OnWindowClose.swift

//
//  OnWindowClose.swift
//
//  Created by David Albert on 12/16/23.
//

import SwiftUI
import AppKit

struct WindowReader: NSViewRepresentable {
    class View: NSView {
        static let didMoveToWindowNotification: NSNotification.Name = NSNotification.Name("viewDidMoveToWindow")

        override func viewDidMoveToWindow() {
            super.viewDidMoveToWindow()
            NotificationCenter.default.post(name: Self.didMoveToWindowNotification, object: self)
        }
    }

    class Coordinator {
        var observer: AnyObject?
    }

    func makeCoordinator() -> Coordinator {
        Coordinator()
    }

    @Binding var window: NSWindow?

    func makeNSView(context: Context) -> View {
        let view = View()
        let observer = NotificationCenter.default.addObserver(forName: View.didMoveToWindowNotification, object: view, queue: nil) { _ in
            window = view.window
        }
        context.coordinator.observer = observer
        return view
    }
    
    func updateNSView(_ nsView: View, context: Context) {
    }

    static func dismantleNSView(_ nsView: View, coordinator: Coordinator) {
        guard let observer = coordinator.observer else {
            return
        }
        NotificationCenter.default.removeObserver(observer)
    }
}

struct OnWindowClose: ViewModifier {
    @State var window: NSWindow?
    @State var observer: AnyObject?

    let action: () -> Void

    func body(content: Content) -> some View {
        content
            .background {
                WindowReader(window: $window)
            }
            .onChange(of: window) {
                // Can't just use onReceive and NotificationCenter.publisher(for:) because window starts as nil, and we don't want
                // to register an observer for every window.
                if let observer {
                    NotificationCenter.default.removeObserver(observer)
                    self.observer = nil
                }
                if let window {
                    observer = NotificationCenter.default.addObserver(forName: NSWindow.willCloseNotification, object: window, queue: nil) { _ in
                        action()
                    }
                }
            }
    }
}

extension View {
    func onWindowClose(perform action: @escaping () -> Void) -> some View {
        modifier(OnWindowClose(action: action))
    }
}