Creating drop downs that controls the Query Loop or Posts that display

Hey there,

I need help please to create a page that displays my job openings (maybe this is a content template) and provides 3 dropdowns that the visitor can use to filter the results. Job openings is a custom post type with a hierarchical taxonomy of location. Country is the parent of state which is the parent of city (Country -> state -> city).

The first dropdown is country and shows all the country terms. When a visitor chooses a country, the job openings would filter to those assigned the selected country. The second dropdown is state and shows all the state terms that are a child to the selected country. When a visitor chooses a state, the job openings would filter to those assigned the selected state. Lastly, the third dropdown is city and shows all the city terms that are a child to the selected state. When a visitor chooses a city, the job openings would filter to those assigned the selected city.

I've tried the following which produces the first dropdown, but struggling to connect all the pieces.

// shortcode to list taxonomies related to job openings: country, state, city dropdowns.
function my_country_dropdown() {
	$args = array(
		 'show_option_none' 	=> 'Select Country',
		 'taxonomy' 			=> 'location',
		 //'value_field'			=> 'term_id',
		 'term_taxonomy_id'		=> array( 82, 83), //filter results to United States (83) and Canada (82)
		 'show_count'			=> 1, // show the number of jobs under each location
		 'hierarchical'			=> 1, // shows the indentations for child taxonomies
	);
	wp_dropdown_categories($args);
} 

add_shortcode('display_country_dropdown', 'my_country_dropdown' );

Thanks,
Fergal