Add a function to generate the opt-out javascript code (#52)

This adds a new method to the Twig extension to insert the JavaScript-based tracking opt-out code as described at https://developer.matomo.org/guides/in-depth-opt-out#opt-out-using-the-matomo-javascript-tracker).

Author: mpdude

README.md

@@ -37,6 +37,10 @@ Somewhere in your views, right before the closing `</body>` tag, insert
 
 This will add the appropriate Matomo tracking code as [described in the API reference](https://developer.matomo.org/api-reference/tracking-javascript#where-can-i-find-the-piwik-tracking-code).
 
+When you want to display the opt-out dialog as [described in the documentation](https://developer.matomo.org/guides/in-depth-opt-out#opt-out-using-the-matomo-javascript-tracker), use the following Twig code:
+
+    {{ piwik_opt_out_code() }}
+
 Configuration
 -------------
 You can configure the bundle in your `config.yml`. Full Example:

Tests/Twig/ExtensionTest.php

@@ -48,6 +48,13 @@ public function testPiwikCodeContainsHostName()
         self::assertStringContainsString($hostname, $extension->piwikCode());
     }
 
+    public function testPiwikOptOutCodeContainsHostName()
+    {
+        $hostname = 'myHost.de';
+        $extension = new Extension(false, 1, $hostname, false);
+        self::assertStringContainsString($hostname, $extension->piwikOptOutCode());
+    }
+
     public function testAdditionalApiCallsCanBeAdded()
     {
         $extension = new Extension(false, 1, 'my.host', false);

Twig/Extension.php

@@ -55,6 +55,7 @@ public function getFunctions(): array
         return [
             new TwigFunction('piwik_code', [$this, 'piwikCode'], ['is_safe' => ['html']]),
             new TwigFunction('piwik', [$this, 'piwikPush']),
+            new TwigFunction('piwik_opt_out_code', [$this, 'piwikOptOutCode'], ['is_safe' => ['html']]),
         ];
     }
 
@@ -107,6 +108,14 @@ public function piwikCode(): string
         return $piwikCode;
     }
 
+    public function piwikOptOutCode(): string
+    {
+        return <<<EOT
+<div id="matomo-opt-out"></div>
+<script src="https://{$this->piwikHost}/index.php?module=CoreAdminHome&action=optOutJS&divId=matomo-opt-out&language=auto&showIntro=1"></script>
+EOT;
+    }
+
     private function addDefaultApiCalls()
     {
         $this->paqs[] = ['enableLinkTracking'];