<?php
/**
 * Generator for the nginx configuration snippet.
 *
 * @package AIBlackout
 */

namespace AIBlackout\Enforcement;

use AIBlackout\Crawlers\UserAgentMatcher;

defined( 'ABSPATH' ) || exit;

/**
 * Generates a copy-paste nginx snippet.
 *
 * @since 1.0.0
 */
class NginxSnippet {

	/**
	 * User-agent matcher.
	 *
	 * @var UserAgentMatcher
	 */
	private $matcher;

	/**
	 * Constructor.
	 *
	 * @param UserAgentMatcher $matcher User-agent matcher.
	 */
	public function __construct( UserAgentMatcher $matcher ) {
		$this->matcher = $matcher;
	}

	/**
	 * Builds the snippet.
	 *
	 * @return string The snippet, or an empty string when nothing is blocked.
	 */
	public function build(): string {
		$tokens = $this->matcher->get_enforceable_tokens();

		if ( empty( $tokens ) ) {
			return '';
		}

		$lines = array(
			'# BEGIN AI Blackout',
			'# Add this inside the server { } block for your site, then reload nginx',
			'# with: sudo nginx -t && sudo systemctl reload nginx',
			'#',
			'# This blocks AI crawlers that identify themselves. It cannot stop a',
			'# crawler that disguises its user agent.',
			'',
			'if ($http_user_agent ~* "(' . implode( '|', array_map( array( $this, 'escape' ), $tokens ) ) . ')") {',
			'    return 403;',
			'}',
			'',
			'# END AI Blackout',
		);

		return implode( "\n", $lines ) . "\n";
	}

	/**
	 * Escapes a token for use inside an nginx regular expression.
	 *
	 * @param string $token User-agent token.
	 * @return string Escaped token.
	 */
	private function escape( string $token ): string {
		return preg_quote( $token, '"' );
	}
}