implement lap edit

MultiChrono/Stopwatch.swift

@@ -12,9 +12,9 @@ class Stopwatch: ObservableObject, Identifiable, Codable {
     struct Lap: Identifiable, Codable {
         let id: UUID
         let number: Int
-        let startTime: Date
-        let endTime: Date
-        let duration: TimeInterval
+        var startTime: Date
+        var endTime: Date
+        var duration: TimeInterval
     }
 
     let id: UUID
@@ -188,4 +188,34 @@ class Stopwatch: ObservableObject, Identifiable, Codable {
     var currentRunStartTime: Date? {
         return startTime
     }
+    
+    func update(lap: Lap) {
+        guard let index = laps.firstIndex(where: { $0.id == lap.id }) else { return }
+        
+        var updatedLap = lap
+        // Recalculate duration in case start/end times were changed
+        updatedLap.duration = updatedLap.endTime.timeIntervalSince(updatedLap.startTime)
+        
+        laps[index] = updatedLap
+        
+        // Recalculate accumulatedTime from all laps
+        // Note: This assumes accumulatedTime is strictly the sum of all closed laps.
+        // If the stopwatch is running, the current "open" lap is not in `laps` yet (it's implicit).
+        // However, `accumulatedTime` tracks the time *before* the current run started.
+        // If we edited a *past* lap, we should update accumulatedTime to be the sum of all past laps.
+        
+        // Let's assume laps are only recorded when paused or when split.
+        // If we claim `accumulatedTime` is the sum of all stored laps:
+        let totalLapDuration = laps.reduce(0) { $0 + $1.duration }
+        accumulatedTime = totalLapDuration
+        
+        if isRunning {
+            // function tick() will update elapsedTime naturally, but to be immediate:
+            if let start = startTime {
+                elapsedTime = accumulatedTime + Date().timeIntervalSince(start)
+            }
+        } else {
+            elapsedTime = accumulatedTime
+        }
+    }
 }