HealthKit Workout Zones

import SwiftUI
import HealthKit

struct ZoneDurationRow: Identifiable {
    let id: Int
    let label: String
    let seconds: Double
}

@MainActor
class WorkoutZoneViewModel: ObservableObject {
    @Published var zoneRows: [ZoneDurationRow] = []
    @Published var errorMessage: String?

    private let store = HKHealthStore()

    func fetchLatestWorkoutZones() async {
        let workoutType = HKObjectType.workoutType()
        let heartRateType = HKQuantityType(.heartRate)

        do {
            try await store.requestAuthorization(
                toShare: [],
                read: [workoutType, heartRateType]
            )
        } catch {
            errorMessage = "Authorization failed: \(error.localizedDescription)"
            return
        }

        let sort = NSSortDescriptor(key: HKSampleSortIdentifierEndDate, ascending: false)
        let query = HKSampleQueryDescriptor(
            predicates: [.workout()],
            sortDescriptors: [SortDescriptor(\.endDate, order: .reverse)],
            limit: 1
        )

        do {
            let results = try await query.result(for: store)
            guard let workout = results.first as? HKWorkout else {
                errorMessage = "No workouts found."
                return
            }

            guard let zoneGroup = workout.zoneGroupsByType[HKQuantityType(.heartRate)] else {
                errorMessage = "No heart rate zone data for this workout."
                return
            }

            zoneRows = zoneGroup.zoneDurations.map { zoneDuration in
                let zone = zoneDuration.zone
                let seconds = zoneDuration.duration
                let label: String
                if let max = zone.maximumQuantity {
                    label = "Zone \(zone.index + 1) (up to \(Int(max.doubleValue(for: .count().unitDivided(by: .minute())))) bpm)"
                } else {
                    label = "Zone \(zone.index + 1) (peak)"
                }
                return ZoneDurationRow(id: zone.index, label: label, seconds: seconds)
            }
        } catch {
            errorMessage = "Query failed: \(error.localizedDescription)"
        }
    }
}

struct WorkoutZoneSummaryView: View {
    @StateObject private var vm = WorkoutZoneViewModel()

    var body: some View {
        NavigationStack {
            List(vm.zoneRows) { row in
                HStack {
                    Text(row.label)
                    Spacer()
                    Text(String(format: "%.0f min", row.seconds / 60))
                        .foregroundStyle(.secondary)
                }
            }
            .navigationTitle("Heart Rate Zones")
            .overlay {
                if let error = vm.errorMessage {
                    ContentUnavailableView(error, systemImage: "heart.slash")
                }
            }
            .task { await vm.fetchLatestWorkoutZones() }
        }
    }
}