import Foundation

/// Stores the last successful local HealthKit sync boundary.
/// This is intentionally independent from the old SwiftUI user/network layer.
struct HealthSyncStateStore {
  private let defaults: UserDefaults
  private let keyPrefix = "native_health_sync_latest_time_"

  init(defaults: UserDefaults = .standard) {
    self.defaults = defaults
  }

  func lastSyncDate(for type: NativeHealthDataType) -> Date? {
    let timestamp = defaults.double(forKey: key(for: type))
    return timestamp > 0 ? Date(timeIntervalSince1970: timestamp) : nil
  }

  func save(date: Date, for type: NativeHealthDataType) {
    defaults.set(date.timeIntervalSince1970, forKey: key(for: type))
  }

  func startDate(for type: NativeHealthDataType, fallbackWeeks: Int = 1) -> Date {
    if let date = lastSyncDate(for: type) {
      return date
    }
    let fallback = Calendar.current.date(byAdding: .weekOfYear, value: -fallbackWeeks, to: Date())
    return Calendar.current.startOfDay(for: fallback ?? Date())
  }

  private func key(for type: NativeHealthDataType) -> String {
    "\(keyPrefix)\(type.rawValue)"
  }
}