cloud-dns-ios/dns/BlockedCount.swift

import SwiftUI
import Foundation

struct BlockedCount: View {

    @State private var txtRecord: String = "..."

    private static let startIndex = 44

    private static let formatter: NumberFormatter = {
        let formatter = NumberFormatter()
        formatter.numberStyle = .decimal

        return formatter
    }()

    var body: some View {
        Text(txtRecord)
        .onAppear {
            fetchTXTRecord()
        }
    }

    func parseResponse(data: Data) -> String? {
        // This is a DNS wire format response and we make a lot of assumptions
        // It is not critical functionality so just let it fail if it fails

        guard data.count > Self.startIndex else {
            return nil
        }

        // Find the first space character (ASCII 32).
        guard let endIndex = data.suffix(from: Self.startIndex).firstIndex(of: 32) else {
            return nil
        }

        guard let numberString = String(data: data[Self.startIndex ..< endIndex], encoding: .utf8)
        else {
            return nil
        }

        return Self.formatter.string(for: Int(numberString))
    }
    
    func fetchTXTRecord() {
        let dohURL = URL(string: "https://dns.sr2.uk/dns-query?dns=DoQBAAABAAAAAAAABXN0YXRzB2ludmFsaWQAABAAAQ")!

        let request = URLRequest(url: dohURL)

        URLSession.shared.dataTask(with: request) { data, response, error in
            DispatchQueue.main.async {
                if error != nil {
                    txtRecord = "Error"
                    return
                }

                guard let data = data else {
                    txtRecord = "Error"
                    return
                }

                guard let count = parseResponse(data: data) else {
                    txtRecord = "Error"
                    return
                }

                txtRecord = count
            }
        }.resume()
    }
}

#Preview {
    BlockedCount()
}