Kissmetrics plugin for WordPress with a simplified class based on their default library

kissmetrics.php

<?php

/*
	Plugin Name: WP Kissmetrics
	Description: Record events using Kissmetrics' PHP API. Intended to be used by developers only.
	Author: evansolomon
	Version: 1.0
*/

/* Forked from https://github.com/kissmetrics/KISSmetrics/blob/master/km.php */

define( 'KISSMETRICS_HOST', 'http://trk.kissmetrics.com:80' );
define( 'KISSMETRICS_API_KEY', /* Your api key here */ );

class WP_Kissmetrics {
	static $id   = null;
	static $key  = null;
	static $time = null;

	/**
	 * Takes one argument, API key
	 * This is required before doing anything else
	 * Example: WP_Kissmetrics::init( KISSMETRICS_API_KEY );
	 * Example: WP_Kissmetrics::init( KISSMETRICS_API_KEY, 1049177863 );
	 */
	static function init( $key, $time = null ) {
		self::$key  = $key;
		self::$time = ( ! is_null( $time ) ) ? $time : time();
	}

	/**
	 * Identify the user we're going to record data about 
	 * This is required before recording any data
	 * If the user has a Kissmetrics auto-generated ID stored in a cookie, it will be automatically aliased
	 */
	static function identify( $id ) {
		self::$id = $id;
		
		/* Use the Kissmetrics auto-generated ID cookie to alias our logged in ID, then delete the cookie */
		if( isset( $_COOKIE['km_ai'] ) ) {
			self::alias( $_COOKIE['km_ai'], self::$id );
			setcookie( 'km_ai', '', time() - 3600 );
		}
	}

	/**
	 * Record data about an identified user
	 * Accepts a single argument 'action' as a string
	 * Example: WP_Kissmetrics::record( 'Viewed Homepage' );
	 *
	 * Also accepts an action + properties of that action as an array
	 * Example: WP_Kissmetrics::record( 'Purchased upgrade', array( 'product'=>'videopress', 'revenue'=>60');
	 */
	static function record( $action, $props = array() ) {
		if( !self::is_initialized_and_identified() )
			return;

		$array = array_merge( $props, array(
			'_n' => $action,
		) );
		
		self::generate_query( 'e', $array );
	}

	/**
	 * Alias a new user identiy to a new one in Kissmetrics' data
	 * Possible use case would be assigning logged out user an identifier and aliasing their User ID after signup
	 * 
	 * Example: WP_Kissmetrics::alias( get_current_user_id(), $_COOKIE['tmp_km_thing'] );
	 */
	static function alias( $name, $alias_to ) {
		if ( !self::is_initialized() )
			return;

		$array = array(
			'_p' => $name,
			'_n' => $alias_to,
		);
		
		self::generate_query( 'a', $array, false );
	}

	/* Protected */

	static protected function reset() {
		self::$id		 = null;
		self::$key	 = null;
	}

	static protected function is_initialized() {
		return self::$key;
	}

	/* Check to make sure both the API key and User ID are set */
	static protected function is_initialized_and_identified() {
		return self::$key && self::$id;
	}

	/* Put together the query we're going to send to Kissmetrics */
	static protected function generate_query( $type, $data, $update = true ) {
		
		$data['_k'] = self::$key;
		$data['_t'] = self::$time;
		
		//Force Kissmetrics to use the time value we pass
		$data['_d'] = 1;

		if( $update )
			$data['_p'] = self::$id;

		$query = '/' . $type . '?' . http_build_query( $data, '', '&' );
		
		//Remove some remnants of http_build_query() that Kissmetrics doesn't like
		$query = str_replace( '+', '%20', $query );
		
		self::send_query( $query ); 
	}

	/* Actually send Kissmetrics some data */
	static protected function send_query( $query ) {
		$request_url = KISSMETRICS_HOST . $query;
		wp_remote_get( $request_url, array( 'blocking'=>false ) );
	}
}

function sample_kissmetrics_usage( $product_id ) {
	WP_Kissmetrics::init( KISSMETRICS_API_KEY );
	WP_Kissmetrics::identify( get_current_blog_id() );
	WP_Kissmetrics::record( 'Viewed shopping cart', array( 'user' => get_current_user_id(), 'product' => $product_id ) );
}
add_action( 'view_shopping_cart', 'sample_kissmetrics_usage', 1 );