pixel.php

<?php

/**
 * Function to get the title of the referring url.
 *
 * @param string $url URL of the referrer.
 * @param int    $post_id ID of the shared post.
 * @return string|void Title of the referring URL, or void if we can't find it.
 */
function wprtt_get_referring_page_title( $url, $post_id ) {
	$response = \wp_remote_get( $url );

	// if there was no issue grabbing the url, continue.
	if ( ! is_wp_error( $response ) ) {

		// find the title element inside of the response body.
		$response = preg_match( '/<title.[^>]*>(.*)<\/title>/siU', $response['body'], $title_matches );

		// if a title element was found, let's get the text from it.
		if ( $title_matches ) {

			// clean up title: remove EOL's and excessive whitespace.
			$title = preg_replace( '/\s+/', ' ', $title_matches[1] );
			$title = trim( $title );
			$title = rawurlencode( $title );

			// return our found title.
			return urldecode( $title );

		} else {

			// if there were no title matches found, use the original post title.
			return \get_the_title( $post_id );

		}
	}
}

/**
 * Generate a random client ID string and set the newspack-cid fallback cookie if not set.
 *
 * @return string Randomly generated client ID.
 */
function wprtt_create_cid_cookie_if_not_set() {
	$cid = (string) \wp_rand( 100000000, 999999999 );

	// phpcs:ignore WordPressVIPMinimum.Functions.RestrictedFunctions.cookies_setcookie
	setcookie( 'newspack-cid', $cid, time() + 30 * DAY_IN_SECONDS, COOKIEPATH, COOKIE_DOMAIN, true );

	return $cid;
}

/**
 * Extracts the Client ID from the _ga cookie
 *
 * @return ?string
 */
function wprtt_extract_cid_from_cookies() {
	if ( isset( $_COOKIE['_ga'] ) ) {
		$cookie_pieces = explode( '.', $_COOKIE['_ga'], 3 ); // phpcs:ignore WordPressVIPMinimum.Variables.RestrictedVariables.cache_constraints___COOKIE, WordPress.Security.ValidatedSanitizedInput.InputNotSanitized
		if ( 1 === count( $cookie_pieces ) ) {
			$cid = reset( $cookie_pieces );
		} else {
			list( $version, $domain_depth, $cid ) = $cookie_pieces;
		}
		return $cid;
	}

	if ( isset( $_COOKIE['newspack-cid'] ) ) {
		return $_COOKIE['newspack-cid'];
	}

	return wprtt_create_cid_cookie_if_not_set();
}

if ( isset( $_GET['post'] ) ) {

	// set up all of our post vars we want to track.
	$shared_post_id = \absint( $_GET['post'] );
	$shared_post    = \get_post( $shared_post_id );

	$shared_post_slug      = rawurlencode( $shared_post->post_name );
	$shared_post_permalink = \get_permalink( $shared_post_id );

	if ( array_key_exists( 'HTTP_REFERER', $_SERVER ) ) {
		if ( isset( $_SERVER['HTTP_REFERER'] ) ) {
			$url = \esc_url_raw( $_SERVER['HTTP_REFERER'] );
		}

		$url_title = \wprtt_get_referring_page_title( $url, $shared_post_id );

		$url_host = \wp_parse_url( $url, PHP_URL_HOST );
		$url_path = \wp_parse_url( $url, PHP_URL_PATH );

	} else {

		$url       = '';
		$url_title = '';
		$url_host  = '';

	}

	// If the request is coming from WP Admin, bail out (when the copied content is inserted into the WP editor, the pixel will be pinged).
	if ( false !== stripos( $url, '/wp-admin/' ) ) {
		exit;
	}

	$value = \get_post_meta( $shared_post_id, 'republication_tracker_tool_sharing', true );
	if ( $value ) {
		if ( isset( $value[ $url ] ) ) {
			$value[ $url ]++;
		} else {
			$value[ $url ] = 1;
		}
	} else {
		$value = array(
			$url => 1,
		);
	}
	$update = \update_post_meta( $shared_post_id, 'republication_tracker_tool_sharing', $value );

	// If we have the necessary GA4 info, let's push data to it.
	// We need both a Measurement ID and an API secret for GA4.
	// https://developers.google.com/analytics/devguides/collection/protocol/ga4/sending-events?client_type=gtag#required_parameters.
	$ga4_id     = \get_option( 'republication_tracker_tool_analytics_ga4_id' );
	$ga4_secret = \get_option( 'republication_tracker_tool_analytics_ga4_secret', false );

	if ( $ga4_id && $ga4_secret && isset( $_GET['ga4'] ) && $_GET['ga4'] === $ga4_id ) {
		$base_url = \add_query_arg(
			[
				'api_secret'     => $ga4_secret,
				'measurement_id' => $ga4_id,
			],
			'https://www.google-analytics.com/mp/collect'
		);
		$payload  = [
			'client_id' => wprtt_extract_cid_from_cookies(),
			'events'    => [
				[
					'name'   => 'page_view',
					// Params for page_view events: https://developers.google.com/analytics/devguides/collection/ga4/views?client_type=gtag.
					'params' => [
						'page_title'       => $url_title,
						'page_location'    => $shared_post_permalink,
						'page_referrer'    => $url,
						'shared_post_id'   => $shared_post->ID,
						'shared_post_slug' => $shared_post_slug,
						'shared_post_url'  => $shared_post_permalink,
					],
				],
			],
		];

		\wp_remote_post(
			$base_url,
			[
				'body' => wp_json_encode( $payload ),
			]
		);
	}
}

header( 'Content-Type: image/png' );
// A transparent 1x1 px .gif image.
echo base64_decode( 'iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEUAAACnej3aAAAAAXRSTlMAQObYZgAAAApJREFUCNdjYAAAAAIAAeIhvDMAAAAASUVORK5CYII=' );
exit;