none7

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Threading;

namespace WindowsFormsApp1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        string key = "";
        char StartChar = '1';
        bool lifeWork = false;
        int line = 0, success = 0;
        private void button1_Click(object sender, EventArgs e)
        {
            key = textBox1.Text;
            StartChar = Convert.ToChar(textBox1.Text.Substring(0, 1));
            timerLog.Interval = 100;
            timerLog.Enabled = true;
            lifeWork = true;
            _ = Work();
        }

        IEnumerable<long> GetWorks(string key)
        {
            long value = EncodeBase36(key);

            while (true)
            {
                long newValue = value - 1;
                if (StartChar != Convert.ToChar(DecodeBase36(newValue).Substring(0, 1)))
                {
                    break;
                }
                yield return newValue;
                value = newValue;
            }
        }
        private async Task Work()
        {
            var set = new HashSet<Task>();
            var jobsSim = new SemaphoreSlim(30, 30);
            var lockSim = new SemaphoreSlim(1, 1);

            foreach(var value in GetWorks(key))
            {
                if (!lifeWork) break;

                // ограничиваем число потоков
                // по большей части лимит нужен, чтобы не зафлудить сервер запросами
                await jobsSim.WaitAsync();
                Task task = GetResponce(DecodeBase36(value));
                await lockSim.WaitAsync();
                set.Add(task);
                lockSim.Release();
                _ = task.ContinueWith(async(t) => {
                    await lockSim.WaitAsync();
                    success++;
                    set.Remove(t);
                    lockSim.Release();
                    jobsSim.Release();
                });
                line++;
            }

            await lockSim.WaitAsync();
            var tasks = set.ToList();
            lockSim.Release();

            await Task.WhenAll(tasks);

            MessageBox.Show("Off work");
        }
        private async Task GetResponce(string value)
        {
            // Тут будет происходить гет запрос и прочая работа с строкой . По времени занимает от 5 до 15 секунд.
            // Так что код сделла чисто для симуляции времени работы .
            Random rnd = new Random();
            int timeOutn = rnd.Next(5, 15);
            await Task.Delay(timeOutn * 1000);
        }
        public static long EncodeBase36(string number, int radix = 36)
        {
            const string Digits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

            if (radix < 2 || radix > Digits.Length)
                throw new ArgumentException("The radix must be >= 2 and <= " +
                    Digits.Length.ToString());

            if (String.IsNullOrEmpty(number))
                return 0;

            // Make sure the arbitrary numeral system number is in upper case
            number = number.ToUpperInvariant();

            long result = 0;
            long multiplier = 1;
            for (int i = number.Length - 1; i >= 0; i--)
            {
                char c = number[i];
                if (i == 0 && c == '-')
                {
                    // This is the negative sign symbol
                    result = -result;
                    break;
                }

                int digit = Digits.IndexOf(c);
                if (digit == -1)
                    throw new ArgumentException(
                        "Invalid character in the arbitrary numeral system number",
                        "number");

                result += digit * multiplier;
                multiplier *= radix;
            }

            return result;
        }

        private void timerLog_Tick(object sender, EventArgs e)
        {
            lbLine.Text = line.ToString();
            lbSuccess.Text = success.ToString();
        }

        public static string DecodeBase36(long decimalNumber, int radix = 36)
        {
            const int BitsInLong = 64;
            const string Digits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

            if (radix < 2 || radix > Digits.Length)
                throw new ArgumentException("The radix must be >= 2 and <= " +
                    Digits.Length.ToString());

            if (decimalNumber == 0)
                return "0";

            int index = BitsInLong - 1;
            long currentNumber = Math.Abs(decimalNumber);
            char[] charArray = new char[BitsInLong];

            while (currentNumber != 0)
            {
                int remainder = (int)(currentNumber % radix);
                charArray[index--] = Digits[remainder];
                currentNumber = currentNumber / radix;
            }

            string result = new String(charArray, index + 1, BitsInLong - index - 1);
            if (decimalNumber < 0)
            {
                result = "-" + result;
            }

            return result;
        }
    }
}