Concatenation adapter

README.md

@@ -350,6 +350,19 @@ $results = array(/* ... */);
 $adapter = new FixedAdapter($nbResults, $results);
 ```
 
+### ConcatenationAdapter
+
+Concatenates the results of other adapter instances into a single adapter.
+It keeps the order of sub adapters and the order of their results.
+
+```php
+<?php
+
+use Pagerfanta\Adapter\ConcatenationAdapter;
+
+$superAdapter = new ConcatenationAdapter(array($adapter1, $adapter2 /* ... */));
+```
+
 ## Views
 
 Views are to render pagerfantas, this way you can reuse your

src/Pagerfanta/Adapter/ConcatenationAdapter.php

@@ -0,0 +1,126 @@
+<?php
+
+namespace Pagerfanta\Adapter;
+
+use Pagerfanta\Exception\InvalidArgumentException;
+
+/**
+ * Adapter that concatenates the results of other adapters.
+ *
+ * @author Surgie Finesse <finesserus@gmail.com>
+ */
+class ConcatenationAdapter implements AdapterInterface
+{
+    /**
+     * @var AdapterInterface[] List of adapters
+     */
+    protected $adapters;
+
+    /**
+     * @var int[]|null Cache of the numbers of results of the adapters. The indexes correspond the indexes of the
+     * `adapters` property.
+     */
+    protected $adaptersNbResultsCache;
+
+    /**
+     * @param AdapterInterface[] $adapters
+     * @throws InvalidArgumentException
+     */
+    public function __construct(array $adapters)
+    {
+        foreach ($adapters as $index => $adapter) {
+            if (!($adapter instanceof AdapterInterface)) {
+                throw new InvalidArgumentException(sprintf(
+                    'Argument $adapters[%s] expected to be a \Pagerfanta\Adapter\AdapterInterface instance, a %s given',
+                    $index,
+                    is_object($adapter) ? sprintf('%s instance', get_class($adapter)) : gettype($adapter)
+                ));
+            }
+        }
+
+        $this->adapters = $adapters;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getNbResults()
+    {
+        if (!isset($this->adaptersNbResultsCache)) {
+            $this->refreshAdaptersNbResults();
+        }
+
+        return array_sum($this->adaptersNbResultsCache);
+    }
+
+    /**
+     * {@inheritdoc}
+     * @return array
+     */
+    public function getSlice($offset, $length)
+    {
+        if (!isset($this->adaptersNbResultsCache)) {
+            $this->refreshAdaptersNbResults();
+        }
+
+        $slice = array();
+        $previousAdaptersNbResultsSum = 0;
+        $requestFirstIndex = $offset;
+        $requestLastIndex  = $offset + $length - 1;
+
+        foreach ($this->adapters as $index => $adapter) {
+            $adapterNbResults  = $this->adaptersNbResultsCache[$index];
+            $adapterFirstIndex = $previousAdaptersNbResultsSum;
+            $adapterLastIndex  = $adapterFirstIndex + $adapterNbResults - 1;
+
+            $previousAdaptersNbResultsSum += $adapterNbResults;
+
+            // The adapter is fully below the requested slice range — skip it
+            if ($adapterLastIndex < $requestFirstIndex) {
+                continue;
+            }
+
+            // The adapter is fully above the requested slice range — finish the gathering
+            if ($adapterFirstIndex > $requestLastIndex) {
+                break;
+            }
+
+            // Else the adapter range definitely intersects with the requested range
+            $fetchOffset = $requestFirstIndex - $adapterFirstIndex;
+            $fetchLength = $length;
+
+            // The requested range start is below the adapter range start
+            if ($fetchOffset < 0) {
+                $fetchLength += $fetchOffset;
+                $fetchOffset = 0;
+            }
+
+            // The requested range end is above the adapter range end
+            if ($fetchOffset + $fetchLength > $adapterNbResults) {
+                $fetchLength = $adapterNbResults - $fetchOffset;
+            }
+
+            // Getting the subslice from the adapter and adding it to the result slice
+            $fetchSlice = $adapter->getSlice($fetchOffset, $fetchLength);
+            foreach ($fetchSlice as $item) {
+                $slice[] = $item;
+            }
+        }
+
+        return $slice;
+    }
+
+    /**
+     * Refreshes the cache of the numbers of results of the adapters.
+     */
+    protected function refreshAdaptersNbResults()
+    {
+        if (!isset($this->adaptersNbResultsCache)) {
+            $this->adaptersNbResultsCache = array();
+        }
+
+        foreach ($this->adapters as $index => $adapter) {
+            $this->adaptersNbResultsCache[$index] = $adapter->getNbResults();
+        }
+    }
+}

tests/Pagerfanta/Tests/Adapter/ConcatenationAdapterTest.php

@@ -0,0 +1,86 @@
+<?php
+
+namespace Pagerfanta\Tests\Adapter;
+
+use Pagerfanta\Adapter\ArrayAdapter;
+use Pagerfanta\Adapter\CallbackAdapter;
+use Pagerfanta\Adapter\ConcatenationAdapter;
+use Pagerfanta\Adapter\FixedAdapter;
+use Pagerfanta\Adapter\NullAdapter;
+use PHPUnit\Framework\TestCase;
+
+class ConcatenationAdapterTest extends TestCase
+{
+    public function testConstructor()
+    {
+        new ConcatenationAdapter(array(
+            new ArrayAdapter(array()),
+            new NullAdapter(),
+            new FixedAdapter(0, array())
+        ));
+
+        $this->setExpectedException(
+            '\Pagerfanta\Exception\InvalidArgumentException',
+            'Argument $adapters[1] expected to be a \Pagerfanta\Adapter\AdapterInterface instance, a string given'
+        );
+        new ConcatenationAdapter(array(
+            new ArrayAdapter(array()),
+            'foo'
+        ));
+    }
+
+    public function testGetNbResults()
+    {
+        $adapter = new ConcatenationAdapter(array(
+            new ArrayAdapter(array('foo', 'bar', 'baz'))
+        ));
+        $this->assertEquals(3, $adapter->getNbResults());
+
+        $adapter = new ConcatenationAdapter(array(
+            new ArrayAdapter(array_fill(0, 4, 'foo')),
+            new ArrayAdapter(array_fill(0, 6, 'bar')),
+            new ArrayAdapter(array('baq'))
+        ));
+        $this->assertEquals(11, $adapter->getNbResults());
+
+        $adapter = new ConcatenationAdapter(array());
+        $this->assertEquals(0, $adapter->getNbResults());
+    }
+
+    public function testGetResults()
+    {
+        $adapter = new ConcatenationAdapter(array(
+            new ArrayAdapter(array(1, 2, 3, 4, 5, 6)),
+            new ArrayAdapter(array(7, 8, 9, 10, 11, 12, 13, 14)),
+            new ArrayAdapter(array(15, 16, 17))
+        ));
+        $this->assertEquals(array(8, 9, 10), $adapter->getSlice(7, 3));
+        $this->assertEquals(array(5, 6, 7, 8), $adapter->getSlice(4, 4));
+        $this->assertEquals(array(6, 7, 8, 9, 10, 11, 12, 13, 14, 15), $adapter->getSlice(5, 10));
+        $this->assertEquals(array(16, 17), $adapter->getSlice(15, 5));
+    }
+
+    public function testWithTraversableAdapter()
+    {
+        $adapter = new ConcatenationAdapter(array(
+            new CallbackAdapter(
+                function () {
+                    return 5;
+                },
+                function ($offset, $length) {
+                    return new \ArrayIterator(array_slice(array(1, 2, 3, 4, 5), $offset, $length));
+                }
+            ),
+            new CallbackAdapter(
+                function () {
+                    return 3;
+                },
+                function ($offset, $length) {
+                    return new \ArrayIterator(array_slice(array(6, 7, 8), $offset, $length));
+                }
+            )
+        ));
+        $this->assertEquals(array(2, 3), $adapter->getSlice(1, 2));
+        $this->assertEquals(array(4, 5, 6), $adapter->getSlice(3, 3));
+    }
+}