Wordpress sort search results by custom order

I want to search "sandwich"
I have
pages as "sandwich", sandwich-toast, sandwich-three-layer, sandwich-simple
posts as "sandwich-recipe", "sandwich-maker-links", "best-sandwich-in-newyork"
CPT as "sandwiches"

What is expected:
I want to search the keyword "sandwich". The expected result should be orderby my preference i.e

1. sandwich (main-page)
2. sandwich-toast (child-page of sandwich)
3. sandwich-three-layer (page) etc (pages)
4. sandwich-recipe (posts) etc
5. sandwiches (custom post type)

What I have tried so far:

<form method="get" id="searchform" action="" role="search" autocomplete="off">
    <label class="sr-only" for="s"><?php esc_html_e( 'Search', 'understrap' ); ?></label>
    <div class="input-group">
        <input class="field form-control" id="s" name="s" type="text" autocomplete="off"
            placeholder="<?php esc_attr_e( 'Search &hellip;', 'understrap' ); ?>" value="<?php the_search_query(); ?>">
        <input type='hidden' name='post_type' value='' />
        <span class="input-group-append">
            <input class="submit btn btn-primary" id="searchsubmit" type="submit"
            value="<?php esc_attr_e( 'Search', 'understrap' ); ?>">
    </span>
    </div>
</form>

while ( have_posts() ) : the_post();
    if ('page' == get_post_type()) {
        get_template_part( 'loop-templates/content', 'search' );
    } else if('post' == get_post_type()) {
        get_template_part( 'loop-templates/content', 'searchblog' );
    } else if('sandwiches' == get_post_type()) {
        get_template_part( 'loop-templates/content', 'searchcpt' );
    } else {        
        get_template_part( 'loop-templates/content', 'search' );
    }
endwhile;

add_filter( 'posts_orderby', 'order_search_by_posttype', 10, 2 );
function order_search_by_posttype( $orderby, $wp_query ){
    if( ! $wp_query->is_admin && $wp_query->is_search ) :
        global $wpdb;
        $orderby =
            "
            CASE WHEN {$wpdb->prefix}posts.post_type = 'page' THEN '1' 
                 WHEN {$wpdb->prefix}posts.post_type = 'post' THEN '2' 
            ELSE {$wpdb->prefix}posts.post_type END ASC,
            {$wpdb->prefix}posts.post_title ASC";
    endif;
    return $orderby;
}

What I think is I need to add some sort of indexing to the pages, posts & custom post type so that I can decide the order the results should be displayed according to the priority I want to set them to display.