using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        var testCase = 4;  // <<<<< Change value here to test 1-4

        var macro = "[0], buy [1:all] from [2:counter]";

        var expressionMatch = @"\[(?<index>\d):?(?<value>[\w\s]*)?\]";

        var argumentsString = String.Empty;

        switch (testCase)

        {

            case 1: argumentsString = "r gem floor"; break; // All parameters specified

            case 2: argumentsString = "r gem"; break; // Use last optional parameter

            case 3: argumentsString = "r  floor"; break; // Extra space to specify default on second param

            case 4: argumentsString = "r"; break; // Use optional param on all.

        }

        var regex = new Regex(expressionMatch, RegexOptions.Compiled);

        var matchCollection = regex.Matches(macro);

        Console.WriteLine("Matches found: {0}", matchCollection.Count);

        foreach (Match match in matchCollection)

        {

            GroupCollection groups = match.Groups;

            Console.WriteLine("'{0}', (optional: '{1}') repeated at positions {2} and {3}",  

                              groups["index"].Value, 

                              groups["value"].Value, 

                              groups[0].Index, 

                              groups[1].Index);

        }

        /* Now we know the groups and possible optional params, let's build a dictionary of <int, string> that we can use */

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

        foreach (Match match in matchCollection)

        {

            var groups = match.Groups;

            // TODO: We proably need to validate that these are actually integers.

            var index = int.Parse(groups["index"].Value);

            var defaultValue = groups["value"].Value;

            if (!String.IsNullOrWhiteSpace(defaultValue))

                values.Add(index, defaultValue);

        }

        /* Now we have a <int, string> dictionary that contains default values, now replace defaults with specified params */

        var arguments = argumentsString.Split(' ');

        // This forces optional params to be at the end? Is there a way we can do optional params in the middle, is there a case where it may be needed?

            // Might be resolved if seperated by double space gives a blank param =>  "r  gem" => "r", "", "gem"  (Tested, this does indeed work)

        for (int i = 0; i < arguments.Length; i++)

        {

            var argument = arguments[i];

            if (!String.IsNullOrWhiteSpace(argument))

                values[i] = argument;

        }

​

        foreach(var kvp in values.OrderBy(kvp => kvp.Key))

            Console.WriteLine("Param [{0}]: {1}", kvp.Key, kvp.Value);

        /* Build the server command */

        var command = Regex.Replace(macro, expressionMatch, (Match match) => String.Format(@"{{{0}}}", match.Groups["index"].Value));

        Console.WriteLine("Command format: {0}", command);

        /* Substitute the values */

        var parameters = values.OrderBy(kvp => kvp.Key).Select(kvp => kvp.Value).ToArray();

        var execute = String.Format(command, parameters);

        Console.WriteLine("Comamnd to execute: {0}", execute);

    }

}