using System;

using System.Text.RegularExpressions;

​

public class DateExtractor

{

    public static string ExtractDate(string input)

    {

        if (string.IsNullOrEmpty(input))

        {

            return null;

        }

​

        // Combine all date formats into a single regex pattern with word boundaries.

        string pattern = @"\b(\d{2}\.\d{2}\.\d{4})\b|\b(\d{2}\.\d{2}\.\d{4}\s/\s\d{2}:\d{2}:\d{2})\b|\b(\d{2}/\d{2}/\d{2}\s\d{2}:\d{2})\b";

​

        Match match = Regex.Match(input, pattern);

​

        while (match.Success)

        {

            string date = null;

​

            if (match.Groups[1].Success)

            {

                date = match.Groups[1].Value;

                if (IsValidDate(date, "dd.MM.yyyy"))

                {

                    return date;

                }

            }

            else if (match.Groups[2].Success)

            {

                date = match.Groups[2].Value.Substring(0, 10);

                if (IsValidDate(date, "dd.MM.yyyy"))

                {

                    return date;

                }

            }

            else if (match.Groups[3].Success)

            {

                date = match.Groups[3].Value.Substring(0, 8);

                if (IsValidDate(date, "dd/MM/yy"))

                {

                    return date;

                }

            }

            match = match.NextMatch();

        }

​

        return null;

    }

​

    private static bool IsValidDate(string date, string format)

    {

        try

        {

            DateTime.ParseExact(date, format, System.Globalization.CultureInfo.InvariantCulture);

            return true;

        }

        catch (FormatException)

        {

            return false;

        }

    }

​

    public static void Main(string[] args)

    {

        string input1 = "Order registration: 05.06.2019";

        string input2 = "Nationality : Kazakh Collection Date : 03.03.2021 / 07:18:19";

        string input3 = "SPEC #: 223456 Collection Date/Time: 02/10/14 14:30 ";

​

        Console.WriteLine($"Input: {input1}, Output: {ExtractDate(input1)}");

        Console.WriteLine($"Input: {input2}, Output: {ExtractDate(input2)}");

        Console.WriteLine($"Input: {input3}, Output: {ExtractDate(input3)}");

    }

}