate per second.
+        return elapsedTime * ratePerSecond;
     }
 
     /// @dev Calculates the refundable amount.
@@ -497,8 +483,8 @@ contract SablierFlow is
     /// @dev The total debt is the sum of the snapshot debt and the ongoing debt. This value is independent of the
     /// stream's balance.
     function _totalDebtOf(uint256 streamId) internal view returns (uint256) {
-        // Calculate the total debt.
-        return _streams[streamId].snapshotDebt + _ongoingDebtOf(streamId);
+        uint256 scaledTotalDebt = _scaledOngoingDebtOf(streamId) + _streams[streamId].snapshotDebt;
+        return Helpers.descaleAmount({ amount: scaledTotalDebt, decimals: _streams[streamId].tokenDecimals });
     }
 
     /// @dev Calculates the uncovered debt.
@@ -525,12 +511,12 @@ contract SablierFlow is
             revert Errors.SablierFlow_RatePerSecondNotDifferent(streamId, newRatePerSecond);
         }
 
-        uint256 ongoingDebt = _ongoingDebtOf(streamId);
+        uint256 scaledOngoingDebt = _scaledOngoingDebtOf(streamId);
 
         // Update the snapshot debt only if the stream has ongoing debt.
-        if (ongoingDebt > 0) {
+        if (scaledOngoingDebt > 0) {
             // Effect: update the snapshot debt.
-            _streams[streamId].snapshotDebt += ongoingDebt;
+            _streams[streamId].snapshotDebt += scaledOngoingDebt;
         }
 
         // Effect: update the snapshot time.
@@ -646,7 +632,7 @@ contract SablierFlow is
             streamId: streamId,
             sender: _streams[streamId].sender,
             recipient: _ownerOf(streamId),
-            totalDebt: _streams[streamId].snapshotDebt
+            totalDebt: _totalDebtOf(streamId)
         });
     }
 
@@ -715,16 +701,17 @@ contract SablierFlow is
 
         // If the stream is solvent, update the total debt normally.
         if (debtToWriteOff == 0) {
-            uint256 ongoingDebt = _ongoingDebtOf(streamId);
-            if (ongoingDebt > 0) {
+            uint256 scaledOngoingDebt = _scaledOngoingDebtOf(streamId);
+            if (scaledOngoingDebt > 0) {
                 // Effect: Update the snapshot debt by adding the ongoing debt.
-                _streams[streamId].snapshotDebt += ongoingDebt;
+                _streams[streamId].snapshotDebt += scaledOngoingDebt;
             }
         }
         // If the stream is insolvent, write off the uncovered debt.
         else {
             // Effect: update the total debt by setting snapshot debt to the stream balance.
-            _streams[streamId].snapshotDebt = _streams[streamId].balance;
+            _streams[streamId].snapshotDebt =
+                Helpers.scaleAmount({ amount: _streams[streamId].balance, decimals: _streams[streamId].tokenDecimals });
         }
 
         // Effect: update the snapshot time.
@@ -742,7 +729,7 @@ contract SablierFlow is
             sender: _streams[streamId].sender,
             recipient: _ownerOf(streamId),
             caller: msg.sender,
-            newTotalDebt: _streams[streamId].snapshotDebt,
+            newTotalDebt: _totalDebtOf(streamId),
             writtenOffDebt: debtToWriteOff
         });
     }
@@ -772,8 +759,11 @@ contract SablierFlow is
             revert Errors.SablierFlow_WithdrawalAddressNotRecipient({ streamId: streamId, caller: msg.sender, to: to });
         }
 
+        uint8 tokenDecimals = _streams[streamId].tokenDecimals;
+
         // Calculate the total debt.
-        uint256 totalDebt = _totalDebtOf(streamId);
+        uint256 scaledTotalDebt = _scaledOngoingDebtOf(streamId) + _streams[streamId].snapshotDebt;
+        uint256 totalDebt = Helpers.descaleAmount(scaledTotalDebt, tokenDecimals);
 
         // Calculate the withdrawable amount.
         uint128 balance = _streams[streamId].balance;
@@ -792,17 +782,20 @@ contract SablierFlow is
             revert Errors.SablierFlow_Overdraw(streamId, amount, withdrawableAmount);
         }
 
+        // Calculate the amount scaled.
+        uint256 scaledAmount = Helpers.scaleAmount(amount, tokenDecimals);
+
         // Safe to use unchecked, `amount` cannot be greater than the balance or total debt at this point.
         unchecked {
             // If the amount is less than the snapshot debt, reduce it from the snapshot debt and leave the snapshot
             // time unchanged.
-            if (amount <= _streams[streamId].snapshotDebt) {
-                _streams[streamId].snapshotDebt -= amount;
+            if (scaledAmount <= _streams[streamId].snapshotDebt) {
+                _streams[streamId].snapshotDebt -= scaledAmount;
             }
             // Else reduce the amount from the ongoing debt by setting snapshot time to `block.timestamp` and set the
             // snapshot debt to the remaining total debt.
             else {
-                _streams[streamId].snapshotDebt = totalDebt - amount;
+                _streams[streamId].snapshotDebt = scaledTotalDebt - scaledAmount;
 
                 // Effect: update the stream time.
                 _streams[streamId].snapshotTime = uint40(block.timestamp);

src/interfaces/ISablierFlowBase.sol

@@ -84,7 +84,7 @@ interface ISablierFlowBase is
     /// @param streamId The stream ID for the query.
     function getSender(uint256 streamId) external view returns (address sender);
 
-    /// @notice Retrieves the snapshot debt of the stream, denoted in token's decimals.
+    /// @notice Retrieves the snapshot debt of the stream, denoted as a fixed-point number where 1e18 is 1 token.
     /// @dev Reverts if `streamId` references a null stream.
     /// @param streamId The stream ID for the query.
     function getSnapshotDebt(uint256 streamId) external view returns (uint256 snapshotDebt);

src/libraries/Helpers.sol

@@ -49,4 +49,34 @@ library Helpers {
         // Calculate the broker fee amount that is going to be transferred to the `broker.account`.
         (brokerFeeAmount, depositAmount) = calculateAmountsFromFee(totalAmount, broker.fee);
     }
+
+    /// @notice Descales the provided `amount` to be denoted in the token's decimals.
+    /// @dev The following logic is used to denormalize the amount:
+    /// - If the token has exactly 18 decimals, the amount is returned as is.
+    /// - if the token has fewer than 18 decimals, the amount is divided by $10^(18 - tokenDecimals)$.
+    function descaleAmount(uint256 amount, uint8 decimals) internal pure returns (uint256) {
+        if (decimals > 18) {
+            return amount;
+        }
+
+        unchecked {
+            uint256 scaleFactor = 10 ** (18 - decimals);
+            return amount / scaleFactor;
+        }
+    }
+
+    /// @notice Scales the provided `amount` to be denoted in 18 decimals.
+    /// @dev The following logic is used to normalize the amount:
+    /// - If the token has exactly 18 decimals, the amount is returned as is.
+    /// - If the token has fewer than 18 decimals, the amount is multiplied by $10^(18 - tokenDecimals)$.
+    function scaleAmount(uint256 amount, uint8 decimals) internal pure returns (uint256) {
+        if (decimals > 18) {
+            return amount;
+        }
+
+        unchecked {
+            uint256 scaleFactor = 10 ** (18 - decimals);
+            return amount * scaleFactor;
+        }
+    }
 }

src/types/DataTypes.sol

@@ -55,9 +55,9 @@ library Flow {
     /// be restarted. Voiding an insolvent stream sets its uncovered debt to zero.
     /// @param token The contract address of the ERC-20 token to stream.
     /// @param tokenDecimals The decimals of the ERC-20 token to stream.
-    /// @param snapshotDebt The amount of tokens that the sender owed to the recipient at snapshot time, denoted in
-    /// token's decimals. This, along with the ongoing debt, can be used to calculate the total debt at any given point
-    /// in time.
+    /// @param snapshotDebt The amount of tokens that the sender owed to the recipient at snapshot time, denoted as a
+    /// 18-decimals fixed-point number. This, along with the ongoing debt, can be used to calculate the total debt at
+    /// any given point in time.
     struct Stream {
         // slot 0
         uint128 balance;

tests/fork/Flow.t.sol

@@ -229,7 +229,6 @@ contract Flow_Fork_Test is Fork_Test {
 
         uint256 beforeSnapshotAmount = flow.getSnapshotDebt(streamId);
         uint256 totalDebt = flow.totalDebtOf(streamId);
-        uint256 ongoingDebt = flow.ongoingDebtOf(streamId);
 
         // Compute the snapshot time that will be stored post withdraw.
         vars.expectedSnapshotTime = getBlockTimestamp();
@@ -250,7 +249,9 @@ contract Flow_Fork_Test is Fork_Test {
 
         // It should update snapshot debt.
         vars.actualSnapshotDebt = flow.getSnapshotDebt(streamId);
-        vars.expectedSnapshotDebt = ongoingDebt + beforeSnapshotAmount;
+        vars.expectedSnapshotDebt = calculateScaledOngoingDebt(
+            flow.getRatePerSecond(streamId).unwrap(), flow.getSnapshotTime(streamId)
+        ) + beforeSnapshotAmount;
         assertEq(vars.actualSnapshotDebt, vars.expectedSnapshotDebt, "AdjustRatePerSecond: snapshot debt");
 
         // It should set the new rate per second
@@ -561,8 +562,10 @@ contract Flow_Fork_Test is Fork_Test {
         uint256 initialTokenBalance = token.balanceOf(address(flow));
         uint256 totalDebt = flow.totalDebtOf(streamId);
 
-        vars.expectedSnapshotTime =
-            withdrawAmount <= flow.getSnapshotDebt(streamId) ? flow.getSnapshotTime(streamId) : getBlockTimestamp();
+        vars.expectedSnapshotTime = withdrawAmount
+            <= getDescaledAmount(flow.getSnapshotDebt(streamId), flow.getTokenDecimals(streamId))
+            ? flow.getSnapshotTime(streamId)
+            : getBlockTimestamp();
 
         (, address caller,) = vm.readCallers();
         address recipient = flow.getRecipient(streamId);

tests/integration/concrete/adjust-rate-per-second/adjustRatePerSecond.t.sol

@@ -119,7 +119,7 @@ contract AdjustRatePerSecond_Integration_Concrete_Test is Integration_Test {
 
         // It should update snapshot debt.
         actualSnapshotDebt = flow.getSnapshotDebt(defaultStreamId);
-        expectedSnapshotDebt = ONE_MONTH_DEBT_6D;
+        expectedSnapshotDebt = ONE_MONTH_DEBT_18D;
         assertEq(actualSnapshotDebt, expectedSnapshotDebt, "snapshot debt");
 
         // It should set the new rate per second

tests/integration/concrete/deposit-and-pause/depositAndPause.t.sol

@@ -56,7 +56,8 @@ contract DepositAndPause_Integration_Concrete_Test is Integration_Test {
 
     function test_WhenCallerSender() external whenNoDelegateCall givenNotNull givenNotPaused {
         uint128 previousStreamBalance = flow.getBalance(defaultStreamId);
-        uint256 previousTotalDebt = flow.totalDebtOf(defaultStreamId);
+        uint256 expectedSnapshotDebt =
+            calculateScaledOngoingDebt(RATE_PER_SECOND_U128, flow.getSnapshotTime(defaultStreamId));
 
         // It should emit 1 {Transfer}, 1 {DepositFlowStream}, 1 {PauseFlowStream}, 1 {MetadataUpdate} events
         vm.expectEmit({ emitter: address(usdc) });
@@ -74,7 +75,7 @@ contract DepositAndPause_Integration_Concrete_Test is Integration_Test {
             streamId: defaultStreamId,
             sender: users.sender,
             recipient: users.recipient,
-            totalDebt: previousTotalDebt
+            totalDebt: flow.totalDebtOf(defaultStreamId)
         });
 
         vm.expectEmit({ emitter: address(flow) });
@@ -99,6 +100,6 @@ contract DepositAndPause_Integration_Concrete_Test is Integration_Test {
 
         // It should update the snapshot debt
         uint256 actualSnapshotDebt = flow.getSnapshotDebt(defaultStreamId);
-        assertEq(actualSnapshotDebt, previousTotalDebt, "snapshot debt");
+        assertEq(actualSnapshotDebt, expectedSnapshotDebt, "snapshot debt");
     }
 }

tests/integration/concrete/pause/pause.t.sol

@@ -51,7 +51,7 @@ contract Pause_Integration_Concrete_Test is Integration_Test {
         assertGt(flow.uncoveredDebtOf(defaultStreamId), 0, "uncovered debt");
 
         // It should pause the stream.
-        test_Pause();
+        _test_Pause();
     }
 
     function test_GivenNoUncoveredDebt() external whenNoDelegateCall givenNotNull givenNotPaused whenCallerSender {
@@ -62,19 +62,20 @@ contract Pause_Integration_Concrete_Test is Integration_Test {
         assertEq(flow.uncoveredDebtOf(defaultStreamId), 0, "uncovered debt");
 
         // It should pause the stream.
-        test_Pause();
+        _test_Pause();
     }
 
-    function test_Pause() internal {
-        uint256 initialTotalDebt = flow.totalDebtOf(defaultStreamId);
+    function _test_Pause() private {
+        uint256 expectedSnapshotDebt =
+            calculateScaledOngoingDebt(RATE_PER_SECOND_U128, flow.getSnapshotTime(defaultStreamId));
 
         // It should emit 1 {PauseFlowStream}, 1 {MetadataUpdate} events.
         vm.expectEmit({ emitter: address(flow) });
         emit ISablierFlow.PauseFlowStream({
             streamId: defaultStreamId,
             sender: users.sender,
             recipient: users.recipient,
-            totalDebt: initialTotalDebt
+            totalDebt: flow.totalDebtOf(defaultStreamId)
         });
 
         vm.expectEmit({ emitter: address(flow) });
@@ -91,6 +92,6 @@ contract Pause_Integration_Concrete_Test is Integration_Test {
 
         // It should update the snapshot debt.
         uint256 actualSnapshotDebt = flow.getSnapshotDebt(defaultStreamId);
-        assertEq(actualSnapshotDebt, initialTotalDebt, "snapshot debt");
+        assertEq(actualSnapshotDebt, expectedSnapshotDebt, "snapshot debt");
     }
 }