Add period collection intersect

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 All notable changes to `period` will be documented in this file
 
+## 1.2.0 - 2019-04-19
+
+- Add period collection intersect
+
 ## 1.1.3 - 2019-04-05
 
 - Even better docblock support for static return types

src/Period.php

@@ -437,6 +437,16 @@ public function diff(Period ...$periods): PeriodCollection
         return $collection;
     }
 
+    /**
+     * @param \Spatie\Period\Period $period
+     *
+     * @return static
+     */
+    public function intersect(Period $period): Period
+    {
+
+    }
+
     public function getPrecisionMask(): int
     {
         return $this->precisionMask;

src/PeriodCollection.php

@@ -91,6 +91,23 @@ public function gaps(): PeriodCollection
         return $boundaries->diff(...$this);
     }
 
+    public function intersect(Period $intersection): PeriodCollection
+    {
+        $intersected = new PeriodCollection();
+
+        foreach ($this as $period) {
+            $overlap = $intersection->overlapSingle($period);
+
+            if ($overlap === null) {
+                continue;
+            }
+
+            $intersected[] = $overlap;
+        }
+
+        return $intersected;
+    }
+
     public function isEmpty(): bool
     {
         return count($this->periods) === 0;

tests/PeriodCollectionTest.php

@@ -141,4 +141,36 @@ public function it_can_determine_whether_a_period_has_a_date()
         $this->assertFalse($period->contains(new DateTimeImmutable('2017-12-31')));
         $this->assertFalse($period->contains(new DateTimeImmutable('2018-02-01')));
     }
+
+    /**
+     * @test
+     *
+     * A        [========================]
+     * B    [================]
+     * C                    [=====================]
+     * D                                    [=====]
+     *
+     * LIMIT        [===============]
+     *
+     * A            [===============]
+     * B            [========]
+     * C                    [=======]
+     */
+    public function intersect_test()
+    {
+        $collection = new PeriodCollection(
+            Period::make('2019-01-05', '2019-01-15'),
+            Period::make('2019-01-01', '2019-01-10'),
+            Period::make('2019-01-10', '2019-01-15'),
+            Period::make('2019-02-01', '2019-02-15'),
+        );
+
+        $intersect = $collection->intersect(Period::make('2019-01-09', '2019-01-11'));
+
+        $this->assertCount(3, $intersect);
+
+        $this->assertTrue($intersect[0]->equals(Period::make('2019-01-09', '2019-01-11')));
+        $this->assertTrue($intersect[1]->equals(Period::make('2019-01-09', '2019-01-10')));
+        $this->assertTrue($intersect[2]->equals(Period::make('2019-01-10', '2019-01-11')));
+    }
 }