From bf14b0e87dc6174523c661b7de073fa952450d9f Mon Sep 17 00:00:00 2001
From: Mahdi Bagheri <mb.programmer@yahoo.com>
Date: Sat, 6 Feb 2021 00:39:27 +0330
Subject: [PATCH] bug fix add month algorithm and add a test to check it

---
 src/Traits/AdditionAndSubstraction.php | 16 ++++++++++------
 tests/CalendarTest.php                 |  3 ++-
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/src/Traits/AdditionAndSubstraction.php b/src/Traits/AdditionAndSubstraction.php
index c39d2b4..92fd7e0 100644
--- a/src/Traits/AdditionAndSubstraction.php
+++ b/src/Traits/AdditionAndSubstraction.php
@@ -11,7 +11,7 @@ public function addYear($count)
         $date = $this->currentCalendar->timestampToDate($this->timestamp + $this->timezoneOffset);
         $timestamp = $this->currentCalendar->dateToTimestamp($date->year + $count, $date->month, $date->day, $date->hour, $date->minute, $date->second);
         $this->timestamp = $timestamp - $this->timezoneOffset;
-        
+
         return $this;
     }
 
@@ -19,11 +19,15 @@ public function addMonth($count)
     {
         $date = $this->currentCalendar->timestampToDate($this->timestamp + $this->timezoneOffset);
         $totalMonth = $date->month + $count;
-        $year = $date->year + floor($totalMonth / 12);
-        $month = $totalMonth % 12;
-        $timestamp = $this->currentCalendar->dateToTimestamp($year, $month, $date->day, $date->hour, $date->minute, $date->second);
+        $year = $date->year + floor($totalMonth / 12) - (($totalMonth % 12) == 0 ? 1 : 0);
+        $month = ($totalMonth % 12) == 0 ? 12 : ($totalMonth % 12);
+
+        $daysInMonth = $this->currentCalendar->daysInMonth($year, $month);
+        $day = $date->day <= $daysInMonth ? $date->day : $daysInMonth;
+
+        $timestamp = $this->currentCalendar->dateToTimestamp($year, $month, $day, $date->hour, $date->minute, $date->second);
         $this->timestamp = $timestamp - $this->timezoneOffset;
-        
+
         return $this;
     }
 
@@ -107,7 +111,7 @@ public function subMinute($count)
     public function subSecond($count)
     {
         $this->timestamp = $this->timestamp - $count;
-        
+
         return $this;
     }
 }
\ No newline at end of file
diff --git a/tests/CalendarTest.php b/tests/CalendarTest.php
index 8511f7a..fa76d77 100644
--- a/tests/CalendarTest.php
+++ b/tests/CalendarTest.php
@@ -22,8 +22,9 @@ public function testJalaliDateTime()
         $this->assertTrue($pasoonate->jalali()->setDate(1399,12,11)->daysInMonth() === 30);
 
         $julianDayNumber = $pasoonate->jalali()->setDate(1399,12,11)->getJulianDayNumber();
-
         $this->assertTrue($pasoonate->jalali()->setJulianDayNumber($julianDayNumber)->gregorian()->getJulianDayNumber() == $julianDayNumber);
+
+        $this->assertEquals($pasoonate->jalali()->setDate(1399,1,31)->addMonth(11)->format('yyyy/MM/dd'), '1399/12/30');
     }
 
     public function testGregorianDateTime()