content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You 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 org.apache.commons.lang3;
  
  import java.util.Random;
  
  /**
   * <p>Operations for random {@code String}s.</p>
   * <p>Currently <em>private high surrogate</em> characters are ignored.
   * These are Unicode characters that fall between the values 56192 (db80)
   * and 56319 (dbff) as we don't know how to handle them.
   * High and low surrogates are correctly dealt with - that is if a
   * high surrogate is randomly chosen, 55296 (d800) to 56191 (db7f)
   * then it is followed by a low surrogate. If a low surrogate is chosen,
   * 56320 (dc00) to 57343 (dfff) then it is placed after a randomly
   * chosen high surrogate. </p>
   * <p/>
   * <p>#ThreadSafe#</p>
   *
   * @version $Id$
   * @since 1.0
   */
  public class RandomStringUtils {
  
      /**
       * <p>Random object used by random method. This has to be not local
       * to the random method so as to not return the same value in the
       * same millisecond.</p>
       */
      private static final Random RANDOM = new Random();
  
      /**
       * <p>{@code RandomStringUtils} instances should NOT be constructed in
       * standard programming. Instead, the class should be used as
       * {@code RandomStringUtils.random(5);}.</p>
       * <p/>
       * <p>This constructor is public to permit tools that require a JavaBean instance
       * to operate.</p>
       */
      public RandomStringUtils() {
          super();
      }
  
      // Random
      //-----------------------------------------------------------------------
  
      /**
       * <p>Creates a random string whose length is the number of characters
       * specified.</p>
       * <p/>
       * <p>Characters will be chosen from the set of all characters.</p>
       *
       * @param count the length of random string to create
       * @return the random string
       */
      public static String random(final int count) {
          return random(count, false, false);
      }
  
      /**
       * <p>Creates a random string whose length is the number of characters
       * specified.</p>
       * <p/>
       * <p>Characters will be chosen from the set of characters whose
       * ASCII value is between {@code 32} and {@code 126} (inclusive).</p>
       *
       * @param count the length of random string to create
       * @return the random string
       */
      public static String randomAscii(final int count) {
          return random(count, 32, 127, false, false);
      }
  
      /**
       * <p>Creates a random string whose length is the number of characters
       * specified.</p>
       * <p/>
       * <p>Characters will be chosen from the set of alphabetic
       * characters.</p>
       *
       * @param count the length of random string to create
       * @return the random string
       */
      public static String randomAlphabetic(final int count) {
          return random(count, true, false);
      }
  
      /**
       * <p>Creates a random string whose length is the number of characters
       * specified.</p>
       * <p/>
       * <p>Characters will be chosen from the set of alpha-numeric
       * characters.</p>
       *
       * @param count the length of random string to create
       * @return the random string
       */
      public static String randomAlphanumeric(final int count) {
          return random(count, true, true);
      }
  
      /**
       * <p>Creates a random string whose length is the number of characters
       * specified.</p>
       * <p/>
       * <p>Characters will be chosen from the set of numeric
       * characters.</p>
       *
       * @param count the length of random string to create
       * @return the random string
       */
      public static String randomNumeric(final int count) {
          return random(count, false, true);
      }
  
      /**
       * <p>Creates a random string whose length is the number of characters
       * specified.</p>
       * <p/>
       * <p>Characters will be chosen from the set of alpha-numeric
       * characters as indicated by the arguments.</p>
       *
       * @param count   the length of random string to create
       * @param letters if {@code true}, generated string will include
       *                alphabetic characters
       * @param numbers if {@code true}, generated string will include
       *                numeric characters
       * @return the random string
       */
      public static String random(final int count, final boolean letters, final boolean numbers) {
          return random(count, 0, 0, letters, numbers);
      }
  
      /**
       * <p>Creates a random string whose length is the number of characters
       * specified.</p>
       * <p/>
       * <p>Characters will be chosen from the set of alpha-numeric
       * characters as indicated by the arguments.</p>
       *
       * @param count   the length of random string to create
       * @param start   the position in set of chars to start at
       * @param end     the position in set of chars to end before
       * @param letters if {@code true}, generated string will include
       *                alphabetic characters
       * @param numbers if {@code true}, generated string will include
       *                numeric characters
       * @return the random string
       */
      public static String random(final int count, final int start, final int end, final boolean letters, final boolean numbers) {
          return random(count, start, end, letters, numbers, null, RANDOM);
      }
  
      /**
       * <p>Creates a random string based on a variety of options, using
       * default source of randomness.</p>
       * <p/>
       * <p>This method has exactly the same semantics as
       * {@link #random(int, int, int, boolean, boolean, char[], Random)}, but
       * instead of using an externally supplied source of randomness, it uses
       * the internal static {@link Random} instance.</p>
       *
       * @param count   the length of random string to create
       * @param start   the position in set of chars to start at
       * @param end     the position in set of chars to end before
       * @param letters only allow letters?
       * @param numbers only allow numbers?
       * @param chars   the set of chars to choose randoms from.
       *                If {@code null}, then it will use the set of all chars.
       * @return the random string
       * @throws ArrayIndexOutOfBoundsException if there are not
       *                                        {@code (end - start) + 1} characters in the set array.
       */
      public static String random(final int count, final int start, final int end, final boolean letters, final boolean numbers, final char... chars) {
          return random(count, start, end, letters, numbers, chars, RANDOM);
      }
  
      /**
       * <p>Creates a random string based on a variety of options, using
       * supplied source of randomness.</p>
       * <p/>
       * <p>If start and end are both {@code 0}, start and end are set
       * to {@code ' '} and {@code 'z'}, the ASCII printable
       * characters, will be used, unless letters and numbers are both
       * {@code false}, in which case, start and end are set to
       * {@code 0} and {@code Integer.MAX_VALUE}.
       * <p/>
       * <p>If set is not {@code null}, characters between start and
       * end are chosen.</p>
       * <p/>
       * <p>This method accepts a user-supplied {@link Random}
       * instance to use as a source of randomness. By seeding a single
       * {@link Random} instance with a fixed seed and using it for each call,
       * the same random sequence of strings can be generated repeatedly
       * and predictably.</p>
       *
       * @param count   the length of random string to create
       * @param start   the position in set of chars to start at
       * @param end     the position in set of chars to end before
       * @param letters only allow letters?
       * @param numbers only allow numbers?
       * @param chars   the set of chars to choose randoms from, must not be empty.
       *                If {@code null}, then it will use the set of all chars.
       * @param random  a source of randomness.
       * @return the random string
       * @throws ArrayIndexOutOfBoundsException if there are not
       *                                        {@code (end - start) + 1} characters in the set array.
       * @throws IllegalArgumentException       if {@code count} &lt; 0 or the provided chars array is empty.
       * @since 2.0
       */
      public static String random(int count, int start, int end, final boolean letters, final boolean numbers,
              final char[] chars, final Random random) {
          if (count == 0) {
              return "";
          } else if (count < 0) {
              throw new IllegalArgumentException("Requested random string length " + count + " is less than 0.");
          }
          if (chars != null && chars.length == 0) {
              throw new IllegalArgumentException("The chars array must not be empty");
          }
  
          if (start == 0 && end == 0) {
              if (chars != null) {
                  end = chars.length;
              } else {
                  if (!letters && !numbers) {
                      end = Integer.MAX_VALUE;
                  } else {
                      end = 'z' + 1;
                      start = ' ';
                  }
              }
          } else {
              if (end <= start) {
                  throw new IllegalArgumentException("Parameter end (" + end + ") must be greater than start (" + start + ")");
              }
          }
  
          final char[] buffer = new char[count];
          final int gap = end - start;
  
          while (count-- != 0) {
              char ch;
              if (chars == null) {
                  ch = (char) (random.nextInt(gap) + start);
              } else {
                  ch = chars[random.nextInt(gap) + start];
              }
              if (letters && Character.isLetter(ch)
                  || numbers && Character.isDigit(ch)
                  || !letters && !numbers) {
                  if (ch >= 56320 && ch <= 57343) {
                      if (count == 0) {
                          count++;
                      } else {
                          // low surrogate, insert high surrogate after putting it in
                          buffer[count] = ch;
                          count--;
                          buffer[count] = (char) (55296 + random.nextInt(128));
                      }
                  } else if (ch >= 55296 && ch <= 56191) {
                      if (count == 0) {
                          count++;
                      } else {
                          // high surrogate, insert low surrogate before putting it in
                          buffer[count] = (char) (56320 + random.nextInt(128));
                          count--;
                          buffer[count] = ch;
                      }
                  } else if (ch >= 56192 && ch <= 56319) {
                      // private high surrogate, no effing clue, so skip it
                      count++;
                  } else {
                      buffer[count] = ch;
                  }
              } else {
                  count++;
              }
          }
          return new String(buffer);
      }
  
      /**
       * <p>Creates a random string whose length is the number of characters
       * specified.</p>
       * <p/>
       * <p>Characters will be chosen from the set of characters
       * specified by the string, must not be empty.
       * If null, the set of all characters is used.</p>
       *
       * @param count the length of random string to create
       * @param chars the String containing the set of characters to use,
       *              may be null, but must not be empty
       * @return the random string
       * @throws IllegalArgumentException if {@code count} &lt; 0 or the string is empty.
       */
      public static String random(final int count, final String chars) {
          if (chars == null) {
              return random(count, 0, 0, false, false, null, RANDOM);
          }
          return random(count, chars.toCharArray());
      }
  
      /**
       * <p>Creates a random string whose length is the number of characters
       * specified.</p>
       * <p/>
       * <p>Characters will be chosen from the set of characters specified.</p>
       *
       * @param count the length of random string to create
       * @param chars the character array containing the set of characters to use,
       *              may be null
       * @return the random string
       * @throws IllegalArgumentException if {@code count} &lt; 0.
       */
      public static String random(final int count, final char... chars) {
          if (chars == null) {
              return random(count, 0, 0, false, false, null, RANDOM);
          }
          return random(count, 0, chars.length, false, false, chars, RANDOM);
      }
  
  }