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package cn.bestwu.lang.util;

import java.util.Random;

/**
 * 随机工具类
 *
 * @author Peter Wu
 */
public class RandomUtil {

  private static final Random RANDOM = new Random();

  /**
   * 随机数字字符串
   *
   * @param num 字符串长度
   * @return 随机数字字符串
   */
  public static String nextIntString(int num) {
    return nextString(num, "0123456789");
  }

  /**
   * 随机字符串
   *
   * @param count 字符串长度
   * @param chars 基本字符
   * @return 随机字符串
   */
  public static String nextString(int count, String chars) {
    if (chars == null) {
      return next(count, 0, 0, false, false, null, RANDOM);
    }
    return nextString(count, chars.toCharArray());
  }

  /**
   * 随机字符串
   *
   * @param count 字符串长度
   * @param chars 基本字符
   * @return 随机字符串
   */
  public static String nextString(int count, char[] chars) {
    if (chars == null) {
      return next(count, 0, 0, false, false, null, RANDOM);
    }
    return next(count, 0, chars.length, false, false, chars, RANDOM);
  }

  /**
   * 随机字符串
   *
   * @param count 字符串长度
   * @param start 起始索引
   * @param end 结束索引
   * @param letters 是否包含字母
   * @param numbers 是否包含数字
   * @param chars 随机字符范围
   * @param random 随机
   * @return 随机字符串
   */
  public static String next(int count, int start, int end, boolean letters,
      boolean numbers, char[] chars, Random random) {
    if (count == 0) {
      return "";
    } else if (count < 0) {
      throw new IllegalArgumentException(
          "Requested next string length " + count
              + " is less than 0.");
    }
    if ((start == 0) && (end == 0)) {
      end = 'z' + 1;
      start = ' ';
      if (!letters && !numbers) {
        start = 0;
        end = Integer.MAX_VALUE;
      }
    }

    char[] buffer = new char[count];
    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);
  }

  /**
   * 随机数字
   *
   * @param num 长度
   * @return 随机数字
   */
  public static int nextInt(int num) {
    return Integer.parseInt(nextIntString(num));
  }

  /**
   * 随机字符串
   *
   * @param num 长度
   * @return 随机字符串
   */
  public static String nextString(int num) {
    return nextString(num, "abcdefghigklmnopqrstuvwxyz");
  }

  /**
   * 随机字符串
   *
   * @param num 长度
   * @return 随机字符串
   */
  public static String nextString2(int num) {
    return nextString(num, "abcdefghigklmnopqrstuvwxyzABCDEFGHIGKLMNOPQRSTUVWXYZ0123456789");
  }
}