implement multi stopwatch

MultiChrono/Stopwatch.swift

@@ -0,0 +1,82 @@
+//
+//  Stopwatch.swift
+//  MultiChrono
+//
+//  Created by Beatrice Dellacà on 26/01/26.
+//
+
+import Foundation
+import Combine
+
+class Stopwatch: ObservableObject, Identifiable {
+    let id = UUID()
+    @Published var name: String
+    @Published var elapsedTime: TimeInterval = 0
+    @Published var isRunning: Bool = false
+    
+    private var timer: AnyCancellable?
+    private var startTime: Date?
+    private var accumulatedTime: TimeInterval = 0
+    
+    init(name: String) {
+        self.name = name
+    }
+    
+    deinit {
+        timer?.cancel()
+    }
+    
+    func start() {
+        guard !isRunning else { return }
+        
+        startTime = Date()
+        isRunning = true
+        
+        timer = Timer.publish(every: 0.1, on: .main, in: .common)
+            .autoconnect()
+            .sink { [weak self] _ in
+                self?.tick()
+            }
+    }
+    
+    func pause() {
+        guard isRunning else { return }
+        
+        timer?.cancel()
+        timer = nil
+        
+        if let startTime = startTime {
+            accumulatedTime += Date().timeIntervalSince(startTime)
+        }
+        
+        isRunning = false
+        startTime = nil
+        
+        // Ensure UI shows accurate accumulated time
+        elapsedTime = accumulatedTime
+    }
+    
+    func reset() {
+        pause()
+        accumulatedTime = 0
+        elapsedTime = 0
+    }
+    
+    private func tick() {
+        guard let startTime = startTime else { return }
+        elapsedTime = accumulatedTime + Date().timeIntervalSince(startTime)
+    }
+    
+    var formattedTime: String {
+        let hours = Int(elapsedTime) / 3600
+        let minutes = Int(elapsedTime) / 60 % 60
+        let seconds = Int(elapsedTime) % 60
+        let tenths = Int((elapsedTime.truncatingRemainder(dividingBy: 1)) * 10)
+        
+        if hours > 0 {
+            return String(format: "%02i:%02i:%02i.%01i", hours, minutes, seconds, tenths)
+        } else {
+            return String(format: "%02i:%02i.%01i", minutes, seconds, tenths)
+        }
+    }
+}