using System;

using Org.BouncyCastle.Crypto.Utilities;

namespace Org.BouncyCastle.Crypto.Digests
{
    /**
    * Draft FIPS 180-2 implementation of SHA-256. <b>Note:</b> As this is
    * based on a draft this implementation is subject to change.
    *
    * <pre>
    *         block  word  digest
    * SHA-1   512    32    160
    * SHA-256 512    32    256
    * SHA-384 1024   64    384
    * SHA-512 1024   64    512
    * </pre>
    */
    public class Sha256Digest
		: GeneralDigest
    {
        private const int DigestLength = 32;

        private uint H1, H2, H3, H4, H5, H6, H7, H8;
        private uint[] X = new uint[64];
        private int xOff;

        public Sha256Digest()
        {
			initHs();
        }

        /**
        * Copy constructor.  This will copy the state of the provided
        * message digest.
        */
        public Sha256Digest(Sha256Digest t) : base(t)
        {
            H1 = t.H1;
            H2 = t.H2;
            H3 = t.H3;
            H4 = t.H4;
            H5 = t.H5;
            H6 = t.H6;
            H7 = t.H7;
            H8 = t.H8;

            Array.Copy(t.X, 0, X, 0, t.X.Length);
            xOff = t.xOff;
        }

        public override string AlgorithmName
		{
			get { return "SHA-256"; }
		}

		public override int GetDigestSize()
		{
			return DigestLength;
		}

		internal override void ProcessWord(
            byte[]  input,
            int     inOff)
		{
			X[xOff] = Pack.BE_To_UInt32(input, inOff);

			if (++xOff == 16)
            {
                ProcessBlock();
            }
        }

		internal override void ProcessLength(
            long bitLength)
        {
            if (xOff > 14)
            {
                ProcessBlock();
            }

            X[14] = (uint)((ulong)bitLength >> 32);
            X[15] = (uint)((ulong)bitLength);
        }

        public override int DoFinal(
            byte[]  output,
            int     outOff)
        {
            Finish();

            Pack.UInt32_To_BE((uint)H1, output, outOff);
            Pack.UInt32_To_BE((uint)H2, output, outOff + 4);
            Pack.UInt32_To_BE((uint)H3, output, outOff + 8);
            Pack.UInt32_To_BE((uint)H4, output, outOff + 12);
            Pack.UInt32_To_BE((uint)H5, output, outOff + 16);
            Pack.UInt32_To_BE((uint)H6, output, outOff + 20);
            Pack.UInt32_To_BE((uint)H7, output, outOff + 24);
            Pack.UInt32_To_BE((uint)H8, output, outOff + 28);

            Reset();

            return DigestLength;
        }

        /**
        * reset the chaining variables
        */
        public override void Reset()
        {
            base.Reset();

			initHs();

            xOff = 0;
			Array.Clear(X, 0, X.Length);
        }

		private void initHs()
		{
            /* SHA-256 initial hash value
            * The first 32 bits of the fractional parts of the square roots
            * of the first eight prime numbers
            */
            H1 = 0x6a09e667;
            H2 = 0xbb67ae85;
            H3 = 0x3c6ef372;
            H4 = 0xa54ff53a;
            H5 = 0x510e527f;
            H6 = 0x9b05688c;
            H7 = 0x1f83d9ab;
            H8 = 0x5be0cd19;
		}

        internal override void ProcessBlock()
        {
            //
            // expand 16 word block into 64 word blocks.
            //
            for (int ti = 16; ti <= 63; ti++)
            {
                X[ti] = Theta1(X[ti - 2]) + X[ti - 7] + Theta0(X[ti - 15]) + X[ti - 16];
            }

            //
            // set up working variables.
            //
            uint a = H1;
            uint b = H2;
            uint c = H3;
            uint d = H4;
            uint e = H5;
            uint f = H6;
            uint g = H7;
            uint h = H8;

			int t = 0;
			for(int i = 0; i < 8; ++i)
			{
				// t = 8 * i
				h += Sum1Ch(e, f, g) + K[t] + X[t];
				d += h;
				h += Sum0Maj(a, b, c);
				++t;

				// t = 8 * i + 1
				g += Sum1Ch(d, e, f) + K[t] + X[t];
				c += g;
				g += Sum0Maj(h, a, b);
				++t;

				// t = 8 * i + 2
				f += Sum1Ch(c, d, e) + K[t] + X[t];
				b += f;
				f += Sum0Maj(g, h, a);
				++t;

				// t = 8 * i + 3
				e += Sum1Ch(b, c, d) + K[t] + X[t];
				a += e;
				e += Sum0Maj(f, g, h);
				++t;

				// t = 8 * i + 4
				d += Sum1Ch(a, b, c) + K[t] + X[t];
				h += d;
				d += Sum0Maj(e, f, g);
				++t;

				// t = 8 * i + 5
				c += Sum1Ch(h, a, b) + K[t] + X[t];
				g += c;
				c += Sum0Maj(d, e, f);
				++t;

				// t = 8 * i + 6
				b += Sum1Ch(g, h, a) + K[t] + X[t];
				f += b;
				b += Sum0Maj(c, d, e);
				++t;

				// t = 8 * i + 7
				a += Sum1Ch(f, g, h) + K[t] + X[t];
				e += a;
				a += Sum0Maj(b, c, d);
				++t;
			}

			H1 += a;
            H2 += b;
            H3 += c;
            H4 += d;
            H5 += e;
            H6 += f;
            H7 += g;
            H8 += h;

            //
            // reset the offset and clean out the word buffer.
            //
            xOff = 0;
			Array.Clear(X, 0, 16);
        }

		private static uint Sum1Ch(
            uint    x,
            uint    y,
            uint    z)
		{
//			return Sum1(x) + Ch(x, y, z);
	        return (((x >> 6) | (x << 26)) ^ ((x >> 11) | (x << 21)) ^ ((x >> 25) | (x << 7)))
				+ ((x & y) ^ ((~x) & z));
		}

		private static uint Sum0Maj(
            uint	x,
            uint    y,
            uint    z)
		{
//			return Sum0(x) + Maj(x, y, z);
	        return (((x >> 2) | (x << 30)) ^ ((x >> 13) | (x << 19)) ^ ((x >> 22) | (x << 10)))
				+ ((x & y) ^ (x & z) ^ (y & z));
		}

//		/* SHA-256 functions */
//        private static uint Ch(
//            uint    x,
//            uint    y,
//            uint    z)
//        {
//            return ((x & y) ^ ((~x) & z));
//        }
//
//        private static uint Maj(
//            uint	x,
//            uint    y,
//            uint    z)
//        {
//            return ((x & y) ^ (x & z) ^ (y & z));
//        }
//
//        private static uint Sum0(
//            uint x)
//        {
//	        return ((x >> 2) | (x << 30)) ^ ((x >> 13) | (x << 19)) ^ ((x >> 22) | (x << 10));
//        }
//
//        private static uint Sum1(
//            uint x)
//        {
//	        return ((x >> 6) | (x << 26)) ^ ((x >> 11) | (x << 21)) ^ ((x >> 25) | (x << 7));
//        }

        private static uint Theta0(
            uint x)
        {
	        return ((x >> 7) | (x << 25)) ^ ((x >> 18) | (x << 14)) ^ (x >> 3);
        }

        private static uint Theta1(
            uint x)
        {
	        return ((x >> 17) | (x << 15)) ^ ((x >> 19) | (x << 13)) ^ (x >> 10);
        }

        /* SHA-256 Constants
        * (represent the first 32 bits of the fractional parts of the
        * cube roots of the first sixty-four prime numbers)
        */
        private static readonly uint[] K = {
            0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5,
			0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
            0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
            0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
            0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc,
            0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
            0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7,
            0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
            0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
            0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
            0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3,
            0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
            0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5,
            0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
            0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
            0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
        };
    }
}
