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/**
 * Copyright 2014 阿信([email protected])
 * 
 * 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 cn.songxinqiang.tool;

import java.util.Arrays;

/**
 * 生成随机验证码，可控制难度
 * 
 * @author 宋信强--2014年9月10日[email protected]
 *
 */
public class RandomCode {

    /**
     * 验证码难度级别，Simple只包含数字，Medium包含数字和小写英文，Hard包含数字和大小写英文
     */
    public enum SecurityCodeLevel {
        Simple,
        Medium,
        Hard
    };

    // 字符集合(除去易混淆的数字0、数字1、字母l、字母o、字母O)
    private final char[] CHAR_CODE = { '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c',
            'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'm', 'n', 'p', 'q', 'r', 's', 't', 'u', 'v',
            'w', 'x', 'y', 'z', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
            'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' };

    /**
     * 产生默认验证码，4位中等难度

     * 调用此方法和调用getSecurityCode(4, SecurityCodeLevel.Medium, false)有一样的行为
     * 
     * @see #getSecurityCode(int, SecurityCodeLevel, boolean)
     * @return 验证码
     */
    public char[] getSecurityCode() {
        return getSecurityCode(4, SecurityCodeLevel.Medium, false);
    }

    /**
     * 获取验证码，指定长度、难度、是否允许重复字符
     * 
     * @param length
     *            长度
     * @param level
     *            难度
     * @param isCanRepeat
     *            是否允许重复字符
     * @return 验证码
     */
    public char[] getSecurityCode(int length, SecurityCodeLevel level, boolean isCanRepeat) {
        // 随机抽取len个字符
        int len = length;
        char[] code;

        // 根据不同的难度截取字符数组
        switch (level) {
            case Simple: {
                code = Arrays.copyOfRange(CHAR_CODE, 0, 9);
                break;
            }
            case Medium: {
                code = Arrays.copyOfRange(CHAR_CODE, 0, 33);
                break;
            }
            case Hard: {
                code = Arrays.copyOfRange(CHAR_CODE, 0, CHAR_CODE.length);
                break;
            }
            default: {
                code = Arrays.copyOfRange(CHAR_CODE, 0, CHAR_CODE.length);
            }
        }

        // 字符集合长度
        int n = code.length;

        // 抛出运行时异常
        if (len > n && isCanRepeat == false) {
            throw new RuntimeException(String.format(
                    "调用SecurityCode.getSecurityCode(%1$s,%2$s,%3$s)出现异常，"
                            + "当isCanRepeat为%3$s时，传入参数%1$s不能大于%4$s", len, level, isCanRepeat, n));
        }
        // 存放抽取出来的字符
        char[] result = new char[len];
        // 判断能否出现重复的字符
        if (isCanRepeat) {
            for (int i = 0; i < result.length; i++) {
                // 索引 0 and n-1
                int r = (int) (Math.random() * n);

                // 将result中的第i个元素设置为codes[r]存放的数值
                result[i] = code[r];
            }
        } else {
            for (int i = 0; i < result.length; i++) {
                // 索引 0 and n-1
                int r = (int) (Math.random() * n);

                // 将result中的第i个元素设置为codes[r]存放的数值
                result[i] = code[r];

                // 必须确保不会再次抽取到那个字符，因为所有抽取的字符必须不相同。
                // 因此，这里用数组中的最后一个字符改写codes[r]，并将n减1
                code[r] = code[n - 1];
                n--;
            }
        }
        return result;
    }
}