/*
 * Copyright 2019 Red Hat, Inc.
 * <p>
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * and Apache License v2.0 which accompanies this distribution.
 * <p>
 * The Eclipse Public License is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * <p>
 * The Apache License v2.0 is available at
 * http://www.opensource.org/licenses/apache2.0.php
 * <p>
 * You may elect to redistribute this code under either of these licenses.
 */
package io.vertx.redis.client.impl;

import io.vertx.core.buffer.Buffer;

import java.nio.charset.StandardCharsets;
import java.util.List;

CRC16 implementation according to CCITT standards.

Note by @antirez: this is actually the XMODEM CRC 16 algorithm, using the
following parameters:

Name                       : "XMODEM", also known as "ZMODEM", "CRC-16/ACORN"
Width                      : 16 bit
Poly                       : 1021 (That is actually x^16 + x^12 + x^5 + 1)
Initialization             : 0000
Reflect Input byte         : False
Reflect Output CRC         : False
Xor constant to output CRC : 0000
Output for "123456789"     : 31C3
/**
 * CRC16 implementation according to CCITT standards.
 * <p>
 * Note by @antirez: this is actually the XMODEM CRC 16 algorithm, using the
 * following parameters:
 * <p>
 * Name                       : "XMODEM", also known as "ZMODEM", "CRC-16/ACORN"
 * Width                      : 16 bit
 * Poly                       : 1021 (That is actually x^16 + x^12 + x^5 + 1)
 * Initialization             : 0000
 * Reflect Input byte         : False
 * Reflect Output CRC         : False
 * Xor constant to output CRC : 0000
 * Output for "123456789"     : 31C3
 */
public class ZModem {

  private static final int[] lookup = new int[]{
    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
  };

  
Convert a string into a redis slot hash.
Params:
str – string
Returns:
hash/**
   * Convert a string into a redis slot hash.
   *
   * @param str string
   * @return hash
   */
  public static int generate(String str) {
    return generate(str.getBytes(StandardCharsets.UTF_8));
  }

  
Convert a string into a redis slot hash.
Params:
utf8 – bytes
Returns:
hash/**
   * Convert a string into a redis slot hash.
   *
   * @param utf8 bytes
   * @return hash
   */
  public static int generate(byte[] utf8) {
    int ch;
    int i = 0;
    int start = -1;
    int result = 0;
    int resultHash = 0;
    int len = utf8.length;

    while (i < len) {
      ch = utf8[i++];
      if (start == -1) {
        if (ch == 0x7B) {
          start = i;
        }
      } else if (ch != 0x7D) {
        resultHash = lookup[(ch ^ (resultHash >> 8)) & 0xFF] ^ (resultHash << 8);
      } else if (i - 1 != start) {
        return resultHash & 0x3FFF;
      }

      result = lookup[(ch ^ (result >> 8)) & 0xFF] ^ (result << 8);
    }

    return result & 0x3FFF;
  }

  
Convert a buffer into a redis slot hash.
Params:
buffer – buffer
Returns:
hash/**
   * Convert a buffer into a redis slot hash.
   *
   * @param buffer buffer
   * @return hash
   */
  public static int generate(Buffer buffer) {
    int ch;
    int i = 0;
    int start = -1;
    int result = 0;
    int resultHash = 0;
    int length = buffer.length();

    while (i < length) {
      ch = buffer.getByte(i++);
      if (start == -1) {
        if (ch == 0x7B) {
          start = i;
        }
      } else if (ch != 0x7D) {
        resultHash = lookup[(ch ^ (resultHash >> 8)) & 0xFF] ^ (resultHash << 8);
      } else if (i - 1 != start) {
        return resultHash & 0x3FFF;
      }

      result = lookup[(ch ^ (result >> 8)) & 0xFF] ^ (result << 8);
    }

    return result & 0x3FFF;
  }

  
Convert an array of multiple strings into a redis slot hash.
Returns -1 if one of the keys is not for the same slot as the others
Params:
keys – list of keys
Returns:
the overall hash/**
   * Convert an array of multiple strings into a redis slot hash.
   * Returns -1 if one of the keys is not for the same slot as the others
   *
   * @param keys list of keys
   * @return the overall hash
   */
  public static int generateMulti(List<String> keys) {
    int i = 1;
    int len = keys.size();
    int base = generate(keys.get(0));

    while (i < len) {
      if (generate(keys.get(i++)) != base) {
        return -1;
      }
    }

    return base;
  }

  
Convert an array of multiple strings into a redis slot hash.
Returns -1 if one of the keys is not for the same slot as the others
Params:
keys – array of keys
Returns:
the overall hash/**
   * Convert an array of multiple strings into a redis slot hash.
   * Returns -1 if one of the keys is not for the same slot as the others
   *
   * @param keys array of keys
   * @return the overall hash
   */
  public static int generateMulti(byte[]... keys) {
    int i = 1;
    int len = keys.length;
    int base = generate(keys[0]);

    while (i < len) {
      if (generate(keys[i++]) != base) {
        return -1;
      }
    }

    return base;
  }
}