using System;

namespace Nequeo.Cryptography.Key.Crypto.Digests
{
    /**
    * base implementation of MD4 family style digest as outlined in
    * "Handbook of Applied Cryptography", pages 344 - 347.
    */
    public abstract class GeneralDigest
		: IDigest
    {
        private const int BYTE_LENGTH = 64;

        private byte[]  xBuf;
        private int     xBufOff;

        private long    byteCount;

        internal GeneralDigest()
        {
            xBuf = new byte[4];
        }

        internal GeneralDigest(GeneralDigest t)
        {
            xBuf = new byte[t.xBuf.Length];
            Array.Copy(t.xBuf, 0, xBuf, 0, t.xBuf.Length);

            xBufOff = t.xBufOff;
            byteCount = t.byteCount;
        }

        public void Update(byte input)
        {
            xBuf[xBufOff++] = input;

            if (xBufOff == xBuf.Length)
            {
                ProcessWord(xBuf, 0);
                xBufOff = 0;
            }

            byteCount++;
        }

        public void BlockUpdate(
            byte[]  input,
            int     inOff,
            int     length)
        {
            //
            // fill the current word
            //
            while ((xBufOff != 0) && (length > 0))
            {
                Update(input[inOff]);
                inOff++;
                length--;
            }

            //
            // process whole words.
            //
            while (length > xBuf.Length)
            {
                ProcessWord(input, inOff);

                inOff += xBuf.Length;
                length -= xBuf.Length;
                byteCount += xBuf.Length;
            }

            //
            // load in the remainder.
            //
            while (length > 0)
            {
                Update(input[inOff]);

                inOff++;
                length--;
            }
        }

        public void Finish()
        {
            long    bitLength = (byteCount << 3);

            //
            // add the pad bytes.
            //
            Update((byte)128);

            while (xBufOff != 0) Update((byte)0);
            ProcessLength(bitLength);
            ProcessBlock();
        }

        public virtual void Reset()
        {
            byteCount = 0;
            xBufOff = 0;
			Array.Clear(xBuf, 0, xBuf.Length);
        }

		public int GetByteLength()
		{
			return BYTE_LENGTH;
		}

		internal abstract void ProcessWord(byte[] input, int inOff);
        internal abstract void ProcessLength(long bitLength);
        internal abstract void ProcessBlock();
        public abstract string AlgorithmName { get; }
		public abstract int GetDigestSize();
        public abstract int DoFinal(byte[] output, int outOff);
    }
}
