WordPress Facebook Instant Articles - How to apply different styles to posts

wpna-article-style-filter-author.php

<?php
/**
 * Changes the Instant Article style for this post based on author.
 *
 * This is fired within the loop.
 *
 * @param  string $style The default style.
 * @return string The new style to apply.
 */
function wpna_author_style( $style ) {
	// If the post was written by the user with ID 5
	// then return the custom style.
	if ( 5 === get_the_author_meta( 'ID' ) ) {
		return 'timsmith';
	}
	
	// If the author was joebloggs then return a
	// custom style.
	if ( 'joebloggs' === get_the_author_meta('user_nicename') ) {
		return 'joebloggs';
	}

	// Else return the default style.
	return $style;
}
add_filter( 'wpna_facebook_post_get_style', 'wpna_author_style', 10, 1 );

wpna-article-style-filter-category.php

<?php
/**
 * Changes the Instant Article style for this post based on category.
 *
 * This is fired within the loop.
 *
 * @param  string $style The default style.
 * @return string The new style to apply.
 */
function wpna_category_style( $style ) {
	// If the post has any of these categories then return a custom style.
	if ( has_category( array( 'actor', 'director' ) ) ) {
		return 'movies';
	}
	// Else return the default style.
	return $style;
}
add_filter( 'wpna_facebook_post_get_style', 'wpna_category_style', 10, 1 );

wpna-article-style-filter-tag.php

<?php
/**
 * Changes the Instant Article style for this post based on tag.
 *
 * This is fired within the loop.
 *
 * @param  string $style The default style.
 * @return string The new style to apply.
 */
function wpna_tag_style( $style ) {
	// If the post has any of these tags then return a custom style.
	if ( has_tag( array( 'romance', 'action', 'comedy' ) ) ) {
		return 'movies';
	}
	// Else return the default style.
	return $style;
}
add_filter( 'wpna_facebook_post_get_style', 'wpna_tag_style', 10, 1 );