PHP function to track events in Amplitude, using their HTTP API

amplitude_track_event.php

/*
 * Usage 1 - track an event
 * $arr_event = array("user_id" => $row['user_id'], "event_type" => "Login");
 * $arr_event['event_properties'] = array("login_method" => $arg['login_method'], "network" => $arg['network']);
 * track_event($arr_event);
 * 
 * Usage 2 - increment a user property
 * $arr_event = array("user_id" => $row['user_id'], "event_type" => "increment");
 * $arr_event['user_properties'] = array("count_logins" => 1);
 * track_event($arr_event);
 */
function track_event($arr_event)
{
	global $arr_config;

	// https://amplitude.com/docs/api/http

	// $arr_event = array()
	// "user_id" => 71
	// "event_type" => "View Profile" / "increment"
	// "event_properties" => array("prop_key" => "prop_value")
	// "user_properties" => array("prop_key" => "prop_value")

	if(!isset($arr_event['user_id'])) // PHP event tracking requires a user_id to log.
	{
		return;
	}

	// always send day and hour (so we can segment on day of week, and time of day) - NB: these should (hopefully) be in the user's local timezone
	$arr_event['event_properties']['day'] = date("D");
	$arr_event['event_properties']['hour'] = date("H");

	// add any UTM params that may be in the URL
	if(isset($_REQUEST['utm_medium']) && isset($_REQUEST['utm_source']) && isset($_REQUEST['utm_campaign']))
	{
		$arr_event['event_properties']['utm_medium'] = $_REQUEST['utm_medium'];
		$arr_event['event_properties']['utm_source'] = $_REQUEST['utm_source'];
		$arr_event['event_properties']['utm_campaign'] = $_REQUEST['utm_campaign'];
	}

	if($arr_event['event_type'] == "increment") // if we're incrementing user_properties
	{
		unset($arr_event['event_type']); // don't need to send this to Amplitude
		unset($arr_event['event_properties']); // don't need to send this to Amplitude for identify
		
		$arr_event['user_properties'] = array('$'.'add' => $arr_event['user_properties']); // nest the values within an $add array key
		
		$command = "curl -sS --data 'api_key=".$arr_config['amplitude_api_key']."' --data 'identification=[".json_encode($arr_event)."]' https://api.amplitude.com/identify";
		exec($command." > /dev/null &");
	}
	else // track normal event
	{
		// add some generic info
		if(!isset($arr_event['time'])) // allow time to be set manually if desired
		{
			$arr_event['time'] = date("U")."000";
		}

		$arr_event['ip'] = $_SERVER['REMOTE_ADDR'];

		$command = "curl -sS --data 'api_key=".$arr_config['amplitude_api_key']."' --data-urlencode 'event=[".json_encode($arr_event)."]' https://api.amplitude.com/httpapi";
		exec($command." > /dev/null &");
	}
}