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ProGuardCORE is a free library to read, analyze, modify, and write Java class files.
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/*
 * ProGuardCORE -- library to process Java bytecode.
 *
 * Copyright (c) 2002-2023 Guardsquare NV
 *
 * 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 proguard.util;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;

/**
 * This class provides some utility methods for working with java.util.List instances.
 *
 * @author Eric Lafortune
 */
public class ListUtil {
  /**
   * Returns a List instance that contains the elements of the two given List instances. The
   * instances may be null. If both instances are null, the result is null too.
   */
  public static  List concatenate(List list1, List list2) {
    if (list1 != null) {
      if (list2 != null) {
        // Combine the lists into a new list.
        List list = new ArrayList<>(list1);
        list.addAll(list2);

        return list;
      } else {
        // Ignore the second (null) list.
        return list1;
      }
    } else {
      // Ignore the first (null) list.
      return list2;
    }
  }

  /** Returns the subset of the given list, containing all strings that match the given filter. */
  public static List filter(Collection list, StringMatcher filter) {
    List filteredList = new ArrayList<>();
    for (String string : list) {
      if (filter.matches(string)) {
        filteredList.add(string);
      }
    }
    return filteredList;
  }

  /** Creates a comma-separated String from the given List of String objects. */
  public static String commaSeparatedString(List list, boolean quoteStrings) {
    if (list == null) {
      return null;
    }

    StringBuilder buffer = new StringBuilder();

    for (int index = 0; index < list.size(); index++) {
      if (index > 0) {
        buffer.append(',');
      }

      String string = list.get(index);

      if (quoteStrings) {
        string = quotedString(string);
      }

      buffer.append(string);
    }

    return buffer.toString();
  }

  /** Creates a List of String objects from the given comma-separated String. */
  public static List commaSeparatedList(String string) {
    if (string == null) {
      return null;
    }

    List list = new ArrayList<>();
    int index = 0;
    while ((index = skipWhitespace(string, index)) < string.length()) {
      int nextIndex;

      // Do we have an opening quote?
      if (string.charAt(index) == '\'') {
        // Parse a quoted string.
        nextIndex = string.indexOf('\'', index + 1);
        if (nextIndex < 0) {
          nextIndex = string.length();
        }

        list.add(string.substring(index + 1, nextIndex));
      } else {
        // Parse a non-quoted string.
        nextIndex = string.indexOf(',', index);
        if (nextIndex < 0) {
          nextIndex = string.length();
        }

        String substring = string.substring(index, nextIndex).trim();
        if (substring.length() > 0) {
          list.add(substring);
        }
      }

      index = nextIndex + 1;
    }

    return list;
  }

  /**
   * Converts a List of Integers to an int array.
   *
   * @param integerList the List of Integers to convert.
   * @return the corresponding int array.
   */
  public static int[] toIntArray(List integerList) {
    int[] intArray = new int[integerList.size()];
    for (int i = 0; i < intArray.length; i++) {
      intArray[i] = integerList.get(i);
    }
    return intArray;
  }

  /** Skips any whitespace characters. */
  private static int skipWhitespace(String string, int index) {
    while (index < string.length() && Character.isWhitespace(string.charAt(index))) {
      index++;
    }
    return index;
  }

  /** Returns a quoted version of the given string, if necessary. */
  private static String quotedString(String string) {
    return string.length() == 0
            || string.indexOf(' ') >= 0
            || string.indexOf('@') >= 0
            || string.indexOf('{') >= 0
            || string.indexOf('}') >= 0
            || string.indexOf('(') >= 0
            || string.indexOf(')') >= 0
            || string.indexOf(':') >= 0
            || string.indexOf(';') >= 0
            || string.indexOf(',') >= 0
        ? ("'" + string + "'")
        : (string);
  }

  public static void main(String[] args) {
    if (args.length == 1) {
      System.out.println("Input string: [" + args[0] + "]");

      List list = commaSeparatedList(args[0]);

      System.out.println("Resulting list:");
      for (String s : list) {
        System.out.println("[" + s + "]");
      }
    } else {
      List list = Arrays.asList(args);

      System.out.println("Input list:");
      for (String s : list) {
        System.out.println("[" + s + "]");
      }

      String string = commaSeparatedString(list, true);

      System.out.println("Resulting string: [" + string + "]");
    }
  }
}