using System;

using System.Collections.Generic;

using System.Linq;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        string input = "Age should be between 1 and 99.";

        string required = "The {0} field is required.";

        string date = "The {0} field is not a valid date.";

        string range = "{0} should be between {1} and {2}.";

​

        bool isRequired = false;

        bool isDate = false;

        string extractedField;

        bool isRange = false;

​

        var possibilities = new []

                            {

                                new KeyValuePair<string,Action>(ToRegex(required), ()=>((Action)(() => { isRequired = true;}))()),

                                new KeyValuePair<string,Action>(ToRegex(date), ()=>((Action)(() => { isDate = true;}))()),

                                new KeyValuePair<string,Action>(ToRegex(range), ()=>((Action)(() => { isRange = true;}))())

                            };

        var result = possibilities

                     .Where(x=>Regex.Match(input,x.Key).Success)

                     .Select(x=> new KeyValuePair<IEnumerable<string>,Action>( 

                                                    Regex.Match(input,x.Key).Groups.Cast<Group>().Where(c=>c.Name.StartsWith("Field")).Select(c=>c.Value),

                                                    x.Value)).First();

​

​

        var fields = result.Key;

        result.Value();

        Console.WriteLine($"{nameof(extractedField)}={string.Join(",",fields)},{Environment.NewLine}{nameof(isRequired)}={isRequired},{Environment.NewLine}{nameof(isDate)}={isDate}");

    }

    public static string ToRegex(string value)

    {

        var result = new List<string>();

        foreach(var item in value.Split(' '))

        {

            if(Regex.Match(item,@"{(?<Value>\d*)}").Success)

            {

                var match = Regex.Match(item,@"{(?<Value>\d*)}");

​

                result.Add(Regex.Replace(item,@"{(?<Value>\d*)}",$"(?<Field{match.Groups["Value"].Value}>\\S*)"));

                continue;

            }

            result.Add(item);

        };

        return string.Join(" ",result);

    }

}