Implement LimitedAdapter (closes #244).

src/Pagerfanta/Adapter/LimitedAdapter.php

@@ -0,0 +1,41 @@
+<?php
+
+/*
+ * This file is part of the Pagerfanta package.
+ *
+ * (c) Pablo Díez <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Pagerfanta\Adapter;
+
+/**
+ * Adapter that allows limit maximum number of results. It can be useful for preventing
+ * slow down queries with large offsets or get rid of errors like "result window too large".
+ *
+ * @author Konstantin Myakshin <[email protected]>
+ */
+class LimitedAdapter implements AdapterInterface
+{
+    private $decorated;
+
+    private $maxNbResults;
+
+    public function __construct(AdapterInterface $decorated, int $maxNbResults)
+    {
+        $this->decorated = $decorated;
+        $this->maxNbResults = $maxNbResults;
+    }
+
+    public function getNbResults()
+    {
+        return min($this->decorated->getNbResults(), $this->maxNbResults);
+    }
+
+    public function getSlice($offset, $length)
+    {
+        return $this->decorated->getSlice($offset, $length);
+    }
+}

tests/Pagerfanta/Tests/Adapter/LimitedAdapterTest.php

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+<?php
+
+namespace Pagerfanta\Tests\Adapter;
+
+use Pagerfanta\Adapter\AdapterInterface;
+use Pagerfanta\Adapter\LimitedAdapter;
+use PHPUnit\Framework\TestCase;
+
+class LimitedAdapterTest extends TestCase
+{
+    /**
+     * @dataProvider nbResultsProvider
+     */
+    public function testNbResults(int $nbResultsFromAdapter, int $maxNbResults, int $result)
+    {
+        $decorated = $this->createMock(AdapterInterface::class);
+
+        $decorated
+            ->expects($this->once())
+            ->method('getNbResults')
+            ->will($this->returnValue($nbResultsFromAdapter)));
+
+        $adapter = new LimitedAdapter($decorated, $maxNbResults);
+        $this->assertSame($result, $adapter->getNbResults());
+    }
+
+    public function testGetSlice()
+    {
+        $decorated = $this->createMock(AdapterInterface::class);
+        $offset = 0;
+        $limit = 5;
+        $result = [0, 1, 2, 3, 4];
+
+        $decorated
+            ->expects($this->once())
+            ->method('getSlice')
+            ->with($offset, $limit)
+            ->will($this->returnValue($result));
+
+        $adapter = new LimitedAdapter($decorated, 100);
+        $this->assertSame($result, $adapter->getSlice($offset, $limit));
+    }
+
+    public function nbResultsProvider()
+    {
+        yield 'Adapter returns more results than allowed.' => [100, 90, 90];
+
+        yield 'Adapter returns less results than allowed.' => [100, 1000, 100];
+    }
+}