From cfaeb3d4e7b750f0ae5ee3fd1a92c8cc0171aa84 Mon Sep 17 00:00:00 2001
From: aliowacom <91871615+aliowacom@users.noreply.github.com>
Date: Wed, 22 Dec 2021 18:27:06 +0100
Subject: [PATCH 1/2] Error "Undefined array key 0" fix

There's an error, if you pass an empty PeriodCollection to `overlap()` or `subtract()` method since there's no check whether the collection actually has any values.

Steps to reproduce:
```php

        $period = Period::make('2021-12-31', '2022-01-01');
        $collection = new PeriodCollection;

        $period->overlap(... $collection); // Throws ErrorException "Undefined array key 0"
        $period->subtract(... $collection); // Throws ErrorException "Undefined array key 0"
```

P.S. Thank you for your products and Merry Christmas! :)
---
 src/PeriodTraits/PeriodOperations.php | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/PeriodTraits/PeriodOperations.php b/src/PeriodTraits/PeriodOperations.php
index 292abad..d7a0aca 100644
--- a/src/PeriodTraits/PeriodOperations.php
+++ b/src/PeriodTraits/PeriodOperations.php
@@ -38,7 +38,9 @@ public function gap(Period $period): ?static
 
     public function overlap(Period ...$others): ?static
     {
-        if (count($others) > 1) {
+        if (count($others) === 0) {
+            return null;
+        } else if (count($others) > 1) {
             return $this->overlapAll(...$others);
         } else {
             $other = $others[0];
@@ -115,7 +117,9 @@ public function overlapAny(Period ...$others): PeriodCollection
      */
     public function subtract(Period ...$others): PeriodCollection
     {
-        if (count($others) > 1) {
+        if (count($others) === 0)
+            return PeriodCollection::make($this);
+        } else if (count($others) > 1) {
             return $this->subtractAll(...$others);
         } else {
             $other = $others[0];

From 8248b83ebc3f7a7ce1aeb1611b9bf91dcb22d7be Mon Sep 17 00:00:00 2001
From: Alex Averkiyev <aleksejs.averkijevs@gmail.com>
Date: Thu, 23 Dec 2021 09:46:03 +0100
Subject: [PATCH 2/2] Empty collection tests

---
 src/PeriodTraits/PeriodOperations.php |  2 +-
 tests/Operations/OverlapTest.php      | 12 ++++++++++++
 tests/Operations/SubtractTest.php     | 14 ++++++++++++++
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/src/PeriodTraits/PeriodOperations.php b/src/PeriodTraits/PeriodOperations.php
index d7a0aca..a3ccd84 100644
--- a/src/PeriodTraits/PeriodOperations.php
+++ b/src/PeriodTraits/PeriodOperations.php
@@ -117,7 +117,7 @@ public function overlapAny(Period ...$others): PeriodCollection
      */
     public function subtract(Period ...$others): PeriodCollection
     {
-        if (count($others) === 0)
+        if (count($others) === 0) {
             return PeriodCollection::make($this);
         } else if (count($others) > 1) {
             return $this->subtractAll(...$others);
diff --git a/tests/Operations/OverlapTest.php b/tests/Operations/OverlapTest.php
index d65e770..1eb3f91 100644
--- a/tests/Operations/OverlapTest.php
+++ b/tests/Operations/OverlapTest.php
@@ -5,6 +5,7 @@
 use Generator;
 use PHPUnit\Framework\TestCase;
 use Spatie\Period\Period;
+use Spatie\Period\PeriodCollection;
 
 class OverlapTest extends TestCase
 {
@@ -178,4 +179,15 @@ public function noOverlappingDates()
          */
         yield [Period::make('2018-02-01', '2018-02-28'), Period::make('2018-01-01', '2018-01-31')];
     }
+
+    /** @test */
+    public function passing_empty_period_collection_returns_null()
+    {
+        $current = Period::make('2018-01-01', '2018-01-31');
+        $emptyCollection = new PeriodCollection;
+
+        $diff = $current->overlap(... $emptyCollection);
+
+        $this->assertNull($diff);
+    }
 }
diff --git a/tests/Operations/SubtractTest.php b/tests/Operations/SubtractTest.php
index 3789786..616a2e3 100644
--- a/tests/Operations/SubtractTest.php
+++ b/tests/Operations/SubtractTest.php
@@ -4,6 +4,7 @@
 
 use PHPUnit\Framework\TestCase;
 use Spatie\Period\Period;
+use Spatie\Period\PeriodCollection;
 
 class SubtractTest extends TestCase
 {
@@ -223,4 +224,17 @@ public function it_can_determine_multiple_diffs_for_sure()
         $this->assertTrue($diff[1]->equals(Period::make('2018-01-11', '2018-01-14')));
         $this->assertTrue($diff[2]->equals(Period::make('2018-01-21', '2018-01-31')));
     }
+
+    /** @test */
+    public function passing_empty_period_collection_returns_same_period_within_collection()
+    {
+        $current = Period::make('2018-01-01', '2018-01-31');
+        $emptyCollection = new PeriodCollection;
+
+        $diff = $current->subtract(... $emptyCollection);
+
+        $this->assertInstanceOf(PeriodCollection::class, $diff);
+        $this->assertCount(1, $diff);
+        $this->assertTrue($diff[0]->equals($current));
+    }
 }