package com.mfyk.util;

import java.security.MessageDigest;

public class Code {
    private Code(){}
    /** 短链接可选字符 */
    private final static char[] chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789".toCharArray();
    /** md5的char值 */
    private final static char[] md5chars = "1234567890EADCBF".toCharArray();
    /** 30位的long类型数值,右移运算可以达30 */
    static long max = Long.parseLong("3FFFFFFF", 16);
    /** 61的最大值以便于从chars中选择字符 */
    static long min = Long.parseLong("0000003D", 16);
    public static String shortText(String md5, int start){
        /** 短链接返回数据 */
        StringBuilder returnValue = new StringBuilder();   
        String subHex = md5.substring(start*8, (start+1)*8);
        /** 获取字串运算索引 */
        long idx = max & Long.parseLong(subHex, 16);
        /** 获取6位数的短码，6*5=30 */
        for(int k = 0; k < 6; k++){   
            int index = (int) (min & idx);   
            returnValue.append(chars[index]);   
            idx = idx >> 5;   
        }  
        return returnValue.toString();
    }
    
    /**
     * md5
     * @param s
     * @return
     */
    public final static String md5(String s) {
        try {
            byte[] btInput = s.getBytes();
            /** 获得MD5摘要算法的 MessageDigest 对象 */
            MessageDigest mdInst = MessageDigest.getInstance("MD5");
            /** 使用指定的字节更新摘要 */
            mdInst.update(btInput);
            /** 获得密文  */
            byte[] md = mdInst.digest();
            int j = md.length;
            char str[] = new char[j * 2];
            int k = 0;
            for (int i = 0; i < j; i++) {
                byte byte0 = md[i];
                str[k++] = md5chars[byte0 >>> 4 & 0xf];
                str[k++] = md5chars[byte0 & 0xf];
            }
            return new String(str);
        } catch (Exception e) {
            return null;
        }
    }
}