Added public functions to check whether shutdown

src/TwabController.sol

@@ -171,6 +171,25 @@ contract TwabController {
 
   /* ============ External Read Functions ============ */
 
+  /**
+   * @notice Returns whether the TwabController has been shutdown at the given timestamp
+   * If the twab is queried at or after this time, whether an absolute timestamp or time range, it will return 0.
+   * @dev This function will return true for any timestamp after the lastObservationAt()
+   * @param timestamp The timestamp to check
+   * @return True if the TwabController is shutdown at the given timestamp, false otherwise.
+   */
+  function isShutdownAt(uint256 timestamp) external view returns (bool) {
+    return TwabLib.isShutdownAt(timestamp, PERIOD_OFFSET);
+  }
+
+  /**
+   * @notice Computes the timestamp after which no more observations will be made.
+   * @return The largest timestamp at which the TwabController can record a new observation.
+   */
+  function lastObservationAt() external view returns (uint256) {
+    return TwabLib.lastObservationAt(PERIOD_OFFSET);
+  }
+
   /**
    * @notice Loads the current TWAB Account data for a specific vault stored for a user.
    * @dev Note this is a very expensive function

src/libraries/TwabLib.sol

@@ -109,7 +109,7 @@ library TwabLib {
     // record a new observation if the delegateAmount is non-zero and time has not overflowed.
     isObservationRecorded =
       _delegateAmount != uint96(0) &&
-      (block.timestamp - PERIOD_OFFSET) <= type(uint32).max;
+      block.timestamp <= lastObservationAt(PERIOD_OFFSET);
 
     accountDetails.balance += _amount;
     accountDetails.delegateBalance += _delegateAmount;
@@ -172,7 +172,7 @@ library TwabLib {
     // record a new observation if the delegateAmount is non-zero and time has not overflowed.
     isObservationRecorded =
       _delegateAmount != uint96(0) &&
-      (block.timestamp - PERIOD_OFFSET) <= type(uint32).max;
+      block.timestamp <= lastObservationAt(PERIOD_OFFSET);
 
     unchecked {
       accountDetails.balance -= _amount;
@@ -250,19 +250,43 @@ library TwabLib {
     if (_targetTime < PERIOD_OFFSET) {
       return 0;
     }
-    uint256 offsetTargetTime = _targetTime - PERIOD_OFFSET;
     // if this is for an overflowed time period, return 0
-    if (offsetTargetTime > type(uint32).max) {
+    if (isShutdownAt(_targetTime, PERIOD_OFFSET)) {
       return 0;
     }
     ObservationLib.Observation memory prevOrAtObservation = _getPreviousOrAtObservation(
       _observations,
       _accountDetails,
-      PeriodOffsetRelativeTimestamp.wrap(uint32(offsetTargetTime))
+      PeriodOffsetRelativeTimestamp.wrap(uint32(_targetTime - PERIOD_OFFSET))
     );
     return prevOrAtObservation.balance;
   }
 
+  /**
+   * @notice Returns whether the TwabController has been shutdown at the given timestamp
+   * If the twab is queried at or after this time, whether an absolute timestamp or time range, it will return 0.
+   * @param timestamp The timestamp to check
+   * @param PERIOD_OFFSET The offset of the first period
+   * @return True if the TwabController is shutdown at the given timestamp, false otherwise.
+   */
+  function isShutdownAt(
+    uint256 timestamp,
+    uint32 PERIOD_OFFSET
+  ) internal pure returns (bool) {
+    return timestamp > lastObservationAt(PERIOD_OFFSET);
+  }
+
+  /**
+   * @notice Computes the largest timestamp at which the TwabController can record a new observation.
+   * @param PERIOD_OFFSET The offset of the first period
+   * @return The largest timestamp at which the TwabController can record a new observation.
+   */
+  function lastObservationAt(
+    uint32 PERIOD_OFFSET
+  ) internal pure returns (uint256) {
+    return uint256(PERIOD_OFFSET) + type(uint32).max;
+  }
+
   /**
    * @notice Looks up a users TWAB for a time range. The time must be before the current overwrite period.
    * @dev If the timestamps in the range are not exact matches of observations, the balance is extrapolated using the previous observation.
@@ -289,8 +313,8 @@ library TwabLib {
     uint256 offsetStartTime = _startTime - PERIOD_OFFSET;
     uint256 offsetEndTime = _endTime - PERIOD_OFFSET;
 
-    // if the either time has overflowed, then return 0.
-    if (offsetStartTime > type(uint32).max || offsetEndTime > type(uint32).max) {
+    // if the range extends into the shutdown period, return 0
+    if (isShutdownAt(_endTime, PERIOD_OFFSET)) {
       return 0;
     }
 

test/TwabController.t.sol

@@ -145,6 +145,17 @@ contract TwabControllerTest is BaseTest {
     vm.stopPrank();
   }
 
+  function testIsShutdownAt() public {
+    assertEq(twabController.isShutdownAt(PERIOD_OFFSET), false, "at beginning");
+    assertEq(twabController.isShutdownAt(PERIOD_OFFSET + PERIOD_LENGTH), false, "after first period");
+    assertEq(twabController.isShutdownAt(type(uint32).max + uint256(PERIOD_OFFSET)), false, "at end");
+    assertEq(twabController.isShutdownAt(type(uint32).max + uint256(PERIOD_OFFSET) + 1), true, "after end");
+  }
+
+  function testLastObservationAt() public {
+    assertEq(twabController.lastObservationAt(), uint256(PERIOD_OFFSET) + type(uint32).max);
+  }
+
   function testGetBalanceAt_beforeHistoryStarted() public {
     // ensure times are finalized
     vm.warp(PERIOD_OFFSET + PERIOD_LENGTH);