// swad_date.c: dates

/*
    SWAD (Shared Workspace At a Distance),
    is a web platform developed at the University of Granada (Spain),
    and used to support university teaching.

    This file is part of SWAD core.
    Copyright (C) 1999-2019 Antonio Caņas Vargas

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Affero General Public License as
    published by the Free Software Foundation, either version 3 of the
    License, or (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Affero General Public License for more details.

    You should have received a copy of the GNU Affero General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/
/*****************************************************************************/
/********************************* Headers ***********************************/
/*****************************************************************************/

#include <string.h>		// For string functions
#include <time.h>		// For time functions (mktime...)

#include "swad_box.h"
#include "swad_calendar.h"
#include "swad_config.h"
#include "swad_database.h"
#include "swad_date.h"
#include "swad_form.h"
#include "swad_global.h"
#include "swad_parameter.h"
#include "swad_setting.h"

/*****************************************************************************/
/************** External global variables from others modules ****************/
/*****************************************************************************/

extern struct Globals Gbl;

/*****************************************************************************/
/***************************** Public constants ******************************/
/*****************************************************************************/

/*****************************************************************************/
/**************************** Private constants ******************************/
/*****************************************************************************/

const unsigned Dat_NumDaysMonth[1 + 12] =
  {
    0,
   31,	//  1: January
   28,	//  2: February
   31,	//  3: Mars
   30,	//  4: April
   31,	//  5: May
   30,	//  6: June
   31,	//  7: July
   31,	//  8: Agoust
   30,	//  9: September
   31,	// 10: October
   30,	// 11: November
   31,	// 12: December
  };

const char *Dat_TimeStatusClassVisible[Dat_NUM_TIME_STATUS] =
  {
   "DATE_RED",		// Dat_PAST
   "DATE_GREEN",	// Dat_PRESENT
   "DATE_BLUE",		// Dat_FUTURE
  };
const char *Dat_TimeStatusClassHidden[Dat_NUM_TIME_STATUS] =
  {
   "DATE_RED_LIGHT",	// Dat_PAST
   "DATE_GREEN_LIGHT",	// Dat_PRESENT
   "DATE_BLUE_LIGHT",	// Dat_FUTURE
  };

/*****************************************************************************/
/****************************** Internal types *******************************/
/*****************************************************************************/

/*****************************************************************************/
/**************************** Private prototypes *****************************/
/*****************************************************************************/

static void Dat_PutIconsDateFormat (void);
static unsigned Dat_GetParamDateFormat (void);

/*****************************************************************************/
/************** Put icons to select the first day of the week ****************/
/*****************************************************************************/

void Dat_PutBoxToSelectDateFormat (void)
  {
   extern const char *Hlp_PROFILE_Settings_dates;
   extern const char *Txt_Dates;
   Dat_Format_t Format;

   /***** Start box *****/
   Box_StartBox (NULL,Txt_Dates,Dat_PutIconsDateFormat,
                 Hlp_PROFILE_Settings_dates,Box_NOT_CLOSABLE);

   /***** Form with list of options *****/
   Frm_StartForm (ActChgDatFmt);

   fprintf (Gbl.F.Out,"<ul class=\"LIST_LEFT\">");
   for (Format = (Dat_Format_t) 0;
	Format <= (Dat_Format_t) (Dat_NUM_OPTIONS_FORMAT - 1);
	Format++)
     {
      fprintf (Gbl.F.Out,"<li class=\"%s\">"
			 "<label>"
			 "<input type=\"radio\" name=\"DateFormat\" value=\"%u\"",
	       (Format == Gbl.Prefs.DateFormat) ? "DAT_N LIGHT_BLUE" :
						  "DAT",
	       (unsigned) Format);
      if (Format == Gbl.Prefs.DateFormat)
	 fprintf (Gbl.F.Out," checked=\"checked\"");
      fprintf (Gbl.F.Out," onclick=\"document.getElementById('%s').submit();\" />",
	       Gbl.Form.Id);
      Dat_PutSpanDateFormat (Format);
      Dat_PutScriptDateFormat (Format);
      fprintf (Gbl.F.Out,"</label>"
			 "</li>");
     }

   /***** End list and form *****/
   fprintf (Gbl.F.Out,"</ul>");

   /***** End form *****/
   Frm_EndForm ();

   /***** End box *****/
   Box_EndBox ();
  }

/*****************************************************************************/
/*************** Put contextual icons in date-format setting *****************/
/*****************************************************************************/

static void Dat_PutIconsDateFormat (void)
  {
   /***** Put icon to show a figure *****/
   Gbl.Figures.FigureType = Fig_DATE_FORMAT;
   Fig_PutIconToShowFigure ();
  }

/*****************************************************************************/
/******* Put script to write current date-time in a given date format ********/
/*****************************************************************************/

void Dat_PutSpanDateFormat (Dat_Format_t Format)
  {
   fprintf (Gbl.F.Out,"<span id=\"date_format_%u\"></span>",
	    (unsigned) Format);
  }

void Dat_PutScriptDateFormat (Dat_Format_t Format)
  {
   fprintf (Gbl.F.Out,"<script type=\"text/javascript\">"
		      "writeLocalDateHMSFromUTC('date_format_%u',%ld,"
		      "%u,'',null,true,false,0x0);"
		      "</script>",
	    (unsigned) Format,(long) Gbl.StartExecutionTimeUTC,
	    (unsigned) Format);
  }

/*****************************************************************************/
/***************************** Change date format ****************************/
/*****************************************************************************/

void Dat_ChangeDateFormat (void)
  {
   /***** Get param with date format *****/
   Gbl.Prefs.DateFormat = Dat_GetParamDateFormat ();

   /***** Store date format in database *****/
   if (Gbl.Usrs.Me.Logged)
      DB_QueryUPDATE ("can not update your setting about date format",
		      "UPDATE usr_data SET DateFormat=%u"
		      " WHERE UsrCod=%ld",
                      (unsigned) Gbl.Prefs.DateFormat,
                      Gbl.Usrs.Me.UsrDat.UsrCod);

   /***** Set settings from current IP *****/
   Set_SetSettingsFromIP ();
  }

/*****************************************************************************/
/********************** Get parameter with date format ***********************/
/*****************************************************************************/

static Dat_Format_t Dat_GetParamDateFormat (void)
  {
   return (Dat_Format_t) Par_GetParToUnsignedLong ("DateFormat",
                                                   0L,
                                                   (unsigned long) (Dat_NUM_OPTIONS_FORMAT - 1),
                                                   (unsigned long) Dat_FORMAT_DEFAULT);
  }

/*****************************************************************************/
/*********************** Get date format from string *************************/
/*****************************************************************************/

Dat_Format_t Dat_GetDateFormatFromStr (const char *Str)
  {
   unsigned UnsignedNum;

   if (sscanf (Str,"%u",&UnsignedNum) == 1)
      if (UnsignedNum < Dat_NUM_OPTIONS_FORMAT)
         return (Dat_Format_t) UnsignedNum;

   return Dat_FORMAT_DEFAULT;
  }

/*****************************************************************************/
/************************** Get current time UTC *****************************/
/*****************************************************************************/

void Dat_GetStartExecutionTimeUTC (void)
  {
   Gbl.StartExecutionTimeUTC = time (NULL);
  }

/*****************************************************************************/
/********************** Get and convert current time *************************/
/*****************************************************************************/

void Dat_GetAndConvertCurrentDateTime (void)
  {
   struct tm *tm_ptr;

   /***** Convert current local time to a struct tblock *****/
   tm_ptr = Dat_GetLocalTimeFromClock (&Gbl.StartExecutionTimeUTC);

   Gbl.Now.Date.Year   = tm_ptr->tm_year + 1900;
   Gbl.Now.Date.Month  = tm_ptr->tm_mon  + 1;
   Gbl.Now.Date.Day    = tm_ptr->tm_mday;
   Gbl.Now.Time.Hour   = tm_ptr->tm_hour;
   Gbl.Now.Time.Minute = tm_ptr->tm_min;
   Gbl.Now.Time.Second = tm_ptr->tm_sec;

   /***** Initialize current date in format YYYYMMDD *****/
   snprintf (Gbl.Now.Date.YYYYMMDD,sizeof (Gbl.Now.Date.YYYYMMDD),
	     "%04u%02u%02u",
             Gbl.Now.Date.Year,Gbl.Now.Date.Month,Gbl.Now.Date.Day);

   /***** Initialize current time in format YYYYMMDDHHMMSS *****/
   snprintf (Gbl.Now.YYYYMMDDHHMMSS,sizeof (Gbl.Now.YYYYMMDDHHMMSS),
	     "%04u%02u%02u%02u%02u%02u",
             Gbl.Now.Date.Year,Gbl.Now.Date.Month,Gbl.Now.Date.Day,
             Gbl.Now.Time.Hour,Gbl.Now.Time.Minute,Gbl.Now.Time.Second);

   /***** Compute what day was yesterday *****/
   Dat_GetDateBefore (&Gbl.Now.Date,&Gbl.Yesterday);
  }

/*****************************************************************************/
/************ Get UNIX time (seconds since 1970 UTC) from string *************/
/*****************************************************************************/

time_t Dat_GetUNIXTimeFromStr (const char *Str)
  {
   time_t Time = (time_t) 0;

   if (Str)
      if (Str[0])
         if (sscanf (Str,"%ld",&Time) != 1)
	    Time = (time_t) 0;

   return Time;
  }

/*****************************************************************************/
/*********** Get a struct Date from a string in YYYYMMDD format **************/
/*****************************************************************************/

bool Dat_GetDateFromYYYYMMDD (struct Date *Date,const char *YYYYMMDD)
  {
   if (YYYYMMDD)
      if (YYYYMMDD[0])
	 if (sscanf (YYYYMMDD,"%04u%02u%02u",&(Date->Year),&(Date->Month),&(Date->Day)) == 3)
	   {
	    Str_Copy (Date->YYYYMMDD,YYYYMMDD,
	              Dat_LENGTH_YYYYMMDD);
	    return true;
	   }

   Date->Year = Date->Month = Date->Day = 0;
   Date->YYYYMMDD[0] = '\0';
   return false;
  }

/*****************************************************************************/
/******************** Write div for client local time ************************/
/*****************************************************************************/

void Dat_ShowClientLocalTime (void)
  {
   extern const char *Txt_Show_calendar;
   extern const char *Txt_Show_agenda;

   /***** Draw the current date and time *****/
   /* Start container */
   fprintf (Gbl.F.Out,"<div id=\"current_date\">");

   /* Month with link to calendar */
   fprintf (Gbl.F.Out,"<div id=\"current_month\">");
   Frm_StartForm (ActSeeCal);
   Frm_LinkFormSubmit (Txt_Show_calendar,"CURRENT_MONTH",NULL);
   fprintf (Gbl.F.Out,"<span id=\"current_month_txt\">"	// JavaScript will write HTML here
                      "</span>"
                      "</a>");
   Frm_EndForm ();
   fprintf (Gbl.F.Out,"</div>");

   /* Day with link to agenda (if I am logged) */
   fprintf (Gbl.F.Out,"<div id=\"current_day\">");
   if (Gbl.Usrs.Me.Logged)
     {
      Frm_StartForm (ActSeeMyAgd);
      Frm_LinkFormSubmit (Txt_Show_agenda,"CURRENT_DAY",NULL);
     }
   fprintf (Gbl.F.Out,"<span id=\"current_day_txt\">"	// JavaScript will write HTML here
		      "</span>");
   if (Gbl.Usrs.Me.Logged)
     {
      fprintf (Gbl.F.Out,"</a>");
      Frm_EndForm ();
     }
   fprintf (Gbl.F.Out,"</div>");

   /* Time */
   fprintf (Gbl.F.Out,"<div id=\"current_time\">"	// JavaScript will write HTML here
            	      "</div>");

   /* End container */
   fprintf (Gbl.F.Out,"</div>");

   /* Write script to draw the month */
   fprintf (Gbl.F.Out,"<script type=\"text/javascript\">\n"
		      "secondsSince1970UTC = %ld;\n"
                      "writeLocalClock();\n"
	              "</script>",
            (long) Gbl.StartExecutionTimeUTC);
  }

/*****************************************************************************/
/***************** Compute local time, adjusting day of week *****************/
/*****************************************************************************/

struct tm *Dat_GetLocalTimeFromClock (const time_t *timep)
  {
   struct tm *tm_ptr;

   if ((tm_ptr = localtime (timep)) == NULL)
      Lay_ShowErrorAndExit ("Can not get local time from clock.");

   /***** Convert from sunday, monday, tuesday...
	  to monday, tuesday, wednesday... *****/
   if (tm_ptr->tm_wday == 0)	// sunday
      tm_ptr->tm_wday = 6;
   else if (tm_ptr->tm_wday >= 1 &&
	    tm_ptr->tm_wday <= 6)	// monday to saturday
      tm_ptr->tm_wday--;
   else				// error!
      tm_ptr->tm_wday = 0;

   return tm_ptr;
  }

/*****************************************************************************/
/********* Convert a struct with Day, Month and Year to a date string ********/
/*****************************************************************************/

void Dat_ConvDateToDateStr (struct Date *Date,char StrDate[Cns_MAX_BYTES_DATE + 1])
  {
   extern const char *Txt_MONTHS_SMALL_SHORT[12];

   if (Date->Day   == 0 ||
       Date->Month == 0 ||
       Date->Year  == 0)
      StrDate[0] = '\0';
   else
      switch (Gbl.Prefs.DateFormat)
        {
	 case Dat_FORMAT_YYYY_MM_DD:
	    snprintf (StrDate,Cns_MAX_BYTES_DATE + 1,
		      "%04u-%02u-%02u",
		      Date->Year,
		      Date->Month,
		      Date->Day);
	    break;
	 case Dat_FORMAT_DD_MONTH_YYYY:
	    snprintf (StrDate,Cns_MAX_BYTES_DATE + 1,
		      "%u&nbsp;%s&nbsp;%04u",
		      Date->Day,
		      Txt_MONTHS_SMALL_SHORT[Date->Month - 1],
		      Date->Year);
	    break;
	 case Dat_FORMAT_MONTH_DD_YYYY:
	    snprintf (StrDate,Cns_MAX_BYTES_DATE + 1,
		      "%s&nbsp;%u,&nbsp;%04u",
		      Txt_MONTHS_SMALL_SHORT[Date->Month - 1],
		      Date->Day,
		      Date->Year);
	    break;
        }
  }

/*****************************************************************************/
/*************** Show forms to enter initial and ending dates ****************/
/*****************************************************************************/

void Dat_PutFormStartEndClientLocalDateTimesWithYesterdayToday (bool SetHMS000000To235959)
  {
   extern const char *The_ClassFormInBox[The_NUM_THEMES];
   extern const char *Txt_START_END_TIME[Dat_NUM_START_END_TIME];
   extern const char *Txt_Yesterday;
   extern const char *Txt_Today;

   /***** Start date-time *****/
   fprintf (Gbl.F.Out,"<tr>"
                      "<td class=\"RIGHT_MIDDLE\">"
                      "<label class=\"%s\">%s:</label>"
                      "</td>"
                      "<td class=\"LEFT_MIDDLE\">",
            The_ClassFormInBox[Gbl.Prefs.Theme],
            Txt_START_END_TIME[Dat_START_TIME]);

   /* Date-time */
   Dat_WriteFormClientLocalDateTimeFromTimeUTC ("Start",
                                                "Start",
                                                Gbl.DateRange.TimeUTC[0],
                                                Cfg_LOG_START_YEAR,
				                Gbl.Now.Date.Year,
				                Dat_FORM_SECONDS_ON,
				                SetHMS000000To235959 ? Dat_HMS_TO_000000 :	// Set hour, minute and second to 00:00:00
				                                       Dat_HMS_DO_NOT_SET,	// Don't set hour, minute and second to 00:00:00
				                false);						// Don't submit on change

   /***** "Yesterday" and "Today" buttons *****/
   fprintf (Gbl.F.Out,"</td>"
                      "<td rowspan=\"2\" class=\"LEFT_MIDDLE\">"
	              "<input type=\"button\" name=\"Yesterday\" value=\"%s\""
                      " onclick=\"setDateToYesterday('Start','End');\" />"
	              "<input type=\"button\" name=\"Today\" value=\"%s\""
                      " onclick=\"setDateToToday('Start','End');\" />"
                      "</td>"
                      "</tr>",
            Txt_Yesterday,
            Txt_Today);

   /***** End date-time *****/
   fprintf (Gbl.F.Out,"<tr>"
                      "<td class=\"RIGHT_MIDDLE\">"
                      "<label class=\"%s\">%s:</label>"
                      "</td>"
                      "<td class=\"LEFT_MIDDLE\">",
            The_ClassFormInBox[Gbl.Prefs.Theme],
            Txt_START_END_TIME[Dat_END_TIME]);
   /* Date-time */
   Dat_WriteFormClientLocalDateTimeFromTimeUTC ("End",
                                                "End",
                                                Gbl.DateRange.TimeUTC[1],
                                                Cfg_LOG_START_YEAR,
				                Gbl.Now.Date.Year,
				                Dat_FORM_SECONDS_ON,
				                SetHMS000000To235959 ? Dat_HMS_TO_235959 :	// Set hour, minute and second to 23:59:59
				                                       Dat_HMS_DO_NOT_SET,	// Don't set hour, minute and second
				                false);						// Don't submit on change
   fprintf (Gbl.F.Out,"</td>"
                      "</tr>");
  }

/*****************************************************************************/
/************* Show forms to enter initial and ending date-times *************/
/*****************************************************************************/

void Dat_PutFormStartEndClientLocalDateTimes (time_t TimeUTC[2],
                                              Dat_FormSeconds FormSeconds)
  {
   extern const char *The_ClassFormInBox[The_NUM_THEMES];
   extern const char *Txt_START_END_TIME[Dat_NUM_START_END_TIME];
   Dat_StartEndTime_t StartEndTime;
   const char *Id[Dat_NUM_START_END_TIME] =
     {
      "Start",	// Dat_START_TIME
      "End"	// Dat_END_TIME
     };

   for (StartEndTime = Dat_START_TIME;
	StartEndTime <= Dat_END_TIME;
	StartEndTime++)
     {
      /* Date-time */
      fprintf (Gbl.F.Out,"<tr>"
	                 "<td class=\"RIGHT_MIDDLE\">"
	                 "<label class=\"%s\">%s:</label>"
	                 "</td>"
                         "<td class=\"LEFT_MIDDLE\">",
               The_ClassFormInBox[Gbl.Prefs.Theme],
               Txt_START_END_TIME[StartEndTime]);
      Dat_WriteFormClientLocalDateTimeFromTimeUTC (Id[StartEndTime],
                                                   Id[StartEndTime],
	                                           TimeUTC[StartEndTime],
	                                           Gbl.Now.Date.Year - 1,
	                                           Gbl.Now.Date.Year + 1,
				                   FormSeconds,
				                   Dat_HMS_DO_NOT_SET,	// Don't set hour, minute and second
				                   false);		// Don't submit on change
      fprintf (Gbl.F.Out,"</td>"
	                 "</tr>");
     }
  }

/*****************************************************************************/
/************************* Show a form to enter a date ***********************/
/*****************************************************************************/

void Dat_WriteFormClientLocalDateTimeFromTimeUTC (const char *Id,
                                                  const char *ParamName,
                                                  time_t TimeUTC,
                                                  unsigned FirstYear,
                                                  unsigned LastYear,
                                                  Dat_FormSeconds FormSeconds,
                                                  Dat_SetHMS SetHMS,
                                                  bool SubmitFormOnChange)
  {
   extern const char *Txt_MONTHS_SMALL[12];
   unsigned Day;
   unsigned Month;
   unsigned Year;
   unsigned Hour;
   unsigned Minute;
   unsigned Second;
   unsigned MinutesIInterval[Dat_NUM_FORM_SECONDS] =
     {
      5,   // Dat_FORM_SECONDS_OFF
      1,   // Dat_FORM_SECONDS_ON
     };


   /***** Start table *****/
   fprintf (Gbl.F.Out,"<table>"
	              "<tr>");

   /***** Year *****/
   fprintf (Gbl.F.Out,"<td class=\"RIGHT_MIDDLE\">"
                      "<select id=\"%sYear\" name=\"%sYear\""
                      " onchange=\""
                      "adjustDateForm('%s');"
                      "setUTCFromLocalDateTimeForm('%s');",
	    Id,ParamName,Id,Id);
   if (SubmitFormOnChange)
      fprintf (Gbl.F.Out,"document.getElementById('%s').submit();",
               Gbl.Form.Id);
   fprintf (Gbl.F.Out,"\">");
   for (Year = FirstYear;
	Year <= LastYear;
	Year++)
      fprintf (Gbl.F.Out,"<option value=\"%u\">%u</option>",
               Year,Year);
   fprintf (Gbl.F.Out,"</select>"
	              "</td>");

   /***** Month *****/
   fprintf (Gbl.F.Out,"<td class=\"CENTER_MIDDLE\">"
                      "<select id=\"%sMonth\" name=\"%sMonth\""
                      " onchange=\""
                      "adjustDateForm('%s');"
                      "setUTCFromLocalDateTimeForm('%s');",
	    Id,ParamName,Id,Id);
   if (SubmitFormOnChange)
      fprintf (Gbl.F.Out,"document.getElementById('%s').submit();",
               Gbl.Form.Id);
   fprintf (Gbl.F.Out,"\">");
   for (Month = 1;
	Month <= 12;
	Month++)
      fprintf (Gbl.F.Out,"<option value=\"%u\">%s</option>",
               Month,Txt_MONTHS_SMALL[Month - 1]);
   fprintf (Gbl.F.Out,"</select>"
	              "</td>");

   /***** Day *****/
   fprintf (Gbl.F.Out,"<td class=\"LEFT_MIDDLE\">"
	              "<select id=\"%sDay\" name=\"%sDay\""
	              " onchange=\"setUTCFromLocalDateTimeForm('%s');",
            Id,ParamName,Id);
   if (SubmitFormOnChange)
      fprintf (Gbl.F.Out,"document.getElementById('%s').submit();",
               Gbl.Form.Id);
   fprintf (Gbl.F.Out,"\">");
   for (Day = 1;
	Day <= 31;
	Day++)
      fprintf (Gbl.F.Out,"<option value=\"%u\">%u</option>",
               Day,Day);
   fprintf (Gbl.F.Out,"</select>"
	              "</td>");

   /***** Hour *****/
   fprintf (Gbl.F.Out,"<td class=\"RIGHT_MIDDLE\">"
                      "<select id=\"%sHour\" name=\"%sHour\""
                      " onchange=\"setUTCFromLocalDateTimeForm('%s');",
            Id,ParamName,Id);
   if (SubmitFormOnChange)
      fprintf (Gbl.F.Out,"document.getElementById('%s').submit();",
               Gbl.Form.Id);
   fprintf (Gbl.F.Out,"\">");
   for (Hour = 0;
	Hour <= 23;
	Hour++)
      fprintf (Gbl.F.Out,"<option value=\"%u\">%02u h</option>",
               Hour,Hour);
   fprintf (Gbl.F.Out,"</select>"
	              "</td>");

   /***** Minute *****/
   fprintf (Gbl.F.Out,"<td class=\"CENTER_MIDDLE\">"
                      "<select id=\"%sMinute\" name=\"%sMinute\""
                      " onchange=\"setUTCFromLocalDateTimeForm('%s');",
	    Id,ParamName,Id);
   if (SubmitFormOnChange)
      fprintf (Gbl.F.Out,"document.getElementById('%s').submit();",
               Gbl.Form.Id);
   fprintf (Gbl.F.Out,"\">");

   for (Minute = 0;
	Minute < 60;
	Minute += MinutesIInterval[FormSeconds])
      fprintf (Gbl.F.Out,"<option value=\"%u\">%02u &#39;</option>",
               Minute,Minute);

   fprintf (Gbl.F.Out,"</select>"
	              "</td>");

   /***** Second *****/
   if (FormSeconds == Dat_FORM_SECONDS_ON)
     {
      fprintf (Gbl.F.Out,"<td class=\"LEFT_MIDDLE\">"
			 "<select id=\"%sSecond\" name=\"%sSecond\""
			 " onchange=\"setUTCFromLocalDateTimeForm('%s');",
	       Id,ParamName,Id);
      if (SubmitFormOnChange)
	 fprintf (Gbl.F.Out,"document.getElementById('%s').submit();",
		  Gbl.Form.Id);
      fprintf (Gbl.F.Out,"\">");
      for (Second = 0;
	   Second <= 59;
	   Second++)
	 fprintf (Gbl.F.Out,"<option value=\"%u\">%02u &quot;</option>",
		  Second,Second);
      fprintf (Gbl.F.Out,"</select>"
			 "</td>");
     }

   /***** End table *****/
   fprintf (Gbl.F.Out,"</tr>"
	              "</table>");

   /***** Hidden field with UTC time (seconds since 1970) used to send time *****/
   fprintf (Gbl.F.Out,"<input type=\"hidden\""
	              " id=\"%sTimeUTC\" name=\"%sTimeUTC\" value=\"%ld\" />",
            Id,ParamName,(long) TimeUTC);

   /***** Script to set selectors to local date and time from UTC time *****/
   fprintf (Gbl.F.Out,"<script type=\"text/javascript\">"
                      "setLocalDateTimeFormFromUTC('%s',%ld);"
	              "adjustDateForm('%s');",
	    Id,(long) TimeUTC,Id);
   switch (SetHMS)
     {
      case Dat_HMS_TO_000000:
	 // Set HH:MM:SS form selectors to 00:00:00
	 fprintf (Gbl.F.Out,"setHMSTo000000('%s');",Id);	// Hidden TimeUTC is also adjusted
	 break;
      case Dat_HMS_TO_235959:
	 // Set HH:MM:SS form selectors to 23:59:59
	 fprintf (Gbl.F.Out,"setHMSTo235959('%s');",Id);	// Hidden TimeUTC is also adjusted
	 break;
      default:
	 break;
     }
   fprintf (Gbl.F.Out,"</script>");
  }

/*****************************************************************************/
/***************** Get an hour-minute time from a form ***********************/
/*****************************************************************************/

time_t Dat_GetTimeUTCFromForm (const char *ParamName)
  {
   /**** Get time ****/
   return Par_GetParToLong (ParamName);
  }

/*****************************************************************************/
/**************** Put a hidden param with time difference ********************/
/**************** between UTC time and client local time, ********************/
/**************** in minutes                              ********************/
/*****************************************************************************/

void Dat_PutHiddenParBrowserTZDiff (void)
  {
   fprintf (Gbl.F.Out,"<input type=\"hidden\""
	              " id=\"BrowserTZName\" name=\"BrowserTZName\""
	              " value=\"\" />"
	              "<input type=\"hidden\""
	              " id=\"BrowserTZDiff\" name=\"BrowserTZDiff\""
	              " value=\"0\" />"
                      "<script type=\"text/javascript\">"
		      "setTZname('BrowserTZName');"
		      "setTZ('BrowserTZDiff');"
		      "</script>");
  }

/*****************************************************************************/
/*************************** Get browser time zone ***************************/
/*****************************************************************************/
// MySQL CONVERT_TZ function may fail around changes related to Daylight Saving Time
// when a fixed amount (for example +01:00) is used as destination time zone,
// because this amount may be different before and after the DST change

void Dat_GetBrowserTimeZone (char BrowserTimeZone[Dat_MAX_BYTES_TIME_ZONE + 1])
  {
   MYSQL_RES *mysql_res;
   MYSQL_ROW row;
   bool TZNameIsUsable = false;
   char IntStr[1 + 10 + 1];
   int ClientUTCMinusLocal;	// Time difference between UTC time and client local time, in minutes

   /***** 1. Get client time zone name *****/
   // We get client time zone using JavaScript jstz script, available in:
   // - http://pellepim.bitbucket.org/jstz/
   // - https://bitbucket.org/pellepim/jstimezonedetect/
   // The return value is an IANA zone info key (aka the Olson time zone database).
   // https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
   // For example, if browser is in Madrid(Spain) timezone, "Europe/Berlin" will be returned.
   Par_GetParToText ("BrowserTZName",BrowserTimeZone,Dat_MAX_BYTES_TIME_ZONE);

   /* Check if client time zone is usable with CONVERT_TZ */
   if (BrowserTimeZone[0])
     {
      /* Try to convert a date from server time zone to browser time zone */
      if (DB_QuerySELECT (&mysql_res,"can not check if time zone name"
				     " is usable",
			  "SELECT CONVERT_TZ(NOW(),@@session.time_zone,'%s')",
                          BrowserTimeZone))
	{
         row = mysql_fetch_row (mysql_res);
         if (row[0] != NULL)
            TZNameIsUsable = true;
	}

      /* Free structure that stores the query result */
      DB_FreeMySQLResult (&mysql_res);
     }

   if (!TZNameIsUsable)
     {
      /***** 2. Get client time zone difference *****/
      // We get client TZ difference using JavaScript getTimezoneOffset() method
      // getTimezoneOffset() returns UTC-time - browser-local-time, in minutes.
      // For example, if browser time zone is GMT+2, -120 will be returned.
      Par_GetParToText ("BrowserTZDiff",IntStr,1 + 10);
      if (sscanf (IntStr,"%d",&ClientUTCMinusLocal) != 1)
	 ClientUTCMinusLocal = 0;

      /* Convert from minutes to +-hh:mm */
      // BrowserTimeZone must have space for strings in +hh:mm format (6 chars + \0)
      if (ClientUTCMinusLocal > 0)
	 snprintf (BrowserTimeZone,Dat_MAX_BYTES_TIME_ZONE + 1,
	           "-%02u:%02u",
		   (unsigned) ClientUTCMinusLocal / 60,
		   (unsigned) ClientUTCMinusLocal % 60);
      else	// ClientUTCMinusLocal <= 0
	 snprintf (BrowserTimeZone,Dat_MAX_BYTES_TIME_ZONE + 1,
	           "+%02u:%02u",
		   (unsigned) (-ClientUTCMinusLocal) / 60,
		   (unsigned) (-ClientUTCMinusLocal) % 60);
     }
  }

/*****************************************************************************/
/************************* Show a form to enter a date ***********************/
/*****************************************************************************/
/*
See the following pages:
http://javascript.internet.com/forms/date-selection-form.html
http://www.java-scripts.net/javascripts/Calendar-Popup.phtml
http://webmonkey.wired.com/webmonkey/98/04/index3a_page10.html?tw=programming
http://www.jsmadeeasy.com/javascripts/Calendars/Select-A-Mo://tech.irt.org/articles/js068/calendar.htm
http://javascript.internet.com/calendars/select-a-month.html
http://javascript.internet.com/forms/country.html
http://javascript.internet.com/forms/category-selection.html
See also http://www.ashleyit.com/rs/jsrs/select/php/select.php
*/
void Dat_WriteFormDate (unsigned FirstYear,unsigned LastYear,
	                const char *Id,
		        struct Date *DateSelected,
                        bool SubmitFormOnChange,bool Disabled)
  {
   extern const char *Txt_MONTHS_SMALL[12];
   unsigned Year;
   unsigned Month;
   unsigned Day;
   unsigned NumDaysSelectedMonth;

   /***** Start table *****/
   fprintf (Gbl.F.Out,"<table>"
	              "<tr>");

   /***** Year *****/
   fprintf (Gbl.F.Out,"<td class=\"CENTER_MIDDLE\">"
                      "<select id=\"%sYear\" name=\"%sYear\""
                      " onchange=\"adjustDateForm('%s');",
	    Id,Id,Id);
   if (SubmitFormOnChange)
      fprintf (Gbl.F.Out,"document.getElementById('%s').submit();",
               Gbl.Form.Id);
   fprintf (Gbl.F.Out,"\"");
   if (Disabled)
      fprintf (Gbl.F.Out," disabled=\"disabled\"");
   fprintf (Gbl.F.Out,">"
	              "<option value=\"0\">-</option>");
   for (Year = FirstYear;
	Year <= LastYear;
	Year++)
     {
      fprintf (Gbl.F.Out,"<option value=\"%u\"",Year);
      if (Year == DateSelected->Year)
	 fprintf (Gbl.F.Out," selected=\"selected\"");
      fprintf (Gbl.F.Out,">%u</option>",Year);
     }
   fprintf (Gbl.F.Out,"</select>"
                      "</td>");

   /***** Month *****/
   fprintf (Gbl.F.Out,"<td class=\"CENTER_MIDDLE\">"
                      "<select id=\"%sMonth\" name=\"%sMonth\""
                      " onchange=\"adjustDateForm('%s');",
	    Id,Id,Id);
   if (SubmitFormOnChange)
      fprintf (Gbl.F.Out,"document.getElementById('%s').submit();",
               Gbl.Form.Id);
   fprintf (Gbl.F.Out,"\"");
   if (Disabled)
      fprintf (Gbl.F.Out," disabled=\"disabled\"");
   fprintf (Gbl.F.Out,"><option value=\"0\">-</option>");
   for (Month = 1;
	Month <= 12;
	Month++)
     {
      fprintf (Gbl.F.Out,"<option value=\"%u\"",Month);
      if (Month == DateSelected->Month)
	 fprintf (Gbl.F.Out," selected=\"selected\"");
      fprintf (Gbl.F.Out,">%s</option>",Txt_MONTHS_SMALL[Month - 1]);
     }
   fprintf (Gbl.F.Out,"</select>"
	              "</td>");

   /***** Day *****/
   fprintf (Gbl.F.Out,"<td class=\"CENTER_MIDDLE\">"
	              "<select id=\"%sDay\" name=\"%sDay\"",
            Id,Id);
   if (SubmitFormOnChange)
      fprintf (Gbl.F.Out," onchange=\"document.getElementById('%s').submit();\"",
               Gbl.Form.Id);
   if (Disabled)
      fprintf (Gbl.F.Out," disabled=\"disabled\"");
   fprintf (Gbl.F.Out,"><option value=\"0\">-</option>");
   NumDaysSelectedMonth = (DateSelected->Month == 0) ? 31 :
	                                               ((DateSelected->Month == 2) ? Dat_GetNumDaysFebruary (DateSelected->Year) :
	                                        	                             Dat_NumDaysMonth[DateSelected->Month]);
   for (Day = 1;
	Day <= NumDaysSelectedMonth;
	Day++)
     {
      fprintf (Gbl.F.Out,"<option value=\"%u\"",Day);
      if (Day == DateSelected->Day)
	 fprintf (Gbl.F.Out," selected=\"selected\"");
      fprintf (Gbl.F.Out,">%u</option>",Day);
     }
   fprintf (Gbl.F.Out,"</select>"
	              "</td>");

   /***** End table *****/
   fprintf (Gbl.F.Out,"</tr>"
	              "</table>");
  }

/*****************************************************************************/
/*************************** Get a date from a form **************************/
/*****************************************************************************/

void Dat_GetDateFromForm (const char *ParamNameDay,const char *ParamNameMonth,const char *ParamNameYear,
                          unsigned *Day,unsigned *Month,unsigned *Year)
  {
   /**** Get day ****/
   *Day   = (unsigned) Par_GetParToUnsignedLong (ParamNameDay  ,1,31,0);

   /**** Get month ****/
   *Month = (unsigned) Par_GetParToUnsignedLong (ParamNameMonth,1,12,0);

   /**** Get year ****/
   *Year  = (unsigned) Par_GetParToUnsignedLong (ParamNameYear ,0,UINT_MAX,0);
  }

/*****************************************************************************/
/******* Set initial date to distant past and end date to current date *******/
/*****************************************************************************/

void Dat_SetIniEndDates (void)
  {
   Gbl.DateRange.TimeUTC[0] = (time_t) 0;
   Gbl.DateRange.TimeUTC[1] = Gbl.StartExecutionTimeUTC;
  }

/*****************************************************************************/
/******** Write parameters of initial and final dates *****/
/*****************************************************************************/

void Dat_WriteParamsIniEndDates (void)
  {
   Par_PutHiddenParamUnsigned ("StartTimeUTC",Gbl.DateRange.TimeUTC[0]);
   Par_PutHiddenParamUnsigned ("EndTimeUTC"  ,Gbl.DateRange.TimeUTC[1]);
  }

/*****************************************************************************/
/************************** Get initial and end dates ************************/
/*****************************************************************************/

void Dat_GetIniEndDatesFromForm (void)
  {
   struct tm tm;
   struct tm *tm_ptr;

   /***** Get initial date *****/
   Gbl.DateRange.TimeUTC[0] = Dat_GetTimeUTCFromForm ("StartTimeUTC");
   if (Gbl.DateRange.TimeUTC[0])
      /* Convert time UTC to a local date */
      tm_ptr = Dat_GetLocalTimeFromClock (&Gbl.DateRange.TimeUTC[0]);
   else	// Gbl.DateRange.TimeUTC[0] == 0 ==> initial date not specified
     {
      tm.tm_year  = Cfg_LOG_START_YEAR - 1900;
      tm.tm_mon   =  0;	// January
      tm.tm_mday  =  1;
      tm.tm_hour  =  0;
      tm.tm_min   =  0;
      tm.tm_sec   =  0;
      tm.tm_isdst = -1;	// a negative value means that mktime() should
				// (use timezone information and system databases to)
				// attempt to determine whether DST
				// is in effect at the specified time.
      if ((Gbl.DateRange.TimeUTC[0] = mktime (&tm)) < 0)
	 Gbl.DateRange.TimeUTC[0] = (time_t) 0;
      tm_ptr = &tm;
     }

   Gbl.DateRange.DateIni.Date.Year   = tm_ptr->tm_year + 1900;
   Gbl.DateRange.DateIni.Date.Month  = tm_ptr->tm_mon  + 1;
   Gbl.DateRange.DateIni.Date.Day    = tm_ptr->tm_mday;
   Gbl.DateRange.DateIni.Time.Hour   = tm_ptr->tm_hour;
   Gbl.DateRange.DateIni.Time.Minute = tm_ptr->tm_min;
   Gbl.DateRange.DateIni.Time.Second = tm_ptr->tm_sec;

   /***** Get end date *****/
   Gbl.DateRange.TimeUTC[1] = Dat_GetTimeUTCFromForm ("EndTimeUTC");
   if (Gbl.DateRange.TimeUTC[1] == 0)	// Gbl.DateRange.TimeUTC[1] == 0 ==> end date not specified
      Gbl.DateRange.TimeUTC[1] = Gbl.StartExecutionTimeUTC;

   /* Convert current time UTC to a local date */
   tm_ptr = Dat_GetLocalTimeFromClock (&Gbl.DateRange.TimeUTC[1]);

   Gbl.DateRange.DateEnd.Date.Year   = tm_ptr->tm_year + 1900;
   Gbl.DateRange.DateEnd.Date.Month  = tm_ptr->tm_mon  + 1;
   Gbl.DateRange.DateEnd.Date.Day    = tm_ptr->tm_mday;
   Gbl.DateRange.DateEnd.Time.Hour   = tm_ptr->tm_hour;
   Gbl.DateRange.DateEnd.Time.Minute = tm_ptr->tm_min;
   Gbl.DateRange.DateEnd.Time.Second = tm_ptr->tm_sec;
  }

/*****************************************************************************/
/****************** Write a UTC date into RFC 822 format *********************/
/*****************************************************************************/
// tm must hold a UTC date

void Dat_WriteRFC822DateFromTM (FILE *File,struct tm *tm_ptr)
  {
   const char *StrDayOfWeek[7] =
     {
      "Sun",
      "Mon",
      "Tue",
      "Wed",
      "Thu",
      "Fri",
      "Sat",
     };
   const char *StrMonth[12] =
     {
      "Jan",
      "Feb",
      "Mar",
      "Apr",
      "May",
      "Jun",
      "Jul",
      "Aug",
      "Sep",
      "Oct",
      "Nov",
      "Dec",
      };

   fprintf (File,"%s, %d %s %d %02d:%02d:%02d UT",
            StrDayOfWeek[tm_ptr->tm_wday],
            tm_ptr->tm_mday,
            StrMonth[tm_ptr->tm_mon],
            tm_ptr->tm_year + 1900,
            tm_ptr->tm_hour,
            tm_ptr->tm_min,
            tm_ptr->tm_sec);
  }

/*****************************************************************************/
/************** Compute the subsequent date of a given date ******************/
/*****************************************************************************/

void Dat_GetDateAfter (struct Date *Date,struct Date *SubsequentDate)
  {
   unsigned NumDaysInMonth = (Date->Month == 2) ? Dat_GetNumDaysFebruary (Date->Year) :
	                                          Dat_NumDaysMonth[Date->Month];

   if (Date->Day == NumDaysInMonth)
     {
      if (Date->Month == 12)
        {
         SubsequentDate->Year  = Date->Year + 1;
         SubsequentDate->Month = 1;
         SubsequentDate->Day   = 1;
        }
      else
        {
         SubsequentDate->Year  = Date->Year;
         SubsequentDate->Month = Date->Month + 1;
         SubsequentDate->Day   = 1;
        }
     }
   else
     {
      SubsequentDate->Year  = Date->Year;
      SubsequentDate->Month = Date->Month;
      SubsequentDate->Day   = Date->Day + 1;
     }
  }

/*****************************************************************************/
/************** Compute the preceding date of a given date *******************/
/*****************************************************************************/

void Dat_GetDateBefore (struct Date *Date,struct Date *PrecedingDate)
  {
   if (Date->Day == 1)
     {
      if (Date->Month == 1)
        {
         PrecedingDate->Year  = Date->Year - 1;
         PrecedingDate->Month = 12;
         PrecedingDate->Day   = 31;
        }
      else
        {
         PrecedingDate->Year  = Date->Year;
         PrecedingDate->Month = Date->Month - 1;
         PrecedingDate->Day   = (PrecedingDate->Month == 2) ? Dat_GetNumDaysFebruary (PrecedingDate->Year) :
                                                              Dat_NumDaysMonth[PrecedingDate->Month];
        }
     }
   else
     {
      PrecedingDate->Year  = Date->Year;
      PrecedingDate->Month = Date->Month;
      PrecedingDate->Day   = Date->Day - 1;
     }
  }

/*****************************************************************************/
/**************** Compute the week before to a given week ********************/
/*****************************************************************************/

void Dat_GetWeekBefore (struct Date *Date,struct Date *PrecedingDate)
  {
   if (Date->Week == 1)
     {
      PrecedingDate->Year = Date->Year - 1;
      PrecedingDate->Week = Dat_GetNumWeeksInYear (PrecedingDate->Year);
     }
   else
     {
      PrecedingDate->Year = Date->Year;
      PrecedingDate->Week = Date->Week - 1;
     }
  }

/*****************************************************************************/
/*************** Compute the month before to a given month *******************/
/*****************************************************************************/

void Dat_GetMonthBefore (struct Date *Date,struct Date *PrecedingDate)
  {
   if (Date->Month == 1)
     {
      PrecedingDate->Year  = Date->Year - 1;
      PrecedingDate->Month = 12;
     }
   else
     {
      PrecedingDate->Year  = Date->Year;
      PrecedingDate->Month = Date->Month - 1;
     }
  }

/*****************************************************************************/
/**************** Compute the year before to a given year ********************/
/*****************************************************************************/

void Dat_GetYearBefore (struct Date *Date,struct Date *PrecedingDate)
  {
   PrecedingDate->Year = Date->Year - 1;
  }

/*****************************************************************************/
/************** Compute the number of days beteen two dates ******************/
/*****************************************************************************/
// If the dates are the same, return 1
// If the old date is the day before the new data, return 2
// ...

unsigned Dat_GetNumDaysBetweenDates (struct Date *DateIni,
                                     struct Date *DateEnd)
  {
   int DiffDays;
   unsigned Year;

   /***** If initial year is less than end year, return 0
          (actually the difference in days should be negative) *****/
   if (DateIni->Year > DateEnd->Year)
      return 0;

   /***** Initial year is less or equal than end year ==> compute difference in days *****/
   DiffDays = (int) Dat_GetDayOfYear (DateEnd) - (int) Dat_GetDayOfYear (DateIni) + 1;
   for (Year = DateIni->Year;
	Year < DateEnd->Year;
	Year++)
      DiffDays += (int) Dat_GetNumDaysInYear (Year);
   return (DiffDays > 0) ? (unsigned) DiffDays :
	                   0;
  }

/*****************************************************************************/
/*************** Compute the number of weeks between two dates ***************/
/*****************************************************************************/
// If the two dates are in the same week, return 1

unsigned Dat_GetNumWeeksBetweenDates (struct Date *DateIni,
                                      struct Date *DateEnd)
  {
   int DiffWeeks;
   unsigned Year;

   /***** If initial year is lower than the ending year, return 0
          (actually the difference should be negative) *****/
   if (DateIni->Year > DateEnd->Year)
      return 0;

   /***** Initial year is lower or equal to ending year ==>
          compute difference in weeks *****/
   DiffWeeks = (int) DateEnd->Week - (int) DateIni->Week + 1;
   for (Year = DateIni->Year;
	Year < DateEnd->Year;
	Year++)
      DiffWeeks += (int) Dat_GetNumWeeksInYear (Year);
   return (DiffWeeks > 0) ? (unsigned) DiffWeeks :
	                    0;
  }

/*****************************************************************************/
/************* Compute the number of months between two dates ****************/
/*****************************************************************************/
// If the two dates are in the same month, return 1

unsigned Dat_GetNumMonthsBetweenDates (struct Date *DateIni,
                                       struct Date *DateEnd)
  {
   int DiffMonths;

   /***** Compute the difference in months *****/
   DiffMonths = ((int) DateEnd->Year  - (int) DateIni->Year) * 12 +
	         (int) DateEnd->Month - (int) DateIni->Month + 1;
   return (DiffMonths > 0) ? (unsigned) DiffMonths :
	                     0;
  }

/*****************************************************************************/
/************** Compute the number of years between two dates ****************/
/*****************************************************************************/
// If the two dates are in the same year, return 1

unsigned Dat_GetNumYearsBetweenDates (struct Date *DateIni,
                                      struct Date *DateEnd)
  {
   int DiffYears;

   /***** Compute the difference in years *****/
   DiffYears = (int) DateEnd->Year - (int) DateIni->Year + 1;
   return (DiffYears > 0) ? (unsigned) DiffYears :
	                    0;
  }

/*****************************************************************************/
/*************** Compute the number of days in a given year ******************/
/*****************************************************************************/

#define NUM_DAYS_YEAR_EXCEPT_FEBRUARY (365 - 28)

unsigned Dat_GetNumDaysInYear (unsigned Year)
  {
   return NUM_DAYS_YEAR_EXCEPT_FEBRUARY + Dat_GetNumDaysFebruary (Year);
  }

/*****************************************************************************/
/****************** Return the number of days of february ********************/
/*****************************************************************************/

unsigned Dat_GetNumDaysFebruary (unsigned Year)
  {
   return (Dat_GetIfLeapYear (Year) ? 29 :
	                              28);
  }

/*****************************************************************************/
/************************* Return true if year is leap ***********************/
/*****************************************************************************/

bool Dat_GetIfLeapYear (unsigned Year)
  {
   return (Year % 4 == 0) && ((Year % 100 != 0) || (Year % 400 == 0));
  }

/*****************************************************************************/
/******* Compute the number of weeks starting in monday of a given year ******/
/*****************************************************************************/
// A week starting on monday is considered belonging to a year only if it has most of its days (4 to 7) belonging to that year
// A year may have 52 (usually) or 53 of those weeks

unsigned Dat_GetNumWeeksInYear (unsigned Year)
  {
   unsigned December31DayOfWeek = Dat_GetDayOfWeek (Year,12,31); // From 0 to 6

   if (December31DayOfWeek == 3)
      return 53;
   if (December31DayOfWeek == 4)
      if (Dat_GetIfLeapYear (Year))
         return 53;
   return 52;
  }

/*****************************************************************************/
/***************** Compute day of the week from a given date *****************/
/*****************************************************************************/
// Return 0 for monday, 1 for tuesday,... 6 for sunday

unsigned Dat_GetDayOfWeek (unsigned Year,unsigned Month,unsigned Day)
  {
   struct tm tm;
   struct tm *tm_ptr;
   time_t t;

   /***** Create clock in UNIX time from date *****/
   tm.tm_year  = Year  - 1900;
   tm.tm_mon   = Month - 1;
   tm.tm_mday  = Day;
   tm.tm_hour  = 0;
   tm.tm_min   = 0;
   tm.tm_sec   = 0;
   tm.tm_isdst = -1;	// a negative value means that mktime() should
			// (use timezone information and system databases to)
			// attempt to determine whether DST
			// is in effect at the specified time.
   if ((t = mktime (&tm)) < 0)
      return 0;

   /***** Compute local time, adjusting day of week *****/
   tm_ptr = Dat_GetLocalTimeFromClock (&t);

   return (unsigned) tm_ptr->tm_wday;
  }

/* Alternative:

   if (Month <= 2)
     {
      Month += 12;
      Year--;
     }
   return (
	   (
            (
	     Day +
	     Month*2 + (Month*3 + 3) / 5 +
	     Year + Year/4 - Year/100 + Year/400 +
	     2
	    ) % 7
	   ) + 5
	  ) % 7;

Code generated by gcc for the alternative:

0000000000001810 <Dat_GetDayOfWeek>:
    1810:	83 fe 02             	cmp    $0x2,%esi
    1813:	77 06                	ja     181b <Dat_GetDayOfWeek+0xb>
    1815:	83 c6 0c             	add    $0xc,%esi
    1818:	83 ef 01             	sub    $0x1,%edi
    181b:	8d 44 17 02          	lea    0x2(%rdi,%rdx,1),%eax
    181f:	ba 1f 85 eb 51       	mov    $0x51eb851f,%edx
    1824:	8d 0c 70             	lea    (%rax,%rsi,2),%ecx
    1827:	89 f8                	mov    %edi,%eax
    1829:	c1 e8 02             	shr    $0x2,%eax
    182c:	01 c1                	add    %eax,%ecx
    182e:	89 f8                	mov    %edi,%eax
    1830:	bf 25 49 92 24       	mov    $0x24924925,%edi
    1835:	f7 e2                	mul    %edx
    1837:	89 d0                	mov    %edx,%eax
    1839:	c1 ea 05             	shr    $0x5,%edx
    183c:	c1 e8 07             	shr    $0x7,%eax
    183f:	01 c1                	add    %eax,%ecx
    1841:	8d 44 76 03          	lea    0x3(%rsi,%rsi,2),%eax
    1845:	29 d1                	sub    %edx,%ecx
    1847:	ba cd cc cc cc       	mov    $0xcccccccd,%edx
    184c:	f7 e2                	mul    %edx
    184e:	c1 ea 02             	shr    $0x2,%edx
    1851:	01 d1                	add    %edx,%ecx
    1853:	89 c8                	mov    %ecx,%eax
    1855:	89 ce                	mov    %ecx,%esi
    1857:	f7 e7                	mul    %edi
    1859:	29 d6                	sub    %edx,%esi
    185b:	d1 ee                	shr    %esi
    185d:	01 f2                	add    %esi,%edx
    185f:	c1 ea 02             	shr    $0x2,%edx
    1862:	8d 04 d5 00 00 00 00 	lea    0x0(,%rdx,8),%eax
    1869:	29 d0                	sub    %edx,%eax
    186b:	29 c1                	sub    %eax,%ecx
    186d:	83 c1 05             	add    $0x5,%ecx
    1870:	89 c8                	mov    %ecx,%eax
    1872:	f7 e7                	mul    %edi
    1874:	89 c8                	mov    %ecx,%eax
    1876:	29 d0                	sub    %edx,%eax
    1878:	d1 e8                	shr    %eax
    187a:	01 d0                	add    %edx,%eax
    187c:	c1 e8 02             	shr    $0x2,%eax
    187f:	8d 14 c5 00 00 00 00 	lea    0x0(,%rax,8),%edx
    1886:	29 c2                	sub    %eax,%edx
    1888:	29 d1                	sub    %edx,%ecx
    188a:	89 c8                	mov    %ecx,%eax
    188c:	c3                   	retq
    188d:	0f 1f 00             	nopl   (%rax)

Understanding the code generated by gcc:

0000000000001810 <Dat_GetDayOfWeek>:
    1810:	83 fe 02             	cmp    $2,Month
    1813:	77 06                	ja     continue

    1815:	83 c6 0c             	add    $12,Month
    1818:	83 ef 01             	sub    $1,Year
continue:
    181b:	8d 44 17 02          	lea    2(Year,Day,1),Suma1	// SumAux = Day + Year + 2

    181f:	ba 1f 85 eb 51       	mov    $0x51eb851f,%edx		// 1374389535

    1824:	8d 0c 70             	lea    (SumAux,Month,2),n	// n = Day + Year + 2 + Month*2
    1827:	89 f8                	mov    Year,%eax
    1829:	c1 e8 02             	shr    $2,%eax			// Year / 4
    182c:	01 c1                	add    %eax,n			// n = Day + Year + 2 + Month*2 + Year/4
    182e:	89 f8                	mov    Year,%eax
    1830:	bf 25 49 92 24       	mov    $0x24924925,%edi		// 613566757
    1835:	f7 e2                	mul    %edx			// Year * 1374389535

    1837:	89 d0                	mov    %edx,%eax		// (Year * 1374389535) / 2^32 = (Year * 2^32 * 2^5 / 100) / 2^32 = (Year * 2^5) / 100
    1839:	c1 ea 05             	shr    $5,%edx			// (Year * 1374389535) / 2^32 / 2^5 = Year / 100
    183c:	c1 e8 07             	shr    $7,%eax			// (Year * 1374389535) / 2^32 / 2^7 = Year / 400
    183f:	01 c1                	add    %eax,n			// n = Day + Year + 2 + Month*2 + Year/4 + Year/400
    1841:	8d 44 76 03          	lea    3(Month,Month,2),%eax	// Month*3 + 3
    1845:	29 d1                	sub    %edx,n			// n = Day + Year + 2 + Month*2 + Year/4 + Year/400 - Year/100

    1847:	ba cd cc cc cc       	mov    $0xcccccccd,%edx
    184c:	f7 e2                	mul    %edx			// (Month*3 + 3) * 3435973837
    184e:	c1 ea 02             	shr    $2,%edx			// (Month*3 + 3) * 3435973837 / 2^32 / 2^2 = (Month*3 + 3) / 5
    1851:	01 d1                	add    %edx,n			// n = Day + Year + 2 + Month*2 + Year/4 + Year/400 - Year/100 + (Month*3 + 3) / 5

    1853:	89 c8                	mov    n,%eax
    1855:	89 ce                	mov    n,%esi

									// Algorithm for remainder: https://doc.lagout.org/security/Hackers%20Delight.pdf, page 209

    1857:	f7 e7                	mul    %edi			// edx = q = M*n/2**32
    1859:	29 d6                	sub    %edx,%esi		// esi = t = n - q
    185b:	d1 ee                	shr    %esi			// esi = t = (n - q)/2
    185d:	01 f2                	add    %esi,%edx		// edx = t = (n - q)/2 + q = (n + q)/2
    185f:	c1 ea 02             	shr    $2,%edx			// edx = q = (n + q)/8 = (n+Mn/2**32)/8 = floor(n/7)
    1862:	8d 04 d5 00 00 00 00 	lea    0(,%rdx,8),%eax		// eax = q*8
    1869:	29 d0                	sub    %edx,%eax		// eax = q*8-q = q*7
    186b:	29 c1                	sub    %eax,%ecx		// ecx = r = n - q*7

    186d:	83 c1 05             	add    $5,Mod			// Mod += 5
    1870:	89 c8                	mov    Mod,%eax

    1872:	f7 e7                	mul    %edi
    1874:	89 c8                	mov    Mod,%eax
    1876:	29 d0                	sub    %edx,%eax
    1878:	d1 e8                	shr    %eax
    187a:	01 d0                	add    %edx,%eax
    187c:	c1 e8 02             	shr    $2,%eax
    187f:	8d 14 c5 00 00 00 00 	lea    0(,%rax,8),%edx
    1886:	29 c2                	sub    %eax,%edx
    1888:	29 d1                	sub    %edx,Mod			// Mod % 7

    188a:	89 c8                	mov    Mod,%eax
    188c:	c3                   	retq
    188d:	0f 1f 00             	nopl   (%rax)

 */

/*****************************************************************************/
/***************** Compute the day of year (from 1 to 366) *******************/
/*****************************************************************************/

unsigned Dat_GetDayOfYear (struct Date *Date)
  {
   unsigned Month;
   unsigned DayYear;

   /* Compute day of year */
   for (Month = 1, DayYear = 0;
	Month < Date->Month;
	Month++)
      DayYear += (Month == 2) ? Dat_GetNumDaysFebruary (Date->Year) :
	                        Dat_NumDaysMonth[Month];
   DayYear += Date->Day;

   return DayYear;
  }

/*****************************************************************************/
/******** Compute Week (and possibly updated Year) from a given date *********/
/*****************************************************************************/
/* The weeks always are counted from monday to sunday.
   01/01/2006 was sunday => it is counted in the week 52 of 2005, which goes from the 26/12/2005 (monday) until the 01/01/2006 (sunday).
   Week 1 of 2006 goes from the 02/01/2006 (monday) until the 08/01/2006 (sunday) */

void Dat_CalculateWeekOfYear (struct Date *Date)
  {
   /*
   If January 1 of Year is...   | ...then first week of Year starts the day  |
   -----------------------------+--------------------------------------------+
   (0) Monday                   | January,   1 of Year                       |
   (1) Tuesday                  | December, 31 of Year-1                     |
   (2) Wednesday                | December, 30 of Year-1                     |
   (3) Thursday                 | December, 29 of Year-1                     |
   (4) Friday                   | January,   4 of Year                       |
   (5) Saturday                 | January,   5 of Year                       |
   (6) Sunday                   | January,   6 of Year                       |
   If December 31 of Year is... | ...then last week of Year ends the day     |
   -----------------------------+--------------------------------------------+
   (0) Monday                   | December, 30 of Year                       |
   (1) Tuesday                  | December, 29 of Year                       |
   (2) Wednesday                | December, 28 of Year                       |
   (3) Thursday                 | January,   3 of Year + 1                   |
   (4) Friday                   | January,   4 of Year + 1                   |
   (5) Saturday                 | January,   5 of Year + 1                   |
   (6) Sunday                   | December, 31 of Year                       |
   */
   int DayThatFirstWeekStarts[7] = {1,0,-1,-2,4,3,2};
   unsigned DayThatLastWeekEnds[7] = {30,29,28,34,33,32,31};
   unsigned January1DayOfWeek   = Dat_GetDayOfWeek (Date->Year, 1, 1); // From 0 to 6
   unsigned December31DayOfWeek = Dat_GetDayOfWeek (Date->Year,12,31); // From 0 to 6

   if (Date->Month == 1 && (int) Date->Day < DayThatFirstWeekStarts[January1DayOfWeek])	// Week is the last week of the year before this
     {
      Date->Year--;
      Date->Week = Dat_GetNumWeeksInYear (Date->Year);
     }
   else if (Date->Month == 12 && Date->Day > DayThatLastWeekEnds[December31DayOfWeek])	// Week is the first week of the year after this
     {
      Date->Year++;
      Date->Week = 1;
     }
   else	// Week corresponds to this year
      Date->Week = ((int) Dat_GetDayOfYear (Date) - DayThatFirstWeekStarts[January1DayOfWeek]) / 7 + 1;
  }

/*****************************************************************************/
/******************* Assign the values of a date to another ******************/
/*****************************************************************************/

void Dat_AssignDate (struct Date *DateDst,struct Date *DateSrc)
  {
   DateDst->Year  = DateSrc->Year;
   DateDst->Month = DateSrc->Month;
   DateDst->Day   = DateSrc->Day;
   DateDst->Week  = DateSrc->Week;
   Str_Copy (DateDst->YYYYMMDD,DateSrc->YYYYMMDD,
             Dat_LENGTH_YYYYMMDD);
  }

/*****************************************************************************/
/****** Write script to automatically update clocks of connected users *******/
/*****************************************************************************/

void Dat_WriteScriptMonths (void)
  {
   extern const char *Txt_MONTHS_SMALL[12];
   extern const char *Txt_MONTHS_SMALL_SHORT[12];
   unsigned NumMonth;

   fprintf (Gbl.F.Out,"var Months = [");
   for (NumMonth = 0;
	NumMonth < 12;
	NumMonth++)
     {
      if (NumMonth)
	 fprintf (Gbl.F.Out,",");
      fprintf (Gbl.F.Out,"'%s'",Txt_MONTHS_SMALL[NumMonth]);
     }
   fprintf (Gbl.F.Out,"];\n");

   fprintf (Gbl.F.Out,"var MonthsShort = [");
   for (NumMonth = 0;
	NumMonth < 12;
	NumMonth++)
     {
      if (NumMonth)
	 fprintf (Gbl.F.Out,",");
      fprintf (Gbl.F.Out,"'%s'",Txt_MONTHS_SMALL_SHORT[NumMonth]);
     }
   fprintf (Gbl.F.Out,"];\n");
  }

/*****************************************************************************/
/********* Write time difference in seconds as hours:minutes:seconds *********/
/*****************************************************************************/
// TimeDiff must be in seconds

void Dat_WriteHoursMinutesSecondsFromSeconds (time_t Seconds)
  {
   time_t Hours   = Seconds / (60 * 60);
   time_t Minutes = (Seconds / 60) % 60;

   Seconds %= 60;
   if (Hours)
      fprintf (Gbl.F.Out,"%ld:%02ld'%02ld&quot;",
               (long) Hours,
               (long) Minutes,
               (long) Seconds);
   else if (Minutes)
      fprintf (Gbl.F.Out,"%ld'%02ld&quot;",
               (long) Minutes,
               (long) Seconds);
   else
      fprintf (Gbl.F.Out,"%ld&quot;",
               (long) Seconds);
  }