<?php
/**
 * Plugin Name: Admin Robots.txt Editor
 * Plugin URI: https://wordpress.org/plugins/admin-robots-txt-editor/
 * Description: Easily create, edit, and manage your site's robots.txt file directly from the WordPress admin panel.
 * Version: 1.0.1
 * Author: Makanikaran
 * Author URI: https://profiles.wordpress.org/makanikaran/
 * License: GPLv2 or later
 * License URI: https://www.gnu.org/licenses/gpl-2.0.html
 * Text Domain: admin-robots-txt-editor
 * Domain Path: /languages
 * Requires at least: 5.0
 * Requires PHP: 7.2
 *
 * @package Admin_Robots_Txt_Editor
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * Path to the site's physical robots.txt file.
 *
 * @var string
 */
if ( ! defined( 'ARTTE_ROBOTS_FILE' ) ) {
	define( 'ARTTE_ROBOTS_FILE', trailingslashit( ABSPATH ) . 'robots.txt' );
}

/**
 * Get the default robots.txt content.
 *
 * @return string Default robots.txt content.
 */
function artte_get_default_robots_content() {
	$sitemap_url = home_url( '/wp-sitemap.xml' );

	$signals  = "# As a condition of accessing this website, you agree to abide by the following\n";
	$signals .= "# content signals:\n#\n";
	$signals .= "# (a) If a content-signal = yes, you may collect content for that use.\n";
	$signals .= "# (b) If a content-signal = no, you may not collect content for that use.\n";
	$signals .= "# (c) If not provided, the operator neither grants nor restricts permission.\n#\n";
	$signals .= "# search: building a search index and providing search results (not AI summaries).\n";
	$signals .= "# ai-input: inputting content into AI models for RAG or real-time answers.\n";
	$signals .= "# ai-train: training or fine-tuning AI models.\n\n";

	$rules  = "User-agent: *\n";
	$rules .= "Disallow: /wp-admin/\n";
	$rules .= "Allow: /wp-admin/admin-ajax.php\n";
	$rules .= "Disallow: /?s=\n";
	$rules .= "Sitemap: {$sitemap_url}\n";

	return $signals . $rules;
}

/**
 * Initialize the WordPress filesystem API.
 *
 * @return WP_Filesystem_Base|false Filesystem object or false on failure.
 */
function artte_get_filesystem() {
	global $wp_filesystem;

	require_once ABSPATH . 'wp-admin/includes/file.php';

	if ( ! $wp_filesystem ) {
		WP_Filesystem();
	}

	if ( ! $wp_filesystem || ! is_object( $wp_filesystem ) ) {
		return false;
	}

	return $wp_filesystem;
}

/**
 * Read the physical robots.txt file.
 *
 * @return string|false File contents or false when unavailable.
 */
function artte_read_robots_file() {
	$filesystem = artte_get_filesystem();

	if (
		! $filesystem ||
		! $filesystem->exists( ARTTE_ROBOTS_FILE ) ||
		! $filesystem->is_file( ARTTE_ROBOTS_FILE )
	) {
		return false;
	}

	if ( ! $filesystem->is_readable( ARTTE_ROBOTS_FILE ) ) {
		return false;
	}

	$content = $filesystem->get_contents( ARTTE_ROBOTS_FILE );

	return false === $content ? false : $content;
}

/**
 * Write the physical robots.txt file.
 *
 * @param string $content Robots.txt content.
 * @return bool True on success, false on failure.
 */
function artte_write_robots_file( $content ) {
	$filesystem = artte_get_filesystem();

	if ( ! $filesystem ) {
		return false;
	}

	return $filesystem->put_contents(
		ARTTE_ROBOTS_FILE,
		$content,
		FS_CHMOD_FILE
	);
}

/**
 * Normalize robots.txt content before saving.
 *
 * Robots.txt is configuration/plain text, so this function intentionally
 * does not use sanitize_textarea_field(). That sanitizer can modify valid
 * robots.txt directives.
 *
 * @param string $content Raw submitted content.
 * @return string Normalized content.
 */
function artte_sanitize_robots_content( $content ) {
	$content = str_replace( "\0", '', $content );
	$content = str_replace( "\r\n", "\n", $content );
	$content = str_replace( "\r", "\n", $content );
	$content = trim( $content );

	return $content . "\n";
}

/**
 * Get the submitted robots.txt content.
 *
 * @return string Sanitized and normalized robots.txt content.
 */
function artte_get_submitted_robots_content() {
	$content = filter_input(
		INPUT_POST,
		'robots_content',
		FILTER_UNSAFE_RAW
	);

	if ( ! is_string( $content ) ) {
		return '';
	}

	return artte_sanitize_robots_content( wp_unslash( $content ) );
}

/**
 * Get the submitted admin action.
 *
 * @return string Sanitized action value.
 */
function artte_get_submitted_action() {
	$action = filter_input(
		INPUT_POST,
		'artte_action',
		FILTER_UNSAFE_RAW
	);

	if ( ! is_string( $action ) ) {
		return '';
	}

	return sanitize_key( $action );
}

/**
 * Determine whether the robots.txt form was submitted.
 *
 * @return bool True when the form was submitted.
 */
function artte_is_robots_form_submitted() {
	$action = filter_input(
		INPUT_POST,
		'artte_action',
		FILTER_UNSAFE_RAW
	);

	$content = filter_input(
		INPUT_POST,
		'robots_content',
		FILTER_UNSAFE_RAW
	);

	return null !== $action || null !== $content;
}

/**
 * Filter WordPress' virtual robots.txt output.
 *
 * A physical robots.txt file is normally served by the web server before
 * WordPress is loaded. When no physical file exists, this filter provides
 * the editor's content through WordPress.
 *
 * @param string $output Existing robots.txt output.
 * @param bool   $public Whether the site is considered public.
 * @return string Robots.txt output.
 */
function artte_output_custom_robots_txt( $output, $public ) {
	if ( ! $public ) {
		return "User-agent: *\nDisallow: /\n";
	}

	$content = artte_read_robots_file();

	if ( false !== $content ) {
		return $content;
	}

	return artte_get_default_robots_content();
}
add_filter( 'robots_txt', 'artte_output_custom_robots_txt', 10, 2 );

/**
 * Add the Robots.txt editor admin menu.
 *
 * @return void
 */
function artte_add_admin_menu() {
	add_menu_page(
		__( 'Robots.txt Editor', 'admin-robots-txt-editor' ),
		__( 'Robots.txt', 'admin-robots-txt-editor' ),
		'manage_options',
		'admin-robots-txt',
		'artte_render_robots_editor',
		'dashicons-media-text',
		91
	);
}
add_action( 'admin_menu', 'artte_add_admin_menu' );

/**
 * Enqueue admin assets for the plugin screen.
 *
 * @param string $hook_suffix Current admin page hook suffix.
 * @return void
 */
function artte_enqueue_admin_assets( $hook_suffix ) {
	if ( 'toplevel_page_admin-robots-txt' !== $hook_suffix ) {
		return;
	}

	wp_enqueue_script(
		'artte-admin',
		plugins_url( 'assets/admin.js', __FILE__ ),
		array(),
		'1.0.1',
		true
	);

	wp_localize_script(
		'artte-admin',
		'artteAdmin',
		array(
			'confirmReset' => __(
				'Are you sure you want to reset robots.txt to the default content?',
				'admin-robots-txt-editor'
			),
		)
	);
}
add_action( 'admin_enqueue_scripts', 'artte_enqueue_admin_assets' );

/**
 * Render the Robots.txt editor page.
 *
 * @return void
 */
function artte_render_robots_editor() {
	if ( ! current_user_can( 'manage_options' ) ) {
		wp_die(
			esc_html__(
				'You are not allowed to access this page.',
				'admin-robots-txt-editor'
			)
		);
	}

	$message = '';
	$success = false;

	/*
	 * Process the submitted form.
	 *
	 * filter_input() is used instead of directly accessing $_POST so that
	 * the submitted values are retrieved through PHP's input filtering API.
	 */
	if ( artte_is_robots_form_submitted() ) {
		check_admin_referer( 'artte_update_robots', 'artte_nonce' );

		$action = artte_get_submitted_action();

		if ( 'save' === $action ) {
			$content = artte_get_submitted_robots_content();

			if ( artte_write_robots_file( $content ) ) {
				$message = __(
					'robots.txt has been updated successfully.',
					'admin-robots-txt-editor'
				);
				$success = true;
			} else {
				$message = __(
					'Unable to write robots.txt. Check the web server file permissions.',
					'admin-robots-txt-editor'
				);
			}
		} elseif ( 'reset' === $action ) {
			$default = artte_get_default_robots_content();

			if ( artte_write_robots_file( $default ) ) {
				$message = __(
					'robots.txt has been reset to the default content.',
					'admin-robots-txt-editor'
				);
				$success = true;
			} else {
				$message = __(
					'Unable to reset robots.txt. Check the web server file permissions.',
					'admin-robots-txt-editor'
				);
			}
		}
	}

	$robots_content = artte_read_robots_file();

	if ( false === $robots_content ) {
		$robots_content = artte_get_default_robots_content();
	}

	$robots_url = home_url( '/robots.txt' );
	?>
	<div class="wrap">
		<h1><?php esc_html_e( 'Robots.txt Editor', 'admin-robots-txt-editor' ); ?></h1>

		<?php if ( $message ) : ?>
			<div class="notice <?php echo $success ? 'notice-success' : 'notice-error'; ?> is-dismissible">
				<p><?php echo esc_html( $message ); ?></p>
			</div>
		<?php endif; ?>

		<p>
			<?php
			printf(
				/* translators: %s: robots.txt URL. */
				esc_html__(
					'Manage the robots.txt file used by your site. View the current public file: %s',
					'admin-robots-txt-editor'
				),
				'<a href="' . esc_url( $robots_url ) . '" target="_blank" rel="noopener noreferrer">' .
				esc_html( $robots_url ) .
				'</a>'
			);
			?>
		</p>

		<form method="post">
			<?php wp_nonce_field( 'artte_update_robots', 'artte_nonce' ); ?>

			<label class="screen-reader-text" for="artte-robots-content">
				<?php esc_html_e( 'robots.txt content', 'admin-robots-txt-editor' ); ?>
			</label>

			<textarea
				id="artte-robots-content"
				name="robots_content"
				rows="25"
				class="large-text code"
				spellcheck="false"
			><?php echo esc_textarea( $robots_content ); ?></textarea>

			<p>
				<button
					type="submit"
					name="artte_action"
					value="save"
					class="button button-primary"
				>
					<?php esc_html_e( 'Save robots.txt', 'admin-robots-txt-editor' ); ?>
				</button>

				<button
					type="submit"
					name="artte_action"
					value="reset"
					class="button button-secondary"
					data-artte-reset="1"
				>
					<?php esc_html_e( 'Reset to Default', 'admin-robots-txt-editor' ); ?>
				</button>
			</p>
		</form>

		<p>
			<em>
				<?php
				esc_html_e(
					'The plugin stores the edited file at the WordPress installation root. If no physical robots.txt exists, WordPress serves the same content through the robots_txt filter.',
					'admin-robots-txt-editor'
				);
				?>
			</em>
		</p>
	</div>
	<?php
}