using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net.Http;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;
using System.Threading.Tasks.Dataflow;

namespace Get_Links
{
    class Files
    {
        IEnumerable<Uri> items;
        int parallel;
        HttpClient http;

        public Files(IEnumerable<Uri> items, int parallel)
        {
            this.items = items;
            this.parallel = parallel;
            http = new HttpClient();
        }

        public Task CopyTo(string path, CancellationToken cancel = default)
        {
            if (!Directory.Exists(path))
                Directory.CreateDirectory(path);
            var action = new ActionBlock<Uri>(
                async x => File.WriteAllBytes($"{Path.Combine(path, x.Host)}.txt", await http.GetByteArrayAsync(x)),
                new ExecutionDataflowBlockOptions { CancellationToken = cancel, MaxDegreeOfParallelism = parallel });
            foreach (var item in items)
                action.Post(item);
            action.Complete();
            return action.Completion;
        }
    }

    class Links : IEnumerable<Uri>
    {
        const string URL_REGEX = @"(http|ftp|https):\/\/[\w\-_]+(\.[\w\-_]+)+([\w\-\.,@?^=%&amp;:/~\+#]*[\w\-\@?^=%&amp;/~\+#])?";

        readonly IEnumerable<Uri> e;

        public Links(string input)
        {
            e = Regex
                .Matches(input, URL_REGEX)
                .Cast<Match>()
                .Select(x => new Uri(x.Value));
        }

        public IEnumerator<Uri> GetEnumerator() => e.GetEnumerator();

        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
    }

    class Program
    {
        static async Task Main(string[] args)
        {
            var files = new Files(new Links("https://2ch.hk https://www.yandex.ru"), 4);
            await files.CopyTo("files");
        }
    }
}