Base64.hpp

#pragma once

#include <string>
#include <array>

#include <samchon/ByteArray.hpp>

namespace samchon
{
namespace library
{
    class Base64
    {
    public:
        template <typename Container>
        static auto encode(const Container &byte_array) -> std::string
        {
            static const std::array<char, 64> BASE64_CHAR_ARRAY =
            {
                'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
                'I', 'J', 'K', 'L', 'M', 'N', 'O', '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',
                'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
                'w', 'x', 'y', 'z', '0', '1', '2', '3',
                '4', '5', '6', '7', '8', '9', '+', '/'
            };

            unsigned char *bytes = (unsigned char*)byte_array.data();
            std::string str;
            str.reserve(byte_array.size() * 4);

            long long left_size = (long long)byte_array.size();

            size_t i = 0;
            size_t j = 0;
            std::array<unsigned char, 3> input;
            std::array<unsigned char, 4> output;

            while (left_size--)
            {
                input[i++] = *(bytes++);
                if (i == 3)
                {
                    output[0] = (input[0] & 0xfc) >> 2;
                    output[1] = ((input[0] & 0x03) << 4) + ((input[1] & 0xf0) >> 4);
                    output[2] = ((input[1] & 0x0f) << 2) + ((input[2] & 0xc0) >> 6);
                    output[3] = input[2] & 0x3f;

                    for (i = 0; (i < 4); i++)
                        str += BASE64_CHAR_ARRAY[output[i]];
                    i = 0;
                }
            }

            if (i)
            {
                for (j = i; j < 3; j++)
                    input[j] = '\0';

                output[0] = (input[0] & 0xfc) >> 2;
                output[1] = ((input[0] & 0x03) << 4) + ((input[1] & 0xf0) >> 4);
                output[2] = ((input[1] & 0x0f) << 2) + ((input[2] & 0xc0) >> 6);
                output[3] = input[2] & 0x3f;

                for (j = 0; (j < i + 1); j++)
                    str += BASE64_CHAR_ARRAY[output[j]];

                while ((i++ < 3))
                    str += '=';

            }
            return str;
        };

        static auto decode(const std::string &str) -> ByteArray
        {
            static const std::array<int, 256> BASE64_DECODE_ARRAY =
            {
                -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* 00-0F */
                -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* 10-1F */
                -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,  /* 20-2F */
                52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,  /* 30-3F */
                -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,  /* 40-4F */
                15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,  /* 50-5F */
                -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,  /* 60-6F */
                41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,  /* 70-7F */
                -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* 80-8F */
                -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* 90-9F */
                -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* A0-AF */
                -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* B0-BF */
                -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* C0-CF */
                -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* D0-DF */
                -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* E0-EF */
                -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1   /* F0-FF */
            };

            ByteArray data;
            data.reserve(str.size() * 3);

            int space_idx = 0, phase;
            int d, prev_d = 0;
            unsigned char c;

            space_idx = 0;
            phase = 0;

            for (size_t i = 0; i < str.size(); i++)
            {
                d = BASE64_DECODE_ARRAY[(int)str[i]];

                if (d != -1)
                {
                    switch (phase)
                    {
                    case 0:
                        ++phase;
                        break;
                    case 1:
                        c = ((prev_d << 2) | ((d & 0x30) >> 4));
                        data.push_back(c);
                        ++phase;
                        break;
                    case 2:
                        c = (((prev_d & 0xf) << 4) | ((d & 0x3c) >> 2));
                        data.push_back(c);
                        ++phase;
                        break;
                    case 3:
                        c = (((prev_d & 0x03) << 6) | d);
                        data.push_back(c);
                        phase = 0;
                        break;
                    }
                    prev_d = d;
                }
            }
            return data;
        };
    };
};
};