import SwiftUI
import UIKit

private final class HostModel: ObservableObject {
  @Published var axis = "vertical"
  @Published var spacing: Double = 0
  @Published var alignment = "leading"
  var onHeight: ((CGFloat) -> Void)?
}

private struct HostContent: View {
  @ObservedObject var model: HostModel
  @ObservedObject var environment: OneNativeEnvironmentModel
  @ObservedObject var children: OneNativeChildren
  // composed, the parent lays this stack out and measures it; only a standalone host
  // answers to Yoga.
  let standalone: Bool

  var body: some View {
    OneNativeEnvironment(model: environment, content: stack)
      .oneNativeMeasured(standalone, model.onHeight)
  }

  @ViewBuilder private var stack: some View {
    if model.axis == "horizontal" {
      HStack(alignment: vertical, spacing: model.spacing) {
        ForEach(children.items) { child in child.content }
      }
    } else {
      VStack(alignment: horizontal, spacing: model.spacing) {
        ForEach(children.items) { child in child.content }
      }
      .frame(maxWidth: .infinity, alignment: alignment)
    }
  }

  // alignment names the cross axis, so it reads as leading/trailing down a column and
  // as top/bottom across a row.
  private var horizontal: HorizontalAlignment {
    switch model.alignment {
    case "center": return .center
    case "trailing": return .trailing
    default: return .leading
    }
  }

  private var vertical: VerticalAlignment {
    switch model.alignment {
    case "center": return .center
    case "trailing": return .bottom
    default: return .top
    }
  }

  private var alignment: Alignment {
    switch model.alignment {
    case "center": return .center
    case "trailing": return .trailing
    default: return .leading
    }
  }
}

@objcMembers
public final class OneNativeHostView: OneNativeContainerView {
  public var onMeasure: ((CGFloat) -> Void)?
  private let model: HostModel
  private let environment: OneNativeEnvironmentModel

  public init() {
    let model = HostModel()
    let environment = OneNativeEnvironmentModel()
    self.model = model
    self.environment = environment
    super.init(wrap: { children, standalone in
      AnyView(HostContent(model: model, environment: environment, children: children, standalone: standalone))
    })
    model.onHeight = { [weak self] height in self?.onMeasure?(height) }
  }

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

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

  public func configureEnvironment(
    colorScheme: String, dynamicTypeSize: String, controlSize: String, locale: String,
    tint: UIColor?, isEnabled: String
  ) {
    environment.configure(
      colorScheme: colorScheme, dynamicTypeSize: dynamicTypeSize, controlSize: controlSize,
      locale: locale, tint: tint, isEnabled: isEnabled)
  }

  public override func reset() {
    environment.reset()
    super.reset()
  }
}