Jungfraujoch/common/time_utc.h

// SPDX-FileCopyrightText: 2024 Filip Leonarski, Paul Scherrer Institute <filip.leonarski@psi.ch>
// SPDX-License-Identifier: GPL-3.0-only

#pragma once

#include <string>
#include <chrono>
#include <regex>
#include <iomanip>
#include <sstream>
#include <stdexcept>
#include <ctime>
#include <cstdio>

inline std::string time_UTC(const std::chrono::time_point<std::chrono::system_clock> &input) {
    auto time_ms = std::chrono::duration_cast<std::chrono::milliseconds>(input.time_since_epoch()).count();

    char buf1[255], buf2[255];
    time_t time = time_ms / (1000);

    std::tm tm_utc{};
#ifdef _WIN32
    if (gmtime_s(&tm_utc, &time) != 0)
#else
    if (gmtime_r(&time, &tm_utc) == nullptr)
#endif
        throw std::runtime_error("gmtime failed");

    strftime(buf1, sizeof(buf1), "%FT%T", &tm_utc);
    snprintf(buf2, sizeof(buf2), ".%03d", static_cast<int>(time_ms % 1000));
    return std::string(buf1) + std::string(buf2) + "Z";
}

inline uint64_t parse_UTC_to_ms(const std::string& utc_string) {
    static const std::regex re(
        R"(^(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2}):(\d{2})(?:\.(\d{1,6}))?Z$)",
        std::regex::ECMAScript);

    std::smatch match;
    if (!std::regex_match(utc_string, match, re)) {
        throw std::runtime_error("Invalid UTC timestamp format: " + utc_string);
    }

    std::tm tm = {};
    tm.tm_year = std::stoi(match[1]) - 1900;
    tm.tm_mon  = std::stoi(match[2]) - 1;
    tm.tm_mday = std::stoi(match[3]);
    tm.tm_hour = std::stoi(match[4]);
    tm.tm_min  = std::stoi(match[5]);
    tm.tm_sec  = std::stoi(match[6]);

    int milliseconds = 0;
    if (match[7].matched) {
        std::string frac = match[7].str();

        if (frac.size() > 3) {
            frac = frac.substr(0, 3);
        } else if (frac.size() < 3) {
            while (frac.size() < 3) frac.push_back('0');
        }

        milliseconds = std::stoi(frac);
    }

#ifdef _WIN32
    time_t t = _mkgmtime(&tm);
#else
    time_t t = timegm(&tm);
#endif
    return static_cast<uint64_t>(t) * 1000ULL + milliseconds;
}

inline std::string utc_to_local_human_readable(const std::string& utc_string) {
    using namespace std::chrono;

    try {
        uint64_t ms_since_epoch = parse_UTC_to_ms(utc_string);
        auto tp = system_clock::time_point(milliseconds(ms_since_epoch));
        time_t t = system_clock::to_time_t(tp);

        std::tm tm_local{};
#ifdef _WIN32
        if (localtime_s(&tm_local, &t) != 0)
#else
        if (localtime_r(&t, &tm_local) == nullptr)
#endif
            return "";

        static const char* months[] = {
            "January", "February", "March", "April", "May", "June",
            "July", "August", "September", "October", "November", "December"
        };

        std::ostringstream out;
        out << months[tm_local.tm_mon] << " "
            << std::setw(2) << std::setfill('0') << tm_local.tm_mday << ", "
            << (tm_local.tm_year + 1900) << " "
            << std::setw(2) << std::setfill('0') << tm_local.tm_hour << ":"
            << std::setw(2) << std::setfill('0') << tm_local.tm_min;

        return out.str();
    } catch (...) {
        return "";
    }
}