#include "describe.hpp"

#include <bigmath/chain/segment.hpp>

#include <sstream>
#include <iomanip>
#include <charconv>
#include <algorithm>

namespace bigmath {

    std::string describe(const segment& s) {
        std::string buf;
        buf.reserve(segment::digit_count * 2);
        u32 group_count = 0;

        isize i = 0;
        while (i < segment::digit_count) {
            u8 val = s[static_cast<u8>(i)];

            // Count repetitions
            isize count = 1;
            while (i + count < segment::digit_count && s[static_cast<u8>(i + count)] == val) {
                ++count;
            }

            if (count > 5) {
                if (!buf.empty() && buf.back() != ' ') {
                    buf.push_back(' ');
                }

                // Append reversed tag directly: "]count x val["
                buf.push_back(']');

                // Fast reverse-append for count digits without heap allocation
                isize temp_count = count;
                do {
                    buf.push_back(static_cast<char>('0' + (temp_count % 10)));
                    temp_count /= 10;
                } while (temp_count > 0);

                buf.append(" x ");
                buf.push_back(static_cast<char>('0' + val));
                buf.push_back('[');

                buf.push_back(' ');
                group_count = 0;
            } else {
                char ch = static_cast<char>('0' + val);
                for (isize j = 0; j < count; ++j) {
                    if (group_count == 3) {
                        buf.push_back(' ');
                        group_count = 0;
                    }
                    buf.push_back(ch);
                    group_count++;
                }
            }

            i += count;
        }

        if (!buf.empty() && buf.back() == ' ') {
            buf.pop_back();
        }

        std::reverse(buf.begin(), buf.end());
        return buf;
    }

}