/* 
 * Bitcoin cryptography library
 * Copyright (c) Project Nayuki
 * 
 * https://www.nayuki.io/page/bitcoin-cryptography-library
 * https://github.com/nayuki/Bitcoin-Cryptography-Library
 */

package hash;

import static java.lang.Integer.rotateLeft;
import java.util.Arrays;
import java.util.Objects;


/**
 * Computes the RIPEMD-160 hash of an array of bytes. Not instantiable.
 */
public final class Ripemd160 {
	
	private static final int BLOCK_LEN = 64;  // In bytes
	
	
	
	/*---- Static functions ----*/
	
	/**
	 * Computes and returns a 20-byte (160-bit) hash of the specified binary message.
	 * Each call will return a new byte array object instance.
	 * @param msg the message to compute the hash of
	 * @return a 20-byte array representing the message's RIPEMD-160 hash
	 * @throws NullPointerException if the message is {@code null}
	 */
	public static byte[] getHash(byte[] msg) {
		// Compress whole message blocks
		Objects.requireNonNull(msg);
		int[] state = {0x67452301, 0xEFCDAB89, 0x98BADCFE, 0x10325476, 0xC3D2E1F0};
		int off = msg.length / BLOCK_LEN * BLOCK_LEN;
		compress(state, msg, off);
		
		// Final blocks, padding, and length
		byte[] block = new byte[BLOCK_LEN];
		System.arraycopy(msg, off, block, 0, msg.length - off);
		off = msg.length % block.length;
		block[off] = (byte)0x80;
		off++;
		if (off + 8 > block.length) {
			compress(state, block, block.length);
			Arrays.fill(block, (byte)0);
		}
		long len = (long)msg.length << 3;
		for (int i = 0; i < 8; i++)
			block[block.length - 8 + i] = (byte)(len >>> (i * 8));
		compress(state, block, block.length);
		
		// Int32 array to bytes in little endian
		byte[] result = new byte[state.length * 4];
		for (int i = 0; i < result.length; i++)
			result[i] = (byte)(state[i / 4] >>> (i % 4 * 8));
		return result;
	}
	
	
	
	/*---- Private functions ----*/
	
	private static void compress(int[] state, byte[] blocks, int len) {
		if (len % BLOCK_LEN != 0)
			throw new IllegalArgumentException();
		for (int i = 0; i < len; i += BLOCK_LEN) {
			
			// Message schedule
			int[] schedule = new int[16];
			for (int j = 0; j < BLOCK_LEN; j++)
				schedule[j / 4] |= (blocks[i + j] & 0xFF) << (j % 4 * 8);
			
			// The 80 rounds
			int al = state[0], ar = state[0];
			int bl = state[1], br = state[1];
			int cl = state[2], cr = state[2];
			int dl = state[3], dr = state[3];
			int el = state[4], er = state[4];
			for (int j = 0; j < 80; j++) {
				int temp;
				temp = rotateLeft(al + f(j, bl, cl, dl) + schedule[RL[j]] + KL[j / 16], SL[j]) + el;
				al = el;
				el = dl;
				dl = rotateLeft(cl, 10);
				cl = bl;
				bl = temp;
				temp = rotateLeft(ar + f(79 - j, br, cr, dr) + schedule[RR[j]] + KR[j / 16], SR[j]) + er;
				ar = er;
				er = dr;
				dr = rotateLeft(cr, 10);
				cr = br;
				br = temp;
			}
			int temp = state[1] + cl + dr;
			state[1] = state[2] + dl + er;
			state[2] = state[3] + el + ar;
			state[3] = state[4] + al + br;
			state[4] = state[0] + bl + cr;
			state[0] = temp;
		}
	}
	
	
	private static int f(int i, int x, int y, int z) {
		assert 0 <= i && i < 80;
		if (i < 16) return x ^ y ^ z;
		if (i < 32) return (x & y) | (~x & z);
		if (i < 48) return (x | ~y) ^ z;
		if (i < 64) return (x & z) | (y & ~z);
		return x ^ (y | ~z);
	}
	
	
	/*---- Class constants ----*/
	
	private static final int[] KL = {0x00000000, 0x5A827999, 0x6ED9EBA1, 0x8F1BBCDC, 0xA953FD4E};  // Round constants for left line
	private static final int[] KR = {0x50A28BE6, 0x5C4DD124, 0x6D703EF3, 0x7A6D76E9, 0x00000000};  // Round constants for right line
	
	private static final int[] RL = {  // Message schedule for left line
		 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
		 7,  4, 13,  1, 10,  6, 15,  3, 12,  0,  9,  5,  2, 14, 11,  8,
		 3, 10, 14,  4,  9, 15,  8,  1,  2,  7,  0,  6, 13, 11,  5, 12,
		 1,  9, 11, 10,  0,  8, 12,  4, 13,  3,  7, 15, 14,  5,  6,  2,
		 4,  0,  5,  9,  7, 12,  2, 10, 14,  1,  3,  8, 11,  6, 15, 13};
	
	private static final int[] RR = {  // Message schedule for right line
		 5, 14,  7,  0,  9,  2, 11,  4, 13,  6, 15,  8,  1, 10,  3, 12,
		 6, 11,  3,  7,  0, 13,  5, 10, 14, 15,  8, 12,  4,  9,  1,  2,
		15,  5,  1,  3,  7, 14,  6,  9, 11,  8, 12,  2, 10,  0,  4, 13,
		 8,  6,  4,  1,  3, 11, 15,  0,  5, 12,  2, 13,  9,  7, 10, 14,
		12, 15, 10,  4,  1,  5,  8,  7,  6,  2, 13, 14,  0,  3,  9, 11};
	
	private static final int[] SL = {  // Left-rotation for left line
		11, 14, 15, 12,  5,  8,  7,  9, 11, 13, 14, 15,  6,  7,  9,  8,
		 7,  6,  8, 13, 11,  9,  7, 15,  7, 12, 15,  9, 11,  7, 13, 12,
		11, 13,  6,  7, 14,  9, 13, 15, 14,  8, 13,  6,  5, 12,  7,  5,
		11, 12, 14, 15, 14, 15,  9,  8,  9, 14,  5,  6,  8,  6,  5, 12,
		 9, 15,  5, 11,  6,  8, 13, 12,  5, 12, 13, 14, 11,  8,  5,  6};
	
	private static final int[] SR = {  // Left-rotation for right line
		 8,  9,  9, 11, 13, 15, 15,  5,  7,  7,  8, 11, 14, 14, 12,  6,
		 9, 13, 15,  7, 12,  8,  9, 11,  7,  7, 12,  7,  6, 15, 13, 11,
		 9,  7, 15, 11,  8,  6,  6, 14, 12, 13,  5, 14, 13, 13,  7,  5,
		15,  5,  8, 11, 14, 14,  6, 14,  6,  9, 12,  9, 12,  5, 15,  8,
		 8,  5, 12,  9, 12,  5, 14,  6,  8, 13,  6,  5, 15, 13, 11, 11};
	
	
	
	/*---- Miscellaneous ----*/
	
	private Ripemd160() {}  // Not instantiable
	
}