<?php
/**
 * Robots module.
 *
 * @package ElevenRank
 * @since   1.0.0
 */

namespace ElevenRank\Modules\Robots;

use ElevenRank\Module;
use ElevenRank\Output_Gate;
use ElevenRank\REST\Robots_Controller;
use ElevenRank\Settings;

defined( 'ABSPATH' ) || exit;

/**
 * The virtual robots.txt file.
 *
 * Nothing is written to disk: the text is handed to WordPress through its `robots_txt` filter.
 * An empty editor means "use the default file" (WordPress's own, plus whatever other modules
 * add, such as the sitemap address). Text the site owner writes replaces it, except when the site
 * asks search engines to stay away: then WordPress's own `Disallow: /` is left untouched.
 *
 * @since 1.0.0
 */
final class Robots_Module implements Module {

	/**
	 * Whether the default file is being worked out, so the owner's text must not be applied.
	 *
	 * @since 1.0.0
	 *
	 * @var bool
	 */
	private $building_default = false;

	/**
	 * Settings store.
	 *
	 * @since 1.0.0
	 *
	 * @var Settings
	 */
	private $settings;

	/**
	 * Output gate.
	 *
	 * @since 1.0.0
	 *
	 * @var Output_Gate
	 */
	private $gate;

	/**
	 * Constructor.
	 *
	 * @since 1.0.0
	 *
	 * @param Settings    $settings Settings store.
	 * @param Output_Gate $gate     Output gate.
	 */
	public function __construct( Settings $settings, Output_Gate $gate ) {
		$this->settings = $settings;
		$this->gate     = $gate;
	}

	/**
	 * Module id.
	 *
	 * @since 1.0.0
	 *
	 * @return string
	 */
	public function id(): string {
		return 'robots';
	}

	/**
	 * Module name.
	 *
	 * @since 1.0.0
	 *
	 * @return string
	 */
	public function label(): string {
		return __( 'robots.txt editor', 'elevenrank' );
	}

	/**
	 * Registers the module's hooks.
	 *
	 * @since 1.0.0
	 *
	 * @return void
	 */
	public function boot(): void {
		add_action( 'rest_api_init', array( $this, 'register_routes' ) );

		if ( $this->gate->is_active() ) {
			add_filter( 'robots_txt', array( $this, 'filter' ), 15, 2 );
		}
	}

	/**
	 * Registers the REST route used by the editor screen.
	 *
	 * @since 1.0.0
	 *
	 * @return void
	 */
	public function register_routes(): void {
		( new Robots_Controller( $this->settings, $this ) )->register_routes();
	}

	/**
	 * Puts the site owner's text in place of the default file.
	 *
	 * @since 1.0.0
	 *
	 * @param string     $output    The robots.txt content so far.
	 * @param string|int $is_public Whether the site is visible to search engines (`0` when it is not).
	 * @return string
	 */
	public function filter( $output, $is_public ): string {
		$output = (string) $output;

		// A site that asks search engines to stay away keeps WordPress's own "Disallow: /", and the
		// default file is the file without the owner's text.
		if ( $this->building_default || ! (int) $is_public ) {
			return $output;
		}

		$custom = (string) $this->settings->value( 'robots', 'content' );

		return '' === trim( $custom ) ? $output : $custom . "\n";
	}

	/**
	 * The file as it would be without any text from the site owner.
	 *
	 * That is WordPress's default file after every other filter has had its say, so it includes
	 * the sitemap address and anything another plugin adds. It is what "reset to default" restores.
	 *
	 * @since 1.0.0
	 *
	 * @return string
	 */
	public function default_text(): string {
		$this->building_default = true;

		try {
			// This runs WordPress's own filter to learn what the file would contain; it is not a new hook.
			return (string) apply_filters( 'robots_txt', $this->core_default(), '1' ); // phpcs:ignore WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedHooknameFound
		} finally {
			$this->building_default = false;
		}
	}

	/**
	 * The file WordPress writes on its own for a site that is open to search engines.
	 *
	 * @since 1.0.0
	 *
	 * @return string
	 */
	private function core_default(): string {
		// Both paths come from admin_url(), so a site that moves or renames its admin folder is described correctly.
		$ajax  = (string) wp_parse_url( admin_url( 'admin-ajax.php' ), PHP_URL_PATH );
		$admin = substr( $ajax, 0, (int) strrpos( $ajax, '/' ) + 1 );

		return "User-agent: *\nDisallow: {$admin}\nAllow: {$ajax}\n";
	}
}