WebView.swift

//
//  WebView.swift
//  Core
//
//  Created by Eric Vitiello on 1/28/20.
//  Copyright © 2020 Eric Vitiello. All rights reserved.
//

import SwiftUI
import Combine
import WebKit


/// A container for using a WKWebView in SwiftUI
public struct WebView: View, UIViewRepresentable {
	@ObservedObject var node: Node
	public let view: WKWebView = WKWebView()
	public var colorScheme: ColorScheme = .light
	
	init(node: Node, colorScheme: ColorScheme) {
		self.colorScheme = colorScheme
		self.node = node
	}
	
	public func makeUIView(context: Context) -> WKWebView {
		self.view.uiDelegate = context.coordinator
		self.view.navigationDelegate = context.coordinator
		self.view.backgroundColor = UIColor.systemBackground
		self.view.isOpaque = false
		return self.view
	}
	
	public func updateUIView(_ uiView: WKWebView, context: Context) {
		self.updateContent(withString: self.node.renderedContent())
	}
	
	public func updateContent(withString content: String) {
		self.view.loadHTMLString(content, baseURL: nil)
	}
	
	public func makeCoordinator() -> Coordinator {
		Coordinator(self, colorScheme: colorScheme, node: node)
	}
	
	/// Coordinator handles delegate communications for the WebView
	public final class Coordinator: NSObject, WKUIDelegate, WKNavigationDelegate {
		var control: WebView
		var colorScheme: ColorScheme = .light
		@ObservedObject var node: Node
		var subscribers: [AnyCancellable] = []

		init(_ control: WebView, colorScheme: ColorScheme, node: Node) {
			self.control = control
			self.colorScheme = colorScheme
			self.node = node
			let subscriber = node.$content.receive(on: RunLoop.main).sink(receiveValue: contentDidChange)
			subscribers.append(subscriber)
		}
		
		deinit {
			for subscriber in subscribers { subscriber.cancel() }
		}
		
		var contentDidChange: (String) -> Void = { content in
			Logger.log("Node Content Changed, rerendering.", severity: .Verbose)
			
		}
				
		public func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
			let fileStem: String = (colorScheme == .dark) ? "markdown-dark" : "markdown-light"
			let cssFileContent = self.cssFileContents(fileStem: fileStem)
			let cssCommonFileContent = self.cssFileContents(fileStem: "markdown-common")
			let jsString = "var styleCommon = document.createElement('style'); styleCommon.innerHTML = '\(cssCommonFileContent)'; document.head.appendChild(styleCommon); var style = document.createElement('style'); style.innerHTML = '\(cssFileContent)'; document.head.appendChild(style); var title = document.createElement('title'); title.innerHTML = 'Node Detail Content'; document.head.appendChild(title);"
			webView.evaluateJavaScript(jsString, completionHandler: nil)
		}
		
		private func cssFileContents(fileStem: String) -> String {
			Logger.log("Current Appearance: \(colorScheme)", severity: .Verbose)
			guard let path = Bundle.main.path(forResource: fileStem, ofType: "css") else { return "" }
			let cssFileContent = try! String(contentsOfFile: path)
			let cssString = cssFileContent.trimmingCharacters(in: .whitespacesAndNewlines).filter { !"\n\r".contains($0) }
			return cssString
		}
	}
}