Customize WordPress pagination - wordpress

Question

Good day, I am creating a plugin that will automatically posts a slideshow article with page break using <!--nextpage--> , my problem is i want to custom the pagination style instead of page: 1,2 i want to show up as next-page and previous-page. how can i achieved this one? i want to put the code inside the plugin i don't want to add codes in the theme.
I have already tried adding this code in my plugin but did not work:
$defaults = array(
'before' => '<h1>' . __( 'Pages:' ),
'after' => '</h1>',
'link_before' => '',
'link_after' => '',
'next_or_number' => 'next',
'separator' => ' ',
'nextpagelink' => __( 'Next page' ),
'previouspagelink' => __( 'Previous page' ),
'pagelink' => 'Page %',
'echo' => 1
);
wp_link_pages( $defaults );
This is the code in my plugin:
$x = "";
foreach ($leadamajig_data->questions as $post)
{
$lead_title = '<p><h1 id="title">' . $post->title . '</a></h1></p>';
$lead_choices = '<p><h1 id="clicked"><a hre="#">' . $post->choices->a . '</a></h1></p>';
$lead_choices2 ='<p><h1 id="clicked2"><a hre="#">' .$post->choices->b . '</a></h1></p>';
$lead_choices3 = '<p><h1 id="clicked3"><a hre="#">' . $post->choices->c . '</a></h1></p>';
$x = $x . $lead_title . $lead_choices . $lead_choices2 . $lead_choices3 . '<!--nextpage-->';
}
$my_post = array(
'post_title' => questions,
'post_content' => $x,
'post_status' => 'publish',
'post_author' => 1
);
wp_insert_post( $my_post );

Answer 1

wp_link_pages() returns the pagination markup you have defined with your $default array of parameters. So you probably already have the html that you want to show returned from the wp_link_pages() function.
Assign wp_link_pages() to a variable and then echo or print out the content where you want your pagination to appear.
Like this:
$defaults = array(
'before' => '<h1>' . __( 'Pages:' ),
'after' => '</h1>',
'link_before' => '',
'link_after' => '',
'next_or_number' => 'next',
'separator' => ' ',
'nextpagelink' => __( 'Next page' ),
'previouspagelink' => __( 'Previous page' ),
'pagelink' => 'Page %',
'echo' => 1
);
$pagination = wp_link_pages( $defaults );
//Put this where you want your pagination to appear:
echo $pagination;