Added diff method

README.md

@@ -639,7 +639,12 @@ public function getNextMonth(): Jalalian
 ```
 
 ---
+```php
+public function diff(Jalalian $ref): array
+$diff = (new Jalalian(1397, 5, 24))->diff(new Jalalian(1398, 6, 30));
+// output: [1, 1, 6]
 
+```
 ### CalendarUtils
 ---
 

src/Jalalian.php

@@ -754,4 +754,35 @@ public function getWeekOfMonth(): int
     {
         return floor(($this->day + 5 - $this->getDayOfWeek()) / 7) + 1;
     }
+
+    public function diff(Jalalian $ref): array
+    {
+        if ($this->equalsTo($ref)) {
+            return [0, 0, 0];
+        }
+
+        $biggerDate = $this->greaterThan($ref) ? $this : $ref;
+        $biggerYear = $biggerDate->getYear();
+        $biggerMonth = $biggerDate->getMonth();
+        $biggerDay = $biggerDate->getDay();
+        $smallerDate = $this->greaterThan($ref) ? $ref : $this;
+        $smallerYear = $smallerDate->getYear();
+        $smallerMonth = $smallerDate->getMonth();
+        $smallerDay = $smallerDate->getDay();
+
+        $yearDiff = $biggerYear - $smallerYear;
+        $monthDiff = $biggerMonth - $smallerMonth;
+        $dayDiff = $biggerDay - $smallerDay;
+        if ($dayDiff < 0) {
+            $dayDiff = $biggerDay +
+                $smallerDate->getEndDayOfMonth()->getDay() - $smallerDate->getDay();
+            $monthDiff--;
+        }
+        if ($monthDiff < 0) {
+            $monthDiff += 12;
+            $yearDiff--;
+        }
+
+        return [$yearDiff, $monthDiff, $dayDiff];
+    }
 }

tests/JalalianTest.php

@@ -370,4 +370,60 @@ public function testGetQuarter()
         $jDate = new Jalalian(1402, 7, 23);
         $this->assertEquals(3, $jDate->getQuarter());
     }
+
+    public function testdiff()
+    {
+        $jDate = new Jalalian(1401, 6, 26);
+
+        //same day
+        $this->assertEquals($jDate->diff(new Jalalian(1401, 6, 26)), [0, 0, 0]);
+
+        //year before
+        $this->assertEquals($jDate->diff(new Jalalian(1401, 6, 25)), [0, 0, 1]);
+
+        //day after
+        $this->assertEquals($jDate->diff(new Jalalian(1401, 6, 27)), [0, 0, 1]);
+
+        //same montt, same year, before
+        $this->assertEquals($jDate->diff(new Jalalian(1401, 6, 24)), [0, 0, 2]);
+
+        //same month, same year, after
+        $this->assertEquals($jDate->diff(new Jalalian(1401, 6, 28)), [0, 0, 2]);
+
+        //same year, before, smaller day
+        $this->assertEquals($jDate->diff(new Jalalian(1401, 4, 12)), [0, 2, 14]);
+
+        //same year, before, greater day
+        $this->assertEquals($jDate->diff(new Jalalian(1401, 4, 27)), [0, 1, 30]);
+
+        //same year, after, smaller day
+        $this->assertEquals($jDate->diff(new Jalalian(1401, 9, 10)), [0, 2, 15]);
+
+        //same year, after, greater day
+        $this->assertEquals($jDate->diff(new Jalalian(1401, 10, 28)), [0, 4, 2]);
+
+        //previous year, smaller month, smaller day
+        $this->assertEquals($jDate->diff(new Jalalian(1389, 4, 12)), [12, 2, 14]);
+
+        //previous year, smaller month, greater day
+        $this->assertEquals($jDate->diff(new Jalalian(1395, 4, 29)), [6, 1, 28]);
+
+        //previous year, greater month, smaller day
+        $this->assertEquals($jDate->diff(new Jalalian(1395, 9, 10)), [5, 9, 16]);
+
+        //previous year, greater month, greater day
+        $this->assertEquals($jDate->diff(new Jalalian(1395, 9, 30)), [5, 8, 26]);
+
+        //greater year, smaller month, smaller day
+        $this->assertEquals($jDate->diff(new Jalalian(1402, 4, 12)), [0, 9, 17]);
+
+        //greater year, smaller month, greater day
+        $this->assertEquals($jDate->diff(new Jalalian(1403, 4, 29)), [1, 10, 3]);
+
+        //greater year, greater month, smaller day
+        $this->assertEquals($jDate->diff(new Jalalian(1405, 9, 10)), [4, 2, 15]);
+
+        //greater year, greater month, greater day
+        $this->assertEquals($jDate->diff(new Jalalian(1405, 9, 30)), [4, 3, 4]);
+    }
 }