package com.intellij.util.io.tar;

/**
 * This class provides static utility methods to work with byte streams.
 *
 */
// CheckStyle:HideUtilityClassConstructorCheck OFF (bc)
// Copy-pasted from org.apache.tools.tar.TarUtils
public class TarUtils {

  private static final int BYTE_MASK = 255;

  /**
   * Parse an octal string from a header buffer. This is used for the
   * file permission mode value.
   *
   * @param header The header buffer from which to parse.
   * @param offset The offset into the buffer from which to parse.
   * @param length The number of header bytes to parse.
   * @return The long value of the octal string.
   */
  public static long parseOctal(byte[] header, int offset, int length) {
    long    result = 0;
    boolean stillPadding = true;
    int     end = offset + length;

    for (int i = offset; i < end; ++i) {
      if (header[i] == 0) {
        break;
      }

      if (header[i] == (byte) ' ' || header[i] == '0') {
        if (stillPadding) {
          continue;
        }

        if (header[i] == (byte) ' ') {
          break;
        }
      }

      stillPadding = false;
      // CheckStyle:MagicNumber OFF
      result = (result << 3) + (header[i] - '0');
      // CheckStyle:MagicNumber ON
    }

    return result;
  }

  /**
   * Parse an entry name from a header buffer.
   *
   * @param header The header buffer from which to parse.
   * @param offset The offset into the buffer from which to parse.
   * @param length The number of header bytes to parse.
   * @return The header's entry name.
   */
  public static StringBuffer parseName(byte[] header, int offset, int length) {
    StringBuffer result = new StringBuffer(length);
    int          end = offset + length;

    for (int i = offset; i < end; ++i) {
      if (header[i] == 0) {
        break;
      }

      result.append((char) header[i]);
    }

    return result;
  }

  /**
   * Determine the number of bytes in an entry name.
   *
   * @param name The header name from which to parse.
   * @param buf The buffer from which to parse.
   * @param offset The offset into the buffer from which to parse.
   * @param length The number of header bytes to parse.
   * @return The number of bytes in a header's entry name.
   */
  public static int getNameBytes(StringBuffer name, byte[] buf, int offset, int length) {
    int i;

    for (i = 0; i < length && i < name.length(); ++i) {
      buf[offset + i] = (byte) name.charAt(i);
    }

    for (; i < length; ++i) {
      buf[offset + i] = 0;
    }

    return offset + length;
  }

  /**
   * Parse an octal integer from a header buffer.
   *
   * @param value The header value
   * @param buf The buffer from which to parse.
   * @param offset The offset into the buffer from which to parse.
   * @param length The number of header bytes to parse.
   * @return The integer value of the octal bytes.
   */
  public static int getOctalBytes(long value, byte[] buf, int offset, int length) {
    int    idx = length - 1;

    buf[offset + idx] = 0;
    --idx;
    buf[offset + idx] = (byte) ' ';
    --idx;

    if (value == 0) {
      buf[offset + idx] = (byte) '0';
      --idx;
    } else {
      for (long val = value; idx >= 0 && val > 0; --idx) {
        // CheckStyle:MagicNumber OFF
        buf[offset + idx] = (byte) ((byte) '0' + (byte) (val & 7));
        val = val >> 3;
        // CheckStyle:MagicNumber ON
      }
    }

    for (; idx >= 0; --idx) {
      buf[offset + idx] = (byte) ' ';
    }

    return offset + length;
  }

  /**
   * Parse an octal long integer from a header buffer.
   *
   * @param value The header value
   * @param buf The buffer from which to parse.
   * @param offset The offset into the buffer from which to parse.
   * @param length The number of header bytes to parse.
   * @return The long value of the octal bytes.
   */
  public static int getLongOctalBytes(long value, byte[] buf, int offset, int length) {
    byte[] temp = new byte[length + 1];

    getOctalBytes(value, temp, 0, length + 1);
    System.arraycopy(temp, 0, buf, offset, length);

    return offset + length;
  }

  /**
   * Parse the checksum octal integer from a header buffer.
   *
   * @param value The header value
   * @param buf The buffer from which to parse.
   * @param offset The offset into the buffer from which to parse.
   * @param length The number of header bytes to parse.
   * @return The integer value of the entry's checksum.
   */
  public static int getCheckSumOctalBytes(long value, byte[] buf, int offset, int length) {
    getOctalBytes(value, buf, offset, length);

    buf[offset + length - 1] = (byte) ' ';
    buf[offset + length - 2] = 0;

    return offset + length;
  }

  /**
   * Compute the checksum of a tar entry header.
   *
   * @param buf The tar entry's header buffer.
   * @return The computed checksum.
   */
  public static long computeCheckSum(byte[] buf) {
    long sum = 0;

    for (int i = 0; i < buf.length; ++i) {
      sum += BYTE_MASK & buf[i];
    }

    return sum;
  }
}