stuff-from-scratch/src/compression/RunLengthEncoder.h

#pragma once

#include "StringUtils.h"

#include <vector>
#include <string>

class RunLengthEncoder
{
public:
    std::string encode(const std::string& string)
    {
        std::string ret;
        if (string.empty())
        {
            return ret;
        }

        char working_char{0};
        unsigned count = 1;
        for(unsigned idx=0; idx<string.size(); idx++)
        {
            auto c = string[idx];
            if (idx == 0)
            {
                working_char = c;
                continue;
            }

            if (c == working_char)
            {
                count++;
            }
            else
            {
                insertCharacter(ret, working_char, count);
                working_char = c;
                count = 1;
            }
        }
        insertCharacter(ret, working_char, count);

        return ret;
    }

    std::string decode(const std::string& string)
    {
        std::string ret;
        if (string.empty())
        {
            return ret;
        }

        unsigned count{0};
        while(count < string.size())
        {
            auto c = string[count];
            if (c == mDelimiter)
            {
                count++;
                std::string reps;
                char working_char{0};
                while(count < string.size())
                {
                    auto rep_char = string[count];
                    count++;
                    if (StringUtils::IsAlphabetical(rep_char))
                    {
                        working_char = rep_char;
                        break;
                    }
                    else
                    {
                        reps += rep_char;
                    }
                }
                for (unsigned idx=0; idx<std::stoul(reps); idx++)
                {
                    ret += working_char;
                }
            }
            else
            {
                ret += c;
                count++;
            }
        }
        return ret;
    }

private:

    void insertCharacter(std::string& output, char c, unsigned count)
    {
        if (count >= 3)
        {
            output += mDelimiter + std::to_string(count) + c;
        }
        else
        {
            for (unsigned jdx=0;jdx<count; jdx++)
            {
                output += c;
            }
        }
    }

    char mDelimiter {'@'};

};