import RastrilloNative
import SwiftUI

/// A thin inset bar shown while `origin` is offline. Entering the offline
/// state is announced to assistive technologies; leaving it is not.
///
/// Pass `summary` once the app's edits are kept in an `Outbox`: the banner
/// then says they are saved on this device, which is only true from then on.
public struct NativeOfflineBanner: View {
  private let connectivity: NativeConnectivity
  private let origin: URL
  private let message: String

  @MainActor public init(connectivity: NativeConnectivity? = nil, origin: URL, message: String? = nil) {
    self.connectivity = connectivity ?? .shared; self.origin = origin
    self.message = message ?? NativeSyncStrings.kit.offlineWaiting
  }

  /// The durable wording, for an app whose changes go through an outbox.
  @MainActor public init(connectivity: NativeConnectivity? = nil, origin: URL, summary: OutboxSummary,
                         strings: NativeSyncStrings = .kit) {
    self.init(connectivity: connectivity, origin: origin, message: strings.offlineDurable)
  }

  public var body: some View {
    let offline = connectivity.isOffline(origin)
    Group {
      if offline {
        Label(message, systemImage: "wifi.slash")
          .font(.callout)
          .frame(maxWidth: .infinity)
          .padding(.horizontal, 12).padding(.vertical, 6)
          .background(.bar)
          .accessibilityElement(children: .combine)
      }
    }
    .onChange(of: offline) { _, now in
      if now { AccessibilityNotification.Announcement(message).post() }
    }
  }
}