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Ruby Collections for Java
There is a newer version: 2.1.2
/**
 *
 * @author Wei-Ming Wu
 *
 *
 * Copyright 2013 Wei-Ming Wu
 *
 * 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 net.sf.rubycollect4j.packer;

import static java.nio.ByteOrder.nativeOrder;
import static net.sf.rubycollect4j.RubyCollections.qr;
import static net.sf.rubycollect4j.RubyCollections.ra;
import static net.sf.rubycollect4j.RubyCollections.rs;
import static net.sf.rubycollect4j.util.ByteUtil.toByteArray;

import java.nio.ByteOrder;
import java.util.Arrays;
import java.util.List;

import net.sf.rubycollect4j.RubyArray;
import net.sf.rubycollect4j.RubyString;
import net.sf.rubycollect4j.block.TransformBlock;
import net.sf.rubycollect4j.util.ByteUtil;

/**
 * 
 * {@link Packer} is designed to implement the {@link RubyArray#pack(String)}.
 * 
 */
public final class Packer {

  private Packer() {};

  /**
   * Packs an array of Object into a binary String.
   * 
   * @param aTemplateString
   *          a String made by Directive
   * @param objs
   *          an array of Object
   * @return binary String
   */
  public static String pack(String aTemplateString, Object... objs) {
    return pack(aTemplateString, Arrays.asList(objs));
  }

  /**
   * Packs a List of Objects into a binary String.
   * 
   * @param aTemplateString
   *          a String made by Directive
   * @param objs
   *          a List of Objects
   * @return binary String
   * @throws IllegalArgumentException
   *           if template string is invalid
   * @throws IllegalArgumentException
   *           if too few arguments
   */
  public static String pack(String aTemplateString, List objs) {
    if (!Directive.verify(aTemplateString))
      throw new IllegalArgumentException("Invalid template string");

    StringBuilder sb = new StringBuilder();
    List templateList = parseTemplate(aTemplateString);
    if (templateList.size() > objs.size())
      throw new IllegalArgumentException("ArgumentError: too few arguments");

    RubyArray items = RubyArray.copyOf(objs);
    for (String template : templateList) {
      Directive d = parseDirective(template);
      template = template.replace(d.toString(), "");
      int count =
          template.isEmpty() ? 1 : template.equals("*") ? Integer.MAX_VALUE
              : rs(template).toI();

      switch (d) {

      case B:
      case b:
        RubyString binaryStr = rs(items.shift().toString()).slice(qr("^[01]+"));
        if (binaryStr == null)
          sb.append("");
        else
          sb.append(d.pack(ByteUtil.fromBinaryString(binaryStr.toS())));

        break;

      case H:
      case h:
        RubyString hexStr =
            rs(items.shift().toString()).slice(qr("^[0-9A-Fa-f]+"));
        if (hexStr == null)
          sb.append("");
        else
          sb.append(d.pack(ByteUtil.fromHexString(hexStr.toS())));

        break;

      default:
        ByteOrder bo = nativeOrder();
        if (template.isEmpty()) {
          sb.append(d.pack(toByteArray(d.cast(items.shift()), bo)));
        } else if (d == Directive.Z && template.charAt(0) == '*') {
          sb.append(d.pack(toByteArray(d.cast(items.shift()), bo)));
          sb.append("\0");
        } else if (template.charAt(0) == '*') {
          while (items.anyʔ()) {
            sb.append(d.pack(toByteArray(d.cast(items.shift()), bo)));
          }
        } else {
          if (d.isWidthAdjustable()) {
            String str = d.pack(toByteArray(d.cast(items.shift()), bo));
            if (str.length() > count) {
              sb.append(str.substring(0, count));
            } else {
              sb.append(str);
              count -= str.length();
              while (count > 0) {
                if (d == Directive.A)
                  sb.append(" ");
                else
                  sb.append("\0");

                count--;
              }
            }
          } else {
            while (count > 0) {
              sb.append(d.pack(toByteArray(d.cast(items.shift()), bo)));
              count--;
            }
          }
        }

      }
    }

    return sb.toString();
  }

  static Directive parseDirective(String template) {
    if (template.length() >= 2) {
      if (Directive.lookup.get(template.substring(0, 2)) != null)
        return Directive.lookup.get(template.substring(0, 2));
    }
    return Directive.lookup.get(template.substring(0, 1));
  }

  static List parseTemplate(String template) {
    return ra(template.split("(?!^)")).sliceBefore(
        ra(Directive.values()).map(new TransformBlock() {

          @Override
          public String yield(Directive item) {
            return item.toString();
          }

        }).join("|")).map(new TransformBlock, String>() {

      @Override
      public String yield(RubyArray item) {
        return item.join();
      }

    });
  }

}