add setting

src/services/trackingcode/GA4TrackingCode.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace matfish\Optimum\services\trackingcode;
+
+use matfish\Optimum\records\Experiment;
+use matfish\Optimum\records\Variant;
+
+class GA4TrackingCode implements TrackingCode
+{
+    /**
+     * Generate the JavaScript tracking event code for GA4 using a Custom Dimension.
+     *
+     * @param Experiment $experiment
+     * @param Variant $variant
+     * @return string
+     */
+    public function generate(Experiment $experiment, Variant $variant): string
+    {
+        return <<<EOD
+        gtag('event','$experiment->handle', {'$experiment->handle':'$variant->name'});
+        EOD;
+    }
+}

src/services/trackingcode/MixpanelTrackingCode.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace matfish\Optimum\services\trackingcode;
+
+use matfish\Optimum\records\Experiment;
+use matfish\Optimum\records\Variant;
+
+class MixpanelTrackingCode implements TrackingCode
+{
+    /**
+     * Generate the JavaScript tracking event code for Mixpanel.
+     *
+     * @param Experiment $experiment
+     * @param Variant $variant
+     * @return string
+     */
+    public function generate(Experiment $experiment, Variant $variant): string
+    {
+        return <<<EOD
+mixpanel.track('\$experiment_started', {
+    'Experiment Name': '$experiment->handle',
+    'Variant Name': '$variant->name'
+});
+EOD;
+    }
+}
+

src/services/trackingcode/TrackingCode.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace matfish\Optimum\services\trackingcode;
+
+
+use matfish\Optimum\records\Experiment;
+use matfish\Optimum\records\Variant;
+
+interface TrackingCode
+{
+    /**
+     * Generate the JavaScript tracking event code.
+     *
+     * @param Experiment $experiment
+     * @param Variant $variant
+     * @return string
+     */
+    public function generate(Experiment $experiment, Variant $variant): string;
+}
+

src/services/trackingcode/TrackingCodeRetriever.php

@@ -0,0 +1,41 @@
+<?php
+
+namespace matfish\Optimum\services\trackingcode;
+
+use matfish\Optimum\Plugin as Optimum;
+use matfish\Optimum\records\Experiment;
+use matfish\Optimum\records\Variant;
+
+class TrackingCodeRetriever
+{
+    /**
+     * Retrieve the JavaScript tracking code.
+     *
+     * @param Experiment $experiment
+     * @param Variant $variant
+     * @return string
+     */
+    public function getTrackingCode(Experiment $experiment, Variant $variant): string
+    {
+        $settings = Optimum::getInstance()->getSettings();
+
+        if ($settings->fireEvent !== null) {
+            return ($settings->fireEvent)($experiment, $variant);
+        }
+
+        $trackingPlatform = $settings->trackingPlatform;
+
+        switch ($trackingPlatform) {
+            case 'ga4':
+                $trackingCode = new GA4TrackingCode();
+                break;
+            case 'mixpanel':
+                $trackingCode = new MixpanelTrackingCode();
+                break;
+            default:
+                throw new \InvalidArgumentException("Unsupported tracking platform: $trackingPlatform. Use the `fireEvent` config setting to specify a custom function.");
+        }
+
+        return $trackingCode->generate($experiment, $variant);
+    }
+}