// From https://github.com/kaishin/Markoff/blob/markoff-2/Markoff/Sources/Views/WebView.swift
// Based on https://github.com/kylehickinson/SwiftUI-WebView

import SwiftUI
import Combine
import WebKit

class WebViewStore: ObservableObject {
    private var observers = Set<NSKeyValueObservation>()
    
    @Published  var webView: WKWebView {
        didSet {
            setupObservers()
        }
    }
    
    init(webView: WKWebView = .init()) {
        self.webView = webView
        
        #if DEBUG
        self.webView
            .configuration
            .preferences
            .setValue(true, forKey: "developerExtrasEnabled")
        #endif
        
        setupObservers()
    }
    
    private func setupObservers() {
        func subscriber<Value>(for keyPath: KeyPath<WKWebView, Value>) -> NSKeyValueObservation {
            webView.observe(keyPath, options: [.prior]) { _, change in
                if change.isPrior {
                    self.objectWillChange.send()
                }
            }
        }
        
        observers = [
            subscriber(for: \.title),
            subscriber(for: \.url),
            subscriber(for: \.isLoading),
            subscriber(for: \.estimatedProgress),
            subscriber(for: \.hasOnlySecureContent),
            subscriber(for: \.serverTrust),
            subscriber(for: \.canGoBack),
            subscriber(for: \.canGoForward)
        ]
    }
}

extension WebViewStore {
    func update(_ HTML: String, baseURL: URL? = nil) {
        webView.evaluateJavaScript("window.pageYOffset") { [weak self] object, error in
            self?.webView.loadHTMLString(HTML, baseURL: baseURL)
            
            if let offset = object as? Int {
                self?.scrollTo(offset)
            }
        }
    }
    
    private func scrollTo(_ YOffset: Int) {
        let script = "window.scrollTo(0, \(YOffset));"
        let scrollScript = WKUserScript(source: script, injectionTime: .atDocumentEnd, forMainFrameOnly: true)
        self.webView.configuration.userContentController.addUserScript(scrollScript)
    }
}

#if os(iOS)
struct WebView: View, UIViewRepresentable {
    let webView: WKWebView
    
    init(webView: WKWebView) {
        self.webView = webView
    }
    
    func makeUIView(context: Context) -> WKWebView {
        return webView
    }
    
    func updateUIView(_ view: WKWebView, context: Context) {}
}
#elseif os(macOS)
struct WebView: View, NSViewRepresentable {
    let webView: WKWebView
    
    init(webView: WKWebView) {
        self.webView = webView
    }
    
    func makeNSView(context: Context) -> WKWebView {
        return webView
    }
    
    func updateNSView(_ view: WKWebView, context: Context) {}
}
#endif