using System;

using System.Collections.Generic;

using System.Linq;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Serialization;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string FormatExpression = @"£###,###,##0.00 a year";

        // Get prefix

        var regex = new Regex("^([^#^0])+");

        Match match = regex.Match(FormatExpression);

        string prefix = match.Value;

        // Get suffix

        regex = new Regex("[^#^0]+$");

        match = regex.Match(FormatExpression);

        string suffix = match.Value;

        // Get remaining numeric string

        var numString = FormatExpression.Substring(prefix.Length, FormatExpression.Length - prefix.Length - suffix.Length);

        // Try and find thousand and decimal seperator and 

        var seperators = new Dictionary<string, int>();

        regex = new Regex("[^#^0]");

        foreach(Match m in regex.Matches(numString)) {

            if (!seperators.ContainsKey(m.Value)) {

                seperators.Add(m.Value, 1);

            }

            else 

            {

                seperators[m.Value]+=1;

            }

        }

        char? thousandseperator = null;

        char? decimalseperator = null;

        switch (seperators.Count) {

            case 0:

                break;

            case 1:

                if (seperators.First().Value==1) {

                    decimalseperator = seperators.First().Key[0];

                }

                else {

                    thousandseperator = seperators.First().Key[0];

                }

                break;

            case 2:

                if (seperators.Last().Value>1) throw new Exception("Invalid format expression");

                thousandseperator = seperators.First().Key[0];

                decimalseperator = seperators.Last().Key[0];

                break;

            default:

                throw new Exception("Invalid format expression");

        }

        int numDecimals = 0;

        bool forceTrailingZeroes = false;

        if (decimalseperator!=null) {

            regex = new Regex("[^" + decimalseperator + "]+$");

            match = regex.Match(numString);

            numDecimals = match.Value.Length;

            regex = new Regex("[^0]");

            forceTrailingZeroes = !regex.IsMatch(match.Value);

        }

        Console.WriteLine("prefix: " + prefix + " length: " + prefix.Length);

        Console.WriteLine("suffix: " + suffix + " length: " + suffix.Length);

        Console.WriteLine("numString: " + numString + " length: " + numString.Length);

        if (decimalseperator!=null) Console.WriteLine("decimalseperator: " + decimalseperator);

        if (thousandseperator!=null) Console.WriteLine("thousandseperator: " + thousandseperator);

        Console.WriteLine("num decimals: " + numDecimals.ToString());

        Console.WriteLine("forceTrailingZeroes: " + forceTrailingZeroes.ToString());

    }

}