<?php
/**
 * Duolangue — Menu synchronization (free).
 *
 * On the front end, every nav-menu item pointing at an object that has a
 * linked translation in the CURRENT language is swapped to that translation
 * (URL, and the label when it was the object's own title).
 *
 * This is the baseline promise of the free edition: linking two pages in the
 * editor is enough for the menu to follow the visitor's language. No menu
 * configuration, no per-menu language, no duplicate menu to maintain.
 *
 * It can also append a language link to chosen menu locations (Settings →
 * Language switcher & menus).
 *
 * Other code may hook wp_nav_menu_objects after priority 10 to handle item
 * types this class does not touch.
 */

defined( 'ABSPATH' ) || exit;

class Duolangue_Menu_Sync {

	public function __construct() {
		add_filter( 'wp_nav_menu_objects', array( $this, 'translate_items' ), 10, 2 );
		add_filter( 'wp_nav_menu_items', array( $this, 'append_language' ), 20, 2 );
	}

	/**
	 * @param array         $items Menu item objects.
	 * @param stdClass|null $args  wp_nav_menu() arguments.
	 * @return array
	 */
	public function translate_items( $items, $args = null ) {
		if ( is_admin() ) {
			return $items;
		}

		/**
		 * Disable the automatic item-level translation (e.g. when every menu
		 * is maintained manually per language).
		 *
		 * @param bool          $enabled
		 * @param stdClass|null $args    wp_nav_menu() arguments.
		 */
		if ( ! apply_filters( 'duolangue_translate_menu_items', true, $args ) ) {
			return $items;
		}

		$current    = duolangue_current_lang();
		$post_types = duolangue_post_types();

		foreach ( $items as $item ) {
			if ( 'post_type' === $item->type && $item->object_id ) {
				if ( ! in_array( (string) $item->object, $post_types, true ) ) {
					continue;
				}
				$this->translate_post_item( $item, $current );
			}
		}

		return $items;
	}

	/**
	 * Swap a page/post item for its linked translation.
	 */
	private function translate_post_item( $item, $current ) {
		$object_id = (int) $item->object_id;

		// Already in the visitor's language (e.g. the item was added from the
		// right language, or a per-language menu was served).
		if ( duolangue_get_post_lang( $object_id ) === $current ) {
			return;
		}

		$translation = duolangue_get_post_translation( $object_id );
		if ( ! $translation
			|| 'publish' !== get_post_status( $translation )
			|| duolangue_get_post_lang( $translation ) !== $current ) {
			// No usable translation: keep the item as-is rather than hiding
			// it — a visible link to the other language beats a hole in the
			// navigation.
			return;
		}

		// Replace the label only when it was the object's own title; a custom
		// navigation label is the author's deliberate wording and is kept.
		if ( (string) $item->title === (string) get_the_title( $object_id ) ) {
			$item->title = get_the_title( $translation );
		}
		if ( (string) $item->attr_title === (string) get_the_title( $object_id ) ) {
			$item->attr_title = get_the_title( $translation );
		}

		$item->url       = get_permalink( $translation );
		$item->object_id = (string) $translation;
	}

	/**
	 * Append a language link to the menus chosen in the settings.
	 *
	 * @param string   $items HTML list items.
	 * @param stdClass $args  wp_nav_menu() arguments.
	 * @return string
	 */
	public function append_language( $items, $args ) {
		if ( is_admin() ) {
			return $items;
		}

		$settings  = duolangue_get_settings();
		$locations = (array) $settings['menu_locations'];

		if ( empty( $locations ) ) {
			return $items;
		}

		// '_all' targets every menu (useful when the theme/builder registers
		// no locations — Oxygen, Bricks…); otherwise match the location.
		if ( ! in_array( '_all', $locations, true ) && ! $this->is_menu_in_locations( $args, $locations ) ) {
			return $items;
		}

		$display = $settings['menu_display'];
		$current = duolangue_current_lang();

		if ( 'both' === $settings['menu_show'] ) {
			foreach ( duolangue_get_languages() as $lang ) {
				$items .= $this->menu_item(
					$lang,
					Duolangue_Router::url_for_lang( $lang['code'] ),
					$display,
					$lang['code'] === $current ? ' current-lang' : ''
				);
			}
			return $items;
		}

		// Default: only the other language.
		return $items . $this->menu_item( duolangue_other_lang(), duolangue_other_lang_url(), $display, '' );
	}

	/**
	 * Is the menu being rendered one of the chosen locations?
	 *
	 * Matches either the location the theme asked for (theme_location), or
	 * the menu itself when it is assigned to a chosen location: page builders
	 * (Oxygen, Bricks…) usually render a menu by its ID, not by location.
	 *
	 * @param stdClass $args      wp_nav_menu() arguments.
	 * @param string[] $locations Locations chosen in the settings.
	 * @return bool
	 */
	private function is_menu_in_locations( $args, $locations ) {
		$location = isset( $args->theme_location ) ? (string) $args->theme_location : '';
		if ( '' !== $location && in_array( $location, $locations, true ) ) {
			return true;
		}

		$menu = isset( $args->menu ) ? wp_get_nav_menu_object( $args->menu ) : false;
		if ( ! $menu ) {
			return false;
		}

		$assigned = get_nav_menu_locations();
		foreach ( $locations as $chosen ) {
			if ( isset( $assigned[ $chosen ] ) && (int) $assigned[ $chosen ] === (int) $menu->term_id ) {
				return true;
			}
		}
		return false;
	}

	private function menu_item( $lang, $url, $display, $extra_class ) {
		return sprintf(
			'<li class="menu-item duolangue-menu-lang duolangue-menu-lang-%s%s"><a href="%s" hreflang="%s" lang="%s">%s</a></li>',
			esc_attr( $lang['code'] ),
			esc_attr( $extra_class ),
			esc_url( $url ),
			esc_attr( str_replace( '_', '-', $lang['locale'] ) ),
			esc_attr( $lang['code'] ),
			esc_html( duolangue_lang_label( $lang, $display ) )
		);
	}
}