using System;

namespace CMLeonOS
{
    public class Sha256
    {
        private static readonly uint[] K = new uint[64] {
            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
        };

        private static uint ROTL(uint x, byte n)
        {
            if (n >= 32) throw new ArgumentException("n");
            return x << n | x >> 32 - n;
        }

        private static uint ROTR(uint x, byte n)
        {
            if (n >= 32) throw new ArgumentException("n");
            return x >> n | x << 32 - n;
        }

        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 Sigma0(uint x)
        {
            return ROTR(x, 2) ^ ROTR(x, 13) ^ ROTR(x, 22);
        }

        private static uint Sigma1(uint x)
        {
            return ROTR(x, 6) ^ ROTR(x, 11) ^ ROTR(x, 25);
        }

        private static uint sigma0(uint x)
        {
            return ROTR(x, 7) ^ ROTR(x, 18) ^ x >> 3;
        }

        private static uint sigma1(uint x)
        {
            return ROTR(x, 17) ^ ROTR(x, 19) ^ x >> 10;
        }


        private uint[] H = new uint[8] {
            0x6A09E667, 0xBB67AE85, 0x3C6EF372, 0xA54FF53A, 0x510E527F, 0x9B05688C, 0x1F83D9AB, 0x5BE0CD19
        };

        private byte[] pendingBlock = new byte[64];
        private uint pendingBlockOff = 0;
        private uint[] uintBuffer = new uint[16];

        private ulong bitsProcessed = 0;

        private bool closed = false;

        private void ProcessBlock(uint[] M)
        {
            if (M.Length != 16) throw new ArgumentException("M");

            // 1. Prepare the message schedule (W[t]):
            uint[] W = new uint[64];
            for (int t = 0; t < 16; ++t)
            {
                W[t] = M[t];
            }

            for (int t = 16; t < 64; ++t)
            {
                W[t] = sigma1(W[t - 2]) + W[t - 7] + sigma0(W[t - 15]) + W[t - 16];
            }

            // 2. Initialize the eight working variables with the (i-1)-st hash value:
            uint a = H[0],
                   b = H[1],
                   c = H[2],
                   d = H[3],
                   e = H[4],
                   f = H[5],
                   g = H[6],
                   h = H[7];

            // 3. For t=0 to 63:
            for (int t = 0; t < 64; ++t)
            {
                uint T1 = h + Sigma1(e) + Ch(e, f, g) + K[t] + W[t];
                uint T2 = Sigma0(a) + Maj(a, b, c);
                h = g;
                g = f;
                f = e;
                e = d + T1;
                d = c;
                c = b;
                b = a;
                a = T1 + T2;
            }

            // 4. Compute the intermediate hash value H:
            H[0] = a + H[0];
            H[1] = b + H[1];
            H[2] = c + H[2];
            H[3] = d + H[3];
            H[4] = e + H[4];
            H[5] = f + H[5];
            H[6] = g + H[6];
            H[7] = h + H[7];
        }

        internal void AddData(byte[] data, uint offset, uint len)
        {
            if (closed)
                throw new InvalidOperationException("Adding data to a closed hasher.");

            if (len == 0)
                return;

            bitsProcessed += len * 8;

            while (len > 0)
            {
                uint amount_to_copy;

                if (len < 64)
                {
                    if (pendingBlockOff + len > 64)
                        amount_to_copy = 64 - pendingBlockOff;
                    else
                        amount_to_copy = len;
                }
                else
                {
                    amount_to_copy = 64 - pendingBlockOff;
                }

                Array.Copy(data, offset, pendingBlock, pendingBlockOff, amount_to_copy);
                len -= amount_to_copy;
                offset += amount_to_copy;
                pendingBlockOff += amount_to_copy;

                if (pendingBlockOff == 64)
                {
                    toUintArray(pendingBlock, uintBuffer);
                    ProcessBlock(uintBuffer);
                    pendingBlockOff = 0;
                }
            }
        }

        internal byte[] GetHash()
        {
            return toByteArray(GetHashUint());
        }

        internal uint[] GetHashUint()
        {
            if (!closed)
            {
                ulong size_temp = bitsProcessed;

                AddData(new byte[1] { 0x80 }, 0, 1);

                uint available_space = 64 - pendingBlockOff;

                if (available_space < 8)
                    available_space += 64;

                // 0-initialized
                byte[] padding = new byte[available_space];
                // Insert length ulong
                for (uint i = 1; i <= 8; ++i)
                {
                    padding[padding.Length - i] = (byte)size_temp;
                    size_temp >>= 8;
                }

                AddData(padding, 0u, (uint)padding.Length);

                if (pendingBlockOff != 0) throw new Exception("Pending block offset should be 0.");

                closed = true;
            }

            return H;
        }

        private static void toUintArray(byte[] src, uint[] dest)
        {
            for (uint i = 0, j = 0; i < dest.Length; ++i, j += 4)
            {
                dest[i] = (uint)src[j + 0] << 24 | (uint)src[j + 1] << 16 | (uint)src[j + 2] << 8 | src[j + 3];
            }
        }

        private static byte[] toByteArray(uint[] src)
        {
            byte[] dest = new byte[src.Length * 4];
            int pos = 0;

            for (int i = 0; i < src.Length; ++i)
            {
                dest[pos++] = (byte)(src[i] >> 24);
                dest[pos++] = (byte)(src[i] >> 16);
                dest[pos++] = (byte)(src[i] >> 8);
                dest[pos++] = (byte)src[i];
            }

            return dest;
        }
    }
}