using System;
using xDataService.Interfaces;

namespace xDataService.Helpers
{
    /// <summary>
    /// this service provide Sequential GUID mechanism for Entity Ids ...
    /// </summary>
    public class XSequentialGuid : IXSequentialGuid
    {
        private static int[] sqlOrderMap = null;
        private static int[] SQLORDERMAP
        {
            get
            {
                if (sqlOrderMap == null)
                {
                    sqlOrderMap = new int[16] {
                    3,
                    2,
                    1,
                    0,
                    5,
                    4,
                    7,
                    6,
                    9,
                    8,
                    15,
                    14,
                    13,
                    12,
                    11,
                    10
                    };
                    // 3 - the least significant byte in Guid ByteArray [for SQL Server ORDER BY clause]
                    // 10 - the most significant byte in Guid ByteArray [for SQL Server ORDERY BY clause]
                }
                return sqlOrderMap;
            }
        }

        private Guid currentGuid;

        public XSequentialGuid()
        {
            currentGuid = Guid.NewGuid();
        }

        public Guid GetCurrentGuid()
        {
            return currentGuid;
        }

        public Guid Next()
        {
            byte[] bytes = currentGuid.ToByteArray();
            for (int mapIndex = 0; mapIndex < 16; mapIndex++)
            {
                int bytesIndex = SQLORDERMAP[mapIndex];
                bytes[bytesIndex]++;
                if (bytes[bytesIndex] != 0)
                {
                    break; // No need to increment more significant bytes
                }
            }
            currentGuid = new Guid(bytes);
            return currentGuid;
        }
    }
}