<?php
/**
 * Optional visitor identity for logged-in users.
 *
 * @package StandChat
 */

namespace StandChat;

defined( 'ABSPATH' ) || exit;

/**
 * "Tell Stand who logged-in visitors are": a private ID and the display name.
 *
 * The private ID is an HMAC of the WordPress user ID with a secret only this
 * site has, so it links one person's chats without revealing the user ID. No
 * email is sent. Stand treats the name as unverified.
 */
final class Identity {

	const SECRET_OPTION = 'stand_chat_identity_secret';

	/**
	 * Identity for StandChat.identify(), or null when it shouldn't be sent.
	 *
	 * @return array{externalId: string, name: string}|null
	 */
	public static function for_current_user(): ?array {
		$settings = Settings::get( 'identity' );
		if ( empty( $settings['enabled'] ) || ! is_user_logged_in() ) {
			return null;
		}
		$user  = wp_get_current_user();
		$roles = is_array( $settings['roles'] ?? null ) ? $settings['roles'] : array();
		if ( empty( array_intersect( (array) $user->roles, $roles ) ) ) {
			return null;
		}
		return array(
			'externalId' => self::external_id( (int) $user->ID ),
			'name'       => mb_substr( (string) $user->display_name, 0, 120 ),
		);
	}

	/**
	 * Private ID for a WordPress user.
	 *
	 * @param int $user_id User ID.
	 */
	public static function external_id( int $user_id ): string {
		return 'wp_' . substr( hash_hmac( 'sha256', 'user:' . $user_id, self::secret() ), 0, 32 );
	}

	/**
	 * The site's identity secret, created on first use.
	 */
	private static function secret(): string {
		$secret = get_option( self::SECRET_OPTION, '' );
		if ( ! is_string( $secret ) || strlen( $secret ) < 32 ) {
			// Two requests making one at once both use the one stored first,
			// so a visitor gets one ID.
			$stored = Option_Queue::stored( self::SECRET_OPTION );
			$new    = wp_generate_password( 64, true, true );
			if ( null === $stored ) {
				Option_Queue::add( self::SECRET_OPTION, $new );
			} elseif ( strlen( $stored ) < 32 ) {
				Option_Queue::swap( self::SECRET_OPTION, $stored, $new );
			}
			$secret = (string) Option_Queue::stored( self::SECRET_OPTION );
		}
		return $secret;
	}
}