Fix incorrect calculation from partially filled cache

When resuming calculation from a partially filled cache,
if the time is the last second of the day, this causes the generator
to consider the wrong frame of reference and therefore generate
the wrong occurrences.
Ref #160

Author: rlanvin

src/RRule.php

@@ -1362,16 +1362,8 @@ public function getIterator()
 
 		if ($occurrence) {
 			$dtstart = clone $occurrence; // since DateTime is not immutable, clone to avoid any problem
-			// so we skip the last occurrence of the cache
-			if ($this->freq === self::SECONDLY) {
-				$dtstart = $dtstart->modify('+'.$this->interval.'second');
-			}
-			else {
-				$dtstart = $dtstart->modify('+1second');
-			}
 		}
-
-		if ($dtstart === null) {
+		elseif ($dtstart === null) {
 			$dtstart = clone $this->dtstart;
 		}
 
@@ -1412,8 +1404,21 @@ public function getIterator()
 			}
 		}
 
+		// if we restarted the calculation from cache, we know that dtstart has already been yielded
+		// so we can skip ahead to the next second to avoid the same date to be yielded again
+		// we need to do that after the correct frame as been set (see https://github.com/rlanvin/php-rrule/issues/160)
+		if ($occurrence) {
+			if ($this->freq === self::SECONDLY) {
+				$dtstart = $dtstart->modify('+'.$this->interval.'second');
+			}
+			else {
+				$dtstart = $dtstart->modify('+1second');
+			}
+		}
+
 		$max_cycles = self::MAX_CYCLES[$this->freq <= self::DAILY ? $this->freq : self::DAILY];
 		for ($i = 0; $i < $max_cycles; $i++) {
+
 			// 1. get an array of all days in the next interval (day, month, week, etc.)
 			// we filter out from this array all days that do not match the BYXXX conditions
 			// to speed things up, we use days of the year (day numbers) instead of date
@@ -1546,6 +1551,7 @@ public function getIterator()
 							$this->total = $total;
 							return;
 						}
+
 						$total += 1;
 						$this->cache[] = clone $occurrence;
 						yield clone $occurrence; // yield
@@ -1576,6 +1582,7 @@ public function getIterator()
 								$this->total = $total;
 								return;
 							}
+
 							$total += 1;
 							$this->cache[] = clone $occurrence;
 							yield clone $occurrence; // yield

tests/RRuleTest.php

@@ -248,15 +248,15 @@ public function testYearly($rule, $occurrences)
 		$this->assertEquals($occurrences, $rule->getOccurrences());
 		$this->assertEquals($occurrences, $rule->getOccurrences(), 'Cached version');
 		foreach ($occurrences as $date) {
-			$this->assertTrue($rule->occursAt($date), $date->format('r').'in cached version');
+			$this->assertTrue($rule->occursAt($date), $date->format('r').' in cached version');
 		}
 		$rule->clearCache();
 		foreach ($occurrences as $date) {
-			$this->assertTrue($rule->occursAt($date), $date->format('r').'in uncached version');
+			$this->assertTrue($rule->occursAt($date), $date->format('r').' in uncached version');
 		}
 		$rule->clearCache();
 		for ($i = 0; $i < count($occurrences); $i++) {
-			$this->assertEquals($rule[$i], $occurrences[$i], 'array access uncached');
+			$this->assertEquals($rule[$i], $occurrences[$i], ' array access uncached');
 		}
 	}
 
@@ -1835,6 +1835,30 @@ public function testDST()
 		$this->assertSame('2022-11-06T01:00:00-05:00 CDT 1667714400', $rrule[1]->format('c T U'));
 	}
 
+	public function testResumeFromPartiallyFilledCache()
+	{
+		// https://github.com/rlanvin/php-rrule/issues/160
+		$rrule = new \RRule\RRule([
+			'DTSTART' => new DateTime('2023-03-31 23:59:59.000000'),
+			'FREQ' => 'MONTHLY',
+			'INTERVAL' => '12',
+			'WKST' => 'MO',
+			'COUNT' => 3
+		]);
+
+		// Break on first loop during first iterator use.
+		foreach ($rrule as $occurrence) {
+			break;
+		}
+
+		// Print first 3 occurrences (cache used).
+		$this->assertEquals([
+			date_create('2023-03-31 23:59:59'),
+			date_create('2024-03-31 23:59:59'),
+			date_create('2025-03-31 23:59:59')
+		],$rrule->getOccurrences());
+	}
+
 ///////////////////////////////////////////////////////////////////////////////
 // GetOccurrences