/*
* Calendar Functions
* (C) 1999-2010,2017 Jack Lloyd
* (C) 2015 Simon Warta (Kullo GmbH)
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/calendar.h>
#include <botan/exceptn.h>
#include <ctime>
#include <sstream>
#include <iomanip>
#include <stdlib.h>

namespace Botan {

namespace {

std::tm do_gmtime(std::time_t time_val)
   {
   std::tm tm;

#if defined(BOTAN_TARGET_OS_HAS_GMTIME_S)
   ::gmtime_s(&tm, &time_val); // Windows
#elif defined(BOTAN_TARGET_OS_HAS_GMTIME_R)
   ::gmtime_r(&time_val, &tm); // Unix/SUSv2
#else
   std::tm* tm_p = std::gmtime(&time_val);
   if (tm_p == nullptr)
      throw Encoding_Error("time_t_to_tm could not convert");
   tm = *tm_p;
#endif

   return tm;
   }

/*
Portable replacement for timegm, _mkgmtime, etc

Algorithm due to Howard Hinnant

See https://howardhinnant.github.io/date_algorithms.html#days_from_civil
for details and explaination. The code is slightly simplified by our assumption
that the date is at least 1970, which is sufficient for our purposes.
*/
size_t days_since_epoch(uint32_t year, uint32_t month, uint32_t day)
   {
   if(month <= 2)
      year -= 1;
   const uint32_t era = year / 400;
   const uint32_t yoe = year - era * 400;      // [0, 399]
   const uint32_t doy = (153*(month + (month > 2 ? -3 : 9)) + 2)/5 + day-1;  // [0, 365]
   const uint32_t doe = yoe * 365 + yoe/4 - yoe/100 + doy;         // [0, 146096]
   return era * 146097 + doe - 719468;
   }

}

std::chrono::system_clock::time_point calendar_point::to_std_timepoint() const
   {
   if(get_year() < 1970)
      throw Invalid_Argument("calendar_point::to_std_timepoint() does not support years before 1970");

   // 32 bit time_t ends at January 19, 2038
   // https://msdn.microsoft.com/en-us/library/2093ets1.aspx
   // Throw after 2037 if 32 bit time_t is used
   if(get_year() > 2037 && sizeof(std::time_t) == 4)
      {
      throw Invalid_Argument("calendar_point::to_std_timepoint() does not support years after 2037 on this system");
      }
   else if(get_year() >= 2400)
      {
      // This upper bound is somewhat arbitrary
      throw Invalid_Argument("calendar_point::to_std_timepoint() does not support years after 2400");
      }

   const uint64_t seconds_64 = (days_since_epoch(get_year(), get_month(), get_day()) * 86400) +
                                (get_hour() * 60 * 60) + (get_minutes() * 60) + get_seconds();

   const time_t seconds_time_t = static_cast<time_t>(seconds_64);

   if(seconds_64 - seconds_time_t != 0)
      {
      throw Invalid_Argument("calendar_point::to_std_timepoint time_t overflow");
      }

   return std::chrono::system_clock::from_time_t(seconds_time_t);
   }

std::string calendar_point::to_string() const
   {
   // desired format: <YYYY>-<MM>-<dd>T<HH>:<mm>:<ss>
   std::stringstream output;
   output << std::setfill('0')
          << std::setw(4) << get_year() << "-"
          << std::setw(2) << get_month() << "-"
          << std::setw(2) << get_day() << "T"
          << std::setw(2) << get_hour() << ":"
          << std::setw(2) << get_minutes() << ":"
          << std::setw(2) << get_seconds();
   return output.str();
   }


calendar_point calendar_value(
   const std::chrono::system_clock::time_point& time_point)
   {
   std::tm tm = do_gmtime(std::chrono::system_clock::to_time_t(time_point));

   return calendar_point(tm.tm_year + 1900,
                         tm.tm_mon + 1,
                         tm.tm_mday,
                         tm.tm_hour,
                         tm.tm_min,
                         tm.tm_sec);
   }

}