<?php
/**
 * Custom class to display navigation menu AMP-Friendly - some like this:
 *
 * <a href="#">Menu</a>         # Parent item with no child elements
 *    <amp-accordion>
 *      <section>
 *          <h6><span>Submenu 1</span></h6># Parent item with childs
 *          <div>
 *                <a href="#">Submenu 2</a>
 *                ....                      #list sub menus
 *          </div>
 *       </section>
 *     </amp-accordion>
 *
 *
 * @since 1.0.0
 */
class Amp_WP_Menu_Walker extends Walker_Nav_Menu {
    /**
     * Start_el method use this property to detect if previous element was
     * an accordion print <h6> element like above html
     *
     * @since 1.0.0
     *
     * @var bool
     */
    protected $accordion_started = false;

    /**
     * flag for detecting childs started or not
     *
     * @since 1.0.0
     *
     * @var bool
     */
    protected $accordion_childs_started = false;

    /**
     * Starts the list before the elements are added.
     *
     * @see   Walker::start_lvl()
     *
     * @param string $output Passed by reference. Used to append additional content.
     * @param int    $depth  Depth of menu item. Used for padding.
     * @param array  $args   An array of wp_nav_menu() arguments.
     *
     * @since 1.0.0
     */
    public function start_lvl(&$output, $depth = 0, $args = array()) {}

    /**
     * Starts the list before the elements are added.
     *
     * @see   Walker::start_lvl()
     *
     * @param string $output Passed by reference. Used to append additional content.
     * @param int    $depth  Depth of menu item. Used for padding.
     * @param array  $args   An array of wp_nav_menu() arguments.
     *
     * @since 1.0.0
     */
    public function end_lvl(&$output, $depth = 0, $args = array()) {
        if ($this->accordion_childs_started && $depth == 0) {
            $this->end_accordion_child_wrapper($output, $depth);
        }
        if ($this->accordion_started && $depth == 0) {
            $this->end_accordion($output, $depth);
        }
    }

    /**
     * Starts the element output.
     *
     * @see   Walker::start_el()
     *
     * @param string $output Passed by reference. Used to append additional content.
     * @param object $item   Menu item data object.
     * @param int    $depth  Depth of menu item. Used for padding.
     * @param array  $args   An array of wp_nav_menu() arguments.
     * @param int    $id     Current item ID.
     *
     * @since 1.0.0
     */
    public function start_el(&$output, $item, $depth = 0, $args = array(), $id = 0) {
        $args = apply_filters('nav_menu_item_args', $args, $item, $depth);

        // Remove menu-item-has-children class
        if ($depth) {
            $index = array_search('menu-item-has-children', $item->classes);
            if ($index !== false) {
                unset($item->classes[$index]);
            }
        }

        $classes = empty($item->classes) ? array() : (array) $item->classes;
        $classes[] = 'menu-item-' . $item->ID;

        if ($depth > 1) {
            $classes[] = 'menu-item-deep';
        }

        $class_names = join(' ', apply_filters('nav_menu_css_class', array_filter($classes), $item, $args, $depth));
        $class_names = $class_names ? ' class="' . esc_attr($class_names) . '"' : '';

        if ($this->has_children && $depth == 0) {
            add_theme_support('amp-wp-has-nav-child', true);
            $this->start_accordion($output, $depth);
            $output .= '<h6><span ' . $class_names . '>';
            $output .= $this->get_anchor_tag($item, $depth, $args, $id);
            $output .= '</span></h6>';
            $this->start_accordion_child_wrapper($output, $depth);
        } else {
            $output .= '<span ' . $class_names . '>';
            $output .= $this->get_anchor_tag($item, $depth, $args, $id);
            $output .= '</span>';
        }
    }

    // start_el
    public function end_el(&$output, $item, $depth = 0, $args = array()) { }

    /**
     * Adds the start code of accordion
     *
     * @param     $output
     * @param int $depth
     *
     * @since 1.0.0
     */
    public function start_accordion(&$output, $depth = 0) {
        $output .= "<amp-accordion><section>";
        $this->accordion_started = true;
        $this->enqueue_accordion = true;
    }

    /**
     * Ads close tag for accordion
     *
     * @param     $output
     * @param int $depth
     *
     * @since 1.0.0
     */
    public function end_accordion(&$output, $depth = 0) {
        $output .= "</section></amp-accordion>";
        $this->accordion_started = false;
    }

    /**
     * Adds acordion childs wrapper div
     *
     * @param     $output
     * @param int $depth
     *
     * @since 1.0.0
     */
    public function start_accordion_child_wrapper(&$output, $depth = 0) {
        $output .= "\n<div>\n";
        $this->accordion_childs_started = true;
    }

    /**
     * Closes the accordion childs wrapper tag
     *
     * @param     $output
     * @param int $depth
     *
     * @since 1.0.0
     */
    public function end_accordion_child_wrapper(&$output, $depth = 0) {
        $output .= "</div>\n";
        $this->accordion_childs_started = false;
    }

    /**
     * @param $item
     * @param $depth
     * @param $args
     * @param $id
     *
     * @since 1.0.0
     *
     * @return string
     */
    public function get_anchor_tag($item, $depth, $args, $id) {
        $current_el = '';
        parent::start_el($current_el, $item, $depth, $args, $id);

        // Unwrap li tag
        if (preg_match('#<\s*li\s* [^>]* > (.+) #ix', $current_el, $matched)) {
            return $matched[1];
        }
        return $this->make_anchor_tag($item, $args, $depth);
    }

    /**
     * Make <a> HTML Tag
     *
     * @copyright Credit goes to wordPress team
     * @see       Walker_Nav_Menu::start_el
     *
     * @param object $item  Menu item data object.
     * @param int    $depth Depth of menu item. Used for padding.
     * @param array  $args  An array of wp_nav_menu() arguments.
     *
     * @since     1.0.0
     *
     * @return string
     */
    protected function make_anchor_tag($item, $args, $depth) {
        $atts = array();
        $atts['title'] = !empty($item->attr_title) ? $item->attr_title : '';
        $atts['target'] = !empty($item->target) ? $item->target : '';
        $atts['rel'] = !empty($item->xfn) ? $item->xfn : '';
        $atts['href'] = !empty($item->url) ? $item->url : '';

        /**
         * Filters the HTML attributes applied to a menu item's anchor element.
         *
         * @since 1.0.0
         *
         * @param array  $atts   {
         *                       The HTML attributes applied to the menu item's `<a>` element, empty strings are ignored.
         *
         * @type string  $title  Title attribute.
         * @type string  $target Target attribute.
         * @type string  $rel    The rel attribute.
         * @type string  $href   The href attribute.
         * }
         *
         * @param object $item   The current menu item.
         * @param array  $args   An array of wp_nav_menu() arguments.
         * @param int    $depth  Depth of menu item. Used for padding.
         */
        $atts = apply_filters('nav_menu_link_attributes', $atts, $item, $args, $depth);

        $attributes = '';
        foreach ($atts as $attr => $value) {
            if (!empty($value)) {
                $value = ( 'href' === $attr ) ? esc_url($value) : esc_attr($value);
                $attributes .= ' ' . $attr . '="' . $value . '"';
            }
        }

        /** This filter is documented in wp-includes/post-template.php */
        $title = apply_filters('the_title', $item->title, $item->ID);

        /**
         * Filters a menu item's title.
         *
         * @since 1.0.0
         *
         * @param string $title The menu item's title.
         * @param object $item  The current menu item.
         * @param array  $args  An array of wp_nav_menu() arguments.
         * @param int    $depth Depth of menu item. Used for padding.
         */
        $title = apply_filters('nav_menu_item_title', $title, $item, $args, $depth);
        $item_output = $args->before;
        $item_output .= '<a' . $attributes . '>';
        $item_output .= $args->link_before . $title . $args->link_after;
        $item_output .= '</a>';
        $item_output .= $args->after;
        return $item_output;
    }
}