per post nav menus

per-post-nav-menu.php

@@ -0,0 +1,176 @@
+<?php
+/**
+ * Plugin Name: Per Post Nav Menu
+ * Plugin URI: http://wordpress.stackexchange.com/q/85243/6035
+ * Description: Change nav menu based on theme location and a per-post selection.
+ * Version: 1.0
+ * Text Domain: wpse
+ * Author: Christopher Davis
+ * Author URI: http://christopherdavis.me
+ * License: GPL-2.0+
+ *
+ * Copyright 2013 Christopher Davis <http://christopherdavis.me>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2, as 
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * @category    WordPress
+ * @author      Christopher Davis <http://christopherdavis.me>
+ * @copyright   2013 Christopher Davis
+ * @license     http://opensource.org/licenses/GPL-2.0 GPL-2.0+
+ */
+
+!defined('ABSPATH') && exit;
+
+PerPostNavMenu::init();
+
+class PerPostNavMenu
+{
+    const NONCE = 'wpse85243_nav_nonce';
+    const FIELD = '_wpse85243_per_post_menu';
+    const LOC   = 'primary'; // the location for twenty twelve
+
+    private static $ins = null;
+
+    public static function instance()
+    {
+        if (is_null(self::$ins)) {
+            self::$ins = new self;
+        }
+
+        return self::$ins;
+    }
+
+    public static function init()
+    {
+        add_action('plugins_loaded', array(self::instance(), '_setup'));
+    }
+
+    public function _setup()
+    {
+        add_action('add_meta_boxes', array($this, 'addBox'));
+        add_action('save_post', array($this, 'save'), 10, 2);
+        add_filter('wp_nav_menu_args', array($this, 'switchMenu'));
+    }
+
+    public function addBox($post_type)
+    {
+        if (!post_type_exists($post_type)) {
+            return;
+        }
+
+        add_meta_box(
+            'wpse85243_nav_menu',
+            __('Nav Menu', 'wpse'),
+            array($this, 'boxCallback'),
+            $post_type,
+            'side',
+            'low'
+        );
+    }
+
+    public function boxCallback($post)
+    {
+        $menu = get_post_meta($post->ID, static::FIELD, true);
+
+        wp_nonce_field(static::NONCE . $post->ID, static::NONCE, false);
+
+        printf(
+            '<label for="%s">%s</label>',
+            esc_attr(static::FIELD),
+            esc_html__('Nav Menu', 'wpse')
+        );
+
+        echo '<br />';
+
+        printf('<select name="%1$s" id="%1$s">', esc_attr(static::FIELD));
+
+        foreach ($this->getNavMenus() as $id => $name) {
+            printf(
+                '<option value="%s" %s>%s</option>',
+                esc_attr($id),
+                selected($menu, $id, false),
+                esc_html($name)
+            );
+        }
+
+        echo '</select>';
+    }
+
+    public function save($post_id, $post)
+    {
+        if (defined('DOING_AUTOSAVE') && DOING_AUTOSAVE) {
+            return;
+        }
+
+        if (
+            !isset($_POST[static::NONCE]) ||
+            !wp_verify_nonce($_POST[static::NONCE], static::NONCE . $post_id)
+        ) {
+            return;
+        }
+
+        $type = get_post_type_object($post->post_type);
+        if (!current_user_can($type->cap->edit_post, $post_id)) {
+            return;
+        }
+
+        $menu = isset($_POST[static::FIELD]) ? $_POST[static::FIELD] : false;
+
+        if ($menu && '-' !== $menu) {
+            update_post_meta($post_id, static::FIELD, absint($menu));
+        } else {
+            delete_post_meta($post_id, static::FIELD);
+        }
+    }
+
+    public function switchMenu($args)
+    {
+        // we can only deal with singular pages
+        if (!is_singular()) {
+            return;
+        }
+
+        $switch = apply_filters(
+            'per_post_nav_menus_switch',
+            isset($args['theme_location']) && static::LOC === $args['theme_location'],
+            $args
+        );
+
+        // if we're allowed to switch, the the `menu` argument to
+        // the correct menu ID.
+        if ($switch) {
+            $menu = get_post_meta(get_queried_object_id(), static::FIELD, true);
+
+            if ('-' !== $menu) {
+                $args['menu'] = absint($menu);
+            }
+        }
+
+        return $args;
+    }
+
+    private function getNavMenus()
+    {
+        $terms = get_terms('nav_menu');
+
+        $menus = array('-' => __('Default', 'wpse'));
+        if ($terms && !is_wp_error($terms)) {
+            foreach($terms as $t) {
+                $menus[$t->term_id] = $t->name;
+            }
+        }
+
+        return apply_filters('per_post_nav_menus_list', $menus);
+    }
+}