[WordPress] How to set permalinks with multiple categories in a hierarchy

What I want to do

For example,

• Tokyo Branch (tokyo)
• Kansai Branch (kansai)
• Blog (blog)
• News (news)

with these four categories:

When two categories, "Tokyo Branch" and "Blog", are set for a post,

If nothing is done, the permalink will be one of the following:

The goal is to make it a directory hierarchy like this. (Like "Tokyo Branch Blog")

If "Kansai Branch" and "News" are set, it should become "/kansai/news/○○/"

Using post_link

We will change the permalink using the "post_link" hook.

post_link | Hook | WordPress Developer Resources

Add the following to functions.php

// Hierarchical permalinks for multiple categories
function permalink_change_post($permalink, $post){
	// Get post categories and store slugs in an array
	$category = get_the_category($post->ID);
	$category_slug = array();

	foreach ($category as $cate){
		array_push($category_slug, $cate->slug);
	}

	// Category 1
	$cate_arr1 = array('tokyo', 'kansai');
	// Category 2
	$cate_arr2 = array('blog', 'news');

	// Difference between "post categories" and "category 1, 2"
	$diff_1 = array_intersect($cate_arr1, $category_slug);
	$diff_2 = array_intersect($cate_arr2, $category_slug);

	// When one of each category 1 and 2 is included
	if(count($diff_1) === 1 && count($diff_2) === 1){
		// Change permalink to hierarchical
		$permalink = home_url('/'.$diff_1[0].'/'.$diff_2[0].'/'.$post->post_name.'/' );
	}

	return $permalink;
}
add_filter('post_link', 'permalink_change_post', 10, 2);

It's a bit messy, but

① First, get the categories of the current post.

② Define the slug of the category you want to be the parent on line 12.

③ Define the slug of the category you want to be the child on line 14.

When one category from ② and one from ③ are set for the current post,

the permalink will be changed to "/②/③/○○/".

Then, the permalink changed.

The URL didn't change just by refreshing the page, so open it again from a list or similar.

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