/*
    pybind11/chrono.h: Transparent conversion between std::chrono and python's datetime

    Copyright (c) 2016 Trent Houliston <trent@houliston.me> and
                       Wenzel Jakob <wenzel.jakob@epfl.ch>

    All rights reserved. Use of this source code is governed by a
    BSD-style license that can be found in the LICENSE file.
*/

#pragma once

#include "pybind11.h"

#include <chrono>
#include <cmath>
#include <ctime>
#include <datetime.h>
#include <mutex>

PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
PYBIND11_NAMESPACE_BEGIN(detail)

template <typename type>
class duration_caster
{
    public:
        using rep = typename type::rep;
        using period = typename type::period;

        // signed 25 bits required by the standard.
        using days = std::chrono::duration<int_least32_t, std::ratio<86400>>;

        bool load(handle src, bool)
        {
            using namespace std::chrono;

            // Lazy initialise the PyDateTime import
            if (!PyDateTimeAPI)
            {
                PyDateTime_IMPORT;
            }

            if (!src)
            {
                return false;
            }

            // If invoked with datetime.delta object
            if (PyDelta_Check(src.ptr()))
            {
                value = type(duration_cast<duration<rep, period>>(
                                 days(PyDateTime_DELTA_GET_DAYS(src.ptr()))
                                 + seconds(PyDateTime_DELTA_GET_SECONDS(src.ptr()))
                                 + microseconds(PyDateTime_DELTA_GET_MICROSECONDS(src.ptr()))));
                return true;
            }

            // If invoked with a float we assume it is seconds and convert
            if (PyFloat_Check(src.ptr()))
            {
                value = type(duration_cast<duration<rep, period>>(
                                 duration<double>(PyFloat_AsDouble(src.ptr()))));
                return true;
            }

            return false;
        }

        // If this is a duration just return it back
        static const std::chrono::duration<rep, period>& get_duration(const std::chrono::duration<rep, period>& src)
        {
            return src;
        }

        // If this is a time_point get the time_since_epoch
        template <typename Clock>
        static std::chrono::duration<rep, period> get_duration(const std::chrono::time_point<Clock, std::chrono::duration<rep, period>>& src)
        {
            return src.time_since_epoch();
        }

        static handle cast(const type& src, return_value_policy /* policy */, handle /* parent */)
        {
            using namespace std::chrono;

            // Use overloaded function to get our duration from our source
            // Works out if it is a duration or time_point and get the duration
            auto d = get_duration(src);

            // Lazy initialise the PyDateTime import
            if (!PyDateTimeAPI)
            {
                PyDateTime_IMPORT;
            }

            // Declare these special duration types so the conversions happen with the correct
            // primitive types (int)
            using dd_t = duration<int, std::ratio<86400>>;
            using ss_t = duration<int, std::ratio<1>>;
            using us_t = duration<int, std::micro>;

            auto dd = duration_cast<dd_t>(d);
            auto subd = d - dd;
            auto ss = duration_cast<ss_t>(subd);
            auto us = duration_cast<us_t>(subd - ss);
            return PyDelta_FromDSU(dd.count(), ss.count(), us.count());
        }

        PYBIND11_TYPE_CASTER(type, const_name("datetime.timedelta"));
};

inline std::tm* localtime_thread_safe(const std::time_t* time, std::tm* buf)
{
#if (defined(__STDC_LIB_EXT1__) && defined(__STDC_WANT_LIB_EXT1__)) || defined(_MSC_VER)

    if (localtime_s(buf, time))
        return nullptr;

    return buf;
#else
    static std::mutex mtx;
    std::lock_guard<std::mutex> lock(mtx);
    std::tm* tm_ptr = std::localtime(time);

    if (tm_ptr != nullptr)
    {
        *buf = *tm_ptr;
    }

    return tm_ptr;
#endif
}

// This is for casting times on the system clock into datetime.datetime instances
template <typename Duration>
class type_caster<std::chrono::time_point<std::chrono::system_clock, Duration>>
{
    public:
        using type = std::chrono::time_point<std::chrono::system_clock, Duration>;
        bool load(handle src, bool)
        {
            using namespace std::chrono;

            // Lazy initialise the PyDateTime import
            if (!PyDateTimeAPI)
            {
                PyDateTime_IMPORT;
            }

            if (!src)
            {
                return false;
            }

            std::tm cal;
            microseconds msecs;

            if (PyDateTime_Check(src.ptr()))
            {
                cal.tm_sec = PyDateTime_DATE_GET_SECOND(src.ptr());
                cal.tm_min = PyDateTime_DATE_GET_MINUTE(src.ptr());
                cal.tm_hour = PyDateTime_DATE_GET_HOUR(src.ptr());
                cal.tm_mday = PyDateTime_GET_DAY(src.ptr());
                cal.tm_mon = PyDateTime_GET_MONTH(src.ptr()) - 1;
                cal.tm_year = PyDateTime_GET_YEAR(src.ptr()) - 1900;
                cal.tm_isdst = -1;
                msecs = microseconds(PyDateTime_DATE_GET_MICROSECOND(src.ptr()));
            }
            else if (PyDate_Check(src.ptr()))
            {
                cal.tm_sec = 0;
                cal.tm_min = 0;
                cal.tm_hour = 0;
                cal.tm_mday = PyDateTime_GET_DAY(src.ptr());
                cal.tm_mon = PyDateTime_GET_MONTH(src.ptr()) - 1;
                cal.tm_year = PyDateTime_GET_YEAR(src.ptr()) - 1900;
                cal.tm_isdst = -1;
                msecs = microseconds(0);
            }
            else if (PyTime_Check(src.ptr()))
            {
                cal.tm_sec = PyDateTime_TIME_GET_SECOND(src.ptr());
                cal.tm_min = PyDateTime_TIME_GET_MINUTE(src.ptr());
                cal.tm_hour = PyDateTime_TIME_GET_HOUR(src.ptr());
                cal.tm_mday = 1;  // This date (day, month, year) = (1, 0, 70)
                cal.tm_mon = 0;   // represents 1-Jan-1970, which is the first
                cal.tm_year = 70; // earliest available date for Python's datetime
                cal.tm_isdst = -1;
                msecs = microseconds(PyDateTime_TIME_GET_MICROSECOND(src.ptr()));
            }
            else
            {
                return false;
            }

            value = time_point_cast<Duration>(system_clock::from_time_t(std::mktime(&cal)) + msecs);
            return true;
        }

        static handle cast(const std::chrono::time_point<std::chrono::system_clock, Duration>& src,
                           return_value_policy /* policy */,
                           handle /* parent */)
        {
            using namespace std::chrono;

            // Lazy initialise the PyDateTime import
            if (!PyDateTimeAPI)
            {
                PyDateTime_IMPORT;
            }

            // Get out microseconds, and make sure they are positive, to avoid bug in eastern
            // hemisphere time zones (cfr. https://github.com/pybind/pybind11/issues/2417)
            using us_t = duration<int, std::micro>;
            auto us = duration_cast<us_t>(src.time_since_epoch() % seconds(1));

            if (us.count() < 0)
            {
                us += seconds(1);
            }

            // Subtract microseconds BEFORE `system_clock::to_time_t`, because:
            // > If std::time_t has lower precision, it is implementation-defined whether the value is
            // rounded or truncated. (https://en.cppreference.com/w/cpp/chrono/system_clock/to_time_t)
            std::time_t tt
                = system_clock::to_time_t(time_point_cast<system_clock::duration>(src - us));

            std::tm localtime;
            std::tm* localtime_ptr = localtime_thread_safe(&tt, &localtime);

            if (!localtime_ptr)
            {
                throw cast_error("Unable to represent system_clock in local time");
            }

            return PyDateTime_FromDateAndTime(localtime.tm_year + 1900,
                                              localtime.tm_mon + 1,
                                              localtime.tm_mday,
                                              localtime.tm_hour,
                                              localtime.tm_min,
                                              localtime.tm_sec,
                                              us.count());
        }
        PYBIND11_TYPE_CASTER(type, const_name("datetime.datetime"));
};

// Other clocks that are not the system clock are not measured as datetime.datetime objects
// since they are not measured on calendar time. So instead we just make them timedeltas
// Or if they have passed us a time as a float we convert that
template <typename Clock, typename Duration>
class type_caster<std::chrono::time_point<Clock, Duration>>
            : public duration_caster<std::chrono::time_point<Clock, Duration>> {};

template <typename Rep, typename Period>
class type_caster<std::chrono::duration<Rep, Period>>
            : public duration_caster<std::chrono::duration<Rep, Period>> {};

PYBIND11_NAMESPACE_END(detail)
PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)