[POC] Allow activating feature flags using cookies

plugins/CoreConsole/FeatureFlags/CliMultiProcessSymfony.php

@@ -19,4 +19,9 @@ public function getName(): string
     {
         return 'CliMultiProcessSymfony';
     }
+
+    public function allowsCookieOverwrite(): bool
+    {
+        return false;
+    }
 }

plugins/CoreConsole/FeatureFlags/SystemSignals.php

@@ -19,4 +19,9 @@ public function getName(): string
     {
         return 'SystemSignals';
     }
+
+    public function allowsCookieOverwrite(): bool
+    {
+        return true;
+    }
 }

plugins/CustomDimensions/FeatureFlags/CustomDimensionReportWithRollUp.php

@@ -19,4 +19,9 @@ public function getName(): string
     {
         return 'CustomDimensionReportWithRollUp';
     }
+
+    public function allowsCookieOverwrite(): bool
+    {
+        return false;
+    }
 }

plugins/FeatureFlags/FeatureFlagInterface.php

@@ -12,4 +12,6 @@
 interface FeatureFlagInterface
 {
     public function getName(): string;
+
+    public function allowsCookieOverwrite(): bool;
 }

plugins/FeatureFlags/FeatureFlagManager.php

@@ -46,17 +46,15 @@ public function isFeatureActive(string $featureFlag): bool
             return $featureFlagObj->getForcedFeatureFlagState();
         }
 
-        $featureActive = false;
-
         foreach ($this->storages as $storage) {
             $isActive = $storage->isFeatureActive($featureFlagObj);
 
             if ($isActive !== null) {
-                $featureActive = $isActive;
+                return $isActive;
             }
         }
 
-        return $featureActive;
+        return false;
     }
 
     /**

plugins/FeatureFlags/FeatureFlags/Example.php

@@ -17,4 +17,9 @@ public function getName(): string
     {
         return 'Example';
     }
+
+    public function allowsCookieOverwrite(): bool
+    {
+        return false;
+    }
 }

plugins/FeatureFlags/Storage/CookieFeatureFlagStorage.php

@@ -0,0 +1,63 @@
+<?php
+
+/**
+ * Matomo - free/libre analytics platform
+ *
+ * @link    https://matomo.org
+ * @license https://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ */
+
+namespace Piwik\Plugins\FeatureFlags\Storage;
+
+use Piwik\Plugins\FeatureFlags\FeatureFlagInterface;
+use Piwik\Plugins\FeatureFlags\FeatureFlagStorageInterface;
+
+class CookieFeatureFlagStorage implements FeatureFlagStorageInterface
+{
+    /**
+     * @internal
+     */
+    public function isFeatureActive(FeatureFlagInterface $feature): ?bool
+    {
+        if (!$feature->allowsCookieOverwrite()) {
+            return false;
+        }
+
+        $cookieName = $this->getCookieNameForFeature($feature->getName());
+
+        if (!isset($_COOKIE[$cookieName])) {
+            return null;
+        }
+
+        return $_COOKIE[$cookieName] == '1';
+    }
+
+    /**
+     * @internal
+     */
+    public function disableFeatureFlag(FeatureFlagInterface $feature): void
+    {
+        // do nothing, as cookie values should only be set in frontend
+    }
+
+    /**
+     * @internal
+     */
+    public function enableFeatureFlag(FeatureFlagInterface $feature): void
+    {
+        // do nothing as cookie values should only be set in frontend
+    }
+
+    /**
+     * @internal
+     */
+    public function deleteFeatureFlag(string $featureName): void
+    {
+        // do nothing as cookie values should only be set in frontend
+    }
+
+    private function getCookieNameForFeature(string $featureName): string
+    {
+        return 'feature_' . $featureName;
+    }
+}

plugins/FeatureFlags/config/config.php

@@ -13,6 +13,7 @@
      * The first one will be overwritten by the second one (if set).
      */
     'featureflag.storages' => [
+        DI::get('Piwik\Plugins\FeatureFlags\Storage\CookieFeatureFlagStorage'),
         DI::get('Piwik\Plugins\FeatureFlags\Storage\ConfigFeatureFlagStorage'),
     ],
     /**

plugins/FeatureFlags/tests/Integration/FeatureFlags/FakeFeatureFlag.php

@@ -17,4 +17,9 @@ public function getName(): string
     {
         return 'NotReal';
     }
+
+    public function allowsCookieOverwrite(): bool
+    {
+        return false;
+    }
 }

plugins/FeatureFlags/tests/System/Commands/FeatureFlags/FakeFeatureFlag.php

@@ -17,4 +17,9 @@ public function getName(): string
     {
         return 'SystemTest';
     }
+
+    public function allowsCookieOverwrite(): bool
+    {
+        return false;
+    }
 }

plugins/FeatureFlags/tests/Unit/FeatureFlagManagerTest.php

@@ -61,7 +61,7 @@
             $logger
         );
 
         $this->assertEquals($expectedOutcome, $sut->isFeatureActive(get_class($mockFeature)));
     }
 
     public function testIsFeatureActiveReturnsForcedStateWithoutConsultingStorages(): void
@@ -82,6 +82,11 @@
             {
                 return true;
             }
+
+            public function allowsCookieOverwrite(): bool
+            {
+                return false;
+            }
         };
 
         $this->assertTrue($sut->isFeatureActive(get_class($featureFlag)));