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/**
 * Copyright 2013-2016 Guoqiang Chen, Shanghai, China. All rights reserved.
 *
 *   Author: Guoqiang Chen
 *    Email: [email protected]
 *   WebURL: https://github.com/subchen
 *
 * 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 jetbrick.util;

import java.util.concurrent.ThreadLocalRandom;

public final class RandomStringUtils {
    private static final char[] HEX_CHARS = "0123456789abcdef".toCharArray();
    private static final char[] BASE62_CHARS = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();

    public static String random(int count) {
        return random(count, false, false);
    }

    public static String randomAscii(int count) {
        return random(count, 32, 127, false, false);
    }

    public static String randomAlphabetic(int count) {
        return random(count, true, false);
    }

    public static String randomAlphanumeric(int count) {
        return random(count, true, true);
    }

    public static String randomNumeric(int count) {
        return random(count, false, true);
    }

    public static String randomHex(int count) {
        return random(count, 0, HEX_CHARS.length, false, false, HEX_CHARS);
    }

    public static String randomBase62(int count) {
        return random(count, 0, BASE62_CHARS.length, false, false, BASE62_CHARS);
    }

    public static String random(int count, boolean letters, boolean numbers) {
        return random(count, 0, 0, letters, numbers);
    }

    public static String random(int count, int start, int end, boolean letters, boolean numbers) {
        return random(count, start, end, letters, numbers, null);
    }

    public static String random(int count, int start, int end, boolean letters, boolean numbers, char[] chars) {
        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;

        ThreadLocalRandom random = ThreadLocalRandom.current();
        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);
    }

    public static String random(int count, String chars) {
        if (chars == null) {
            return random(count, 0, 0, false, false, null);
        }
        return random(count, chars.toCharArray());
    }

    public static String random(int count, char[] chars) {
        if (chars == null) {
            return random(count, 0, 0, false, false, null);
        }
        return random(count, 0, chars.length, false, false, chars);
    }
}