add WorkoutStateManager for ViewModel functionality

WorkoutsPlus/Features/WorkoutSession/WorkoutStateManager.swift

@@ -0,0 +1,61 @@
+//
+//  WorkoutStateManager.swift
+//  WorkoutsPlus
+//
+//  Created by Felix Förtsch on 21.11.24.
+//
+
+import SwiftUI
+import SwiftData
+
+@Observable
+final class WorkoutStateManager {
+		private let modelContext: ModelContext
+		private(set) var activeWorkoutSession: WorkoutSession?
+		var isWorkoutInProgress: Bool { activeWorkoutSession != nil }
+		
+		init(modelContext: ModelContext) {
+				self.modelContext = modelContext
+		}
+		
+		func startWorkout(_ workout: Workout) {
+				let session = WorkoutSession(start: workout)
+				modelContext.insert(session)
+				activeWorkoutSession = session
+		}
+		
+		func stopWorkout() {
+				if let _ = activeWorkoutSession {
+						activeWorkoutSession = nil
+				}
+		}
+		
+		func cancelWorkout(context: ModelContext) {
+				if let session = activeWorkoutSession {
+						context.delete(session)
+						activeWorkoutSession = nil
+				}
+		}
+		
+		func prevExercise() {
+				if let session = activeWorkoutSession {
+						session.workoutSessionItems[session.currentExercise].startDate = Date.now
+						if session.currentExercise > 0 {
+								session.currentExercise -= 1
+						}
+				}
+		}
+		
+		func nextExercise() {
+				if let session = activeWorkoutSession {
+						session.workoutSessionItems[session.currentExercise].stopDate = Date.now
+						if session.currentExercise < session.workoutSessionItems.count - 1 {
+								session.currentExercise += 1
+						}
+				}
+		}
+		
+		func getWorkoutDuration() -> String {
+				activeWorkoutSession?.getFormattedDuration() ?? "00:00:00"
+		}
+}