import SwiftUI
import os

extension Logger {
  fileprivate static let nav = Logger(subsystem: Bundle.main.bundleIdentifier ?? "unknown", category: "nav")
}

enum Selection: String, CaseIterable, Codable, Sendable {
  case first
  case second
  
  var opposite : Selection {
    switch self {
    case .first:
        .second
    case .second:
        .first
    }
  }
}

struct Path : Hashable, CustomStringConvertible {
  let string : String
  let value : Int
  var selection : Selection { Selection(rawValue: string) ?? .first }
  var description: String { "Path: \(string)-\(value)" }
}

@Observable final class Navigation: CustomStringConvertible {
  var selection : Selection?
  var firstPath : [Path]
  var secondPath : [Path]

  internal init(selection: Selection = .first, firstPath : [Path] = [], secondPath : [Path] = []) {
    self.selection = selection
    self.firstPath = firstPath
    self.secondPath = secondPath
  }
  
  func navigate(selection: Selection) {
    Logger.nav.log("nav to selection: \(selection.rawValue, privacy: .public)")
    self.selection = selection
  }
  
  func navigate(path: Path) {
    Logger.nav.log("nav to path: \(path, privacy: .public)")
    let pathSelection = path.selection
    if selection == pathSelection {
      Logger.nav.log("just path")
      self.path.append(path)
    } else {
      Logger.nav.log("selection: \(pathSelection.rawValue, privacy: .public) and path")
      self.selection = pathSelection // here is the bug?
      self.path = [path]
    }
  }
  
  var path : [Path] {
    get {
      guard let selection else { return [] }
      switch selection {
      case .first:
        return firstPath
      case .second:
        return secondPath
      }
    } set {
      guard let selection else { return }
      switch selection {
      case .first:
        firstPath = newValue
      case .second:
        secondPath = newValue
      }
    }
  }
  
  var description : String {
    let sv = selection?.rawValue ?? "nil"
    return "s: \(sv) fp: \(firstPath) sp: \(secondPath)"
  }
}

struct SelectionView : View {
  let navigation: Navigation
  let selection : Selection
  
  var body: some View {
    Text("Selection: \(selection.rawValue)")
    Text("\(navigation)")
    
    let link = Path(string:selection.opposite.rawValue, value: 1)
    NavigationLink("Nav Link: \(link)", value: link)
    let sel = selection.opposite
    Button("Nav Sel: \(sel.rawValue)") { navigation.navigate(selection: sel)}
    let path = Path(string: selection.opposite.rawValue, value: 100)
    Button("Nav Path: \(path)") { navigation.navigate(path: path)}
  }
}

struct DestinationView : View {
  let navigation: Navigation
  let path : Path
  
  var body: some View {
    Group {
      Text("Destination: \(path)")
      Text("\(navigation)")

      let link = Path(string:path.string, value: path.value + 1)
      NavigationLink("Nav Link: \(link)", value: link)
      let path = Path(string:path.string, value: path.value + 100)
      Button("Nav Path: \(path)") { navigation.navigate(path: path)}
    }.navigationTitle(Text("\(path)"))
  }
}

struct ContentView: View {
  @State private var navigation = Navigation()

  var body: some View {
    @Bindable var nav = navigation
    NavigationSplitView {
      List(Selection.allCases, id: \.self, selection: $nav.selection) { selection in
        Text(selection.rawValue)
      }
      .navigationTitle(Text("Root"))
    } detail: {
      if let selection = nav.selection {
        NavigationStack(path: $nav.path) {
          SelectionView(navigation: navigation, selection: selection)
            .navigationDestination(for: Path.self) { DestinationView(navigation: navigation, path: $0) }
        }
        .navigationTitle(Text(selection.rawValue))
      } else {
        Text("Select Something")
      }
    }
  }
}