<?php
/**
 * Per-user menu-order persistence and fail-safe merging.
 *
 * @package AdminGrip
 */

namespace AdminGrip;

/**
 * Integrates a saved AdminGrip order with WordPress's menu-order filters.
 */
final class Admin_Menu_Order {
	/**
	 * Site-specific user option name.
	 */
	const OPTION_NAME = 'admingrip_menu_order';

	/**
	 * Maximum number of accepted menu slugs.
	 */
	const MAX_ENTRIES = 200;

	/**
	 * Maximum byte length of a single exact menu slug.
	 */
	const MAX_SLUG_LENGTH = 512;

	/**
	 * Registers menu-order filters.
	 *
	 * @return void
	 */
	public function register() {
		add_filter( 'custom_menu_order', array( $this, 'enable_custom_menu_order' ) );
		add_filter( 'menu_order', array( $this, 'apply_saved_order' ), 1000 );
	}

	/**
	 * Enables WordPress's menu-order filter only when AdminGrip has an order.
	 *
	 * @param bool $enabled Whether another component enabled custom ordering.
	 * @return bool
	 */
	public function enable_custom_menu_order( $enabled ) {
		if ( ! self::is_supported_context() ) {
			return $enabled;
		}

		$saved = get_user_option( self::OPTION_NAME, get_current_user_id() );

		return ( is_array( $saved ) && ! empty( $saved ) ) ? true : $enabled;
	}

	/**
	 * Applies the current user's saved order without adding unavailable items.
	 *
	 * @param array $current_order Current WordPress/plugin menu order.
	 * @return array
	 */
	public function apply_saved_order( $current_order ) {
		if ( ! self::is_supported_context() ) {
			return $current_order;
		}

		$saved_order = get_user_option( self::OPTION_NAME, get_current_user_id() );

		return self::merge( $saved_order, $current_order );
	}

	/**
	 * Determines whether this is the supported normal site-admin context.
	 *
	 * @return bool
	 */
	public static function is_supported_context() {
		return is_admin() && ! is_network_admin() && ! is_user_admin();
	}

	/**
	 * Validates exact menu slugs without rewriting their persistent identity.
	 *
	 * A null result means the entire submitted value is invalid. Valid input is
	 * returned with duplicate slugs removed in first-seen order.
	 *
	 * @param mixed $order Candidate order.
	 * @return array|null
	 */
	public static function normalize_order( $order ) {
		if ( ! is_array( $order ) || count( $order ) > self::MAX_ENTRIES ) {
			return null;
		}

		$normalized = array();

		foreach ( $order as $slug ) {
			if ( ! is_string( $slug ) || '' === $slug || self::MAX_SLUG_LENGTH < strlen( $slug ) ) {
				return null;
			}

			if ( trim( $slug ) !== $slug || 1 !== preg_match( '//u', $slug ) || preg_match( '/[\x00-\x1F\x7F]/u', $slug ) ) {
				return null;
			}

			if ( function_exists( 'wp_check_invalid_utf8' ) && wp_check_invalid_utf8( $slug, true ) !== $slug ) {
				return null;
			}

			if ( ! in_array( $slug, $normalized, true ) ) {
				$normalized[] = $slug;
			}
		}

		return $normalized;
	}

	/**
	 * Fail-safely merges a saved slug list with the currently available order.
	 *
	 * @param mixed $saved_order   Stored AdminGrip order.
	 * @param array $current_order Current WordPress/plugin order.
	 * @return array
	 */
	public static function merge( $saved_order, $current_order ) {
		if ( ! is_array( $current_order ) ) {
			return $current_order;
		}

		$normalized = self::normalize_order( $saved_order );

		if ( null === $normalized || empty( $normalized ) ) {
			return $current_order;
		}

		$merged = array();

		foreach ( $normalized as $slug ) {
			if ( in_array( $slug, $current_order, true ) && ! in_array( $slug, $merged, true ) ) {
				$merged[] = $slug;
			}
		}

		foreach ( $current_order as $slug ) {
			if ( ! in_array( $slug, $merged, true ) ) {
				$merged[] = $slug;
			}
		}

		return $merged;
	}
}