<?php
/**
 * Send Tracks events on behalf of a user.
 *
 * @package WooCommerce\Tracks
 */

defined( 'ABSPATH' ) || exit;

/**
 * WC_Tracks_Client class.
 */
class WC_Tracks_Client {

	/**
	 * Pixel URL.
	 */
	const PIXEL = 'https://pixel.wp.com/t.gif';

	/**
	 * Browser type.
	 */
	const BROWSER_TYPE = 'php-agent';

	/**
	 * User agent.
	 */
	const USER_AGENT_SLUG = 'tracks-client';

	/**
	 * Initialize tracks client class
	 *
	 * @return void
	 */
	public static function init() {
		// Use wp hook for setting the identity cookie to avoid headers already sent warnings.
		add_action( 'admin_init', array( __CLASS__, 'maybe_set_identity_cookie' ) );
	}

	/**
	 * Check if identiy cookie is set, if not set it.
	 *
	 * @return void
	 */
	public static function maybe_set_identity_cookie() {
		// Bail if cookie already set.
		if ( isset( $_COOKIE['tk_ai'] ) ) {
			return;
		}

		$user = wp_get_current_user();

		// We don't want to track user events during unit tests/CI runs.
		if ( $user instanceof WP_User && 'wptests_capabilities' === $user->cap_key ) {
			return false;
		}
		$user_id = $user->ID;
		$anon_id = get_user_meta( $user_id, '_woocommerce_tracks_anon_id', true );

		// If an id is still not found, create one and save it.
		if ( ! $anon_id ) {
			$anon_id = self::get_anon_id();
			update_user_meta( $user_id, '_woocommerce_tracks_anon_id', $anon_id );
		}

		// Don't set cookie on API requests.
		if (
			! ( defined( 'REST_REQUEST' ) && REST_REQUEST ) &&
			! ( defined( 'XMLRPC_REQUEST' ) && XMLRPC_REQUEST )
		) {
			wc_setcookie( 'tk_ai', $anon_id );
		}
	}

	/**
	 * Record a Tracks event
	 *
	 * @param  array $event Array of event properties.
	 * @return bool|WP_Error         True on success, WP_Error on failure.
	 */
	public static function record_event( $event ) {
		if ( ! $event instanceof WC_Tracks_Event ) {
			$event = new WC_Tracks_Event( $event );
		}

		if ( is_wp_error( $event ) ) {
			return $event;
		}

		$pixel = $event->build_pixel_url( $event );

		if ( ! $pixel ) {
			return new WP_Error( 'invalid_pixel', 'cannot generate tracks pixel for given input', 400 );
		}

		return self::record_pixel( $pixel );
	}

	/**
	 * Synchronously request the pixel.
	 *
	 * @param string $pixel pixel url and query string.
	 * @return bool Always returns true.
	 */
	public static function record_pixel( $pixel ) {
		// Add the Request Timestamp and URL terminator just before the HTTP request.
		$pixel .= '&_rt=' . self::build_timestamp() . '&_=_';

		wp_safe_remote_get(
			$pixel,
			array(
				'blocking'    => false,
				'redirection' => 2,
				'httpversion' => '1.1',
				'timeout'     => 1,
			)
		);

		return true;
	}

	/**
	 * Create a timestap representing milliseconds since 1970-01-01
	 *
	 * @return string A string representing a timestamp.
	 */
	public static function build_timestamp() {
		$ts = round( microtime( true ) * 1000 );

		return number_format( $ts, 0, '', '' );
	}

	/**
	 * Get a user's identity to send to Tracks. If Jetpack exists, default to its implementation.
	 *
	 * @param int $user_id User id.
	 * @return array Identity properties.
	 */
	public static function get_identity( $user_id ) {
		$jetpack_lib = '/tracks/client.php';

		if ( class_exists( 'Jetpack' ) && file_exists( jetpack_require_lib_dir() . $jetpack_lib ) ) {
			include_once jetpack_require_lib_dir() . $jetpack_lib;

			if ( function_exists( 'jetpack_tracks_get_identity' ) ) {
				return jetpack_tracks_get_identity( $user_id );
			}
		}

		// Start with a previously set cookie.
		$anon_id = isset( $_COOKIE['tk_ai'] ) ? sanitize_text_field( wp_unslash( $_COOKIE['tk_ai'] ) ) : false;

		// If there is no cookie, apply a saved id.
		if ( ! $anon_id ) {
			$anon_id = get_user_meta( $user_id, '_woocommerce_tracks_anon_id', true );
		}

		// If an id is still not found, create one and save it.
		if ( ! $anon_id ) {
			$anon_id = self::get_anon_id();

			update_user_meta( $user_id, '_woocommerce_tracks_anon_id', $anon_id );
		}

		return array(
			'_ut' => 'anon',
			'_ui' => $anon_id,
		);
	}

	/**
	 * Grabs the user's anon id from cookies, or generates and sets a new one
	 *
	 * @return string An anon id for the user
	 */
	public static function get_anon_id() {
		static $anon_id = null;

		if ( ! isset( $anon_id ) ) {

			// Did the browser send us a cookie?
			if ( isset( $_COOKIE['tk_ai'] ) ) {
				$anon_id = sanitize_text_field( wp_unslash( $_COOKIE['tk_ai'] ) );
			} else {

				$binary = '';

				// Generate a new anonId and try to save it in the browser's cookies.
				// Note that base64-encoding an 18 character string generates a 24-character anon id.
				for ( $i = 0; $i < 18; ++$i ) {
					$binary .= chr( wp_rand( 0, 255 ) );
				}

				$anon_id = 'woo:' . base64_encode( $binary );
			}
		}

		return $anon_id;
	}
}

WC_Tracks_Client::init();