ShortID.h

//
//  ShortID.h
//  SocketServer
//
//  Created by Kay Makowsky on 16.06.16.
//  Copyright © 2016 Kay Makowsky. All rights reserved.
//

#ifndef ShortID_h
#define ShortID_h

#include <string>
#include <cmath>

const static std::string Alphabet = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

class ShortID
{
public:
    static double BcPow(double a, double b)
    {
        return std::floor(std::pow(a, b));
    }
    
    static long Decode(std::string value, int pad = 0)
    {
        long len = value.length() - 1;
        unsigned long result = 0;
        
        for (long t = len; t >= 0; t--)
        {
            unsigned long bcp = (unsigned long)BcPow(Alphabet.length(), len - t);
            result += (unsigned long)Alphabet.find(value[t]) * bcp;
        }
        
        if (pad > 0)
        {
            result -= (unsigned long)BcPow(Alphabet.length(), pad);
        }
        
        return result;
    }
    
    static std::string Encode(unsigned long value, int pad = 0)
    {
        std::string result = "";
        
        if (pad > 0)
        {
            value += (unsigned long)BcPow(Alphabet.length(), pad);
        }
        int lg = std::log(value) / std::log(Alphabet.length());
        for (int t = (value != 0 ? lg : 0); t >= 0; t--)
        {
            unsigned long bcp = (unsigned long)BcPow(Alphabet.length(), t);
            unsigned long a = ((unsigned long)std::floor((double)value / (double)bcp)) % (unsigned long)Alphabet.length();
            result += Alphabet[(int)a];
            value  = value - (a * bcp);
        }
        
        return result;
    }
    
private:
    static std::string reverseString(std::string value)
    {
        return std::string (value.rbegin(), value.rend());
    }
};

#endif