package org.infinispan.commons.hash;

import java.io.IOException;
import java.io.ObjectInput;
import java.util.Collections;
import java.util.Set;

import org.infinispan.commons.marshall.Ids;
import org.infinispan.commons.marshall.WrappedBytes;
import org.infinispan.commons.marshall.exts.NoStateExternalizer;

import net.jcip.annotations.Immutable;
import net.jcip.annotations.ThreadSafe;

/**
 * A CRC16 implementation in Java.
 *
 * @see <a href="https://github.com/lettuce-io/lettuce-core/blob/2ad862f5a1db860d57236c21c473cfd9aefebfea/src/main/java/io/lettuce/core/codec/CRC16.java">Lettuce Implementation.</a>
 * @see <a href="https://introcs.cs.princeton.edu/java/61data/CRC16.java">Princeton implementation.</a>
 * @since 15.0
 */
@ThreadSafe
@Immutable
public class CRC16 implements Hash {

   private final static CRC16 instance = new CRC16();

   private CRC16() { }

   public static CRC16 getInstance() {
      return instance;
   }

   @Override
   public int hash(byte[] payload) {
      int crc = 0x0000;
      for (byte b : payload) {
         crc = (crc >>> 8) ^ CRC16Table.table[(crc ^ b) & 0xff];
      }
      return crc;
   }

   @Override
   public int hash(int hashcode) {
      byte b0 = (byte) hashcode;
      byte b1 = (byte) (hashcode >>> 8);
      byte b2 = (byte) (hashcode >>> 16);
      byte b3 = (byte) (hashcode >>> 24);
      return hash(new byte[] { b0, b1, b2, b3 });
   }

   @Override
   public int hash(Object o) {
      if (o instanceof byte[]) {
         return hash((byte[]) o);
      }

      if (o instanceof WrappedBytes) {
         return hash(((WrappedBytes) o).getBytes());
      }

      return hash(o.hashCode());
   }

   @Override
   public String toString() {
      return "CRC16";
   }

   private static class CRC16Table {

      private CRC16Table() { }

      // See: https://github.com/lettuce-io/lettuce-core/blob/2ad862f5a1db860d57236c21c473cfd9aefebfea/src/main/java/io/lettuce/core/codec/CRC16.java#L35
      private static final int[] table = { 0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7, 0x8108, 0x9129,
            0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF, 0x1231, 0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6,
            0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE, 0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7,
            0x44A4, 0x5485, 0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D, 0x3653, 0x2672, 0x1611, 0x0630,
            0x76D7, 0x66F6, 0x5695, 0x46B4, 0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D, 0xC7BC, 0x48C4, 0x58E5,
            0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823, 0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B,
            0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12, 0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58,
            0xBB3B, 0xAB1A, 0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41, 0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD,
            0xAD2A, 0xBD0B, 0x8D68, 0x9D49, 0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0x0E70, 0xFF9F, 0xEFBE,
            0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78, 0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F,
            0x1080, 0x00A1, 0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067, 0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C,
            0xE37F, 0xF35E, 0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256, 0xB5EA, 0xA5CB, 0x95A8, 0x8589,
            0xF56E, 0xE54F, 0xD52C, 0xC50D, 0x34E2, 0x24C3, 0x14A0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405, 0xA7DB, 0xB7FA,
            0x8799, 0x97B8, 0xE75F, 0xF77E, 0xC71D, 0xD73C, 0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634,
            0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB, 0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x08E1,
            0x3882, 0x28A3, 0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A, 0x4A75, 0x5A54, 0x6A37, 0x7A16,
            0x0AF1, 0x1AD0, 0x2AB3, 0x3A92, 0xFD2E, 0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9, 0x7C26, 0x6C07,
            0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0x0CC1, 0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8,
            0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0 };
   }

   public static class Externalizer extends NoStateExternalizer<CRC16> {

      @Override
      public Set<Class<? extends CRC16>> getTypeClasses() {
         return Collections.singleton(CRC16.class);
      }

      @Override
      public CRC16 readObject(ObjectInput input) throws IOException, ClassNotFoundException {
         return getInstance();
      }

      @Override
      public Integer getId() {
         return Ids.CRC16_HASH;
      }
   }
}
