Issue #2598298 by mollux, borisson_: Create Facet processors - Do now show facet with only X items

src/Plugin/facetapi/processor/MinimumCountProcessor.php

+<?php
+/**
+ * @file
+ * Contains \Drupal\facetapi\Plugin\facetapi\processor.
+ */
+
+namespace Drupal\facetapi\Plugin\facetapi\processor;
+
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\facetapi\FacetInterface;
+use Drupal\facetapi\Processor\BuildProcessorInterface;
+use Drupal\facetapi\Processor\ProcessorPluginBase;
+use Drupal\facetapi\Result\Result;
+
+/**
+ * Provides a minimum count processor..
+ *
+ * @FacetApiProcessor(
+ *   id = "minimum_count",
+ *   label = @Translation("Minimum count"),
+ *   description = @Translation("Hide facets with less than x items."),
+ *   stages = {
+ *     "build" = 50
+ *   }
+ * )
+ */
+class MinimumCountProcessor extends ProcessorPluginBase implements BuildProcessorInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build(FacetInterface $facet, array $results) {
+    $processor_configs = $facet->getProcessorConfigs();
+    $config = $processor_configs[$this->getPluginId()];
+
+    /** @var Result $result */
+    foreach ($results as $id => $result) {
+      if ($result->getCount() < $config['settings']['minimum_items']) {
+        unset($results[$id]);
+      }
+    }
+
+    return $results;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildConfigurationForm(array $form, FormStateInterface $form_state, FacetInterface $facet) {
+    $processor_configs = $facet->getProcessorConfigs();
+    $config = $processor_configs[$this->getPluginId()];
+
+    $build['minimum_items'] = array(
+      '#title' => 'Minimum items',
+      '#type' => 'number',
+      '#min' => 1,
+      '#default_value' => $config['settings']['minimum_items'],
+      '#description' => 'Hide block if the facet contains less than this number of results',
+    );
+
+    return $build;
+  }
+
+}

tests/src/Unit/Plugin/processor/MinimumCountProcessorTest.php

+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Tests\facetapi\Plugin\Processor\MinimumCountProcessorTest.
+ */
+
+namespace Drupal\Tests\facetapi\Unit\Plugin\Processor;
+
+use Drupal\facetapi\Entity\Facet;
+use Drupal\facetapi\Plugin\facetapi\processor\MinimumCountProcessor;
+use Drupal\facetapi\Processor\BuildProcessorInterface;
+use Drupal\facetapi\Result\Result;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @group facetapi
+ */
+class MinimumCountProcessorTest extends UnitTestCase {
+
+  /**
+   * The processor to be tested.
+   *
+   * @var BuildProcessorInterface
+   */
+  protected $processor;
+
+  /**
+   * An array containing the results before the processor has ran.
+   *
+   * @var \Drupal\facetapi\Result\Result[]
+   */
+  protected $original_results;
+
+  /**
+   * Creates a new processor object for use in the tests.
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->original_results = [
+      new Result('llama', 10),
+      new Result('badger', 5),
+      new Result('duck', 15),
+    ];
+
+    $this->processor = new MinimumCountProcessor([], 'minimum_count', []);
+  }
+
+  /**
+   * Test filtering of results
+   */
+  public function testFilterResults() {
+
+    $facet = new Facet([], 'facet');
+    $facet->setResults($this->original_results);
+    $facet->setProcessorConfigs([
+      'minimum_count' => [
+        'settings' => ['minimum_items' => 6]
+      ]
+    ]);
+
+    $sorted_results = $this->processor->build($facet, $this->original_results);
+
+    $this->assertCount(2, $sorted_results);
+
+    $this->assertEquals(10, $sorted_results[0]->getCount());
+    $this->assertEquals('llama', $sorted_results[0]->getValue());
+    $this->assertEquals(15, $sorted_results[2]->getCount());
+    $this->assertEquals('duck', $sorted_results[2]->getValue());
+  }
+
+}