Handle case of RRULE:COUNT=1 (any FREQ)

Outlook, as reported in u01jmg3#293, may in some cases reduce `COUNT` to `1`.

Whilst not disallowed in the RFC5545 spec (or any of its errata to date),
having a `COUNT` of `1` has no practical purpose that I can see.

We currently only check we've reached the count-limit *after* we've generated
the first few recurrences of an event and - more pressingly - *after* we've
appended the first candidate to the array of generated recurrences.

In this case `PHP_MAX_INT` could be replaced with some suitable default number,
akin to the current `defaultSpan` property used to put a limit on UNTIL.
But that's something for another PR.

src/ICal/ICal.php

@@ -1363,7 +1363,7 @@ protected function processRecurrences()
              *   enddate = <icalDate> || <icalDateTime>
              */
             $count      = 1;
-            $countLimit = (isset($rrules['COUNT'])) ? intval($rrules['COUNT']) : 0;
+            $countLimit = (isset($rrules['COUNT'])) ? intval($rrules['COUNT']) : PHP_INT_MAX;
             $until      = date_create()->modify("{$this->defaultSpan} years")->setTime(23, 59, 59)->getTimestamp();
 
             if (isset($rrules['UNTIL'])) {
@@ -1373,7 +1373,7 @@ protected function processRecurrences()
             $eventRecurrences = array();
 
             $frequencyRecurringDateTime = clone $initialEventDate;
-            while ($frequencyRecurringDateTime->getTimestamp() <= $until) {
+            while ($frequencyRecurringDateTime->getTimestamp() <= $until && $count < $countLimit) {
                 $candidateDateTimes = array();
 
                 // phpcs:ignore Squiz.ControlStructures.SwitchDeclaration.MissingDefault
@@ -1587,14 +1587,11 @@ function ($yearDay) use ($matchingDays) {
                         $this->eventCount++;
                     }
 
-                    // Count all evaluated candidates including excluded ones
-                    if (isset($rrules['COUNT'])) {
-                        $count++;
-
-                        // If RRULE[COUNT] is reached then break
-                        if ($count >= $countLimit) {
-                            break 2;
-                        }
+                    // Count all evaluated candidates including excluded ones,
+                    // and if RRULE[COUNT] (if set) is reached then break.
+                    $count++;
+                    if ($count >= $countLimit) {
+                        break 2;
                     }
                 }
 

tests/RecurrencesTest.php

@@ -429,6 +429,23 @@ public function testYearlyWithByMonthAndByMonthDay()
         );
     }
 
+    public function testCountIsOne()
+    {
+        $checks = array(
+            array('index' => 0, 'dateString' => '20211201T090000', 'message' => '1st and only expected event: '),
+        );
+        $this->assertVEVENT(
+            'UTC',
+            array(
+                'DTSTART:20211201T090000',
+                'DTEND:20211201T100000',
+                'RRULE:FREQ=DAILY;COUNT=1',
+            ),
+            1,
+            $checks
+        );
+    }
+
     public function assertVEVENT($defaultTimezone, $veventParts, $count, $checks)
     {
         $options = $this->getOptions($defaultTimezone);