A simple demo wp plugin to show how I add a second AMP tracker to AIWP

aiwp-jer-second-amp-tracker-plugin.php

<?php
/**
 * Plugin Name: AIWP Jer's Filter Demo
 * Plugin URI: https://jerclarke.org
 * Description: Simple demo of Jer's filters for AIWP
 * Author: Jer Clarke
 * Version: 0.1
 * Author URI: https://jerclarke.org
 * Text Domain: jer-demo
 * Domain Path: /languages
 */

$Jer_AIWP_AMP_Extra_Tracker_Demo = new Jer_AIWP_AMP_Extra_Tracker_Demo();

class Jer_AIWP_AMP_Extra_Tracker_Demo {

	public function __construct() {

		add_action('amp_post_template_footer', array( $this, 'action_amp_post_template_footer_to_create_custom_aiwp_amp_trackers' ), 1 );
		add_action('aiwp_analytics_amp_config', array($this, 'action_aiwp_analytics_amp_config'));
	}

	/**
	 * Create AIWP AMP objects for our custom tracker(s) and mark them to be filtered later
	 * 
	 * AIWP only supports one tracker and tracker object, which automatically has the 
	 * measurement_id configured in the plugin.
	 * 
	 * We hack around this by creating a second object right before the tracker code is output,
	 * then reconfiguring it to use our measurement_id with filters during display
	 * 
	 * Problem: We can't change AIWP_Tracking_GA4_AMP->measurement_id because it's `protected`
	 * 
	 * Solution: We set ->gv_override_measurement_id property in the new object upon creation
	 * then in ->filter_aiwp_amp_config_to_replace_measurement_id_for_custom_trackers() we use 
	 * the ->gv_override_measurement_id to update the config array that ultimately defines the 
	 * JSON output.
	 * 
	 * @return void
	 */
	public function action_amp_post_template_footer_to_create_custom_aiwp_amp_trackers() {
	
		$tracker_aiwp_amp = new AIWP_Tracking_GA4_AMP;
		
		$tracker_aiwp_amp->gv_override_measurement_id = "G-8KG160R08Q";
	}

	/**
	 * Filter the AIWP AMP tracker object to insert our custom configuration
	 * 
	 * The AIWP AMP object we filter here has a ->config array which is ultimately converted
	 * into JSON to feed into the Thyngster/google-analytics-4-for-amp <amp-analytics> setup.	
	 * 
	 * We must use ->get() and ->set() because the ->config property is `protected`
	 *
	 * @param AIWP_Tracking_GA4_AMP $aiwp_amp
	 * @return void
	 */
	public function action_aiwp_analytics_amp_config(AIWP_Tracking_GA4_AMP $aiwp_amp) {
		
		$config = $aiwp_amp->get();

		$config = $this->filter_aiwp_amp_config_to_replace_measurement_id_for_custom_trackers($config, $aiwp_amp);

		$aiwp_amp->set($config);

		return;
	}

	/**
	 * Filter AIWP AMP tracker $config array for our custom tracker to insert our custom ->measurement_id
	 * 
	 * @see $this->action_amp_post_template_footer_to_create_custom_aiwp_amp_trackers() docs for more details
	 * 
	 * Thyngster docs describing how to work with the config JSON array:
	 * @link https://www.thyngster.com/how-to-track-amp-pages-with-google-analytics-4
	 *
	 * @param array $config from AIWP_Tracking_GA4_AMP->get()
	 * @param AIWP_Tracking_GA4_AMP $aiwp_amp
	 * @return void
	 */
	public function filter_aiwp_amp_config_to_replace_measurement_id_for_custom_trackers($config, AIWP_Tracking_GA4_AMP $aiwp_amp) {
	
		// Only filter AIWP AMP trackers that we created and inserted a custom measurement_id into
		if (!isset($aiwp_amp->gv_override_measurement_id)) {

			return $config;
		}
		
		// We require this later, and if it's not here, the plugin is configured in a way we're not expecting
		if (!isset($config['vars']['GA4_MEASUREMENT_ID'])) {
			
			gv_error("ERROR GV_GA_Manager->filter_aiwp_amp_config_to_replace_measurement_id_for_custom_trackers() didn't find ");

			return $config;
		}

		/**
		 * There are two places where the measurement_id is stored:
		 * 
		 * "vars": {
		 *  	"GA4_MEASUREMENT_ID": "G-8KG160R08Q",
		 * 	...
		 * 	"config": {
		 * 		"G-8KG160R08Q": {
		 * 			"groups": "default"
		 * 		}
		 * 	}
		 * },
		 * 
		 * We update the first one directly, then replace the second one using
		 * the old value of the first one and the array. 
		 * 
		 * Hopefully this will ensure it behaves exactly the same as the main tracker
		 */
		
		$new_config = $config;

		$new_config['vars']['GA4_MEASUREMENT_ID'] = $aiwp_amp->gv_override_measurement_id;

		// Remove and back up the old config sub-array
		$previous_measurement_id = $config['vars']['GA4_MEASUREMENT_ID'];

		if (isset($config['vars']['config'][$previous_measurement_id])) {
			
			$config_array = $config['vars']['config'][$previous_measurement_id];
			unset($new_config['vars']['config'][$previous_measurement_id]);
			
			// Re-insert the old config sub-array but with the new measurement_id as it's key
			$new_config['vars']['config'][$aiwp_amp->gv_override_measurement_id] = $config_array;
		}

		return $new_config;
	}
}