Function to generate [JBBP DSL script](https://github.com/raydac/java-binary-block-parser) from a class contains fields marked by `@Bin` annotations

class2jbbp

  /**
   * Generates <a href="https://github.com/raydac/java-binary-block-parser">JBBP DSL script</a> from class @BIN annotated fields. Extra field of @BIN annotation is used as expression for array length if the text starts with 'expr:'
   * <p>Example code:
   * <pre>{@code
   *    public static class Chunk {
   *      @Bin(outOrder = 1, type = BinType.INT)
   *      int length;
   *      @Bin(outOrder = 2, type = BinType.INT)
   *      int type;
   *      @Bin(outOrder = 3, type = BinType.BYTE_ARRAY, extra = "expr:length")
   *      byte[] data;
   *      @Bin(outOrder = 4, type = BinType.INT)
   *      int crc;
   *    }
   *
   *    public static class PNGFormat {
   *      @Bin(outOrder = 1, type = BinType.LONG)
   *      long header;
   *      @Bin(outOrder = 2, type = BinType.STRUCT_ARRAY)
   *      Chunk[] chunks;
   *    }
   * 
   *    public static void main(String... args) throws Exception {
   *      System.out.println(class2jbbp(PNGFormat.class));
   *    }
   * }</pre>
   * </p>
   * 
   * @param klazz source class for generating, must not be null
   * @return generated JBBP DSL script for the class and its fields, it can be empty but can't be null
   * 
   * @author Igor Maznitsa
   */
  public static String class2jbbp(final Class<?> klazz) {
    class Item implements Comparable<Item> {

      final String fieldName;
      final Class<?> fieldType;
      final JBBPBitOrder bitOrder;
      final JBBPBitNumber bitNumber;
      final boolean array;
      final BinType type;
      final int order;
      final String extra;

      Item(final int order, final Bin binAnnotation, final Field fld) {
        this.array = fld.getType().isArray();
        if (this.array) {
          this.fieldType = fld.getType().getComponentType();
        } else {
          this.fieldType = fld.getType();
        }
        this.fieldName = binAnnotation.name().isEmpty() ? fld.getName() : binAnnotation.name();
        this.bitOrder = binAnnotation.bitOrder();
        this.bitNumber = binAnnotation.outBitNumber();
        this.type = binAnnotation.type();
        this.order = binAnnotation.outOrder() < 0 ? order : binAnnotation.outOrder();
        String expr = binAnnotation.extra();
        expr = expr.startsWith("expr:") ? expr.substring(5) : null;
        this.extra = expr;
      }

      @Override
      public int compareTo(final Item o) {
        if (this.order < o.order) {
          return -1;
        }
        if (this.order > o.order) {
          return 1;
        }
        return 0;
      }

      @Override
      public String toString() {
        final StringBuilder result = new StringBuilder();
        switch (this.type) {
          case UNDEFINED:
            throw new IllegalArgumentException("Detected undefined field : " + this.fieldName);
          case STRUCT:
          case STRUCT_ARRAY: {
            result.append(this.fieldName);
            if (this.array) {
              result.append(" [").append(this.extra == null || this.extra.isEmpty() ? "_" : this.extra).append("] ");
            }
            result.append(" {").append(class2jbbp(this.fieldType)).append("}");
          }
          break;
          default: {
            final String[] splitted = this.type.name().toLowerCase(Locale.ENGLISH).split("\\_");
            result.append(splitted[0]);
            if (splitted.length > 1) {
              result.append(" [").append(this.extra == null || this.extra.isEmpty() ? "_" : this.extra).append("]");
            }
            result.append(' ').append(this.fieldName).append("; ");
          }
          break;
        }
        return result.toString();
      }
    }

    final List<Item> items = new ArrayList<>();
    int index = 0;

    for (final Field f : klazz.getDeclaredFields()) {
      final Bin anno = f.getAnnotation(Bin.class);
      if (anno != null) {
        items.add(new Item(index++, anno, f));
      }
    }
    Collections.sort(items);

    final StringBuilder result = new StringBuilder();

    for (final Item i : items) {
      result.append(i.toString());
    }

    return result.toString();
  }