facade2.swift

import UIKit

class MarkdownPreviewViewController: UIViewController {
    @IBOutlet weak var markdownTextView: UITextView!
    private var markdownPreviewer = MarkdownPreviewer()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        Task {
            await prepareMarkdown(from: "https://www.awesomemarkdownresourcetouse.com")
        }
    }
}

extension MarkdownPreviewViewController {
    func prepareMarkdown(from url: String) async {
        do {
            try await markdownPreviewer.showMarkdown(in: markdownTextView, url: url)
        } catch {
            print(error.localizedDescription)
        }
    }
}


@MainActor class MarkdownPreviewer {
    private struct MarkdownWorker {
        static func parse(markdown: String) -> String { markdown }
        @discardableResult static func cache(markdown: String) -> String { markdown }
    }
    
    private func prepareMarkdown(contentsOf url: String) async throws -> String {
        let url = URL(string: url)!
        let (data, _) = try await URLSession.shared.data(from: url)
        let downloadedMarkdownData = String(data: data, encoding: .utf8) ?? ""
        let parsedMarkdown = MarkdownWorker.parse(markdown: downloadedMarkdownData)
        let cachedMarkdown = MarkdownWorker.cache(markdown: parsedMarkdown)
        return cachedMarkdown
    }
    
    func showMarkdown(in textview: UITextView, url: String) async throws {
        do {
            let markdownData = try await prepareMarkdown(contentsOf: url)
            textview.text = markdownData
        } catch {
            print(error.localizedDescription)
        }
        
    }
}