When\When::generateOccurrences PHP Method

    public function generateOccurrences()
    {
        self::prepareDateElements();
        $count = 0;
        $dateLooper = clone $this->startDate;
        // add the start date to the list of occurrences
        if ($this->occursOn($dateLooper)) {
            $this->addOccurrence($this->generateTimeOccurrences($dateLooper));
        } else {
            switch ($this->RFC5545_COMPLIANT) {
                case self::NOTICE:
                    trigger_error('InvalidStartDate: startDate is outside the bounds of the occurrence parameters.');
                    break;
                case self::IGNORE:
                    break;
                case self::EXCEPTION:
                default:
                    throw new InvalidStartDate();
                    break;
            }
        }
        while ($dateLooper < $this->until && count($this->occurrences) < $this->count) {
            $occurrences = array();
            if ($this->freq === "yearly") {
                if (isset($this->bymonths)) {
                    foreach ($this->bymonths as $month) {
                        if (isset($this->bydays)) {
                            $dateLooper->setDate($dateLooper->format("Y"), $month, 1);
                            // get the number of days
                            $totalDays = $dateLooper->format("t");
                            $today = 0;
                            while ($today < $totalDays) {
                                if ($this->occursOn($dateLooper)) {
                                    $occurrences = array_merge($occurrences, $this->generateTimeOccurrences($dateLooper));
                                }
                                $dateLooper->add(new \DateInterval('P1D'));
                                $today++;
                            }
                        } else {
                            $dateLooper->setDate($dateLooper->format("Y"), $month, $dateLooper->format("j"));
                            if ($this->occursOn($dateLooper)) {
                                $occurrences = array_merge($occurrences, $this->generateTimeOccurrences($dateLooper));
                            }
                        }
                    }
                } else {
                    $dateLooper->setDate($dateLooper->format("Y"), 1, 1);
                    $leapYear = (int) $dateLooper->format("L");
                    if ($leapYear) {
                        $days = 366;
                    } else {
                        $days = 365;
                    }
                    $day = 0;
                    while ($day < $days) {
                        if ($this->occursOn($dateLooper)) {
                            $occurrences = array_merge($occurrences, $this->generateTimeOccurrences($dateLooper));
                        }
                        $dateLooper->add(new \DateInterval('P1D'));
                        $day++;
                    }
                }
                $occurrences = $this->prepareOccurrences($occurrences, $count);
                $this->addOccurrence($occurrences);
                $dateLooper = clone $this->startDate;
                $dateLooper->add(new \DateInterval('P' . $this->interval * ++$count . 'Y'));
            } else {
                if ($this->freq === "monthly") {
                    $days = (int) $dateLooper->format("t");
                    $day = (int) $dateLooper->format("j");
                    while ($day <= $days) {
                        if ($this->occursOn($dateLooper)) {
                            $occurrences = array_merge($occurrences, $this->generateTimeOccurrences($dateLooper));
                        }
                        $dateLooper->add(new \DateInterval('P1D'));
                        $day++;
                    }
                    $occurrences = $this->prepareOccurrences($occurrences, $count);
                    $this->addOccurrence($occurrences);
                    $dateLooper = clone $this->startDate;
                    $dateLooper->setDate($dateLooper->format("Y"), $dateLooper->format("n"), 1);
                    $dateLooper->add(new \DateInterval('P' . $this->interval * ++$count . 'M'));
                } else {
                    if ($this->freq === "weekly") {
                        $dateLooper->setDate($dateLooper->format("Y"), $dateLooper->format("n"), $dateLooper->format("j"));
                        $wkst = self::abbrevToDayName($this->wkst);
                        $daysLeft = 7;
                        // not very happy with this
                        if ($count === 0) {
                            $startWeekDay = clone $this->startDate;
                            $startWeekDay->modify("next " . $wkst);
                            $startWeekDay->setTime($dateLooper->format('H'), $dateLooper->format('i'), $dateLooper->format('s'));
                            $daysLeft = (int) $dateLooper->diff($startWeekDay)->format("%a");
                            $startWeekDay->modify("last " . $wkst);
                        }
                        while ($daysLeft > 0) {
                            if ($this->occursOn($dateLooper)) {
                                $occurrences = array_merge($occurrences, $this->generateTimeOccurrences($dateLooper));
                            }
                            $dateLooper->add(new \DateInterval('P1D'));
                            $daysLeft--;
                        }
                        $occurrences = $this->prepareOccurrences($occurrences, $count);
                        $this->addOccurrence($occurrences);
                        $dateLooper = clone $this->startDate;
                        $dateLooper->setDate($startWeekDay->format("Y"), $startWeekDay->format("n"), $startWeekDay->format('j'));
                        $dateLooper->add(new \DateInterval('P' . $this->interval * (++$count * 7) . 'D'));
                    } else {
                        if ($this->freq === "daily") {
                            if ($this->occursOn($dateLooper)) {
                                $this->addOccurrence($this->generateTimeOccurrences($dateLooper));
                            }
                            $dateLooper = clone $this->startDate;
                            $dateLooper->setDate($dateLooper->format("Y"), $dateLooper->format("n"), $dateLooper->format('j'));
                            $dateLooper->add(new \DateInterval('P' . $this->interval * ++$count . 'D'));
                        } else {
                            if ($this->freq === "hourly") {
                                $occurrence = array();
                                if ($this->occursOn($dateLooper)) {
                                    $occurrence[] = $dateLooper;
                                    $this->addOccurrence($occurrence);
                                }
                                $dateLooper = clone $this->startDate;
                                $dateLooper->add(new \DateInterval('PT' . $this->interval * ++$count . 'H'));
                            } else {
                                if ($this->freq === "minutely") {
                                    $occurrence = array();
                                    if ($this->occursOn($dateLooper)) {
                                        $occurrence[] = $dateLooper;
                                        $this->addOccurrence($occurrence);
                                    }
                                    $dateLooper = clone $this->startDate;
                                    $dateLooper->add(new \DateInterval('PT' . $this->interval * ++$count . 'M'));
                                } else {
                                    if ($this->freq === "secondly") {
                                        $occurrence = array();
                                        if ($this->occursOn($dateLooper)) {
                                            $occurrence[] = $dateLooper;
                                            $this->addOccurrence($occurrence);
                                        }
                                        $dateLooper = clone $this->startDate;
                                        $dateLooper->add(new \DateInterval('PT' . $this->interval * ++$count . 'S'));
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
        // generateTimeOccurrences can overshoot $this->count, so trim:
        if ($this->count && count($this->occurrences) >= $this->count) {
            $this->occurrences = array_slice($this->occurrences, 0, $this->count);
        }
    }

 /**
  * Every Sunday in January every other year at 8:30 am and 9:30 am
  * DTSTART;TZID=America/New_York:19970105T083000
  * RRULE:FREQ=YEARLY;INTERVAL=2;BYMONTH=1;BYDAY=SU;BYHOUR=8,9;BYMINUTE=30
  */
 function testYearlyTheninthnode()
 {
     $results[] = new DateTime("2015-09-17 00:00:00");
     $results[] = new DateTime("2016-09-17 00:00:00");
     $results[] = new DateTime("2017-09-17 00:00:00");
     $results[] = new DateTime("2018-09-17 00:00:00");
     $results[] = new DateTime("2019-09-17 00:00:00");
     $r = new When();
     $r->startDate(new DateTime('2015-09-17 00:00:00'));
     $r->freq('yearly');
     $r->interval(1);
     $r->count(5);
     $r->generateOccurrences();
     $occurrences = $r->occurrences;
     foreach ($results as $key => $result) {
         $this->assertEquals($result, $occurrences[$key]);
     }
 }