/*
    Copyright (C) 1995-1997 AROS - The Amiga Replacement OS
    $Id: amiga2date.c,v 1.7 1997/02/03 02:58:30 ldp Exp $

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

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

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

        AROS_LH2(void, Amiga2Date,

/*  SYNOPSIS */
        AROS_LHA(ULONG             , seconds, D0),
        AROS_LHA(struct ClockData *, result, A0),

/*  LOCATION */
        struct Library *, UtilityBase, 20, Utility)

/*  FUNCTION
        Convert the time value given as the number of seconds since the
        1st of January 1978 (00:00:00 1.1.78), to a more useful values,
        which is easier for most people to understand. These values will
        be stored in the ClockData structure whose address is passed as
        an argument.

    INPUTS
        seconds     -   Number of seconds since 1.1.78 00:00:00
        result      -   The ClockData structure to store the information
                        in.

    RESULT
        The ClockData structure will contain the converted time values.

    NOTES

    EXAMPLE

    BUGS

    SEE ALSO

    INTERNALS
        Some information about some constants I use:

             731 =  365 + 366, the number of days between 1.1.1978 and
                    1.1.1976. Using 1976 makes working out leap years
                    simpler.
            1461 =  The number of days in four years including 1 leap year.
                    (eg 365*3 + 366)
           86400 =  The number of seconds in one day.

        I used these as constants so that they don't have to be computed
        on the fly, or read from variables.

    HISTORY
        29-10-95    digulla automatically created from
                            utility_lib.fd and clib/utility_protos.h
        19-05-96    iaint   Wrote, with a little help from a Perl package.
        11-08-96    iaint   Updated for the new AROS format.
        17-08-96    iaint   Removed calls to unimplemented UDivMod32/UMult32
        24-02-97    iaint   Reimplemented, actually works now :)

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

    static const ULONG dim[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
    ULONG days;
    UWORD leap, temp, year;

    days = seconds / 86400;
    result->wday = days % 7;

    result->sec = seconds % 60;
    seconds /= 60;
    result->min = seconds % 60;
    seconds /= 60;
    result->hour = seconds % 24;

    /*  Calculate the current year.

        Firstly, if the year is less than 1980, then the leap year
        handling is not required...

    */
    if(days < 1096)
    {
        result->year = 1978;

        if(days > 729)
            leap = TRUE;
        else
            leap = FALSE;

        year = (days / 365);
        days = days - (year * 365);
    }
    else
    {
        /*
            We need to get into a year that follows a leap year, there
            are two cases, >2100 and <=2100

            If the year is after 2100, which is not a leap year, then
            start point is 2101.

            The first day in year 2101 is ...
        */
        if(days > 44925)
        {
            days -= 44926;
            result->year = 2101;
        }
        /*
            Otherwise, we just set everything up so that we are relative
            to 1981.
        */
        else
        {
            result->year = 1981;
            days -= 1096;
        }

        /*
            From here, we know that every remaining set of 4 years
            has 1 leap year...
        */
        year = days / 1461;
        days -= year * 1461;
        result->year += year * 4;

        if(days > 1095)
            leap = TRUE;
        else
            leap = FALSE;

        year = days / 365;
        days -= year * 365;

        /* Now days is the number of days in the current year... */
    } /* (not less than 1981) */

    /* days now contains the days since the beginning of the current year */
    for(temp = 0; (temp == 1) ? (days >= 28 + leap) : (days >= dim[temp]); temp++)
        days -= (temp == 1) ? (28 + leap) : dim[temp];

    result->month = temp + 1;
    result->mday = days + 1;
    result->year += year;

    AROS_LIBFUNC_EXIT

} /* Amiga2Date */