Update collection join method, its readme and test

README.md

@@ -86,7 +86,7 @@ contain both joined ranges.
 
 - getFrom - returns first date in range,
 - getTo - returns last date in range,
-- unwrap - get range in array format,
+- unwrap - gets range in array format,
 - intersect - finds intersection between current and given range,
 - overlaps - tests if current and given range overlap,
 - join - finds common range between current and given range,
@@ -105,10 +105,10 @@ That means calling `$coll->add(...)` twice on the same
 collection will create two instances and neither of them will
 contain both added ranges.
 
-- getRanges - get ranges in current collection,
-- unwrap - get underlying date ranges in array format,
-- add - add given ranges to collection,
+- getRanges - gets ranges in current collection,
+- unwrap - gets underlying date ranges in array format,
+- add - adds given ranges to collection,
 - includes - tests if collection includes given date or range,
-- join - joins ranges in current collection if possible,
+- join - adds given ranges to current collection and joins ranges in current collection if possible,
 - intersect - calculates all intersections with given ranges,
 - subtract - subtracts given ranges from current collection.

src/DateRangeCollection.php

@@ -139,12 +139,17 @@ public static function wrap($collection)
     }
 
     /**
+     * @param array|self $collection
      * @return static
      */
-    public function join()
+    public function join($collection = NULL)
     {
         $ranges = $this->ranges;
 
+        if ($collection) {
+            $ranges = array_merge($ranges, static::wrap($collection)->ranges);
+        }
+
         for ($i = 0; $i < count($ranges); $i++) {
             $a = $ranges[$i];
 

tests/DateRangeCollection/Join.phpt

@@ -28,4 +28,14 @@ Assert::equal([
     ['from' => new \DateTime('2017-01-01'), 'to' => new \DateTime('2017-12-31'),],
     ['from' => new \DateTime('2015-01-01'), 'to' => new \DateTime('2015-12-31'),],
     ['from' => new \DateTime('2015-01-01'), 'to' => new \DateTime('2016-12-30'),],
-]))->join()->unwrap());
+]))->join()->unwrap());
+
+Assert::equal([
+    ['from' => new \DateTime('2015-01-01'), 'to' => new \DateTime('2016-12-30'),],
+    ['from' => new \DateTime('2017-01-01'), 'to' => new \DateTime('2017-12-31'),],
+], (new \Danoha\DateRangeCollection([
+    ['from' => new \DateTime('2015-01-01'), 'to' => new \DateTime('2016-12-30'),],
+]))->join([
+    ['from' => new \DateTime('2017-01-01'), 'to' => new \DateTime('2017-12-31'),],
+    ['from' => new \DateTime('2015-01-01'), 'to' => new \DateTime('2015-12-31'),],
+])->unwrap());