import SwiftUI
import UIKit

private final class LazyVStackModel: ObservableObject {
  @Published var alignment = "center"
  @Published var spacing = -1.0
}

private struct LazyVStackContent: View {
  @ObservedObject var model: LazyVStackModel
  @ObservedObject var children: OneNativeChildren
  let standalone: Bool
  @ObservedObject var bridge: OneNativeSchemeBridge

  // negative is how React Native says the caller left spacing out, which keeps the
  // stack on the platform default rather than an arbitrary constant.
  var body: some View {
    LazyVStack(alignment: alignment, spacing: model.spacing >= 0 ? model.spacing : nil) {
      ForEach(children.items) { child in child.content }
    }
    .oneNativeScheme(standalone, bridge.scheme)
  }

  // every value the TypeScript side accepts has a case here, so an unknown one cannot
  // reach the view and quietly land somewhere the props did not ask for.
  private var alignment: HorizontalAlignment {
    switch model.alignment {
    case "leading": return .leading
    case "center": return .center
    case "trailing": return .trailing
    default: preconditionFailure("invalid Swift.LazyVStack alignment: \(model.alignment)")
    }
  }
}

@objcMembers
public final class OneNativeLazyVStackView: OneNativeContainerView {
  private let model: LazyVStackModel
  private let bridge: OneNativeSchemeBridge
  private var traitRegistration: NSObjectProtocol?

  public init() {
    let model = LazyVStackModel()
    let bridge = OneNativeSchemeBridge()
    self.model = model
    self.bridge = bridge
    super.init(wrap: { children, standalone in
      AnyView(LazyVStackContent(model: model, children: children, standalone: standalone, bridge: bridge))
    })
    traitRegistration = registerForTraitChanges([UITraitUserInterfaceStyle.self]) {
      [weak bridge] (view: OneNativeLazyVStackView, _: UITraitCollection) in
      bridge?.sync(view.traitCollection)
    }
  }

  required init?(coder: NSCoder) { fatalError("init(coder:) is unavailable") }

  public override func didMoveToWindow() {
    bridge.sync(traitCollection)
    super.didMoveToWindow()
  }

  public func configure(alignment: String, spacing: Double) {
    if model.alignment != alignment { model.alignment = alignment }
    if model.spacing != spacing { model.spacing = spacing }
  }
}