#pragma once

#include "logging.hpp"

#include <algorithm>
#include <charconv>
#include <chrono>
#include <cstddef>
#include <cstdint>
#include <format>
#include <optional>
#include <ratio>
#include <string>
#include <string_view>

namespace redfish
{

namespace time_utils
{

/**
 * @brief Convert string that represents value in Duration Format to its numeric
 *        equivalent.
 */
inline std::optional<std::chrono::milliseconds>
    fromDurationString(std::string_view v)
{
    std::chrono::milliseconds out = std::chrono::milliseconds::zero();
    enum class ProcessingStage
    {
        // P1DT1H1M1.100S
        P,
        Days,
        Hours,
        Minutes,
        Seconds,
        Milliseconds,
        Done,
    };
    ProcessingStage stage = ProcessingStage::P;

    while (!v.empty())
    {
        if (stage == ProcessingStage::P)
        {
            if (v.front() != 'P')
            {
                return std::nullopt;
            }
            v.remove_prefix(1);
            stage = ProcessingStage::Days;
            continue;
        }
        if (stage == ProcessingStage::Days)
        {
            if (v.front() == 'T')
            {
                v.remove_prefix(1);
                stage = ProcessingStage::Hours;
                continue;
            }
        }
        uint64_t ticks = 0;
        auto [ptr, ec] = std::from_chars(v.begin(), v.end(), ticks);
        if (ec != std::errc())
        {
            BMCWEB_LOG_ERROR("Failed to convert string \"{}\" to decimal", v);
            return std::nullopt;
        }
        size_t charactersRead = static_cast<size_t>(ptr - v.data());
        if (ptr >= v.end())
        {
            BMCWEB_LOG_ERROR("Missing postfix");
            return std::nullopt;
        }
        if (*ptr == 'D')
        {
            if (stage > ProcessingStage::Days)
            {
                return std::nullopt;
            }
            out += std::chrono::days(ticks);
        }
        else if (*ptr == 'H')
        {
            if (stage > ProcessingStage::Hours)
            {
                return std::nullopt;
            }
            out += std::chrono::hours(ticks);
        }
        else if (*ptr == 'M')
        {
            if (stage > ProcessingStage::Minutes)
            {
                return std::nullopt;
            }
            out += std::chrono::minutes(ticks);
        }
        else if (*ptr == '.')
        {
            if (stage > ProcessingStage::Seconds)
            {
                return std::nullopt;
            }
            out += std::chrono::seconds(ticks);
            stage = ProcessingStage::Milliseconds;
        }
        else if (*ptr == 'S')
        {
            // We could be seeing seconds for the first time, (as is the case in
            // 1S) or for the second time (in the case of 1.1S).
            if (stage <= ProcessingStage::Seconds)
            {
                out += std::chrono::seconds(ticks);
                stage = ProcessingStage::Milliseconds;
            }
            else if (stage > ProcessingStage::Milliseconds)
            {
                BMCWEB_LOG_ERROR("Got unexpected information at end of parse");
                return std::nullopt;
            }
            else
            {
                // Seconds could be any form of (1S, 1.1S, 1.11S, 1.111S);
                // Handle them all milliseconds are after the decimal point,
                // so they need right padded.
                if (charactersRead == 1)
                {
                    ticks *= 100;
                }
                else if (charactersRead == 2)
                {
                    ticks *= 10;
                }
                out += std::chrono::milliseconds(ticks);
                stage = ProcessingStage::Milliseconds;
            }
        }
        else
        {
            BMCWEB_LOG_ERROR("Unknown postfix {}", *ptr);
            return std::nullopt;
        }

        v.remove_prefix(charactersRead + 1U);
    }
    return out;
}

/**
 * @brief Convert time value into duration format that is based on ISO 8601.
 *        Example output: "P12DT1M5.5S"
 *        Ref: Redfish Specification, Section 9.4.4. Duration values
 */
inline std::string toDurationString(std::chrono::milliseconds ms)
{
    if (ms < std::chrono::milliseconds::zero())
    {
        return "";
    }

    std::chrono::days days = std::chrono::floor<std::chrono::days>(ms);
    ms -= days;

    std::chrono::hours hours = std::chrono::floor<std::chrono::hours>(ms);
    ms -= hours;

    std::chrono::minutes minutes = std::chrono::floor<std::chrono::minutes>(ms);
    ms -= minutes;

    std::chrono::seconds seconds = std::chrono::floor<std::chrono::seconds>(ms);
    ms -= seconds;
    std::string daysStr;
    if (days.count() > 0)
    {
        daysStr = std::format("{}D", days.count());
    }
    std::string hoursStr;
    if (hours.count() > 0)
    {
        hoursStr = std::format("{}H", hours.count());
    }
    std::string minStr;
    if (minutes.count() > 0)
    {
        minStr = std::format("{}M", minutes.count());
    }
    std::string secStr;
    if (seconds.count() != 0 || ms.count() != 0)
    {
        secStr = std::format("{}.{:03}S", seconds.count(), ms.count());
    }

    return std::format("P{}T{}{}{}", daysStr, hoursStr, minStr, secStr);
}

inline std::optional<std::string>
    toDurationStringFromUint(const uint64_t timeMs)
{
    constexpr uint64_t maxTimeMs =
        static_cast<uint64_t>(std::chrono::milliseconds::max().count());

    if (maxTimeMs < timeMs)
    {
        return std::nullopt;
    }

    std::string duration = toDurationString(std::chrono::milliseconds(timeMs));
    if (duration.empty())
    {
        return std::nullopt;
    }

    return std::make_optional(duration);
}

namespace details
{
// Returns year/month/day triple in civil calendar
// Preconditions:  z is number of days since 1970-01-01 and is in the range:
//                   [numeric_limits<Int>::min(),
//                   numeric_limits<Int>::max()-719468].
// Algorithm sourced from
// https://howardhinnant.github.io/date_algorithms.html#civil_from_days
// All constants are explained in the above
template <class IntType>
constexpr std::tuple<IntType, unsigned, unsigned>
    civilFromDays(IntType z) noexcept
{
    z += 719468;
    IntType era = (z >= 0 ? z : z - 146096) / 146097;
    unsigned doe = static_cast<unsigned>(z - era * 146097); // [0, 146096]
    unsigned yoe = (doe - doe / 1460 + doe / 36524 - doe / 146096) /
                   365;                                     // [0, 399]
    IntType y = static_cast<IntType>(yoe) + era * 400;
    unsigned doy = doe - (365 * yoe + yoe / 4 - yoe / 100); // [0, 365]
    unsigned mp = (5 * doy + 2) / 153;                      // [0, 11]
    unsigned d = doy - (153 * mp + 2) / 5 + 1;              // [1, 31]
    unsigned m = mp < 10 ? mp + 3 : mp - 9;                 // [1, 12]

    return std::tuple<IntType, unsigned, unsigned>(y + (m <= 2), m, d);
}

template <typename IntType, typename Period>
std::string toISO8061ExtendedStr(std::chrono::duration<IntType, Period> t)
{
    using seconds = std::chrono::duration<int>;
    using minutes = std::chrono::duration<int, std::ratio<60>>;
    using hours = std::chrono::duration<int, std::ratio<3600>>;
    using days = std::chrono::duration<
        IntType, std::ratio_multiply<hours::period, std::ratio<24>>>;

    // d is days since 1970-01-01
    days d = std::chrono::duration_cast<days>(t);

    // t is now time duration since midnight of day d
    t -= d;

    // break d down into year/month/day
    int year = 0;
    int month = 0;
    int day = 0;
    std::tie(year, month, day) = details::civilFromDays(d.count());
    // Check against limits.  Can't go above year 9999, and can't go below epoch
    // (1970)
    if (year >= 10000)
    {
        year = 9999;
        month = 12;
        day = 31;
        t = days(1) - std::chrono::duration<IntType, Period>(1);
    }
    else if (year < 1970)
    {
        year = 1970;
        month = 1;
        day = 1;
        t = std::chrono::duration<IntType, Period>::zero();
    }

    hours hr = duration_cast<hours>(t);
    t -= hr;

    minutes mt = duration_cast<minutes>(t);
    t -= mt;

    seconds se = duration_cast<seconds>(t);

    t -= se;

    std::string subseconds;
    if constexpr (std::is_same_v<typename decltype(t)::period, std::milli>)
    {
        using MilliDuration = std::chrono::duration<int, std::milli>;
        MilliDuration subsec = duration_cast<MilliDuration>(t);
        subseconds = std::format(".{:03}", subsec.count());
    }
    else if constexpr (std::is_same_v<typename decltype(t)::period, std::micro>)
    {
        using MicroDuration = std::chrono::duration<int, std::micro>;
        MicroDuration subsec = duration_cast<MicroDuration>(t);
        subseconds = std::format(".{:06}", subsec.count());
    }

    return std::format("{:04}-{:02}-{:02}T{:02}:{:02}:{:02}{}+00:00", year,
                       month, day, hr.count(), mt.count(), se.count(),
                       subseconds);
}
} // namespace details

// Returns the formatted date time string.
// Note that the maximum supported date is 9999-12-31T23:59:59+00:00, if
// the given |secondsSinceEpoch| is too large, we return the maximum supported
// date.
inline std::string getDateTimeUint(uint64_t secondsSinceEpoch)
{
    using DurationType = std::chrono::duration<uint64_t>;
    DurationType sinceEpoch(secondsSinceEpoch);
    return details::toISO8061ExtendedStr(sinceEpoch);
}

// Returns the formatted date time string with millisecond precision
// Note that the maximum supported date is 9999-12-31T23:59:59+00:00, if
// the given |secondsSinceEpoch| is too large, we return the maximum supported
// date.
inline std::string getDateTimeUintMs(uint64_t milliSecondsSinceEpoch)
{
    using DurationType = std::chrono::duration<uint64_t, std::milli>;
    DurationType sinceEpoch(milliSecondsSinceEpoch);
    return details::toISO8061ExtendedStr(sinceEpoch);
}

// Returns the formatted date time string with microsecond precision
inline std::string getDateTimeUintUs(uint64_t microSecondsSinceEpoch)
{
    using DurationType = std::chrono::duration<uint64_t, std::micro>;
    DurationType sinceEpoch(microSecondsSinceEpoch);
    return details::toISO8061ExtendedStr(sinceEpoch);
}

inline std::string getDateTimeStdtime(std::time_t secondsSinceEpoch)
{
    using DurationType = std::chrono::duration<std::time_t>;
    DurationType sinceEpoch(secondsSinceEpoch);
    return details::toISO8061ExtendedStr(sinceEpoch);
}

/**
 * Returns the current Date, Time & the local Time Offset
 * information in a pair
 *
 * @param[in] None
 *
 * @return std::pair<std::string, std::string>, which consist
 * of current DateTime & the TimeOffset strings respectively.
 */
inline std::pair<std::string, std::string> getDateTimeOffsetNow()
{
    std::time_t time = std::time(nullptr);
    std::string dateTime = getDateTimeStdtime(time);

    /* extract the local Time Offset value from the
     * received dateTime string.
     */
    std::string timeOffset("Z00:00");
    std::size_t lastPos = dateTime.size();
    std::size_t len = timeOffset.size();
    if (lastPos > len)
    {
        timeOffset = dateTime.substr(lastPos - len);
    }

    return std::make_pair(dateTime, timeOffset);
}

using usSinceEpoch = std::chrono::duration<int64_t, std::micro>;
std::optional<usSinceEpoch> dateStringToEpoch(std::string_view datetime);
} // namespace time_utils
} // namespace redfish