Add filter to post thumbnail ID

[claytoncollie]

I created an issue for this a while back before knowing how to create a PR. But now with my new super powers, I was able to make this addition. :)

My use case was that I had a list of people in the search results and I needed a way to have a fallback image for when the person did not have a featured image. The results display the featured image and not having an image threw off my styling.

Here is the callback I am using with this filter.

/**
 * When a featured image is not present, use another attachment ID provided by database option.
 *
 * @param int $post_thumbnail_id Post thumbnail ID.
 * @param int $post_id Post ID.
 *
 * @return int
 */
function prefix_get_post_thumbnail_id( $post_thumbnail_id, $post_id ) {

	if ( ! in_array( get_post_type( $post_id ), array( 'your_post_type' ), true ) ) {
		return $post_thumbnail_id;
	}

	if ( ! has_post_thumbnail( $post_id ) ) {
		$post_thumbnail_id = intval( 'your_fallback_image_id' );
	} else {
		$post_thumbnail_id = get_post_thumbnail_id( $post_id );
	}
		
	return $post_thumbnail_id;

}```

[rayrutjes]

Thanks a lot for your active participation in this plugin. We wanted to let you know that we chose to go in another direction regarding the way we integrate Algolia to WordPress. More information can be found here.