using System;
using System.Collections;

namespace DTS.Serialization.IRIGCH10.Utils
{
    /// <summary>
    /// helper class for getting BCD values as defined in chapter 10 for things like dates,
    /// also contains 16/32 bit checksum functions
    /// </summary>
    public abstract class Utils
    {
        public static byte[] GetBCDBytes(int value)
        {
            if (value < 0 || value > 9999)
            {
                throw new ArgumentOutOfRangeException("value must be between 0, 9999");
            }

            var bcd = 0;
            for (var digit = 0; digit < 4; ++digit)
            {
                var nibble = value % 10;
                bcd |= nibble << (digit * 4);
                value /= 10;
            }
            return new byte[] { (byte)(bcd & 0xff), (byte)((bcd >> 8) & 0xff) };
        }
        public static ushort GetCheckSum8(byte[] bytes)
        {
            ushort crc = 0;
            foreach (var v in bytes)
            {
                crc += v;
            }
            return crc;
        }
        /// <summary>
        /// computes a 16 bit checksum per ch10
        /// </summary>
        /// <param name="bytes"></param>
        /// <returns></returns>
        public static ushort GetCheckSum16(byte[] bytes)
        {
            //we might want to pad with a 0 byte or drop a byte if odd number of bytes?
            //currently we only use this for packet headers, which are always of a set length, this
            //is just here for sanity
            System.Diagnostics.Trace.Assert(0 == bytes.Length % 2, "requires even length incoming data");

            ushort crc = 0;
            var uints = new ushort[bytes.Length / 2];
            Buffer.BlockCopy(bytes, 0, uints, 0, bytes.Length);
            for (var i = 0; i < uints.Length; i++)
            {
                crc += uints[i];
            }
            return crc;
        }
        /// <summary>
        /// computes a 32 bit checksum per ch 10,
        /// we use this currently for data packet checksums
        /// </summary>
        /// <param name="bytes"></param>
        /// <returns></returns>
        public static uint GetCheckSum32(byte[] bytes)
        {
            //most packets should be filled in after the data portion with filler bytes to have
            //a length divisible by 4, this is just a sanity check
            System.Diagnostics.Trace.Assert(0 == bytes.Length % 4);

            uint crc = 0;
            var uints = new uint[bytes.Length / 4];
            Buffer.BlockCopy(bytes, 0, uints, 0, bytes.Length);
            for (var i = 0; i < uints.Length; i++)
            {
                crc += uints[i];
            }
            return crc;
        }
        /// <summary>
        /// returns an int given a bitarray and the starting and stopping point for bits of interest
        /// This allows you to return an int from 1-4 bytes
        /// </summary>
        /// <param name="ba"></param>
        /// <param name="startIndex"></param>
        /// <param name="endIndex"></param>
        /// <returns></returns>
        public static int BitArrayToInt32(BitArray ba, int startIndex, int endIndex)
        {
            var n = 0;
            var bit = 0;
            for (var i = startIndex; i <= endIndex; i++)
            {
                if (ba.Get(i))
                {
                    n |= 1 << bit;
                }
                bit++;
            }
            return n;
        }
        public static void SetBits(BitArray b, uint value, int startIndex, int endIndex)
        {
            var ba = new BitArray(BitConverter.GetBytes(value));

            var bit = 0;
            for (var i = startIndex; i <= endIndex; i++)
            {
                b.Set(i, ba.Get(bit));
                bit++;
            }
        }
    }
}