Add "page-a" slug to category link if user visit category link from "page-a"

Question

I have Area pages like below:

http://www.example.com/area1

http://www.example.com/area2

On each area page common wp menus are displaying categories. To illustrate:

Menu Items:

-> category1

-> category2

I have set my Permalink settings as below:

Custom Structure: http://www.example.com/artiklar/%post_id%

So for now My category URL is:

http://www.example.com/artiklar/category/category1

But my requirements is when user visit category page suppose category1 from area page say area1 then category URL turns out like below URL:

http://www.example.com/artiklar/category/category1?tag=area1

And if category menu is visited from area 2 then it should be :

http://www.example.com/artiklar/category/category1?tag=area2

Please suggest, I am not getting any idea by searching on web how to implement this kind of structure.

EDIT:

Trying to make it more clear that I want to append slug of page to category URL (page from where user will visit category link, slug of that page will get added to category URL at end of URL)

Answer 1

You would want to filter the category link to add the custom variable to the category link. You can make use of the get_term_link filter to filter the category link address

Here is a very basic idea:

Suppose that we, taken from OP, that you need to add the custom variable only to terms belonging to the build in taxonomy category, and only when we are on a real page and we want to add the page ID as value to the URL, we can create a filter function to just do exactly that, and by using add_query_arg(), we can add a new query variable, lets call it frompage, to the URL.

Here is a basic function, which you can extend and modify as you see fit. I have commented the code to make it easy to follow

add_filter( 'term_link', function ( $termlink, $term, $taxonomy )
{
    // If this is not a page, return the unmodified term link
    if ( !is_page() ) // Change this to what is specific to your needs
        return $termlink;

    // Only target the build in taxonomy 'category'
    if ( $taxonomy !== 'category' ) // Adjust to your exact taxonomy
        return $termlink;

    // Get the current viewed paged id
    $current_id = get_queried_object_id();

    // Make sure we actually have a value, if not, return the term link
    if ( $current_id == 0 )
        return $termlink;

    // If we reached this point, we are good to go and should add our query var to the URL
    $termlink = esc_url( add_query_arg( ['frompage' => $current_id], $termlink ) );

    return  $termlink;
}, 10, 3 );

You can then retrieve the value as follow:

$value = filter_input( INPUT_GET, 'frompage', FILTER_VALIDATE_INT ); 
if ( $value )
    echo $value;

Note that I have used filter_input here to get the $_GET value. That is because that filter_input validates if the passed value exists and either returns it or returns false. Also, you can pass a filter to be used on the value, in this case FILTER_VALIDATE_INT. All in all, it is a much better and safer way than $_GET( 'frompage )`