/*

 * The MIT License (MIT)

 *

 * Copyright (c) 2015-2019 Derick Rethans

 *

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to deal

 * in the Software without restriction, including without limitation the rights

 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

 * copies of the Software, and to permit persons to whom the Software is

 * furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

 * THE SOFTWARE.

 */

#include "timelib.h"

#include "timelib_private.h"

/*                                    dec  jan  feb  mrt  apr  may  jun  jul  aug  sep  oct  nov  dec */

static int days_in_month_leap[13] = {  31,  31,  29,  31,  30,  31,  30,  31,  31,  30,  31,  30,  31 };

static int days_in_month[13]      = {  31,  31,  28,  31,  30,  31,  30,  31,  31,  30,  31,  30,  31 };

static void do_range_limit(timelib_sll start, timelib_sll end, timelib_sll adj, timelib_sll *a, timelib_sll *b)

{

  if (*a < start) {

    /* We calculate 'a + 1' first as 'start - *a - 1' causes an int64_t overflows if *a is

     * LONG_MIN. 'start' is 0 in this context, and '0 - LONG_MIN > LONG_MAX'. */

    timelib_sll a_plus_1 = *a + 1;

    *b -= (start - a_plus_1) / adj + 1;

    /* This code add the extra 'adj' separately, as otherwise this can overflow int64_t in

     * situations where *b is near LONG_MIN. */

    *a += adj * ((start - a_plus_1) / adj);

    *a += adj;

  }

  if (*a >= end) {

    *b += *a / adj;

    *a -= adj * (*a / adj);

  }

}

static void inc_month(timelib_sll *y, timelib_sll *m)

{

  (*m)++;

  if (*m > 12) {

    *m -= 12;

    (*y)++;

  }

}

static void dec_month(timelib_sll *y, timelib_sll *m)

{

  (*m)--;

  if (*m < 1) {

    *m += 12;

    (*y)--;

  }

}

static void do_range_limit_days_relative(timelib_sll *base_y, timelib_sll *base_m, timelib_sll *y, timelib_sll *m, timelib_sll *d, timelib_sll invert)

{

  timelib_sll leapyear;

  timelib_sll month, year;

  timelib_sll days;

  do_range_limit(1, 13, 12, base_m, base_y);

  year = *base_y;

  month = *base_m;

/*

  printf( "S: Y%d M%d   %d %d %d   %d\n", year, month, *y, *m, *d, days);

*/

  if (!invert) {

    while (*d < 0) {

      dec_month(&year, &month);

      leapyear = timelib_is_leap(year);

      days = leapyear ? days_in_month_leap[month] : days_in_month[month];

      /* printf( "I  Y%d M%d   %d %d %d   %d\n", year, month, *y, *m, *d, days); */

      *d += days;

      (*m)--;

    }

  } else {

    while (*d < 0) {

      leapyear = timelib_is_leap(year);

      days = leapyear ? days_in_month_leap[month] : days_in_month[month];

      /* printf( "I  Y%d M%d   %d %d %d   %d\n", year, month, *y, *m, *d, days); */

      *d += days;

      (*m)--;

      inc_month(&year, &month);

    }

  }

  /*

  printf( "E: Y%d M%d   %d %d %d   %d\n", year, month, *y, *m, *d, days);

  */

}

static int do_range_limit_days(timelib_sll *y, timelib_sll *m, timelib_sll *d)

{

  timelib_sll leapyear;

  timelib_sll previous_month, previous_year;

  timelib_sll days_in_previous_month;

  int retval = 0;

  int *days_per_month_current_year;

  /* can jump an entire leap year period quickly */

  if (*d >= DAYS_PER_ERA || *d <= -DAYS_PER_ERA) {

    *y += YEARS_PER_ERA * (*d / DAYS_PER_ERA);

    *d -= DAYS_PER_ERA * (*d / DAYS_PER_ERA);

  }

  do_range_limit(1, 13, 12, m, y);

  leapyear = timelib_is_leap(*y);

  days_per_month_current_year = leapyear ? days_in_month_leap : days_in_month;

  while (*d <= 0 && *m > 0) {

    previous_month = (*m) - 1;

    if (previous_month < 1) {

      previous_month += 12;

      previous_year = (*y) - 1;

    } else {

      previous_year = (*y);

    }

    leapyear = timelib_is_leap(previous_year);

    days_in_previous_month = leapyear ? days_in_month_leap[previous_month] : days_in_month[previous_month];

    *d += days_in_previous_month;

    (*m)--;

    retval = 1;

  }

  while (*d > 0 && *m <= 12 && *d > days_per_month_current_year[*m]) {

    *d -=  days_per_month_current_year[*m];

    (*m)++;

    retval = 1;

  }

  return retval;

}

static void do_adjust_for_weekday(timelib_time* time)

{

  timelib_sll current_dow, difference;

  current_dow = timelib_day_of_week(time->y, time->m, time->d);

  if (time->relative.weekday_behavior == 2)

  {

    /* To make "this week" work, where the current DOW is a "sunday" */

    if (current_dow == 0 && time->relative.weekday != 0) {

      time->relative.weekday -= 7;

    }

    /* To make "sunday this week" work, where the current DOW is not a

     * "sunday" */

    if (time->relative.weekday == 0 && current_dow != 0) {

      time->relative.weekday = 7;

    }

    time->d -= current_dow;

    time->d += time->relative.weekday;

    return;

  }

  difference = time->relative.weekday - current_dow;

  if ((time->relative.d < 0 && difference < 0) || (time->relative.d >= 0 && difference <= -time->relative.weekday_behavior)) {

    difference += 7;

  }

  if (time->relative.weekday >= 0) {

    time->d += difference;

  } else {

    time->d -= (7 - (abs(time->relative.weekday) - current_dow));

  }

  time->relative.have_weekday_relative = 0;

}

void timelib_do_rel_normalize(timelib_time *base, timelib_rel_time *rt)

{

  do_range_limit(0, 1000000, 1000000, &rt->us, &rt->s);

  do_range_limit(0, 60, 60, &rt->s, &rt->i);

  do_range_limit(0, 60, 60, &rt->i, &rt->h);

  do_range_limit(0, 24, 24, &rt->h, &rt->d);

  do_range_limit(0, 12, 12, &rt->m, &rt->y);

  do_range_limit_days_relative(&base->y, &base->m, &rt->y, &rt->m, &rt->d, rt->invert);

  do_range_limit(0, 12, 12, &rt->m, &rt->y);

}

static void magic_date_calc(timelib_time *time)

{

  timelib_sll y, ddd, mi, mm, dd, g;

  /* The algorithm doesn't work before the year 1 */

  if (time->d < -719498) {

    return;

  }

  g = time->d + HINNANT_EPOCH_SHIFT - 1;

  y = (10000 * g + 14780) / 3652425;

  ddd = g - ((365*y) + (y/4) - (y/100) + (y/400));

  if (ddd < 0) {

    y--;

    ddd = g - ((365*y) + (y/4) - (y/100) + (y/400));

  }

  mi = (100 * ddd + 52) / 3060;

  mm = ((mi + 2) % 12) + 1;

  y = y + (mi + 2) / 12;

  dd = ddd - ((mi * 306 + 5) / 10) + 1;

  time->y = y;

  time->m = mm;

  time->d = dd;

}

void timelib_do_normalize(timelib_time* time)

{

  if (time->us != TIMELIB_UNSET) do_range_limit(0, 1000000, 1000000, &time->us, &time->s);

  if (time->s != TIMELIB_UNSET) do_range_limit(0, 60, 60, &time->s, &time->i);

  if (time->s != TIMELIB_UNSET) do_range_limit(0, 60, 60, &time->i, &time->h);

  if (time->s != TIMELIB_UNSET) do_range_limit(0, 24, 24, &time->h, &time->d);

  do_range_limit(1, 13, 12, &time->m, &time->y);

  /* Short cut if we're doing things against the Epoch */

  if (time->y == 1970 && time->m == 1 && time->d != 1) {

    magic_date_calc(time);

  }

  do {} while (do_range_limit_days(&time->y, &time->m, &time->d));

  do_range_limit(1, 13, 12, &time->m, &time->y);

}

static void do_adjust_relative(timelib_time* time)

{

  if (time->relative.have_weekday_relative) {

    do_adjust_for_weekday(time);

  }

  timelib_do_normalize(time);

  if (time->have_relative) {

    time->us += time->relative.us;

    time->s += time->relative.s;

    time->i += time->relative.i;

    time->h += time->relative.h;

    time->d += time->relative.d;

    time->m += time->relative.m;

    time->y += time->relative.y;

  }

  switch (time->relative.first_last_day_of) {

    case TIMELIB_SPECIAL_FIRST_DAY_OF_MONTH: /* first */

      time->d = 1;

      break;

    case TIMELIB_SPECIAL_LAST_DAY_OF_MONTH: /* last */

      time->d = 0;

      time->m++;

      break;

  }

  timelib_do_normalize(time);

}

static void do_adjust_special_weekday(timelib_time* time)

{

  timelib_sll count, dow, rem;

  count = time->relative.special.amount;

  dow = timelib_day_of_week(time->y, time->m, time->d);

  /* Add increments of 5 weekdays as a week, leaving the DOW unchanged. */

  time->d += (count / 5) * 7;

  /* Deal with the remainder. */

  rem = (count % 5);

  if (count > 0) {

    if (rem == 0) {

      /* Head back to Friday if we stop on the weekend. */

      if (dow == 0) {

        time->d -= 2;

      } else if (dow == 6) {

        time->d -= 1;

      }

    } else if (dow == 6) {

      /* We ended up on Saturday, but there's still work to do, so move

       * to Sunday and continue from there. */

      time->d += 1;

    } else if (dow + rem > 5) {

      /* We're on a weekday, but we're going past Friday, so skip right

       * over the weekend. */

      time->d += 2;

    }

  } else {

    /* Completely mirror the forward direction. This also covers the 0

     * case, since if we start on the weekend, we want to move forward as

     * if we stopped there while going backwards. */

    if (rem == 0) {

      if (dow == 6) {

        time->d += 2;

      } else if (dow == 0) {

        time->d += 1;

      }

    } else if (dow == 0) {

      time->d -= 1;

    } else if (dow + rem < 1) {

      time->d -= 2;

    }

  }

  time->d += rem;

}

static void do_adjust_special(timelib_time* time)

{

  if (time->relative.have_special_relative) {

    switch (time->relative.special.type) {

      case TIMELIB_SPECIAL_WEEKDAY:

        do_adjust_special_weekday(time);

        break;

    }

  }

  timelib_do_normalize(time);

  memset(&(time->relative.special), 0, sizeof(time->relative.special));

}

static void do_adjust_special_early(timelib_time* time)

{

  if (time->relative.have_special_relative) {

    switch (time->relative.special.type) {

      case TIMELIB_SPECIAL_DAY_OF_WEEK_IN_MONTH:

        time->d = 1;

        time->m += time->relative.m;

        time->relative.m = 0;

        break;

      case TIMELIB_SPECIAL_LAST_DAY_OF_WEEK_IN_MONTH:

        time->d = 1;

        time->m += time->relative.m + 1;

        time->relative.m = 0;

        break;

    }

  }

  switch (time->relative.first_last_day_of) {

    case TIMELIB_SPECIAL_FIRST_DAY_OF_MONTH: /* first */

      time->d = 1;

      break;

    case TIMELIB_SPECIAL_LAST_DAY_OF_MONTH: /* last */

      time->d = 0;

      time->m++;

      break;

  }

  timelib_do_normalize(time);

}

static void do_adjust_timezone(timelib_time *tz, timelib_tzinfo *tzi)

{

  switch (tz->zone_type) {

    case TIMELIB_ZONETYPE_OFFSET:

      tz->is_localtime = 1;

      tz->sse += -tz->z;

      return;

    case TIMELIB_ZONETYPE_ABBR: {

      tz->is_localtime = 1;

      tz->sse += (-tz->z - tz->dst * SECS_PER_HOUR);

      return;

    }

    case TIMELIB_ZONETYPE_ID:

      tzi = tz->tz_info;

      TIMELIB_BREAK_INTENTIONALLY_MISSING

    default: {

      /* No timezone in struct, fallback to reference if possible */

      int32_t              current_offset = 0;

      timelib_sll          current_transition_time = 0;

      unsigned int         current_is_dst = 0;

      int32_t              after_offset = 0;

      timelib_sll          after_transition_time = 0;

      timelib_sll          adjustment;

      int                  in_transition;

      int32_t              actual_offset;

      timelib_sll          actual_transition_time;

      if (!tzi) {

        return;

      }

      timelib_get_time_zone_offset_info(tz->sse, tzi, &current_offset, &current_transition_time, &current_is_dst);

      timelib_get_time_zone_offset_info(tz->sse - current_offset, tzi, &after_offset, &after_transition_time, NULL);

      actual_offset = after_offset;

      actual_transition_time = after_transition_time;

      if (current_offset == after_offset && tz->have_zone) {

        /* Make sure we're not missing a DST change because we don't know the actual offset yet */

        if (current_offset >= 0 && tz->dst && !current_is_dst) {

            /* Timezone or its DST at or east of UTC, so the local time, interpreted as UTC, leaves DST (as defined in the actual timezone) before the actual local time */

            int32_t              earlier_offset;

            timelib_sll          earlier_transition_time;

            timelib_get_time_zone_offset_info(tz->sse - current_offset - 7200, tzi, &earlier_offset, &earlier_transition_time, NULL);

            if ((earlier_offset != after_offset) && (tz->sse - earlier_offset < after_transition_time)) {

                /* Looking behind a bit clarified the actual offset to use */

                actual_offset = earlier_offset;

                actual_transition_time = earlier_transition_time;

            }

        } else if (current_offset <= 0 && current_is_dst && !tz->dst) {

            /* Timezone west of UTC, so the local time, interpreted as UTC, leaves DST (as defined in the actual timezone) after the actual local time */

            int32_t              later_offset;

            timelib_sll          later_transition_time;

            timelib_get_time_zone_offset_info(tz->sse - current_offset + 7200, tzi, &later_offset, &later_transition_time, NULL);

            if ((later_offset != after_offset) && (tz->sse - later_offset >= later_transition_time)) {

                /* Looking ahead a bit clarified the actual offset to use */

                actual_offset = later_offset;

                actual_transition_time = later_transition_time;

            }

        }

      }

      tz->is_localtime = 1;

      in_transition = (

        actual_transition_time != INT64_MIN &&

        ((tz->sse - actual_offset) >= (actual_transition_time + (current_offset - actual_offset))) &&

        ((tz->sse - actual_offset) < actual_transition_time)

      );

      if ((current_offset != actual_offset) && !in_transition) {

        adjustment = -actual_offset;

      } else {

        adjustment = -current_offset;

      }

      tz->sse += adjustment;

      timelib_set_timezone(tz, tzi);

      return;

    }

  }

  return;

}

timelib_sll timelib_epoch_days_from_time(timelib_time *time)

{

  timelib_sll y = time->y; // Make copy, as we don't want to change the original one

  timelib_sll era, year_of_era, day_of_year, day_of_era;

  y -= time->m <= 2;

  era = (y >= 0 ? y : y - 399) / YEARS_PER_ERA;

  year_of_era = y - era * YEARS_PER_ERA;                                                        // [0, 399]

  day_of_year = (153 * (time->m + (time->m > 2 ? -3 : 9)) + 2)/5 + time->d - 1;                 // [0, 365]

  day_of_era = year_of_era * DAYS_PER_YEAR + year_of_era / 4 - year_of_era / 100 + day_of_year; // [0, 146096]

  return era * DAYS_PER_ERA + day_of_era - HINNANT_EPOCH_SHIFT;

}

void timelib_update_ts(timelib_time* time, timelib_tzinfo* tzi)

{

  do_adjust_special_early(time);

  do_adjust_relative(time);

  do_adjust_special(time);

  /* You might be wondering, why this code does this in two steps. This is because

   * timelib_epoch_days_from_time(time) * SECS_PER_DAY with the lowest limit of

   * timelib_epoch_days_from_time() is less than the range of an int64_t. This then overflows. In

   * order to be able to still allow for any time in that day that only halfly fits in the int64_t

   * range, we add the time element first, which is always positive, and then twice half the value

   * of the earliest day as expressed as unix timestamp. */

  time->sse = timelib_hms_to_seconds(time->h, time->i, time->s);

  time->sse += timelib_epoch_days_from_time(time) * (SECS_PER_DAY / 2);

  time->sse += timelib_epoch_days_from_time(time) * (SECS_PER_DAY / 2);

  // This modifies time->sse, if needed

  do_adjust_timezone(time, tzi);

  time->sse_uptodate = 1;

  time->have_relative = time->relative.have_weekday_relative = time->relative.have_special_relative = time->relative.first_last_day_of = 0;

}

#if 0

int main(void)

{

  timelib_sll res;

  timelib_time time;

  time = timelib_strtotime("10 Feb 2005 06:07:03 PM CET"); /* 1108055223 */

  printf ("%04d-%02d-%02d %02d:%02d:%02d.%-5d %+04d %1d",

    time.y, time.m, time.d, time.h, time.i, time.s, time.f, time.z, time.dst);

  if (time.have_relative) {

    printf ("%3dY %3dM %3dD / %3dH %3dM %3dS",

      time.relative.y, time.relative.m, time.relative.d, time.relative.h, time.relative.i, time.relative.s);

  }

  if (time.have_weekday_relative) {

    printf (" / %d", time.relative.weekday);

  }

  res = time2unixtime(&time);

  printf("%Ld\n", res);

  return 0;

}

#endif