Sort filter values in a locale aware way

src/Filters/Block.php

@@ -906,14 +906,23 @@ private function getFeaturesBlock($filter, $selectedFilters, $idLang)
      */
     private function sortFeatureBlock($featureBlock)
     {
+        $collator = $this->getValuesCollator();
+
         //Natural sort
         foreach ($featureBlock as $key => $value) {
             $temp = [];
             foreach ($featureBlock[$key]['values'] as $idFeatureValue => $featureValueInfos) {
                 $temp[$idFeatureValue] = $featureValueInfos['name'];
             }
 
-            natcasesort($temp);
+            if ($collator !== null) {
+                // Locale aware sort so accented characters (e.g. Czech č, š, ř) are ordered
+                // according to the current language rules instead of by their raw byte value,
+                // which pushed them after every plain ASCII letter.
+                $collator->asort($temp);
+            } else {
+                natcasesort($temp);
+            }
             $temp2 = [];
 
             foreach ($temp as $keytemp => $valuetemp) {
@@ -926,6 +935,37 @@ private function sortFeatureBlock($featureBlock)
         return $featureBlock;
     }
 
+    /**
+     * Builds a locale aware collator for sorting filter values, or null when the intl
+     * extension is not available (the caller then falls back to natcasesort()).
+     *
+     * @return \Collator|null
+     */
+    private function getValuesCollator()
+    {
+        if (!class_exists('Collator')) {
+            return null;
+        }
+
+        $locale = isset($this->context->language->locale) ? $this->context->language->locale : '';
+        if ($locale === '') {
+            // No usable locale (e.g. a language without one configured); fall back to natcasesort.
+            return null;
+        }
+
+        $collator = collator_create($locale);
+        if ($collator === null) {
+            return null;
+        }
+
+        // Case insensitive (as natcasesort was) but accent and locale aware.
+        $collator->setStrength(\Collator::SECONDARY);
+        // Keep the "natural" numeric ordering natcasesort provided (e.g. 2 before 10).
+        $collator->setAttribute(\Collator::NUMERIC_COLLATION, \Collator::ON);
+
+        return $collator;
+    }
+
     /**
      * Add the categories filter condition based on the parent and config variables
      *

tests/php/FacetedSearch/Filters/BlockTest.php

@@ -1189,6 +1189,48 @@ private function mockLayeredCategory($result)
             ->andReturn($result);
     }
 
+    /**
+     * Feature filter values must be sorted in a locale aware way: accented characters such as the
+     * Czech "Č" have to be ordered next to their base letter instead of after every ASCII letter.
+     *
+     * @see https://github.com/PrestaShop/ps_facetedsearch/issues/1201
+     */
+    public function testSortFeatureBlockSortsValuesLocaleAware()
+    {
+        if (!class_exists('Collator')) {
+            $this->markTestSkipped('The intl extension is required for locale aware sorting.');
+        }
+
+        $this->contextMock->language->locale = 'cs-CZ';
+
+        $featureBlock = [
+            10 => [
+                'values' => [
+                    1 => ['name' => 'Value'],
+                    2 => ['name' => 'Else'],
+                    3 => ['name' => 'Beta'],
+                    4 => ['name' => 'Černá'],
+                    5 => ['name' => 'Czech'],
+                    6 => ['name' => 'Other'],
+                    7 => ['name' => 'Alpha'],
+                ],
+            ],
+        ];
+
+        $method = new \ReflectionMethod(Block::class, 'sortFeatureBlock');
+        $method->setAccessible(true);
+        $sorted = $method->invoke($this->block, $featureBlock);
+
+        $names = array_values(array_map(function ($value) {
+            return $value['name'];
+        }, $sorted[10]['values']));
+
+        $this->assertSame(
+            ['Alpha', 'Beta', 'Czech', 'Černá', 'Else', 'Other', 'Value'],
+            $names
+        );
+    }
+
     private function getPriceSpecificationMock()
     {
         // Mock symbols