/**
   * Returns compact class host.
   *
   * @param obj Object to compact.
   * @return String.
   */
  @Nullable
  public static Object compactObject(Object obj) {
    if (obj == null) return null;

    if (obj instanceof Enum) return obj.toString();

    if (obj instanceof String || obj instanceof Boolean || obj instanceof Number) return obj;

    if (obj instanceof Collection) {
      Collection col = (Collection) obj;

      Object[] res = new Object[col.size()];

      int i = 0;

      for (Object elm : col) res[i++] = compactObject(elm);

      return res;
    }

    if (obj.getClass().isArray()) {
      Class<?> arrType = obj.getClass().getComponentType();

      if (arrType.isPrimitive()) {
        if (obj instanceof boolean[]) return Arrays.toString((boolean[]) obj);
        if (obj instanceof byte[]) return Arrays.toString((byte[]) obj);
        if (obj instanceof short[]) return Arrays.toString((short[]) obj);
        if (obj instanceof int[]) return Arrays.toString((int[]) obj);
        if (obj instanceof long[]) return Arrays.toString((long[]) obj);
        if (obj instanceof float[]) return Arrays.toString((float[]) obj);
        if (obj instanceof double[]) return Arrays.toString((double[]) obj);
      }

      Object[] arr = (Object[]) obj;

      int iMax = arr.length - 1;

      StringBuilder sb = new StringBuilder("[");

      for (int i = 0; i <= iMax; i++) {
        sb.append(compactObject(arr[i]));

        if (i != iMax) sb.append(", ");
      }

      sb.append("]");

      return sb.toString();
    }

    return U.compact(obj.getClass().getName());
  }
  /**
   * Concat arrays in one.
   *
   * @param arrays Arrays.
   * @return Summary array.
   */
  public static int[] concat(int[]... arrays) {
    assert arrays != null;
    assert arrays.length > 1;

    int len = 0;

    for (int[] a : arrays) len += a.length;

    int[] r = Arrays.copyOf(arrays[0], len);

    for (int i = 1, shift = 0; i < arrays.length; i++) {
      shift += arrays[i - 1].length;
      System.arraycopy(arrays[i], 0, r, shift, arrays[i].length);
    }

    return r;
  }
  /**
   * Run command in separated console.
   *
   * @param workFolder Work folder for command.
   * @param args A string array containing the program and its arguments.
   * @return Started process.
   * @throws IOException If failed to start process.
   */
  public static Process openInConsole(@Nullable File workFolder, String... args)
      throws IOException {
    String[] commands = args;

    String cmd = F.concat(Arrays.asList(args), " ");

    if (U.isWindows()) commands = F.asArray("cmd", "/c", String.format("start %s", cmd));

    if (U.isMacOs())
      commands =
          F.asArray(
              "osascript",
              "-e",
              String.format("tell application \"Terminal\" to do script \"%s\"", cmd));

    if (U.isUnix()) commands = F.asArray("xterm", "-sl", "1024", "-geometry", "200x50", "-e", cmd);

    ProcessBuilder pb = new ProcessBuilder(commands);

    if (workFolder != null) pb.directory(workFolder);

    return pb.start();
  }