using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;

namespace BallotDrawRandNumGen.WebApi
{
    public class BallotDrawHelper
    {      
        private static readonly object syncLock = new object();

        public virtual int[] GenerateRandomPositions(int count)
        {
            if (count <= 0)
                throw new ArgumentOutOfRangeException("count");

            lock (syncLock)
            {
                //get the set of numbers from 1 to {count} 
                var positions = Enumerable.Range(1, count).ToList();
                // create a list to hold the new numbers
                var perm = new List<int>();
                for (int i = 0; i < count; i++)
                {
                    // find the random index for list
                    int n = RandomNumberGenerator.GetInt32(positions.Count);
                    // push the value corresponds to the random index to the result list
                    perm.Add(positions[n]);
                    // remove the selected number from the lot
                    positions.RemoveAt(n);
                }
                return perm.ToArray();
            }
        }
    }
}