/*
            JavaScript functions for somali traditional astronomy

                  by Jama Musse Jama --  february 2005
                       http://www.redsea-online.com/

                This program is in the public domain.
*/

var SomWeekdays = new Array("Axad", "Isniin", "Salaasa", "Arbaca", "Khamiis", "Jimce", "Sabti");

var SomMonthsNames = new Array( 
"Dago (Sako)", 
"Bil Dhurro Hore", 
"Bil Dhurro Danbe", 
"Rajal Hore", 
"Rajal Dhexe", 
"Rajal Danbe", 
"Sabbuux", 
"Waaberriis", 
"Soon", 
"Soon Fur", 
"Sidataal", 
"Carrafo"
);

var IslamMonthsNames = new Array(
"Muharram",
"Safar",
"Rabi`al-Awwal",
"Rabi`ath-Thani",
"Jumada l-Ula",
"Jumada t-Tania",
"Rajab",
"Sha`ban",
"Ramadan",
"Shawwal",
"Dhu l-Qa`da",
"Dhu l-Hijja"
);


/*  ASTOR  --  Arc-seconds to radians.  */

/*  You may notice that a variety of array variables logically local
    to functions are declared globally here.  In JavaScript, construction
    of an array variable from source code occurs as the code is
    interpreted.  Making these variables pseudo-globals permits us
    to avoid overhead constructing and disposing of them in each
    call on the function in which whey are used.  */

var J0000 = 1721424.5;                // Julian date of Gregorian epoch: 0000-01-01
var J1970 = 2440587.5;                // Julian date at Unix epoch: 1970-01-01
var JMJD  = 2400000.5;                // Epoch of Modified Julian Date system
var J1900 = 2415020.5;                // Epoch (day 1) of Excel 1900 date system (PC)
var J1904 = 2416480.5;                // Epoch (day 0) of Excel 1904 date system (Mac)

var NormLeap = new Array("Normal year", "Leap year");

/*  WEEKDAY_BEFORE  --  Return Julian date of given weekday (0 = Sunday)
                        in the seven days ending on jd.  */

function weekday_before(weekday, jd)
{
    return jd - jwday(jd - weekday);
}

/*  SEARCH_WEEKDAY  --  Determine the Julian date for: 

            weekday      Day of week desired, 0 = Sunday
            jd           Julian date to begin search
            direction    1 = next weekday, -1 = last weekday
            offset       Offset from jd to begin search
*/

function search_weekday(weekday, jd, direction, offset)
{
    return weekday_before(weekday, jd + (direction * offset));
}

//  Utility weekday functions, just wrappers for search_weekday

function nearest_weekday(weekday, jd)
{
    return search_weekday(weekday, jd, 1, 3);
}

function next_weekday(weekday, jd)
{
    return search_weekday(weekday, jd, 1, 7);
}

function next_or_current_weekday(weekday, jd)
{
    return search_weekday(weekday, jd, 1, 6);
}

function previous_weekday(weekday, jd)
{
    return search_weekday(weekday, jd, -1, 1);
}

function previous_or_current_weekday(weekday, jd)
{
    return search_weekday(weekday, jd, 1, 0);
}

function TestSomething()
{
}

//  LEAP_GREGORIAN  --  Is a given year in the Gregorian calendar a leap year ?

function leap_gregorian(year)
{
    return ((year % 4) == 0) &&
            (!(((year % 100) == 0) && ((year % 400) != 0)));
}

//  GREGORIAN_TO_JD  --  Determine Julian day number from Gregorian calendar date

var GREGORIAN_EPOCH = 1721425.5;

function gregorian_to_jd(year, month, day)
{
    return (GREGORIAN_EPOCH - 1) +
           (365 * (year - 1)) +
           Math.floor((year - 1) / 4) +
           (-Math.floor((year - 1) / 100)) +
           Math.floor((year - 1) / 400) +
           Math.floor((((367 * month) - 362) / 12) +
           ((month <= 2) ? 0 :
                               (leap_gregorian(year) ? -1 : -2)
           ) +
           day);
}

//  JD_TO_GREGORIAN  --  Calculate Gregorian calendar date from Julian day

function jd_to_gregorian(jd) {
    var wjd, depoch, quadricent, dqc, cent, dcent, quad, dquad,
        yindex, dyindex, year, yearday, leapadj;

    wjd = Math.floor(jd - 0.5) + 0.5;
    depoch = wjd - GREGORIAN_EPOCH;
    quadricent = Math.floor(depoch / 146097);
    dqc = mod(depoch, 146097);
    cent = Math.floor(dqc / 36524);
    dcent = mod(dqc, 36524);
    quad = Math.floor(dcent / 1461);
    dquad = mod(dcent, 1461);
    yindex = Math.floor(dquad / 365);
    year = (quadricent * 400) + (cent * 100) + (quad * 4) + yindex;
    if (!((cent == 4) || (yindex == 4))) {
        year++;
    }
    yearday = wjd - gregorian_to_jd(year, 1, 1);
    leapadj = ((wjd < gregorian_to_jd(year, 3, 1)) ? 0
                                                  :
                  (leap_gregorian(year) ? 1 : 2)
              );
    month = Math.floor((((yearday + leapadj) * 12) + 373) / 367);
    day = (wjd - gregorian_to_jd(year, month, 1)) + 1;

    return new Array(year, month, day);
}

//  ISO_TO_JULIAN  --  Return Julian day of given ISO year, week, and day

function n_weeks(weekday, jd, nthweek)
{
    var j = 7 * nthweek;

    if (nthweek > 0) {
        j += previous_weekday(weekday, jd);
    } else {
        j += next_weekday(weekday, jd);
    }
    return j;
}

function iso_to_julian(year, week, day)
{
    return day + n_weeks(0, gregorian_to_jd(year - 1, 12, 28), week);
}

//  JD_TO_ISO  --  Return array of ISO (year, week, day) for Julian day


/*  PAD  --  Pad a string to a given length with a given fill character.  */

function pad(str, howlong, padwith) {
    var s = str.toString();

    while (s.length < howlong) {
        s = padwith + s;
    }
    return s;
}

//  JULIAN_TO_JD  --  Determine Julian day number from Julian calendar date

var JULIAN_EPOCH = 1721423.5;

function leap_julian(year)
{
    return (year % 4) == ((year > 0) ? 0 : 3);
}

function julian_to_jd(year, month, day)
{

    /* Adjust negative common era years to the zero-based notation we use.  */

    if (year < 1) {
        year++;
    }

    /* Algorithm as given in Meeus, Astronomical Algorithms, Chapter 7, page 61 */

    if (month <= 2) {
        year--;
        month += 12;
    }

    return ((Math.floor((365.25 * (year + 4716))) +
            Math.floor((30.6001 * (month + 1))) +
            day) - 1524.5);
}

//  JD_TO_JULIAN  --  Calculate Julian calendar date from Julian day

function jd_to_julian(td) {
    var z, a, alpha, b, c, d, e, year, month, day;

    td += 0.5;
    z = Math.floor(td);

    a = z;
    b = a + 1524;
    c = Math.floor((b - 122.1) / 365.25);
    d = Math.floor(365.25 * c);
    e = Math.floor((b - d) / 30.6001);

    month = Math.floor((e < 14) ? (e - 1) : (e - 13));
    year = Math.floor((month > 2) ? (c - 4716) : (c - 4715));
    day = b - d - Math.floor(30.6001 * e);

    /*  If year is less than 1, subtract one to convert from
        a zero based date system to the common era system in
        which the year -1 (1 B.C.E) is followed by year 1 (1 C.E.).  */

    if (year < 1) {
        year--;
    }

    return new Array(year, month, day);
}

//  LEAP_ISLAMIC  --  Is a given year a leap year in the Islamic calendar ?

function leap_islamic(year)
{
    return (((year * 11) + 14) % 30) < 11;
}

//  ISLAMIC_TO_JD  --  Determine Julian day from Islamic date

var ISLAMIC_EPOCH = 1948439.5;
var ISLAMIC_WEEKDAYS = new Array("al-'ahad", "al-'ithnayn",
                                 "ath-thalatha'", "al-'arb`a'",
                                 "al-khamis", "al-jum`a", "as-sabt");

function islamic_to_jd(year, month, day)
{
    return (day +
            Math.ceil(29.5 * (month - 1)) +
            (year - 1) * 354 +
            Math.floor((3 + (11 * year)) / 30) +
            ISLAMIC_EPOCH) - 1;
}

//  JD_TO_ISLAMIC  --  Calculate Islamic date from Julian day

function jd_to_islamic(jd)
{
    var year, month, day;

    jd = Math.floor(jd) + 0.5;
    year = Math.floor(((30 * (jd - ISLAMIC_EPOCH)) + 10646) / 10631);
    month = Math.min(12,
                Math.ceil((jd - (29 + islamic_to_jd(year, 1, 1))) / 29.5) + 1);
    day = (jd - islamic_to_jd(year, month, 1)) + 1;
    return new Array(year, month, day);
}


/*  updateFromGregorian  --  Update all calendars from Gregorian.
                             "Why not Julian date?" you ask.  Because
                             starting from Gregorian guarantees we're
                             already snapped to an integral second, so
                             we don't get roundoff errors in other
                             calendars.  */

function updateFromGregorian()
{
    var j, year, mon, mday, hour, min, sec,
        weekday, julcal, hebcal, islcal, hmindex, utime, isoweek,
        may_countcal, mayhaabcal, maytzolkincal, bahcal, frrcal,
        indcal, isoday, xgregcal;
    var iyear, imonth, iday, iwday, ileap;
    

    year = new Number(document.gregorian.year.value);
    mon = document.gregorian.month.selectedIndex;
    mday = new Number(document.gregorian.day.value);
    hour = min = sec = 0;
    hour = new Number(document.gregorian.hour.value);
    min = new Number(document.gregorian.min.value);
    sec = new Number(document.gregorian.sec.value);
    
    j = gregorian_to_jd(year, mon + 1, mday) +
           (Math.floor(sec + 60 * (min + 60 * hour) + 0.5) / 86400.0);
    
    //  Update day of week in Gregorian box
    weekday = jwday(j);
    document.gregorian.wday.value = Weekdays[weekday];

    //  Update leap year status in Gregorian box
    document.gregorian.leap.value = NormLeap[leap_gregorian(year) ? 1 : 0];
  
    //  Update Islamic Calendar
    islcal = jd_to_islamic(j);
    iyear  = islcal[0];
    imonth = islcal[1] - 1;
    iday   = islcal[2];
    iwday  = "yawm " + ISLAMIC_WEEKDAYS[weekday];
    ileap  = NormLeap[leap_islamic(islcal[0]) ? 1 : 0];
    swday  = SomWeekdays[weekday];

    if (document.islamic){    
       // Update islamic date
	   document.islamic.leap.value = ileap;
	   document.islamic.wday.value = iwday;
	   document.islamic.day.value  = iday;
	   document.islamic.month.selectedIndex = imonth;
	   document.islamic.year.value = iyear;

	   // Update somali date - readonly
       document.somali.wday.value = swday;
	   document.somali.day.value  = iday;
	   document.somali.month.value = SomMonthsNames[imonth];
    } else {
      // Update islamic date
      document.gregorian.islamicdayofweek.value = iwday;
      document.gregorian.islamicdate.value = iday + " " + IslamMonthsNames[imonth] + " " + iyear;
      document.gregorian.islamicleap.value = ileap;

      // Update Somali date
      document.gregorian.somalidayofweek.value = swday;
      document.gregorian.somalidate.value = iday + " " + SomMonthsNames[imonth];        
    }
}

//  calcGregorian  --  Perform calculation starting with a Gregorian date

function calcGregorian()
{
    updateFromGregorian();
}


//  calcIslamic  --  Update from Islamic calendar

function calcIslamic()
{
    setJulian(islamic_to_jd((new Number(document.islamic.year.value)),
                           document.islamic.month.selectedIndex + 1,
                           (new Number(document.islamic.day.value))));
}


//  calcGregSerial  --  Update from Gregorian serial day number

function calcGregSerial()
{
    setJulian((new Number(document.gregserial.day.value)) + J0000);
}

//  calcExcelSerial1900  --  Perform calculation starting with an Excel 1900 serial date

function calcExcelSerial1900()
{
    var d = new Number(document.excelserial1900.day.value);

    /* Idiot Kode Kiddies didn't twig to the fact
       (proclaimed in 1582) that 1900 wasn't a leap year,
       so every Excel day number in every database on Earth
       which represents a date subsequent to February 28,
       1900 is off by one.  Note that there is no
       acknowledgement of this betrayal or warning of its
       potential consequences in the Excel help file.  Thank
       you so much Mister Talking Paper Clip.  Some day
       we're going to celebrate your extinction like it was
       February 29 ... 1900.  */

    if (d > 60) {
        d--;
    }

    setJulian((d - 1) + J1900);
}

//  calcExcelSerial1904  --  Perform calculation starting with an Excel 1904 serial date

function calcExcelSerial1904()
{
    setJulian((new Number(document.excelserial1904.day.value)) + J1904);
}

//  calcUnixTime  --  Update from specified Unix time() value

function calcUnixTime()
{
    var t = new Number(document.unixtime.time.value);

    setJulian(J1970 + (t / (60 * 60 * 24)));
}

//  calcIsoWeek  --  Update from specified ISO year, week, and day

function calcIsoWeek()
{
    var year = new Number(document.isoweek.year.value),
        week = new Number(document.isoweek.week.value),
        day = new Number(document.isoweek.day.value);

    setJulian(iso_to_julian(year, week, day));
}

//  calcIsoDay  --  Update from specified ISO year and day of year

function calcIsoDay()
{
    var year = new Number(document.isoday.year.value),
        day = new Number(document.isoday.day.value);

    setJulian(iso_day_to_julian(year, day));
}

function calcJulian()
{
    var j, date, time;

    j = new Number(document.julianday.day.value);
    date = jd_to_gregorian(j);
    time = jhms(j);
    document.gregorian.year.value = date[0];
    document.gregorian.month.selectedIndex = date[1] - 1;
    document.gregorian.day.value = date[2];
    document.gregorian.hour.value = pad(time[0], 2, " ");
    document.gregorian.min.value = pad(time[1], 2, "0");
    document.gregorian.sec.value = pad(time[2], 2, "0");
    updateFromGregorian();
}

//  setJulian  --  Set Julian date and update all calendars

function setJulian(j)
{
    document.julianday.day.value = new Number(j);
    calcJulian();
}