Add Tail and Reverse Operations.

README.md

@@ -111,6 +111,17 @@ Collection::with(['A' => 'A', 'B' => 'B', 'C' => 'C', 'D' => 'D', 'E' => 'E'])
     )
     ->all(); // [0 => 'a', 1 => 'b', 2 => 'c', 3 = >'d', 4 => 'e']
 
+// Tail
+Collection::with(range('a', 'z'))
+    ->tail(3)
+    ->all(); // [23 => 'x', 24 => 'y', 25 => 'z']
+
+// Reverse
+Collection::with(range('a', 'z'))
+    ->tail(4)
+    ->reverse()
+    ->all(); // [25 => 'z', 24 => 'y', 23 => 'x', 22 => 'w']
+
 Collection::with(['A' => 'A', 'B' => 'B', 'C' => 'C', 'D' => 'D', 'E' => 'E'])
     ->walk(
         static function ($value, $key) {

spec/drupol/collection/CollectionSpec.php

@@ -918,6 +918,20 @@ static function ($carry, $item) {
             ->shouldIterateAs([0, 1, 3, 6, 10, 15]);
     }
 
+    public function it_can_reverse(): void
+    {
+        $this
+            ->beConstructedThrough('with', [range('A', 'F')]);
+
+        $this
+            ->reverse()
+            ->shouldIterateAs([5 => 'F', 4 => 'E', 3 => 'D', 2 => 'C', 1 => 'B', 0 => 'A']);
+
+        $this
+            ->skip(3, 3)
+            ->shouldIterateAs([]);
+    }
+
     public function it_can_rsample(): void
     {
         $this
@@ -1066,6 +1080,24 @@ public function it_can_split(): void
             ->shouldIterateAs([0 => [1, 2, 3], 1 => [4, 5, 6], 2 => [7, 8, 9], 3 => [10, 11, 12], 4 => [13, 14, 15]]);
     }
 
+    public function it_can_tail(): void
+    {
+        $this
+            ->beConstructedThrough('with', [range('A', 'F')]);
+
+        $this
+            ->tail(3)
+            ->shouldIterateAs([3 => 'D', 4 => 'E', 5 => 'F']);
+
+        $this
+            ->tail(-5)
+            ->shouldIterateAs([]);
+
+        $this
+            ->tail(100)
+            ->shouldIterateAs(range('A', 'F'));
+    }
+
     public function it_can_until(): void
     {
         $collatz = static function (int $initial = 1): int {

src/Collection.php

@@ -30,11 +30,13 @@
 use drupol\collection\Operation\Prepend;
 use drupol\collection\Operation\Range;
 use drupol\collection\Operation\Reduction;
+use drupol\collection\Operation\Reverse;
 use drupol\collection\Operation\Scale;
 use drupol\collection\Operation\Skip;
 use drupol\collection\Operation\Slice;
 use drupol\collection\Operation\Sort;
 use drupol\collection\Operation\Split;
+use drupol\collection\Operation\Tail;
 use drupol\collection\Operation\Until;
 use drupol\collection\Operation\Walk;
 use drupol\collection\Operation\Zip;
@@ -410,6 +412,16 @@ public function reduction(callable $callback, $initial = null): BaseInterface
         return $this->run(new Reduction($callback, $initial));
     }
 
+    /**
+     * {@inheritdoc}
+     *
+     * @return \drupol\collection\Contract\Collection
+     */
+    public function reverse(): BaseInterface
+    {
+        return $this->run(new Reverse());
+    }
+
     /**
      * {@inheritdoc}
      *
@@ -477,6 +489,16 @@ public function split(callable ...$callbacks): BaseInterface
         return $this->run(new Split(...$callbacks));
     }
 
+    /**
+     * {@inheritdoc}
+     *
+     * @return \drupol\collection\Contract\Collection
+     */
+    public function tail(int $length): BaseInterface
+    {
+        return $this->run(new Tail($length));
+    }
+
     /**
      * {@inheritdoc}
      *

src/Contract/Collection.php

@@ -43,12 +43,14 @@ interface Collection extends
     Rebaseable,
     Reduceable,
     Reductionable,
+    Reverseable,
     RSampleable,
     Scaleable,
     Skipable,
     Sliceable,
     Sortable,
     Splitable,
+    Tailable,
     Untilable,
     Walkable,
     Zipable

src/Contract/Reverseable.php

@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace drupol\collection\Contract;
+
+/**
+ * Interface Reverseable.
+ */
+interface Reverseable
+{
+    /**
+     * TODO.
+     *
+     * @return \drupol\collection\Contract\Collection<mixed>
+     */
+    public function reverse(): Base;
+}

src/Contract/Tailable.php

@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace drupol\collection\Contract;
+
+/**
+ * Interface Tailable.
+ */
+interface Tailable
+{
+    /**
+     * @param int $length
+     *
+     * @return \drupol\collection\Contract\Collection<mixed>
+     */
+    public function tail(int $length): Base;
+}

src/Operation/Reverse.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace drupol\collection\Operation;
+
+use Closure;
+use drupol\collection\Contract\Operation;
+use drupol\collection\Transformation\All;
+use Generator;
+
+/**
+ * Class Reverse.
+ */
+final class Reverse implements Operation
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function on(iterable $collection): Closure
+    {
+        return static function () use ($collection): Generator {
+            $all = (new All())->on($collection);
+
+            for (end($all); null !== ($key = key($all)); prev($all)) {
+                yield $key => current($all);
+            }
+        };
+    }
+}

src/Operation/Tail.php

@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace drupol\collection\Operation;
+
+use Closure;
+use drupol\collection\Contract\Operation;
+use drupol\collection\Transformation\Count;
+use Generator;
+
+/**
+ * Class Tail.
+ */
+final class Tail implements Operation
+{
+    /**
+     * @var int
+     */
+    private $length;
+
+    /**
+     * Tail constructor.
+     *
+     * @param int $length
+     */
+    public function __construct(int $length)
+    {
+        $this->length = $length;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function on(iterable $collection): Closure
+    {
+        $offset = (new Count())->on($collection) - $this->length;
+        $length = $this->length;
+
+        return static function () use ($offset, $length, $collection): Generator {
+            yield from (new Limit($length))->on((new Skip($offset))->on($collection)())();
+        };
+    }
+}