ms_load_current_site_and_network() WordPress Function

function ms_load_current_site_and_network( $domain, $path, $subdomain = false ) {
	global $current_site, $current_blog;

	// If the network is defined in wp-config.php, we can simply use that.
	if ( defined( 'DOMAIN_CURRENT_SITE' ) && defined( 'PATH_CURRENT_SITE' ) ) {
		$current_site         = new stdClass;
		$current_site->id     = defined( 'SITE_ID_CURRENT_SITE' ) ? SITE_ID_CURRENT_SITE : 1;
		$current_site->domain = DOMAIN_CURRENT_SITE;
		$current_site->path   = PATH_CURRENT_SITE;
		if ( defined( 'BLOG_ID_CURRENT_SITE' ) ) {
			$current_site->blog_id = BLOG_ID_CURRENT_SITE;
		} elseif ( defined( 'BLOGID_CURRENT_SITE' ) ) { // Deprecated.
			$current_site->blog_id = BLOGID_CURRENT_SITE;
		}

		if ( 0 === strcasecmp( $current_site->domain, $domain ) && 0 === strcasecmp( $current_site->path, $path ) ) {
			$current_blog = get_site_by_path( $domain, $path );
		} elseif ( '/' !== $current_site->path && 0 === strcasecmp( $current_site->domain, $domain ) && 0 === stripos( $path, $current_site->path ) ) {
			// If the current network has a path and also matches the domain and path of the request,
			// we need to look for a site using the first path segment following the network's path.
			$current_blog = get_site_by_path( $domain, $path, 1 + count( explode( '/', trim( $current_site->path, '/' ) ) ) );
		} else {
			// Otherwise, use the first path segment (as usual).
			$current_blog = get_site_by_path( $domain, $path, 1 );
		}
	} elseif ( ! $subdomain ) {
		/*
		 * A "subdomain" installation can be re-interpreted to mean "can support any domain".
		 * If we're not dealing with one of these installations, then the important part is determining
		 * the network first, because we need the network's path to identify any sites.
		 */
		$current_site = wp_cache_get( 'current_network', 'site-options' );
		if ( ! $current_site ) {
			// Are there even two networks installed?
			$networks = get_networks( array( 'number' => 2 ) );
			if ( count( $networks ) === 1 ) {
				$current_site = array_shift( $networks );
				wp_cache_add( 'current_network', $current_site, 'site-options' );
			} elseif ( empty( $networks ) ) {
				// A network not found hook should fire here.
				return false;
			}
		}

		if ( empty( $current_site ) ) {
			$current_site = WP_Network::get_by_path( $domain, $path, 1 );
		}

		if ( empty( $current_site ) ) {
			/**
			 * Fires when a network cannot be found based on the requested domain and path.
			 *
			 * At the time of this action, the only recourse is to redirect somewhere
			 * and exit. If you want to declare a particular network, do so earlier.
			 *
			 * @since 4.4.0
			 *
			 * @param string $domain       The domain used to search for a network.
			 * @param string $path         The path used to search for a path.
			 */
			do_action( 'ms_network_not_found', $domain, $path );

			return false;
		} elseif ( $path === $current_site->path ) {
			$current_blog = get_site_by_path( $domain, $path );
		} else {
			// Search the network path + one more path segment (on top of the network path).
			$current_blog = get_site_by_path( $domain, $path, substr_count( $current_site->path, '/' ) );
		}
	} else {
		// Find the site by the domain and at most the first path segment.
		$current_blog = get_site_by_path( $domain, $path, 1 );
		if ( $current_blog ) {
			$current_site = WP_Network::get_instance( $current_blog->site_id ? $current_blog->site_id : 1 );
		} else {
			// If you don't have a site with the same domain/path as a network, you're pretty screwed, but:
			$current_site = WP_Network::get_by_path( $domain, $path, 1 );
		}
	}

	// The network declared by the site trumps any constants.
	if ( $current_blog && $current_blog->site_id != $current_site->id ) {
		$current_site = WP_Network::get_instance( $current_blog->site_id );
	}

	// No network has been found, bail.
	if ( empty( $current_site ) ) {
		/** This action is documented in wp-includes/ms-settings.php */
		do_action( 'ms_network_not_found', $domain, $path );

		return false;
	}

	// During activation of a new subdomain, the requested site does not yet exist.
	if ( empty( $current_blog ) && wp_installing() ) {
		$current_blog          = new stdClass;
		$current_blog->blog_id = 1;
		$blog_id               = 1;
		$current_blog->public  = 1;
	}

	// No site has been found, bail.
	if ( empty( $current_blog ) ) {
		// We're going to redirect to the network URL, with some possible modifications.
		$scheme      = is_ssl() ? 'https' : 'http';
		$destination = "$scheme://{$current_site->domain}{$current_site->path}";

		/**
		 * Fires when a network can be determined but a site cannot.
		 *
		 * At the time of this action, the only recourse is to redirect somewhere
		 * and exit. If you want to declare a particular site, do so earlier.
		 *
		 * @since 3.9.0
		 *
		 * @param WP_Network $current_site The network that had been determined.
		 * @param string     $domain       The domain used to search for a site.
		 * @param string     $path         The path used to search for a site.
		 */
		do_action( 'ms_site_not_found', $current_site, $domain, $path );

		if ( $subdomain && ! defined( 'NOBLOGREDIRECT' ) ) {
			// For a "subdomain" installation, redirect to the signup form specifically.
			$destination .= 'wp-signup.php?new=' . str_replace( '.' . $current_site->domain, '', $domain );
		} elseif ( $subdomain ) {
			/*
			 * For a "subdomain" installation, the NOBLOGREDIRECT constant
			 * can be used to avoid a redirect to the signup form.
			 * Using the ms_site_not_found action is preferred to the constant.
			 */
			if ( '%siteurl%' !== NOBLOGREDIRECT ) {
				$destination = NOBLOGREDIRECT;
			}
		} elseif ( 0 === strcasecmp( $current_site->domain, $domain ) ) {
			/*
			 * If the domain we were searching for matches the network's domain,
			 * it's no use redirecting back to ourselves -- it'll cause a loop.
			 * As we couldn't find a site, we're simply not installed.
			 */
			return false;
		}

		return $destination;
	}

	// Figure out the current network's main site.
	if ( empty( $current_site->blog_id ) ) {
		$current_site->blog_id = get_main_site_id( $current_site->id );
	}

	return true;
}