/*

 * 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"

static int m_table_common[13] = { -1, 0, 3, 3, 6, 1, 4, 6, 2, 5, 0, 3, 5 }; /* 1 = jan */

static int m_table_leap[13] =   { -1, 6, 2, 3, 6, 1, 4, 6, 2, 5, 0, 3, 5 }; /* 1 = jan */

static timelib_sll positive_mod(timelib_sll x, timelib_sll y)

{

  timelib_sll tmp;

  tmp = x % y;

  if (tmp < 0) {

    tmp += y;

  }

  return tmp;

}

static timelib_sll century_value(timelib_sll j)

{

  return 6 - positive_mod(j, 4) * 2;

}

static timelib_sll timelib_day_of_week_ex(timelib_sll y, timelib_sll m, timelib_sll d, int iso)

{

  timelib_sll c1, y1, m1, dow;

  /* Only valid for Gregorian calendar, commented out as we don't handle

   * Julian calendar. We just return the 'wrong' day of week to be

   * consistent. */

  c1 = century_value(positive_mod(y, 400) / 100);

  y1 = positive_mod(y, 100);

  m1 = timelib_is_leap(y) ? m_table_leap[m] : m_table_common[m];

  dow = positive_mod((c1 + y1 + m1 + (y1 / 4) + d), 7);

  if (iso) {

    if (dow == 0) {

      dow = 7;

    }

  }

  return dow;

}

timelib_sll timelib_day_of_week(timelib_sll y, timelib_sll m, timelib_sll d)

{

  return timelib_day_of_week_ex(y, m, d, 0);

}

timelib_sll timelib_iso_day_of_week(timelib_sll y, timelib_sll m, timelib_sll d)

{

  return timelib_day_of_week_ex(y, m, d, 1);

}

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

static int d_table_common[13]  = {  0,   0,  31,  59,  90, 120, 151, 181, 212, 243, 273, 304, 334 };

static int d_table_leap[13]    = {  0,   0,  31,  60,  91, 121, 152, 182, 213, 244, 274, 305, 335 };

static int ml_table_common[13] = {  0,  31,  28,  31,  30,  31,  30,  31,  31,  30,  31,  30,  31 };

static int ml_table_leap[13]   = {  0,  31,  29,  31,  30,  31,  30,  31,  31,  30,  31,  30,  31 };

timelib_sll timelib_day_of_year(timelib_sll y, timelib_sll m, timelib_sll d)

{

  return (timelib_is_leap(y) ? d_table_leap[m] : d_table_common[m]) + d - 1;

}

timelib_sll timelib_days_in_month(timelib_sll y, timelib_sll m)

{

  return timelib_is_leap(y) ? ml_table_leap[m] : ml_table_common[m];

}

void timelib_isoweek_from_date(timelib_sll y, timelib_sll m, timelib_sll d, timelib_sll *iw, timelib_sll *iy)

{

  int y_leap, prev_y_leap, doy, jan1weekday, weekday;

  y_leap = timelib_is_leap(y);

  prev_y_leap = timelib_is_leap(y-1);

  doy = timelib_day_of_year(y, m, d) + 1;

  if (y_leap && m > 2) {

    doy++;

  }

  jan1weekday = timelib_day_of_week(y, 1, 1);

  weekday = timelib_day_of_week(y, m, d);

  if (weekday == 0) weekday = 7;

  if (jan1weekday == 0) jan1weekday = 7;

  /* Find if Y M D falls in YearNumber Y-1, WeekNumber 52 or 53 */

  if (doy <= (8 - jan1weekday) && jan1weekday > 4) {

    *iy = y - 1;

    if (jan1weekday == 5 || (jan1weekday == 6 && prev_y_leap)) {

      *iw = 53;

    } else {

      *iw = 52;

    }

  } else {

    *iy = y;

  }

  /* 8. Find if Y M D falls in YearNumber Y+1, WeekNumber 1 */

  if (*iy == y) {

    int i;

    i = y_leap ? 366 : 365;

    if ((i - (doy - y_leap)) < (4 - weekday)) {

      *iy = y + 1;

      *iw = 1;

      return;

    }

  }

  /* 9. Find if Y M D falls in YearNumber Y, WeekNumber 1 through 53 */

  if (*iy == y) {

    int j;

    j = doy + (7 - weekday) + (jan1weekday - 1);

    *iw = j / 7;

    if (jan1weekday > 4) {

      *iw -= 1;

    }

  }

}

void timelib_isodate_from_date(timelib_sll y, timelib_sll m, timelib_sll d, timelib_sll *iy, timelib_sll *iw, timelib_sll *id)

{

  timelib_isoweek_from_date(y, m, d, iw, iy);

  *id = timelib_day_of_week_ex(y, m, d, 1);

}

timelib_sll timelib_daynr_from_weeknr(timelib_sll iy, timelib_sll iw, timelib_sll id)

{

  timelib_sll dow, day;

  /* Figure out the dayofweek for y-1-1 */

  dow = timelib_day_of_week(iy, 1, 1);

  /* then use that to figure out the offset for day 1 of week 1 */

  day = 0 - (dow > 4 ? dow - 7 : dow);

  /* Add weeks and days */

  return day + ((iw - 1) * 7) + id;

}

void timelib_date_from_isodate(timelib_sll iy, timelib_sll iw, timelib_sll id, timelib_sll *y, timelib_sll *m, timelib_sll *d)

{

  timelib_sll daynr = timelib_daynr_from_weeknr(iy, iw, id) + 1;

  int *table;

  bool is_leap_year;

  // Invariant: is_leap_year == timelib_is_leap(*y)

  *y = iy;

  is_leap_year = timelib_is_leap(*y);

  // Establish invariant that daynr >= 0

  while (daynr <= 0) {

    *y -= 1;

    daynr += (is_leap_year = timelib_is_leap(*y)) ? 366 : 365;

  }

  // Establish invariant that daynr <= number of days in *yr

  while (daynr > (is_leap_year ? 366 : 365)) {

    daynr -= is_leap_year ? 366 : 365;

    *y += 1;

    is_leap_year = timelib_is_leap(*y);

  }

  table = is_leap_year ? ml_table_leap : ml_table_common;

  // Establish invariant that daynr <= number of days in *m

  *m = 1;

  while (daynr > table[*m]) {

    daynr -= table[*m];

    *m += 1;

  }

  *d = daynr;

}

int timelib_valid_time(timelib_sll h, timelib_sll i, timelib_sll s)

{

  if (h < 0 || h > 23 || i < 0 || i > 59 || s < 0 || s > 59) {

    return 0;

  }

  return 1;

}

int timelib_valid_date(timelib_sll y, timelib_sll m, timelib_sll d)

{

  if (m < 1 || m > 12 || d < 1 || d > timelib_days_in_month(y, m)) {

    return 0;

  }

  return 1;

}

#if 0

int main(void)

{

  printf("dow = %d\n", timelib_day_of_week(1978, 12, 22)); /* 5 */

  printf("dow = %d\n", timelib_day_of_week(2005,  2, 19)); /* 6 */

}

#endif