/*
    Copyright (C) 1995-1997 AROS - The Amiga Replacement OS
    $Id: date2amiga.c,v 1.6 1997/02/03 02:58:31 ldp Exp $

    Desc: Convert a human understandable date to a machine form.
    Lang: english
*/
#include "utility_intern.h"

/*****************************************************************************

    NAME */
#include <utility/date.h>
#include <proto/utility.h>

        AROS_LH1(ULONG, Date2Amiga,

/*  SYNOPSIS */
        AROS_LHA(struct ClockData *, date, A0),

/*  LOCATION */
        struct UtilityBase *, UtilityBase, 21, Utility)

/*  FUNCTION
        Converts the information given in the struct ClockData *date, into
        the number of seconds that have past since the 1st of January 1978.

    INPUTS
        date    -   Contains the information about the time.

    RESULT
        The number of seconds since 1.1.1978

    NOTES

    EXAMPLE

    BUGS

    SEE ALSO
        Amiga2Date(), CheckData()

    INTERNALS
        Bit of a hack in the leap year handling.

    HISTORY
        29-10-95    digulla automatically created from
                            utility_lib.fd and clib/utility_protos.h

*****************************************************************************/
{
    AROS_LIBFUNC_INIT

    /* This array contains the number of days that have been in the year
       up to the start of the month. Does not take into account leap years.
    */
    static const UWORD dayspermonth[12] = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 };

    ULONG time;
    UWORD year, leaps;

    year = date->year - 1978;

    time = date->sec + (date->min * 60) + (date->hour * 3600);
    time += ((date->mday - 1) + dayspermonth[date->month - 1]) * 86400;
    time += year * 31536000;

    /* How do we calculate leap years? That is a very good question.
       The year 1978 is NOT a leap year, but 1980 is...

       I want to arrange it so that the last year of any four year group
       is a leap year. So the first year I can really deal with is either
       1977 or 1981. So I choose 1977 (the year I was born in :)

        Then, to get the number of leap years I divide by 4.
        However, if year is a year which is a leap year, then this year
        will not be counted, so I have to check for this.

        If year % 4 == 3, then we are in a leap year, and if the month
        is after February, then I can add a leap year.
    */

    year++;
    leaps = year / 4;
    if( (year % 4 == 3) && (date->month > 2))
        leaps++;

    /* If the year is greater than the year 2100, or it is the
       year 2100 and after February, then we also have to subtract
       a leap year, as the year 2100 is NOT a leap year.
    */
    if( ( year > 123) || ((year == 123) && (date->month > 2)) )
        leaps--;

    time += leaps * 86400;

    return time;

    AROS_LIBFUNC_EXIT
} /* Date2Amiga */