WordPress.com plugin for running Optimizely experiments

optimizely.php

<?php
/*
	Plugin Name: Optimizely
	Description: Runs Optimizely experiments.
	Author: koop, evansolomon
	Version: 0.2
*/

class WPCOM_Optimizely {
	public $version;
	public $url;

	private $_checks = array();

	function __construct( $project_id, $version ) {
		$this->version = $version;

		// Generate project JavaScript URL
		$scheme    = is_ssl() ? 'https' : 'http';
		$this->url = "{$scheme}://cdn.optimizely.com/js/{$project_id}.js";

		add_filter( 'optimizely_maybe_experiment', array( $this, 'checks' ), 10, 3 );

		$this->add_check( array( $this, 'disabled_sites' ) );
		$this->add_check( array( $this, 'language' ) );
		$this->add_check( array( $this, 'front_page_only' ) );
		$this->add_check( array( $this, 'logged_out_users' ) );
		$this->add_check( array( $this, 'user_id_floor' ) );
	}

	/**
	 * Potentially run an experiment.
	 *
	 * The 'optimizely_maybe_experiment' filter determines whether to run a given experiment.
	 *
	 * If any experiment is added, the Optimizely project script will be included.
	 *
	 * For each added experiment, the wpcom_optimizely.$EXPERIMENT_SLUG variable will
	 * be defined in JavaScript.
	 */
	function maybe_experiment( $experiment ) {
		// If the optimizely_maybe_experiment filter returns false, bail.
		if ( ! apply_filters( 'optimizely_maybe_experiment', true, $experiment->args, $experiment ) )
			return;

		// Enqueue the Optimizely script
		wp_enqueue_script( 'optimizely', $this->url, array('jquery'), $this->version );

		// Register the slug through JavaScript
		wp_localize_script( 'optimizely', 'wpcom_optimizely', array( $experiment->slug => true ) );
	}

	/**
	 * Provides a shorthand for validating an experiment via callbacks.
	 * If any check returns 'false' (explicitly), the experiment will not run.
	 */
	function add_check( $callback, $param = false ) {
		$this->_checks[] = $callback;
	}

	/**
	 * Attached to the optimizely_maybe_experiment filter.
	 * Runs our checks. If any return 'false', bail!
	 */
	function checks( $enable_exp, $args, $experiment ) {
		foreach ( $this->_checks as $check ) {
			if ( false === call_user_func( $check, $args, $experiment ) )
				return false;
		}
		return $enable_exp;
	}

	/**
	 * Disables all experiments for select sites.
	 */
	function disabled_sites( $args ) {
		global $blog_id;

		switch ( $blog_id ) {
			case 24588526: // TechCrunch
				return false;
		}
	}

	/**
	 * Optionally limits targets by user language.
	 *
	 * Determined by the boolean 'language' argument. Default 'en', for ENglish.
	 */
	function language( $args ) {
		// If a language isn't set, we always want the experiment to run.
		if ( empty( $args['language'] ) )
			return true;

		if ( $args['language'] != get_bloginfo( 'language' ) )
			return false;
	}

	/**
	 * Optionally limits targets only to front page.
	 *
	 * Determined by the boolean 'front_page_only' argument. Default false, for all pages.
	 */
	function front_page_only( $args ) {
		if ( $args['front_page_only'] )
			return is_home();
	}	

	/**
	 * Optionally limits targets only to logged out users.
	 *
	 * Determined by the boolean 'logged_out_users' argument. Default false, for all users.
	 */
	function logged_out_users( $args ) {
		if ( $args['logged_out_users'] )
			return ! is_user_logged_in();
	}	

	/**
	 * Optionally limits targets only to new users, defined by minimum user_id.
	 *
	 * Determined by the integer 'user_id_floor' argument. Default 0, for all users.
	 */
	function user_id_floor( $args ) {
		if ( $args['user_id_floor'] ) {
			global $current_user;
			return ( $args['user_id_floor'] < $current_user->ID );
		}
	}	

}

class WPCOM_Optimizely_Experiment {
	public $slug;
	public $args;
	public $project;

	/**
	 * Register a new Optimizely experiment.
	 *
	 * @param $slug string
	 * @param $args array - Optional.
	 *
	 * 'actions'     => Evaluates the experiment on a specific actions.
	 *                  If not provided, experiment evaluates immediately. Default ''.
	 *                  Accepts a string or array. Arrays can be used to hook to multiple actions.
	 * 'language'   => Limits an experiment by user language. Default 'en'.
	 */
	function __construct( $project, $slug, $args = array() ) {
		$defaults = array(
			'actions'            => '',
			'language'           => 'en',
			'front_page_only'    => false,
			'logged_out_users'   => false,
			'user_id_floor'      => 0,
		);

		$args = wp_parse_args( $args, $defaults );

		$this->project = $project;
		$this->slug    = $slug;
		$this->args    = $args;

		if ( empty( $args['actions'] ) )
			$this->maybe_load();
		elseif( is_array( $args['actions'] ) ) {
			foreach( $args['actions'] as $action ) {
				add_action( $action, array( $this, 'maybe_load' ) );
			}
		}
		else
			add_action( $args['actions'], array( $this, 'maybe_load' ) );
	}

	function maybe_load() {
		$this->project->maybe_experiment( $this );
	}

}


$wpcom_optimizely = new WPCOM_Optimizely( 7144006, '201111130a' );

/**
 * Add a new Optimizely experiment.
 */
function optimizely_experiment( $slug, $args = array() ) {
	global $wpcom_optimizely;

	new WPCOM_Optimizely_Experiment( $wpcom_optimizely, $slug, $args );
}

/**
 * Example experiment using multiple actions
 */
optimizely_experiment( 'fake_test', array(
	'actions' => array( 'load-themes.php', 'load-post-new.php' ),
) );