[LIB][Util] Add Ring Buffer data structure

src/Util/ds/RingBuffer.php

@@ -0,0 +1,58 @@
+<?php
+
+// {{{ License
+// This file is part of GNU social - https://www.gnu.org/software/social
+//
+// GNU social is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GNU social is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with GNU social.  If not, see <http://www.gnu.org/licenses/>.
+// }}}
+
+namespace App\Util\ds;
+
+use Ds\Deque;
+use Functional as F;
+
+class RingBuffer implements \Serializable
+{
+    private int $capacity;
+    private Deque $elements;
+
+    public function __construct(int $c)
+    {
+        $this->capacity = $c;
+        $this->elements = new Deque();
+    }
+
+    public function serialize()
+    {
+        return serialize($this->capacity) . serialize($this->elements);
+    }
+
+    public function unserialize($data)
+    {
+        list($this->capacity, $this->elements) = F\map(explode(';', $data), F\ary('unserialize', 1));
+    }
+
+    public function add($e)
+    {
+        if ($this->capacity !== 0 && $this->elements->count() >= $this->capacity) {
+            $this->elements->shift();
+        }
+        $this->elements->unshift($e);
+    }
+
+    public function remove(int $index)
+    {
+        return $this->elements->remove($index);
+    }
+}