/*
 * Copyright (C) 2017-2017 DataStax Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.datastax.oss.protocol.internal.util;

import java.nio.ByteBuffer;
import java.util.Arrays;

Simple utility methods to make working with bytes (blob) easier.
Note that this is an internal class. If you need those methods in a client application based on the Java driver, com.datastax.oss.driver.api.core.data.ByteUtils (in 
java-driver-core) is a better alternative: it is part of the public API, and therefore offers stronger guarantees in terms of backward compatibility. /**
 * Simple utility methods to make working with bytes (blob) easier.
 *
 * <p><b>Note that this is an internal class.</b> If you need those methods in a client application
 * based on the Java driver, {@code com.datastax.oss.driver.api.core.data.ByteUtils} (in {@code
 * java-driver-core}) is a better alternative: it is part of the public API, and therefore offers
 * stronger guarantees in terms of backward compatibility.
 */
public final class Bytes {

  private Bytes() {}

  private static final byte[] charToByte = new byte[256];
  private static final char[] byteToChar = new char[16];

  static {
    for (char c = 0; c < charToByte.length; ++c) {
      if (c >= '0' && c <= '9') {
        charToByte[c] = (byte) (c - '0');
      } else if (c >= 'A' && c <= 'F') {
        charToByte[c] = (byte) (c - 'A' + 10);
      } else if (c >= 'a' && c <= 'f') {
        charToByte[c] = (byte) (c - 'a' + 10);
      } else {
        charToByte[c] = (byte) -1;
      }
    }

    for (int i = 0; i < 16; ++i) {
      byteToChar[i] = Integer.toHexString(i).charAt(0);
    }
  }

  
Converts a blob to its CQL hex string representation.
A CQL blob string representation consists of the hexadecimal representation of the blob
bytes prefixed by "0x".
Params:
bytes – the blob/bytes to convert to a string.
Returns:
the CQL string representation of bytes. If bytes is null, this method returns null./**
   * Converts a blob to its CQL hex string representation.
   *
   * <p>A CQL blob string representation consists of the hexadecimal representation of the blob
   * bytes prefixed by "0x".
   *
   * @param bytes the blob/bytes to convert to a string.
   * @return the CQL string representation of {@code bytes}. If {@code bytes} is {@code null}, this
   *     method returns {@code null}.
   */
  public static String toHexString(ByteBuffer bytes) {
    if (bytes == null) {
      return null;
    }

    if (bytes.remaining() == 0) {
      return "0x";
    }

    char[] array = new char[2 * (bytes.remaining() + 1)];
    array[0] = '0';
    array[1] = 'x';
    return toRawHexString(bytes, array, 2);
  }

  private static String toRawHexString(ByteBuffer bytes, char[] array, int offset) {
    int size = bytes.remaining();
    int bytesOffset = bytes.position();
    assert array.length >= offset + 2 * size;
    for (int i = 0; i < size; i++) {
      int bint = bytes.get(i + bytesOffset);
      array[offset + i * 2] = byteToChar[(bint & 0xf0) >> 4];
      array[offset + 1 + i * 2] = byteToChar[bint & 0x0f];
    }
    return new String(array);
  }

  
Converts a blob to its CQL hex string representation.
A CQL blob string representation consists of the hexadecimal representation of the blob
bytes prefixed by "0x".
Params:
byteArray – the blob/bytes array to convert to a string.
Returns:
the CQL string representation of bytes. If bytes is null, this method returns null./**
   * Converts a blob to its CQL hex string representation.
   *
   * <p>A CQL blob string representation consists of the hexadecimal representation of the blob
   * bytes prefixed by "0x".
   *
   * @param byteArray the blob/bytes array to convert to a string.
   * @return the CQL string representation of {@code bytes}. If {@code bytes} is {@code null}, this
   *     method returns {@code null}.
   */
  public static String toHexString(byte[] byteArray) {
    return toHexString(ByteBuffer.wrap(byteArray));
  }

  
Parse an hex string representing a CQL blob.
The input should be a valid representation of a CQL blob, i.e. it must start by "0x"
followed by the hexadecimal representation of the blob bytes.
Params:
str – the CQL blob string representation to parse.
Throws:
IllegalArgumentException – if str is not a valid CQL blob string.
Returns:
the bytes corresponding to str. If str is null, this method returns null./**
   * Parse an hex string representing a CQL blob.
   *
   * <p>The input should be a valid representation of a CQL blob, i.e. it must start by "0x"
   * followed by the hexadecimal representation of the blob bytes.
   *
   * @param str the CQL blob string representation to parse.
   * @return the bytes corresponding to {@code str}. If {@code str} is {@code null}, this method
   *     returns {@code null}.
   * @throws IllegalArgumentException if {@code str} is not a valid CQL blob string.
   */
  public static ByteBuffer fromHexString(String str) {
    if ((str.length() & 1) == 1) {
      throw new IllegalArgumentException(
          "A CQL blob string must have an even length (since one byte is always 2 hexadecimal character)");
    }

    if (str.charAt(0) != '0' || str.charAt(1) != 'x') {
      throw new IllegalArgumentException("A CQL blob string must start with \"0x\"");
    }

    return ByteBuffer.wrap(fromRawHexString(str, 2));
  }

  private static byte[] fromRawHexString(String str, int strOffset) {
    byte[] bytes = new byte[(str.length() - strOffset) / 2];
    for (int i = 0; i < bytes.length; i++) {
      byte halfByte1 = charToByte[str.charAt(strOffset + i * 2)];
      byte halfByte2 = charToByte[str.charAt(strOffset + i * 2 + 1)];
      if (halfByte1 == -1 || halfByte2 == -1) {
        throw new IllegalArgumentException("Non-hex characters in " + str);
      }
      bytes[i] = (byte) ((halfByte1 << 4) | halfByte2);
    }
    return bytes;
  }

  
Extract the content of the provided ByteBuffer as a byte array. 
This method works with any type of ByteBuffer (direct and non-direct ones), but when the buffer is backed by an array, it will try to avoid copy when possible. As a consequence, changes to the returned byte array may or may not reflect into the initial buffer. 
Params:
bytes – the buffer whose contents to extract.
Returns:
a byte array with the contents of bytes. That array may be the array backing bytes if this can avoid a copy./**
   * Extract the content of the provided {@code ByteBuffer} as a byte array.
   *
   * <p>This method works with any type of {@code ByteBuffer} (direct and non-direct ones), but when
   * the buffer is backed by an array, it will try to avoid copy when possible. As a consequence,
   * changes to the returned byte array may or may not reflect into the initial buffer.
   *
   * @param bytes the buffer whose contents to extract.
   * @return a byte array with the contents of {@code bytes}. That array may be the array backing
   *     {@code bytes} if this can avoid a copy.
   */
  public static byte[] getArray(ByteBuffer bytes) {
    int length = bytes.remaining();

    if (bytes.hasArray()) {
      int boff = bytes.arrayOffset() + bytes.position();
      if (boff == 0 && length == bytes.array().length) {
        return bytes.array();
      } else {
        return Arrays.copyOfRange(bytes.array(), boff, boff + length);
      }
    }
    // else, DirectByteBuffer.get() is the fastest route
    byte[] array = new byte[length];
    bytes.duplicate().get(array);
    return array;
  }

  
Overwrites all the remaining bytes of the given buffer with zeroes. /** Overwrites all the remaining bytes of the given buffer with zeroes. */
  public static void erase(ByteBuffer bytes) {
    if (!bytes.isReadOnly()) {
      while (bytes.hasRemaining()) {
        bytes.put((byte) 0);
      }
    }
  }
}