using System;
using System.Collections.Generic;
using System.Text;
using Sunweaver.Commands.Attributes;

namespace Sunweaver.Commands
{
    [BasePair("Return a random value between 1 and the top value of the integer stack, inclusive. " +
        @"Preserves sign, eg: ""-3 rand"" produces values in [-1, -2, -3].")]
    public class rand : Abstracts.UnaryOperation
    {
        public override void Operation(long a)
        {
            long return_me = 0;
            ulong range = (ulong)Math.Abs(a);
            
            if (range > 0)
            {
                //Prevent a modulo bias; see http://stackoverflow.com/a/10984975/238419.
                ulong ulongRand;
                do
                {
                    byte[] buf = new byte[8];
                    DNASystem.rand.NextBytes(buf);
                    ulongRand = (ulong)BitConverter.ToInt64(buf, 0);
                } while (ulongRand >= ulong.MaxValue - ulong.MaxValue % range);

                return_me = (long)(ulongRand % range) + 1;
            }

            VM.Stack.Push(Math.Sign(a) * return_me);
        }
    }
}