xref: /webtrees/app/Date.php (revision f7cf8a155e2743f3d124eef3d30a558ab062fa4b)
1<?php
2
3/**
4 * webtrees: online genealogy
5 * Copyright (C) 2021 webtrees development team
6 * This program is free software: you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation, either version 3 of the License, or
9 * (at your option) any later version.
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program. If not, see <https://www.gnu.org/licenses/>.
16 */
17
18declare(strict_types=1);
19
20namespace Fisharebest\Webtrees;
21
22use DomainException;
23use Fisharebest\ExtCalendar\GregorianCalendar;
24use Fisharebest\Webtrees\Date\AbstractCalendarDate;
25use Fisharebest\Webtrees\Date\FrenchDate;
26use Fisharebest\Webtrees\Date\GregorianDate;
27use Fisharebest\Webtrees\Date\HijriDate;
28use Fisharebest\Webtrees\Date\JalaliDate;
29use Fisharebest\Webtrees\Date\JewishDate;
30use Fisharebest\Webtrees\Date\JulianDate;
31use Fisharebest\Webtrees\Date\RomanDate;
32
33use function app;
34use function trigger_error;
35
36use const E_USER_DEPRECATED;
37
38/**
39 * A representation of GEDCOM dates and date ranges.
40 *
41 * Since different calendars start their days at different times, (civil
42 * midnight, solar midnight, sunset, sunrise, etc.), we convert on the basis of
43 * midday.
44 *
45 * We assume that years start on the first day of the first month. Where
46 * this is not the case (e.g. England prior to 1752), we need to use modified
47 * years or the OS/NS notation "4 FEB 1750/51".
48 */
49class Date
50{
51    /** @var string Optional qualifier, such as BEF, FROM, ABT */
52    public $qual1 = '';
53
54    /** @var AbstractCalendarDate  The first (or only) date */
55    private $date1;
56
57    /** @var string  Optional qualifier, such as TO, AND */
58    public $qual2 = '';
59
60    /** @var AbstractCalendarDate|null Optional second date */
61    private $date2;
62
63    /** @var string Optional text, as included with an INTerpreted date */
64    private $text = '';
65
66    /**
67     * Create a date, from GEDCOM data.
68     *
69     * @param string $date A date in GEDCOM format
70     */
71    public function __construct(string $date)
72    {
73        // Extract any explanatory text
74        if (preg_match('/^(.*) ?[(](.*)[)]/', $date, $match)) {
75            $date       = $match[1];
76            $this->text = $match[2];
77        }
78        if (preg_match('/^(FROM|BET) (.+) (AND|TO) (.+)/', $date, $match)) {
79            $this->qual1 = $match[1];
80            $this->date1 = $this->parseDate($match[2]);
81            $this->qual2 = $match[3];
82            $this->date2 = $this->parseDate($match[4]);
83        } elseif (preg_match('/^(TO|FROM|BEF|AFT|CAL|EST|INT|ABT) (.+)/', $date, $match)) {
84            $this->qual1 = $match[1];
85            $this->date1 = $this->parseDate($match[2]);
86        } else {
87            $this->date1 = $this->parseDate($date);
88        }
89    }
90
91    /**
92     * When we copy a date object, we need to create copies of
93     * its child objects.
94     */
95    public function __clone()
96    {
97        $this->date1 = clone $this->date1;
98        if ($this->date2 !== null) {
99            $this->date2 = clone $this->date2;
100        }
101    }
102
103    /**
104     * Convert a calendar date, such as "12 JUN 1943" into calendar date object.
105     * A GEDCOM date range may have two calendar dates.
106     *
107     * @param string $date
108     *
109     * @return AbstractCalendarDate
110     * @throws DomainException
111     */
112    private function parseDate(string $date): AbstractCalendarDate
113    {
114        // Valid calendar escape specified? - use it
115        if (preg_match('/^(@#D(?:GREGORIAN|JULIAN|HEBREW|HIJRI|JALALI|FRENCH R|ROMAN)+@) ?(.*)/', $date, $match)) {
116            $cal  = $match[1];
117            $date = $match[2];
118        } else {
119            $cal = '';
120        }
121        // A date with a month: DM, M, MY or DMY
122        if (preg_match('/^(\d?\d?) ?(JAN|FEB|MAR|APR|MAY|JUN|JUL|AUG|SEP|OCT|NOV|DEC|TSH|CSH|KSL|TVT|SHV|ADR|ADS|NSN|IYR|SVN|TMZ|AAV|ELL|VEND|BRUM|FRIM|NIVO|PLUV|VENT|GERM|FLOR|PRAI|MESS|THER|FRUC|COMP|MUHAR|SAFAR|RABI[AT]|JUMA[AT]|RAJAB|SHAAB|RAMAD|SHAWW|DHUAQ|DHUAH|FARVA|ORDIB|KHORD|TIR|MORDA|SHAHR|MEHR|ABAN|AZAR|DEY|BAHMA|ESFAN) ?((?:\d{1,4}(?: B\.C\.)?|\d\d\d\d\/\d\d)?)$/', $date, $match)) {
123            $d = $match[1];
124            $m = $match[2];
125            $y = $match[3];
126        } elseif (preg_match('/^(\d{1,4}(?: B\.C\.)?|\d\d\d\d\/\d\d)$/', $date, $match)) {
127            // A date with just a year
128            $d = '';
129            $m = '';
130            $y = $match[1];
131        } else {
132            // An invalid date - do the best we can.
133            $d = '';
134            $m = '';
135            $y = '';
136            // Look for a 3/4 digit year anywhere in the date
137            if (preg_match('/\b(\d{3,4})\b/', $date, $match)) {
138                $y = $match[1];
139            }
140            // Look for a month anywhere in the date
141            if (preg_match('/(JAN|FEB|MAR|APR|MAY|JUN|JUL|AUG|SEP|OCT|NOV|DEC|TSH|CSH|KSL|TVT|SHV|ADR|ADS|NSN|IYR|SVN|TMZ|AAV|ELL|VEND|BRUM|FRIM|NIVO|PLUV|VENT|GERM|FLOR|PRAI|MESS|THER|FRUC|COMP|MUHAR|SAFAR|RABI[AT]|JUMA[AT]|RAJAB|SHAAB|RAMAD|SHAWW|DHUAQ|DHUAH|FARVA|ORDIB|KHORD|TIR|MORDA|SHAHR|MEHR|ABAN|AZAR|DEY|BAHMA|ESFAN)/', $date, $match)) {
142                $m = $match[1];
143                // Look for a day number anywhere in the date
144                if (preg_match('/\b(\d\d?)\b/', $date, $match)) {
145                    $d = $match[1];
146                }
147            }
148        }
149
150        // Unambiguous dates - override calendar escape
151        if (preg_match('/^(TSH|CSH|KSL|TVT|SHV|ADR|ADS|NSN|IYR|SVN|TMZ|AAV|ELL)$/', $m)) {
152            $cal = JewishDate::ESCAPE;
153        } elseif (preg_match('/^(VEND|BRUM|FRIM|NIVO|PLUV|VENT|GERM|FLOR|PRAI|MESS|THER|FRUC|COMP)$/', $m)) {
154            $cal = FrenchDate::ESCAPE;
155        } elseif (preg_match('/^(MUHAR|SAFAR|RABI[AT]|JUMA[AT]|RAJAB|SHAAB|RAMAD|SHAWW|DHUAQ|DHUAH)$/', $m)) {
156            $cal = HijriDate::ESCAPE; // This is a WT extension
157        } elseif (preg_match('/^(FARVA|ORDIB|KHORD|TIR|MORDA|SHAHR|MEHR|ABAN|AZAR|DEY|BAHMA|ESFAN)$/', $m)) {
158            $cal = JalaliDate::ESCAPE; // This is a WT extension
159        } elseif (preg_match('/^\d{1,4}( B\.C\.)|\d\d\d\d\/\d\d$/', $y)) {
160            $cal = JulianDate::ESCAPE;
161        }
162
163        // Ambiguous dates - don't override calendar escape
164        if ($cal === '') {
165            if (preg_match('/^(JAN|FEB|MAR|APR|MAY|JUN|JUL|AUG|SEP|OCT|NOV|DEC)$/', $m)) {
166                $cal =  GregorianDate::ESCAPE;
167            } elseif (preg_match('/^[345]\d\d\d$/', $y)) {
168                // Year 3000-5999
169                $cal = JewishDate::ESCAPE;
170            } else {
171                $cal = GregorianDate::ESCAPE;
172            }
173        }
174        // Now construct an object of the correct type
175        switch ($cal) {
176            case GregorianDate::ESCAPE:
177                return new GregorianDate([
178                    $y,
179                    $m,
180                    $d,
181                ]);
182            case JulianDate::ESCAPE:
183                return new JulianDate([
184                    $y,
185                    $m,
186                    $d,
187                ]);
188            case JewishDate::ESCAPE:
189                return new JewishDate([
190                    $y,
191                    $m,
192                    $d,
193                ]);
194            case HijriDate::ESCAPE:
195                return new HijriDate([
196                    $y,
197                    $m,
198                    $d,
199                ]);
200            case FrenchDate::ESCAPE:
201                return new FrenchDate([
202                    $y,
203                    $m,
204                    $d,
205                ]);
206            case JalaliDate::ESCAPE:
207                return new JalaliDate([
208                    $y,
209                    $m,
210                    $d,
211                ]);
212            case RomanDate::ESCAPE:
213                return new RomanDate([
214                    $y,
215                    $m,
216                    $d,
217                ]);
218            default:
219                throw new DomainException('Invalid calendar');
220        }
221    }
222
223    /**
224     * A list of supported calendars and their names.
225     *
226     * @return array<string>
227     */
228    public static function calendarNames(): array
229    {
230        return [
231            /* I18N: The gregorian calendar */
232            'gregorian' => I18N::translate('Gregorian'),
233            /* I18N: The julian calendar */
234            'julian'    => I18N::translate('Julian'),
235            /* I18N: The French calendar */
236            'french'    => I18N::translate('French'),
237            /* I18N: The Hebrew/Jewish calendar */
238            'jewish'    => I18N::translate('Jewish'),
239            /* I18N: The Arabic/Hijri calendar */
240            'hijri'     => I18N::translate('Hijri'),
241            /* I18N: The Persian/Jalali calendar */
242            'jalali'    => I18N::translate('Jalali'),
243        ];
244    }
245
246    /**
247     * Convert a date to the preferred format and calendar(s) display.
248     *
249     * @param bool|null   $url               Wrap the date in a link to calendar.php
250     * @param string|null $date_format       Override the default date format
251     * @param bool|null   $convert_calendars Convert the date into other calendars
252     *
253     * @return string
254     */
255    public function display($url = false, $date_format = null, $convert_calendars = true): string
256    {
257        // Do we need a new DateFormatterService class?
258        if (app()->has(Tree::class)) {
259            $tree            = app(Tree::class);
260            $CALENDAR_FORMAT = $tree->getPreference('CALENDAR_FORMAT');
261        } else {
262            $tree            = null;
263            $CALENDAR_FORMAT = '';
264        }
265
266        $date_format = $date_format ?? I18N::dateFormat();
267
268        if ($convert_calendars) {
269            $calendar_format = explode('_and_', $CALENDAR_FORMAT);
270        } else {
271            $calendar_format = [];
272        }
273
274        // Two dates with text before, between and after
275        $q1 = $this->qual1;
276        $d1 = $this->date1->format($date_format, $this->qual1);
277        $q2 = $this->qual2;
278        if ($this->date2 === null) {
279            $d2 = '';
280        } else {
281            $d2 = $this->date2->format($date_format, $this->qual2);
282        }
283        // Con vert to other calendars, if requested
284        $conv1 = '';
285        $conv2 = '';
286        foreach ($calendar_format as $cal_fmt) {
287            if ($cal_fmt !== 'none') {
288                $d1conv = $this->date1->convertToCalendar($cal_fmt);
289                if ($d1conv->inValidRange()) {
290                    $d1tmp = $d1conv->format($date_format, $this->qual1);
291                } else {
292                    $d1tmp = '';
293                }
294                if ($this->date2 === null) {
295                    $d2conv = null;
296                    $d2tmp  = '';
297                } else {
298                    $d2conv = $this->date2->convertToCalendar($cal_fmt);
299                    if ($d2conv->inValidRange()) {
300                        $d2tmp = $d2conv->format($date_format, $this->qual2);
301                    } else {
302                        $d2tmp = '';
303                    }
304                }
305                // If the date is different from the unconverted date, add it to the date string.
306                if ($d1 != $d1tmp && $d1tmp !== '') {
307                    if ($url) {
308                        if ($CALENDAR_FORMAT !== 'none') {
309                            $conv1 .= ' <span dir="' . I18N::direction() . '">(<a href="' . $d1conv->calendarUrl($date_format, $tree) . '" rel="nofollow">' . $d1tmp . '</a>)</span>';
310                        } else {
311                            $conv1 .= ' <span dir="' . I18N::direction() . '"><br><a href="' . $d1conv->calendarUrl($date_format, $tree) . '" rel="nofollow">' . $d1tmp . '</a></span>';
312                        }
313                    } else {
314                        $conv1 .= ' <span dir="' . I18N::direction() . '">(' . $d1tmp . ')</span>';
315                    }
316                }
317                if ($this->date2 !== null && $d2 != $d2tmp && $d1tmp != '') {
318                    if ($url) {
319                        $conv2 .= ' <span dir="' . I18N::direction() . '">(<a href="' . $d2conv->calendarUrl($date_format, $tree) . '" rel="nofollow">' . $d2tmp . '</a>)</span>';
320                    } else {
321                        $conv2 .= ' <span dir="' . I18N::direction() . '">(' . $d2tmp . ')</span>';
322                    }
323                }
324            }
325        }
326
327        // Add URLs, if requested
328        if ($url) {
329            $d1 = '<a href="' . $this->date1->calendarUrl($date_format, $tree) . '" rel="nofollow">' . $d1 . '</a>';
330            if ($this->date2 instanceof AbstractCalendarDate) {
331                $d2 = '<a href="' . $this->date2->calendarUrl($date_format, $tree) . '" rel="nofollow">' . $d2 . '</a>';
332            }
333        }
334
335        // Localise the date
336        switch ($q1 . $q2) {
337            case '':
338                $tmp = $d1 . $conv1;
339                break;
340            case 'ABT':
341                /* I18N: Gedcom ABT dates */
342                $tmp = I18N::translate('about %s', $d1 . $conv1);
343                break;
344            case 'CAL':
345                /* I18N: Gedcom CAL dates */
346                $tmp = I18N::translate('calculated %s', $d1 . $conv1);
347                break;
348            case 'EST':
349                /* I18N: Gedcom EST dates */
350                $tmp = I18N::translate('estimated %s', $d1 . $conv1);
351                break;
352            case 'INT':
353                /* I18N: Gedcom INT dates */
354                $tmp = I18N::translate('interpreted %s (%s)', $d1 . $conv1, e($this->text));
355                break;
356            case 'BEF':
357                /* I18N: Gedcom BEF dates */
358                $tmp = I18N::translate('before %s', $d1 . $conv1);
359                break;
360            case 'AFT':
361                /* I18N: Gedcom AFT dates */
362                $tmp = I18N::translate('after %s', $d1 . $conv1);
363                break;
364            case 'FROM':
365                /* I18N: Gedcom FROM dates */
366                $tmp = I18N::translate('from %s', $d1 . $conv1);
367                break;
368            case 'TO':
369                /* I18N: Gedcom TO dates */
370                $tmp = I18N::translate('to %s', $d1 . $conv1);
371                break;
372            case 'BETAND':
373                /* I18N: Gedcom BET-AND dates */
374                $tmp = I18N::translate('between %s and %s', $d1 . $conv1, $d2 . $conv2);
375                break;
376            case 'FROMTO':
377                /* I18N: Gedcom FROM-TO dates */
378                $tmp = I18N::translate('from %s to %s', $d1 . $conv1, $d2 . $conv2);
379                break;
380            default:
381                $tmp = I18N::translate('Invalid date');
382                break;
383        }
384
385        if (strip_tags($tmp) === '') {
386            return '';
387        }
388
389        return '<span class="date">' . $tmp . '</span>';
390    }
391
392    /**
393     * Get the earliest calendar date from this GEDCOM date.
394     *
395     * In the date “FROM 1900 TO 1910”, this would be 1900.
396     *
397     * @return AbstractCalendarDate
398     */
399    public function minimumDate(): AbstractCalendarDate
400    {
401        return $this->date1;
402    }
403
404    /**
405     * Get the latest calendar date from this GEDCOM date.
406     *
407     * In the date “FROM 1900 TO 1910”, this would be 1910.
408     *
409     * @return AbstractCalendarDate
410     */
411    public function maximumDate(): AbstractCalendarDate
412    {
413        return $this->date2 ?? $this->date1;
414    }
415
416    /**
417     * Get the earliest Julian day number from this GEDCOM date.
418     *
419     * @return int
420     */
421    public function minimumJulianDay(): int
422    {
423        return $this->minimumDate()->minimumJulianDay();
424    }
425
426    /**
427     * Get the latest Julian day number from this GEDCOM date.
428     *
429     * @return int
430     */
431    public function maximumJulianDay(): int
432    {
433        return $this->maximumDate()->maximumJulianDay();
434    }
435
436    /**
437     * Get the middle Julian day number from the GEDCOM date.
438     *
439     * For a month-only date, this would be somewhere around the 16th day.
440     * For a year-only date, this would be somewhere around 1st July.
441     *
442     * @return int
443     */
444    public function julianDay(): int
445    {
446        return intdiv($this->minimumJulianDay() + $this->maximumJulianDay(), 2);
447    }
448
449    /**
450     * Offset this date by N years, and round to the whole year.
451     *
452     * This is typically used to create an estimated death date,
453     * which is before a certain number of years after the birth date.
454     *
455     * @param int    $years     a number of years, positive or negative
456     * @param string $qualifier typically “BEF” or “AFT”
457     *
458     * @return Date
459     */
460    public function addYears(int $years, string $qualifier = ''): Date
461    {
462        $tmp               = clone $this;
463        $tmp->date1->year  += $years;
464        $tmp->date1->month = 0;
465        $tmp->date1->day   = 0;
466        $tmp->date1->setJdFromYmd();
467        $tmp->qual1 = $qualifier;
468        $tmp->qual2 = '';
469        $tmp->date2 = null;
470
471        return $tmp;
472    }
473
474    /**
475     * Calculate the the age of a person (n years), on a given date.
476     *
477     * @param Date $d1
478     * @param Date $d2
479     *
480     * @return int
481     *
482     * @deprecated since 2.0.4.  Will be removed in 2.1.0
483     */
484    public static function getAgeYears(Date $d1, Date $d2): int
485    {
486        trigger_error('Date::getAgeYears() is deprecated. Use class Age instead.', E_USER_DEPRECATED);
487
488        if (self::compare($d1, $d2) === 0) {
489            // Overlapping dates
490            $jd = $d1->minimumJulianDay();
491        } else {
492            // Non-overlapping dates
493            $jd = $d2->minimumJulianDay();
494        }
495
496        if ($jd && $d1->minimumJulianDay() && $d1->minimumJulianDay() <= $jd) {
497            return $d1->minimumDate()->getAge($jd);
498        }
499
500        return -1;
501    }
502
503    /**
504     * Calculate the the age of a person (n days), on a given date.
505     *
506     * @param Date $d1
507     * @param Date $d2
508     *
509     * @return int
510     *
511     * @deprecated since 2.0.4.  Will be removed in 2.1.0
512     */
513    public static function getAgeDays(Date $d1, Date $d2): int
514    {
515        trigger_error('Date::getAgeDays() is deprecated. Use class Age instead.', E_USER_DEPRECATED);
516
517        if ($d2->maximumJulianDay() >= $d1->minimumJulianDay() && $d2->minimumJulianDay() <= $d1->maximumJulianDay()) {
518            // Overlapping dates
519            $jd = $d1->minimumJulianDay();
520        } else {
521            // Non-overlapping dates
522            $jd = $d2->minimumJulianDay();
523        }
524
525        // Days - integer only (for sorting, rather than for display)
526        if ($jd && $d1->minimumJulianDay()) {
527            return $jd - $d1->minimumJulianDay();
528        }
529
530        return -1;
531    }
532
533    /**
534     * Calculate the the age of a person, on a date.
535     *
536     * @param Date      $d1
537     * @param Date|null $d2
538     *
539     * @return string
540     *
541     * @deprecated since 2.0.4.  Will be removed in 2.1.0
542     */
543    public static function getAge(Date $d1, Date $d2 = null): string
544    {
545        trigger_error('Date::getAge() is deprecated. Use class Age instead.', E_USER_DEPRECATED);
546
547        if ($d2 instanceof self) {
548            if ($d2->maximumJulianDay() >= $d1->minimumJulianDay() && $d2->minimumJulianDay() <= $d1->maximumJulianDay()) {
549                // Overlapping dates
550                $jd = $d1->minimumJulianDay();
551            } else {
552                // Non-overlapping dates
553                $jd = $d2->minimumJulianDay();
554            }
555        } else {
556            // If second date not specified, use today’s date
557            $jd = Carbon::now()->julianDay();
558        }
559
560        // Just years, in local digits, with warning for negative/
561        if ($jd && $d1->minimumJulianDay()) {
562            if ($d1->minimumJulianDay() > $jd) {
563                return view('icons/warning');
564            }
565
566            $years = $d1->minimumDate()->getAge($jd);
567
568            return I18N::number($years);
569        }
570
571        return '';
572    }
573
574    /**
575     * Calculate the years/months/days between two events
576     * Return a gedcom style age string: "1y 2m 3d" (for fact details)
577     *
578     * @param Date      $d1
579     * @param Date|null $d2
580     *
581     * @return string
582     *
583     * @deprecated since 2.0.4.  Will be removed in 2.1.0
584     */
585    public static function getAgeGedcom(Date $d1, Date $d2 = null): string
586    {
587        trigger_error('Date::getAgeGedcom() is deprecated. Use class Age instead.', E_USER_DEPRECATED);
588
589        if ($d2 === null) {
590            return $d1->date1->getAgeFull(Carbon::now()->julianDay());
591        }
592
593        if (self::compare($d1, $d2) !== 0) {
594            return $d1->date1->getAgeFull($d2->minimumJulianDay());
595        }
596
597        if ($d1->minimumJulianDay() == $d2->minimumJulianDay()) {
598            return '0d';
599        }
600
601        return '';
602    }
603
604    /**
605     * Compare two dates, so they can be sorted.
606     *
607     * return -1 if $a<$b
608     * return +1 if $b>$a
609     * return  0 if dates same/overlap
610     * BEF/AFT sort as the day before/after
611     *
612     * @param Date $a
613     * @param Date $b
614     *
615     * @return int
616     */
617    public static function compare(Date $a, Date $b): int
618    {
619        // Get min/max JD for each date.
620        switch ($a->qual1) {
621            case 'BEF':
622                $amin = $a->minimumJulianDay() - 1;
623                $amax = $amin;
624                break;
625            case 'AFT':
626                $amax = $a->maximumJulianDay() + 1;
627                $amin = $amax;
628                break;
629            default:
630                $amin = $a->minimumJulianDay();
631                $amax = $a->maximumJulianDay();
632                break;
633        }
634        switch ($b->qual1) {
635            case 'BEF':
636                $bmin = $b->minimumJulianDay() - 1;
637                $bmax = $bmin;
638                break;
639            case 'AFT':
640                $bmax = $b->maximumJulianDay() + 1;
641                $bmin = $bmax;
642                break;
643            default:
644                $bmin = $b->minimumJulianDay();
645                $bmax = $b->maximumJulianDay();
646                break;
647        }
648        if ($amax < $bmin) {
649            return -1;
650        }
651
652        if ($amin > $bmax && $bmax > 0) {
653            return 1;
654        }
655
656        if ($amin < $bmin && $amax <= $bmax) {
657            return -1;
658        }
659
660        if ($amin > $bmin && $amax >= $bmax && $bmax > 0) {
661            return 1;
662        }
663
664        return 0;
665    }
666
667    /**
668     * Check whether a gedcom date contains usable calendar date(s).
669     *
670     * An incomplete date such as "12 AUG" would be invalid, as
671     * we cannot sort it.
672     *
673     * @return bool
674     */
675    public function isOK(): bool
676    {
677        return $this->minimumJulianDay() && $this->maximumJulianDay();
678    }
679
680    /**
681     * Calculate the gregorian year for a date. This should NOT be used internally
682     * within WT - we should keep the code "calendar neutral" to allow support for
683     * jewish/arabic users. This is only for interfacing with external entities,
684     * such as the ancestry.com search interface or the dated fact icons.
685     *
686     * @return int
687     */
688    public function gregorianYear(): int
689    {
690        if ($this->isOK()) {
691            $gregorian_calendar = new GregorianCalendar();
692            [$year] = $gregorian_calendar->jdToYmd($this->julianDay());
693
694            return $year;
695        }
696
697        return 0;
698    }
699}
700