/* $Id: date_type.h 18585 2009-12-21 16:13:30Z rubidium $ */

/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD 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 General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
 */

/** @file date_type.h Types related to the dates in OpenTTD. */

#ifndef DATE_TYPE_H
#define DATE_TYPE_H

/**
 * 1 day is 74 ticks; _date_fract used to be uint16 and incremented by 885. On
 *                    an overflow the new day begun and 65535 / 885 = 74.
 * 1 tick is approximately 30 ms.
 * 1 day is thus about 2 seconds (74 * 30 = 2220) on a machine that can run OpenTTD normally
 */
enum {
	DAY_TICKS = 74,          ///< ticks per day
	DAYS_IN_YEAR = 365,      ///< days per year
	DAYS_IN_LEAP_YEAR = 366, ///< sometimes, you need one day more...
};

/*
 * ORIGINAL_BASE_YEAR, ORIGINAL_MAX_YEAR and DAYS_TILL_ORIGINAL_BASE_YEAR are
 * primarily used for loading newgrf and savegame data and returning some
 * newgrf (callback) functions that were in the original (TTD) inherited
 * format, where '_date == 0' meant that it was 1920-01-01.
 */

/** The minimum starting year/base year of the original TTD */
#define ORIGINAL_BASE_YEAR 1920
/** The original ending year */
#define ORIGINAL_END_YEAR 2051
/** The maximum year of the original TTD */
#define ORIGINAL_MAX_YEAR 2090

/**
 * Calculate the number of leap years till a given year.
 *
 * Each passed leap year adds one day to the 'day count'.
 *
 * A special case for the year 0 as no year has been passed,
 * but '(year - 1) / 4' does not yield '-1' to counteract the
 * '+1' at the end of the formula as divisions round to zero.
 *
 * @param year the year to get the leap years till.
 * @return the number of leap years.
 */
#define LEAP_YEARS_TILL(year) ((year) == 0 ? 0 : ((year) - 1) / 4 - ((year) - 1) / 100 + ((year) - 1) / 400 + 1)

/**
 * Calculate the date of the first day of a given year.
 * @param year the year to get the first day of.
 * @return the date.
 */
#define DAYS_TILL(year) (DAYS_IN_YEAR * (year) + LEAP_YEARS_TILL(year))

/**
 * The offset in days from the '_date == 0' till
 * 'ConvertYMDToDate(ORIGINAL_BASE_YEAR, 0, 1)'
 */
#define DAYS_TILL_ORIGINAL_BASE_YEAR DAYS_TILL(ORIGINAL_BASE_YEAR)

/** The absolute minimum & maximum years in OTTD */
#define MIN_YEAR 0

/** The default starting year */
#define DEF_START_YEAR 1950

/**
 * MAX_YEAR, nicely rounded value of the number of years that can
 * be encoded in a single 32 bits date, about 2^31 / 366 years.
 */
#define MAX_YEAR 5000000

/** The number of days till the last day */
#define MAX_DAY (DAYS_TILL(MAX_YEAR + 1) - 1)

typedef int32  Date;      ///< The type to store our dates in
typedef uint16 DateFract; ///< The fraction of a date we're in, i.e. the number of ticks since the last date changeover
typedef int32  Ticks;     ///< The type to store ticks in

typedef int32  Year;  ///< Type for the year, note: 0 based, i.e. starts at the year 0.
typedef uint8  Month; ///< Type for the month, note: 0 based, i.e. 0 = January, 11 = December.
typedef uint8  Day;   ///< Type for the day of the month, note: 1 based, first day of a month is 1.

/**
 * Data structure to convert between Date and triplet (year, month, and day).
 * @see ConvertDateToYMD(), ConvertYMDToDate()
 */
struct YearMonthDay {
	Year  year;   ///< Year (0...)
	Month month;  ///< Month (0..11)
	Day   day;    ///< Day (1..31)
};

static const Year  INVALID_YEAR  = -1; ///< Representation of an invalid year
static const Date  INVALID_DATE  = -1; ///< Representation of an invalid date
static const Ticks INVALID_TICKS = -1; ///< Representation of an invalid number of ticks

#endif /* DATE_TYPE_H */
