package org.bouncycastle.crypto.digests;

import org.bouncycastle.crypto.util.Pack;
import org.bouncycastle.util.Memoable;

/**
 * implementation of SHA-1 as outlined in "Handbook of Applied Cryptography", pages 346 - 349.
 *
 * It is interesting to ponder why the, apart from the extra IV, the other difference here from MD5
 * is the "endianness" of the word processing!
 */
public class SHA1Digest
    extends GeneralDigest
{
    private static final int    DIGEST_LENGTH = 20;

    private int     H1, H2, H3, H4, H5;

    private int[]   X = new int[80];
    private int     xOff;

    /**
     * Standard constructor
     */
    public SHA1Digest()
    {
        reset();
    }

    /**
     * Copy constructor.  This will copy the state of the provided
     * message digest.
     */
    public SHA1Digest(SHA1Digest t)
    {
        super(t);

        copyIn(t);
    }

    private void copyIn(SHA1Digest t)
    {
        H1 = t.H1;
        H2 = t.H2;
        H3 = t.H3;
        H4 = t.H4;
        H5 = t.H5;

        System.arraycopy(t.X, 0, X, 0, t.X.length);
        xOff = t.xOff;
    }

    public String getAlgorithmName()
    {
        return "SHA-1";
    }

    public int getDigestSize()
    {
        return DIGEST_LENGTH;
    }

    protected void processWord(
        byte[]  in,
        int     inOff)
    {
        // Note: Inlined for performance
//        X[xOff] = Pack.bigEndianToInt(in, inOff);
        int n = in[  inOff] << 24;
        n |= (in[++inOff] & 0xff) << 16;
        n |= (in[++inOff] & 0xff) << 8;
        n |= (in[++inOff] & 0xff);
        X[xOff] = n;

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

    protected void processLength(
        long    bitLength)
    {
        if (xOff > 14)
        {
            processBlock();
        }

        X[14] = (int)(bitLength >>> 32);
        X[15] = (int)(bitLength & 0xffffffff);
    }

    public int doFinal(
        byte[]  out,
        int     outOff)
    {
        finish();

        Pack.intToBigEndian(H1, out, outOff);
        Pack.intToBigEndian(H2, out, outOff + 4);
        Pack.intToBigEndian(H3, out, outOff + 8);
        Pack.intToBigEndian(H4, out, outOff + 12);
        Pack.intToBigEndian(H5, out, outOff + 16);

        reset();

        return DIGEST_LENGTH;
    }

    /**
     * reset the chaining variables
     */
    public void reset()
    {
        super.reset();

        H1 = 0x67452301;
        H2 = 0xefcdab89;
        H3 = 0x98badcfe;
        H4 = 0x10325476;
        H5 = 0xc3d2e1f0;

        xOff = 0;
        for (int i = 0; i != X.length; i++)
        {
            X[i] = 0;
        }
    }

    //
    // Additive constants
    //
    private static final int    Y1 = 0x5a827999;
    private static final int    Y2 = 0x6ed9eba1;
    private static final int    Y3 = 0x8f1bbcdc;
    private static final int    Y4 = 0xca62c1d6;
   
    private int f(
        int    u,
        int    v,
        int    w)
    {
        return ((u & v) | ((~u) & w));
    }

    private int h(
        int    u,
        int    v,
        int    w)
    {
        return (u ^ v ^ w);
    }

    private int g(
        int    u,
        int    v,
        int    w)
    {
        return ((u & v) | (u & w) | (v & w));
    }

    protected void processBlock()
    {
        //
        // expand 16 word block into 80 word block.
        //
        for (int i = 16; i < 80; i++)
        {
            int t = X[i - 3] ^ X[i - 8] ^ X[i - 14] ^ X[i - 16];
            X[i] = t << 1 | t >>> 31;
        }

        //
        // set up working variables.
        //
        int     A = H1;
        int     B = H2;
        int     C = H3;
        int     D = H4;
        int     E = H5;

        //
        // round 1
        //
        int idx = 0;
        
        for (int j = 0; j < 4; j++)
        {
            // E = rotateLeft(A, 5) + f(B, C, D) + E + X[idx++] + Y1
            // B = rotateLeft(B, 30)
            E += (A << 5 | A >>> 27) + f(B, C, D) + X[idx++] + Y1;
            B = B << 30 | B >>> 2;
        
            D += (E << 5 | E >>> 27) + f(A, B, C) + X[idx++] + Y1;
            A = A << 30 | A >>> 2;
       
            C += (D << 5 | D >>> 27) + f(E, A, B) + X[idx++] + Y1;
            E = E << 30 | E >>> 2;
       
            B += (C << 5 | C >>> 27) + f(D, E, A) + X[idx++] + Y1;
            D = D << 30 | D >>> 2;

            A += (B << 5 | B >>> 27) + f(C, D, E) + X[idx++] + Y1;
            C = C << 30 | C >>> 2;
        }
        
        //
        // round 2
        //
        for (int j = 0; j < 4; j++)
        {
            // E = rotateLeft(A, 5) + h(B, C, D) + E + X[idx++] + Y2
            // B = rotateLeft(B, 30)
            E += (A << 5 | A >>> 27) + h(B, C, D) + X[idx++] + Y2;
            B = B << 30 | B >>> 2;   
            
            D += (E << 5 | E >>> 27) + h(A, B, C) + X[idx++] + Y2;
            A = A << 30 | A >>> 2;
            
            C += (D << 5 | D >>> 27) + h(E, A, B) + X[idx++] + Y2;
            E = E << 30 | E >>> 2;
            
            B += (C << 5 | C >>> 27) + h(D, E, A) + X[idx++] + Y2;
            D = D << 30 | D >>> 2;

            A += (B << 5 | B >>> 27) + h(C, D, E) + X[idx++] + Y2;
            C = C << 30 | C >>> 2;
        }
        
        //
        // round 3
        //
        for (int j = 0; j < 4; j++)
        {
            // E = rotateLeft(A, 5) + g(B, C, D) + E + X[idx++] + Y3
            // B = rotateLeft(B, 30)
            E += (A << 5 | A >>> 27) + g(B, C, D) + X[idx++] + Y3;
            B = B << 30 | B >>> 2;
            
            D += (E << 5 | E >>> 27) + g(A, B, C) + X[idx++] + Y3;
            A = A << 30 | A >>> 2;
            
            C += (D << 5 | D >>> 27) + g(E, A, B) + X[idx++] + Y3;
            E = E << 30 | E >>> 2;
            
            B += (C << 5 | C >>> 27) + g(D, E, A) + X[idx++] + Y3;
            D = D << 30 | D >>> 2;

            A += (B << 5 | B >>> 27) + g(C, D, E) + X[idx++] + Y3;
            C = C << 30 | C >>> 2;
        }

        //
        // round 4
        //
        for (int j = 0; j <= 3; j++)
        {
            // E = rotateLeft(A, 5) + h(B, C, D) + E + X[idx++] + Y4
            // B = rotateLeft(B, 30)
            E += (A << 5 | A >>> 27) + h(B, C, D) + X[idx++] + Y4;
            B = B << 30 | B >>> 2;
            
            D += (E << 5 | E >>> 27) + h(A, B, C) + X[idx++] + Y4;
            A = A << 30 | A >>> 2;
            
            C += (D << 5 | D >>> 27) + h(E, A, B) + X[idx++] + Y4;
            E = E << 30 | E >>> 2;
            
            B += (C << 5 | C >>> 27) + h(D, E, A) + X[idx++] + Y4;
            D = D << 30 | D >>> 2;

            A += (B << 5 | B >>> 27) + h(C, D, E) + X[idx++] + Y4;
            C = C << 30 | C >>> 2;
        }


        H1 += A;
        H2 += B;
        H3 += C;
        H4 += D;
        H5 += E;

        //
        // reset start of the buffer.
        //
        xOff = 0;
        for (int i = 0; i < 16; i++)
        {
            X[i] = 0;
        }
    }

    public Memoable copy()
    {
        return new SHA1Digest(this);
    }

    public void reset(Memoable other)
    {
        SHA1Digest d = (SHA1Digest)other;

        super.copyIn(d);
        copyIn(d);
    }
}