RNSSplitHostController.swift

import Foundation
import UIKit

/// @class RNSSplitHostController
/// @brief A controller associated with the RN native component representing Split host.
///
/// Manages a collection of RNSSplitScreenComponentView instances,
/// synchronizes appearance settings with props, observes component lifecycle, and emits events.
@objc
public class RNSSplitHostController: UISplitViewController, ReactMountingTransactionObserving,
  RNSOrientationProvidingSwift
{
  private var needsChildViewControllersUpdate = false
  private var isLayoutDirectionUpdatePending = false

  private var splitAppearanceCoordinator: RNSSplitAppearanceCoordinator
  private var splitAppearanceApplicator: RNSSplitAppearanceApplicator

  private var reactEventEmitter: RNSSplitHostComponentEventEmitter {
    return splitHostComponentView.reactEventEmitter()
  }

  private let splitHostComponentView: RNSSplitHostComponentView

  /// This variable is keeping the value of how many columns were set in the initial render. It's used for validation, because Split doesn't support changing number of columns dynamically.
  private let fixedColumnsCount: Int

  private let minNumberOfColumns: Int = 2
  private let maxNumberOfColumns: Int = 3
  private let maxNumberOfInspectors: Int = 1

  /// Tracks currently visible columns of the UISplitViewController.
  ///
  /// This set is kept in sync via `UISplitViewControllerDelegate` methods (`willShow` / `willHide`)
  /// to reflect which columns are currently rendered in the UI.
  /// It ensures that only visible columns are considered (e.g. for accessing topViewController),
  /// avoiding crashes when certain columns are collapsed or hidden.
  private var visibleColumns: Set<UISplitViewController.Column> = []

  ///
  /// @brief Initializes the Split host controller with provided style.
  ///
  /// The style for the Split component can be passed only in the initialization method and cannot be changed dynamically.
  ///
  /// @param splitHostComponentView The view managed by this controller.
  /// @param numberOfColumns Expected number of visible columns.
  ///
  @objc public init(
    splitHostComponentView: RNSSplitHostComponentView,
    numberOfColumns: Int
  ) {
    self.splitHostComponentView = splitHostComponentView
    self.splitAppearanceCoordinator = RNSSplitAppearanceCoordinator()
    self.splitAppearanceApplicator = RNSSplitAppearanceApplicator()
    self.fixedColumnsCount = numberOfColumns

    super.init(style: RNSSplitHostController.styleByNumberOfColumns(numberOfColumns))

    delegate = self
  }

  required init?(coder aDecoder: NSCoder) {
    return nil
  }

  // MARK: Signals

  @objc
  public func setNeedsUpdateOfChildViewControllers() {
    needsChildViewControllersUpdate = true
  }

  @objc
  public func setNeedsAppearanceUpdate() {
    splitAppearanceCoordinator.needs(.generalUpdate)
  }

  @objc
  public func setNeedsSecondaryScreenNavBarUpdate() {
    // We noticed a bug on the pure-native component, which is blocking dynamic updates for showsSecondaryOnlyButton.
    // Toggling this flag doesn't refresh the component and is updated after triggerig some other interaction, like changing layout.
    // We noticed that we can forcefully refresh navigation bar from UINavigationController level by toggling setNavigationBarHidden.
    // After some testing, it looks well and I haven't noticed any flicker - missing button is appearing naturally.
    // Please note that this is a hack rather than a solution so feel free to remove this code in case of any problems and treat the bug with toggling button as a platform's issue.
    splitAppearanceCoordinator.needs(.secondaryScreenNavBarUpdate)
  }

  @objc
  public func setNeedsDisplayModeUpdate() {
    splitAppearanceCoordinator.needs(.displayModeUpdate)
  }

  @objc
  public func setNeedsOrientationUpdate() {
    splitAppearanceCoordinator.needs(.orientationUpdate)
  }

  @objc
  public func setNeedsLayoutDirectionUpdateBelowIOS17() {
    if self.parent != nil {
      splitAppearanceCoordinator.needs(.layoutDirectionUpdateBelowIOS17)
    } else {
      isLayoutDirectionUpdatePending = true
    }
  }

  // MARK: Updating

  @objc
  public func updateChildViewControllersIfNeeded() {
    if needsChildViewControllersUpdate {
      updateChildViewControllers()
    }
  }

  ///
  /// @brief Creates and attaches the Split child controllers based on the current React subviews.
  ///
  /// It validates constraints for Split hierarchy and it will crash after recognizing an invalid state,
  /// e. g. dynamically changed number of columns or number of columns that isn't between defined bounds.
  /// If Split constraints are met, it attaches SplitScreen representatives to SplitHost component.
  ///
  @objc
  public func updateChildViewControllers() {
    precondition(
      needsChildViewControllersUpdate,
      "[RNScreens] Child view controller must be invalidated when update is forced!")

    let currentColumns = filterSubviews(
      ofType: RNSSplitScreenColumnType.column, in: splitReactSubviews)
    let currentInspectors = filterSubviews(
      ofType: RNSSplitScreenColumnType.inspector, in: splitReactSubviews)

    validateColumns(currentColumns)
    validateInspectors(currentInspectors)

    let currentViewControllers = currentColumns.map {
      RNSSplitNavigationController(rootViewController: $0.controller)
    }

    viewControllers = currentViewControllers

    #if compiler(>=6.2)
      maybeSetupInspector(currentInspectors)
    #endif

    for controller in currentViewControllers {
      controller.viewFrameOriginChangeObserver = self
    }

    needsChildViewControllersUpdate = false
  }

  func updateSplitAppearanceIfNeeded() {
    splitAppearanceApplicator.updateAppearanceIfNeeded(
      self.splitHostComponentView, self, self.splitAppearanceCoordinator)
  }

  ///
  /// @brief Triggering appearance updates on secondary column's UINavigationBar component
  ///
  /// It validates that the secondary VC is valid UINavigationController and it updates the navbar
  /// state by toggling it's visibility, what should be performed in a single batch of updates.
  ///
  public func refreshSecondaryNavBar() {
    let secondaryViewController = viewController(for: .secondary)
    assert(
      secondaryViewController != nil,
      "[RNScreens] Failed to refresh secondary nav bar. Secondary view controller is nil.")
    assert(
      secondaryViewController is UINavigationController,
      "[RNScreens] Expected UINavigationController but got \(type(of: secondaryViewController))")
    let navigationController = secondaryViewController as! UINavigationController

    /// The assumption is that it should come in a single batch and it won't cause any delays in rendering the content.
    navigationController.setNavigationBarHidden(true, animated: false)
    navigationController.setNavigationBarHidden(false, animated: false)
  }

  // MARK: Helpers

  ///
  /// @brief Gets the appropriate style for a specified number of columns.
  ///
  /// This utility maps a given number of columns to the corresponding UISplitViewController.Style.
  ///
  /// @param numberOfColumns The number of columns for the SplitView.
  /// @return A UISplitViewController.Style corresponding to the provided column count.
  ///
  static func styleByNumberOfColumns(_ numberOfColumns: Int) -> UISplitViewController.Style {
    switch numberOfColumns {
    case 2:
      return .doubleColumn
    case 3:
      return .tripleColumn
    default:
      return .unspecified
    }
  }

  ///
  /// @brief Filters the given subviews array by a specific column type.
  ///
  /// Iterates over the provided subviews array and returns only the elements that match
  /// the specified RNSSplitScreenColumnType (e.g., .column, .inspector).
  ///
  /// @param type The target RNSSplitScreenColumnType to filter for.
  /// @param subviews The array of RNSSplitScreenComponentView elements to filter.
  /// @return A filtered array of RNSSplitScreenComponentView objects with the specified column type.
  ///
  func filterSubviews(
    ofType type: RNSSplitScreenColumnType, in subviews: [RNSSplitScreenComponentView]
  ) -> [RNSSplitScreenComponentView] {
    return subviews.filter { $0.columnType == type }
  }

  // MARK: Public setters

  ///
  /// @brief Shows or hides the inspector screen.
  /// @remarks Inspector column is only available for iOS 26 or higher.
  ///
  /// @param showInspector Determines whether the inspector column should be visible.
  ///
  @objc
  public func toggleSplitViewInspector(_ showInspector: Bool) {
    #if compiler(>=6.2)
      if showInspector {
        maybeShowInspector()
      } else {
        maybeHideInspector()
      }
    #endif
  }

  ///
  /// @brief Programmatically shows a specific column identified by its string name.
  ///
  /// Maps the string column name to the corresponding `UISplitViewController.Column` and calls `show(_:)`.
  ///
  /// @param columnName A string representing the column to show: `"primary"`, `"supplementary"`, or `"secondary"`.
  ///
  @objc
  public func showColumnNamed(_ columnName: String) {
    guard let column = splitViewColumnFromString(columnName) else {
      assertionFailure("[RNScreens] Unknown column name: \(columnName)")
      return
    }

    show(column)
  }

  ///
  /// @brief Maps a string column name to its corresponding `UISplitViewController.Column` value.
  ///
  /// @param name The column name string: `"primary"`, `"supplementary"`, or `"secondary"`.
  /// @return The corresponding `UISplitViewController.Column`, or `nil` if the name is not recognized.
  ///
  private func splitViewColumnFromString(_ name: String) -> UISplitViewController.Column? {
    switch name {
    case "primary":
      return .primary
    case "supplementary":
      return .supplementary
    case "secondary":
      return .secondary
    default:
      return nil
    }
  }

  // MARK: ReactMountingTransactionObserving

  ///
  /// @brief Called before mounting transaction.
  ///
  @objc
  public func reactMountingTransactionWillMount() {
    // noop
  }

  ///
  /// @brief Called after mounting transaction.
  ///
  /// Updates children and the appearance, checks if the hierarchy is valid after applying updates.
  ///
  @objc
  public func reactMountingTransactionDidMount() {
    updateChildViewControllersIfNeeded()
    updateSplitAppearanceIfNeeded()
    validateSplitViewHierarchy()
  }

  // MARK: RNSSplitHostOrientationProviding
  @objc
  public func evaluateOrientation() -> RNSOrientationSwift {
    return convertToSwiftEnum(splitHostComponentView.orientation)
  }

  func convertToSwiftEnum(_ orientation: RNSOrientation) -> RNSOrientationSwift {
    switch orientation {
    case RNSOrientation.inherit:
      return .inherit
    case RNSOrientation.all:
      return .all
    case RNSOrientation.allButUpsideDown:
      return .allButUpsideDown
    case RNSOrientation.portrait:
      return .portrait
    case RNSOrientation.portraitUp:
      return .portraitUp
    case RNSOrientation.portraitDown:
      return .portraitDown
    case RNSOrientation.landscape:
      return .landscape
    case RNSOrientation.landscapeLeft:
      return .landscapeLeft
    case RNSOrientation.landscapeRight:
      return .landscapeRight
    @unknown default:
      return .inherit
    }
  }

  // MARK: Validators

  ///
  /// @brief Validates that child structure meets required constraints defined for columns and the inspector.
  ///
  func validateSplitViewHierarchy() {
    let columns = filterSubviews(
      ofType: RNSSplitScreenColumnType.column, in: splitReactSubviews)
    let inspectors = filterSubviews(
      ofType: RNSSplitScreenColumnType.inspector, in: splitReactSubviews)

    validateColumns(columns)
    validateInspectors(inspectors)
  }

  ///
  /// @brief Ensures that number of columns is valid and hasn't changed dynamically.
  ///
  func validateColumns(_ columns: [RNSSplitScreenComponentView]) {
    assert(
      columns.count >= minNumberOfColumns
        && columns.count <= maxNumberOfColumns,
      "[RNScreens] Split can only have from \(minNumberOfColumns) to \(maxNumberOfColumns) columns"
    )

    assert(
      columns.count == fixedColumnsCount,
      "[RNScreens] Split number of columns shouldn't change dynamically")
  }

  ///
  /// @brief Ensures that at most one inspector is present.
  ///
  func validateInspectors(_ inspectors: [RNSSplitScreenComponentView]) {
    assert(
      inspectors.count <= maxNumberOfInspectors,
      "[RNScreens] Split can only have \(maxNumberOfInspectors) inspector")
  }
}

extension RNSSplitHostController {

  ///
  /// @brief Gets the children RNSSplitScreenController instances.
  ///
  /// Accesses Split controllers associated with presented columns. It asserts that each view controller is a navigation controller and its topViewController is of type RNSSplitScreenController.
  ///
  /// @return An array of RNSSplitScreenController corresponding to current split view columns.
  ///
  var splitScreenControllers: [RNSSplitScreenController] {
    return visibleColumns.compactMap { column in
      let viewController = self.viewController(for: column)
      assert(viewController != nil, "[RNScreens] viewController for column \(column) is nil.")

      let splitNavigationController = viewController as? RNSSplitNavigationController
      assert(
        splitNavigationController != nil,
        "[RNScreens] Expected RNSSplitNavigationController but got \(type(of: viewController))")

      let maybeSplitScreenController = splitNavigationController?.topViewController
      assert(
        maybeSplitScreenController != nil,
        "[RNScreens] RNSSplitScreenController is nil for column \(column)")
      assert(
        maybeSplitScreenController is RNSSplitScreenController,
        "[RNScreens] Expected RNSSplitScreenController but got \(type(of: maybeSplitScreenController))"
      )

      return maybeSplitScreenController as? RNSSplitScreenController
    }
  }

  ///
  /// @brief Gets all React subviews of type RNSSplitScreenComponentView.
  ///
  /// Accesses all the subviews from the reactSubviews collection. It asserts that each one is a RNSSplitScreenComponentView.
  ///
  /// @return An array of RNSSplitScreenComponentView subviews which are children of the host component view.
  ///
  var splitReactSubviews: [RNSSplitScreenComponentView] {
    return self.splitHostComponentView.reactSubviews().lazy.map { subview in
      assert(
        subview is RNSSplitScreenComponentView,
        "[RNScreens] Expected RNSSplitScreenComponentView but got \(type(of: subview))")

      return subview as! RNSSplitScreenComponentView
    }
  }
}

extension RNSSplitHostController: RNSSplitNavigationControllerViewFrameObserver {

  ///
  /// @brief Notifies that an origin of parent RNSSplitNavigationController frame has changed.
  ///
  /// It iterates over children controllers and notifies them for the layout update.
  ///
  /// @param splitNavCtrl The navigation controller whose frame origin changed.
  ///
  func splitNavCtrlViewDidChangeFrameOrigin(
    _ splitNavCtrl: RNSSplitNavigationController
  ) {
    for controller in self.splitScreenControllers {
      controller.columnPositioningDidChangeIn(splitViewController: self)
    }
  }
}

/// This extension is a workaround for missing UISplitViewController symbols introduced in iOS 26,
/// allowing the project to compile and run on iOS 18 or earlier versions.

#if compiler(>=6.2)
  extension RNSSplitHostController {

    ///
    /// @brief Sets up the inspector column if available.
    /// @remarks Inspector columns is available only on iOS 26 or higher.
    ///
    /// Attaches a view controller for the inspector column.
    ///
    /// @param inspectors An array of inspector-type RNSSplitScreenComponentView subviews.
    ///
    func maybeSetupInspector(_ inspectors: [RNSSplitScreenComponentView]) {
      #if !os(tvOS)
        if #available(iOS 26.0, *) {
          let inspector = inspectors.first
          if inspector != nil {
            let inspectorViewController = RNSSplitNavigationController(
              rootViewController: inspector!.controller)
            setViewController(inspectorViewController, for: .inspector)
          }
        }
      #endif
    }

    ///
    /// @brief Shows the inspector column when available.
    /// @remarks Inspector columns is available only on iOS 26 or higher.
    ///
    /// Uses the UISplitViewController's new API introduced in iOS 26 to show the inspector column.
    ///
    func maybeShowInspector() {
      #if !os(tvOS)
        if #available(iOS 26.0, *) {
          show(.inspector)
        }
      #endif
    }

    ///
    /// @brief Hides the inspector column when available.
    /// @remarks Inspector columns is available only on iOS 26 or higher.
    ///
    /// Uses the UISplitViewController's new API introduced in iOS 26 to hide the inspector column.
    ///
    func maybeHideInspector() {
      #if !os(tvOS)
        if #available(iOS 26.0, *) {
          hide(.inspector)
        }
      #endif
    }
  }
#endif

extension RNSSplitHostController: UISplitViewControllerDelegate {
  public func splitViewController(
    _ svc: UISplitViewController, willShow column: UISplitViewController.Column
  ) {
    visibleColumns.insert(column)
  }

  public func splitViewController(
    _ svc: UISplitViewController, willHide column: UISplitViewController.Column
  ) {
    visibleColumns.remove(column)
  }

  public func splitViewControllerDidCollapse(_ svc: UISplitViewController) {
    reactEventEmitter.emitOnCollapse()
  }

  public func splitViewControllerDidExpand(_ svc: UISplitViewController) {
    reactEventEmitter.emitOnExpand()
  }

  #if compiler(>=6.2)
    ///
    /// @brief Called after a column in the split view controller has been hidden from the interface.
    ///
    /// Currently emits onHideInspector event for the inspector if applicable.
    ///
    /// @param svc The split view controller that just hid the column.
    /// @param column The column that was hidden.
    ///
    public func splitViewController(
      _ svc: UISplitViewController, didHide column: UISplitViewController.Column
    ) {
      #if !os(tvOS)
        if #available(iOS 26.0, *) {
          // TODO: we may consider removing this logic, because it could be handled by onViewDidDisappear on the column level
          // On the other hand, maybe dedicated event related to the inspector would be a better approach.
          // For now I am leaving it, but feel free to drop this method if there's any reason that `onDidDisappear` works better.

          if column != .inspector {
            return
          }

          // `didHide` for modal is called on finger down for dismiss, what is problematic, because we can cancel dismissing modal.
          // In this scenario, the modal inspector might receive an invalid state and will deviate from the JS value.
          // Therefore, for event emissions, we need to ensure that the view was detached from the view hierarchy, by checking its window.
          if let inspectorViewController = viewController(for: .inspector) {
            if inspectorViewController.view.window == nil {
              reactEventEmitter.emitOnHideInspector()
            }
          }

        }
      #endif
    }
  #endif

  @objc
  public func splitViewController(
    _ svc: UISplitViewController, willChangeTo displayMode: UISplitViewController.DisplayMode
  ) {
    if self.displayMode != displayMode {
      reactEventEmitter.emitOnDisplayModeWillChange(from: self.displayMode, to: displayMode)
    }
  }

  public func splitViewController(
    _ svc: UISplitViewController,
    topColumnForCollapsingToProposedTopColumn proposedTopColumn: UISplitViewController.Column
  ) -> UISplitViewController.Column {
    if splitHostComponentView.hasCustomTopColumnForCollapsing {
      return splitHostComponentView.topColumnForCollapsingColumn
    }
    return proposedTopColumn
  }

  public override func didMove(toParent parent: UIViewController?) {
    super.didMove(toParent: parent)

    if parent != nil && isLayoutDirectionUpdatePending {
      isLayoutDirectionUpdatePending = false
      splitAppearanceApplicator.updateLayoutDirectionBelowIOS17(
        self.splitHostComponentView, self)
    }
  }
}