/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.driver.core.utils;

import java.lang.reflect.Constructor;
import java.nio.ByteBuffer;
import java.util.Arrays;

/** Simple utility methods to make working with bytes (blob) easier. */
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);
    }
  }

  /*
   * We use reflexion to get access to a String protected constructor
   * (if available) so we can build avoid copy when creating hex strings.
   * That's stolen from Cassandra's code.
   */
  private static final Constructor<String> stringConstructor;

  static {
    Constructor<String> c;
    try {
      c = String.class.getDeclaredConstructor(int.class, int.class, char[].class);
      c.setAccessible(true);
    } catch (Exception e) {
      c = null;
    }
    stringConstructor = c;
  }

  private static String wrapCharArray(char[] c) {
    if (c == null) return null;

    String s = null;
    if (stringConstructor != null) {
      try {
        s = stringConstructor.newInstance(0, c.length, c);
      } catch (Exception e) {
        // Swallowing as we'll just use a copying constructor
      }
    }
    return s == null ? new String(c) : s;
  }

  /**
   * Converts a blob to its CQL hex string representation.
   *
   * <p>A CQL blob string representation consist 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);
  }

  /**
   * Converts a blob to its CQL hex string representation.
   *
   * <p>A CQL blob string representation consist of the hexadecimal representation of the blob
   * bytes.
   *
   * @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 toRawHexString(ByteBuffer bytes) {
    if (bytes == null) return null;

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

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

  /**
   * Converts a blob to its CQL hex string representation.
   *
   * <p>A CQL blob string representation consist 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.
   *
   * <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));
  }

  /**
   * Extract the content of the provided {@code ByteBuffer} as a byte array.
   *
   * <p>This method work with any type of {@code ByteBuffer} (direct and non-direct ones), but when
   * the {@code ByteBuffer} is backed by an array, this method will try to avoid copy when possible.
   * As a consequence, changes to the returned byte array may or may not reflect into the initial
   * {@code ByteBuffer}.
   *
   * @param bytes the buffer whose content to extract.
   * @return a byte array with the content 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;
  }

  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 wrapCharArray(array);
  }

  /**
   * Converts a CQL hex string representation into a byte array.
   *
   * <p>A CQL blob string representation consist of the hexadecimal representation of the blob
   * bytes.
   *
   * @param str the string converted in hex representation.
   * @param strOffset he offset for starting the string conversion
   * @return the byte array which the String was representing.
   */
  public 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;
  }
}
