Custom nav menu is created with default pages, but not hooked to theme's custom menu location

Question

The script below creates a nav menu and assigns a page to it. Everything's working perfectly except that the nav menu is not being automatically assigned to my theme's "Header-menu" location.

Any ideas why?

//Register menu locations for the theme
add_action( 'init', 'register_my_menus' );
function register_my_menus() {
  register_nav_menus(
    array('header-menu' => __( 'Header Menu' ), 'footer-menu' => __( 'Footer Menu' ))
  );
}

//Create a nav menu, add a page to it and assign it to the theme's "header-menu" location.
$menu_id = wp_create_nav_menu( 'header-menu' );
$menu = array( 
    'menu-item-type' => 'custom', 
    'menu-item-url' => get_home_url('/'),
    'menu-item-title' => 'Home', 
    'menu-item-status' => 'publish', 
    'theme_location' => 'header-menu', //Just a guess but didn't work!!!
    );
wp_update_nav_menu_item( $menu_id, 0, $menu );

Answer 1

wp_create_nav_menu() function accepts the menu name and not the menu location. and as for wp_update_menu_item() well its for items and not the menu itself. After digging in the code i found out that "assignment" of 'theme location' to a menu is not done using of the nav_menu API in WordPress but with theme options so:

//first get the current theme
$theme = get_current_theme();
//get theme's mods
$mods = get_option("mods_$theme");
//update mods with menu id at theme location
$mods['nav_menu_locations']['header-menu'] = $menu_id;
update_option("mods_$theme", $mods);

hope this helps :)