# Сначала нужно сохранить данные о коммите в файл:
# (printf "commit %s\0" $(git cat-file commit HEAD | wc -c); git cat-file commit HEAD) >> file.txt
#
# Дальше нужно указать с какого байта начинаем декрементить счетчик.
# Пока что это место нахожу с момощью ручек в дебаг режиме.
#include <iostream>
#include <fstream>
#include <cassert>
#include <vector>

#include <openssl/sha.h>
#include <iomanip>
#include <algorithm>
#include <cmath>

#include <chrono>


std::vector<unsigned char> read(const std::string & path) {
	std::ifstream input(path, std::ios::binary);
	assert(input.is_open());

	std::vector<unsigned char> result;
	while (!input.eof())
	{
		const auto ch = input.get();
		result.push_back(ch);
	}
	assert(result.size() > 1);
	result.pop_back();

	return result;
}

template <class ContainerT>
void update(ContainerT & buffer, size_t position) {
	if (buffer[position] < u'0')
	{
		buffer[position] = u'9';
		// Уменьшаем предыдищуй разряд и обновляем его
		buffer[position - 1] -= 1;
		update(buffer, position - 1);
	}
}

template <class ContainerT>
void decrease(ContainerT & buffer, size_t position) {
	buffer[position] -= 1;
	update(buffer, position);
}

template <class ContainerT>
std::string to_string(const ContainerT & buffer) {
	std::stringstream result;
	result << std::hex << std::setfill('0');
	for (const auto byte : buffer)
	{
		result << std::setw(2) << (int)byte;
	}
	return result.str();
}

template <class ContainerT>
ContainerT from_string(const std::string & string) {
	ContainerT result;
	for (auto i = 0U; i < string.size(); i += 2) {
		//! Note: С unsigned char не работает.
		unsigned int buffer;

		std::istringstream iss(string.substr(i, 2));
		iss >> std::hex >> buffer;

		result.push_back(buffer);
	}
	return result;
}

int main() {
	using ContainerT = std::vector<unsigned char>;
	ContainerT target = from_string<ContainerT>("aaaaaa");
	ContainerT buffer = read("/home/alex/CLionProjects/git-hash/file.txt");
	ContainerT result(SHA_DIGEST_LENGTH);

	size_t iterations = 0;

	const auto time_start = std::chrono::high_resolution_clock::now();

	while (!std::equal(target.begin(), target.end(), result.begin())) {
		iterations++;

		decrease(buffer, 99);

		SHA1(buffer.data(), buffer.size(), result.data());

		if (iterations % (2 << 17) == 0)
		{
			const auto ratio = static_cast<double>(iterations) / std::pow(16, target.size() * 2);

			const auto time_now = std::chrono::high_resolution_clock::now();
			const auto elapsed_in_sec = std::chrono::duration_cast<std::chrono::seconds>(time_now - time_start).count();

			const auto estimated = elapsed_in_sec / ratio;

			std::cout << std::dec << "[" << iterations << "] Compute " << round(ratio * 10000) / 100 << "%, ";
			std::cout << "Elapsed " << elapsed_in_sec << " sec, Estimated " << std::round(estimated) << " sec." << std::endl;
		}
	}
	const auto ratio = static_cast<double>(iterations) / std::pow(16, target.size() * 2);

	const auto time_now = std::chrono::high_resolution_clock::now();
	const auto elapsed_in_sec = std::chrono::duration_cast<std::chrono::seconds>(time_now - time_start).count();

	std::cout << std::dec << "[" << iterations << "] Compute " << ratio * 100 << "%, ";
	std::cout << "Elapsed " << elapsed_in_sec << " sec." << std::endl;
	std::cout << "Result hash: " << to_string(result) << std::endl;

	for (const auto symbol : buffer) {
		std::cout << symbol;
	}
	std::cout << std::endl;

	return 0;
}