using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DTS.Serialization.IRIGCH10.Packets
{
    /// <summary>
    /// this class helps encapsulate a secondary time format header, but it's really
    /// only designed for one type of format currently
    /// </summary>
    public class SecondaryTimeFormatHeader : ISecondaryTimeFormatHeader
    {
        private byte[] _bytes = new byte[SECONDARY_TIME_HEADER_LENGTH];
        public int NanoSeconds { get; }
        public int Seconds { get; }
        public ushort Reserved { get; }
        public ushort CheckSum { get; }

        public DateTime LocalTime
        {
            get => (new DateTime(1970, 1, 1)).AddSeconds(Seconds).AddTicks(NanoSeconds / 100).ToLocalTime();
        }
        public SecondaryTimeFormatHeader(byte[] input)
        {
            Array.Copy(input, 0, _bytes, 0, SECONDARY_TIME_HEADER_LENGTH);
            NanoSeconds = BitConverter.ToInt32(_bytes, 0);
            Seconds = BitConverter.ToInt32(_bytes, 4);
            Reserved = BitConverter.ToUInt16(_bytes, 8);
            CheckSum = BitConverter.ToUInt16(_bytes, 10);
            byte[] bytesToCompute;
            using (var ms = new MemoryStream())
            {
                using (var bw = new BinaryWriter(ms))
                {
                    bw.Write(BitConverter.GetBytes(NanoSeconds));
                    bw.Write(BitConverter.GetBytes(Seconds));
                    bw.Write(Reserved);
                }
                bytesToCompute = ms.ToArray();
            }
            var computedChecksum = Utils.Utils.GetCheckSum8(bytesToCompute);
            if (computedChecksum != CheckSum)
            {
                System.Diagnostics.Trace.WriteLine("Secondary time header CRC does not match expectations");
            }
        }
        public static byte[] GetBytes(int nanoseconds, int seconds)
        {
            using (var ms = new MemoryStream())
            {
                using (var bw = new BinaryWriter(ms))
                {
                    bw.Write(BitConverter.GetBytes(nanoseconds));
                    bw.Write(BitConverter.GetBytes(seconds));
                    bw.Write((ushort)0);

                    bw.Write(Utils.Utils.GetCheckSum8(ms.ToArray()));
                }
                return ms.ToArray();
            }
        }
        public const int SECONDARY_TIME_HEADER_LENGTH = 12;
    }
}