<?php

/**
 * Includes a few useful predicates in the bootstrapped `infiniteScroll` JS object
 * that is served along with the rest of the document upon initial page request.
 */
add_filter( 'infinite_scroll_js_settings', 'mcsf_extra_js_settings' );
function mcsf_extra_js_settings( $js_settings ) {
	$js_settings['query_args']['extra'] = array(
		'is_home' => is_home(),
		'is_front_page' => is_front_page(),
		'is_admin' => is_admin()
	);
	return $js_settings;
}

/**
 * Whitelists the `extra` variable that holds the predicates, so that IS doesn't ignore
 * it when reconstructing the original query using the query args from the IS AJAX
 * request.
 *
 * Filter priority is not actually necessary.
 */
add_filter( 'infinite_scroll_allowed_vars', 'mcsf_allow_extra_vars', 11 );
function mcsf_allow_extra_vars( $allowed_vars ) {
	$allowed_vars[] = 'extra';
	return $allowed_vars;
}

/**
 * Now that we've made these predicates available, let's use them do make our adjustments
 * to $query_args.
 *
 * Filter priority is indeed important, as we need to run this after `inject_query_args`.
 */
function mcsf_infinite_scroll_query_args_adjust( $query_args ) {
	if ( array_key_exists( 'extra', $query_args ) ) {
		$extra = $query_args['extra'];

		if ( $extra['is_admin'] ) {
			return $query_args;
		}

		if ( $extra['is_home'] || $extra['is_front_page'] ) {
		   $query_args['posts_per_page'] = 13;
		} else {
		   $query_args['posts_per_page'] = 9;
		}
	}

	return $query_args;
}
add_filter( 'infinite_scroll_query_args', 'mcsf_infinite_scroll_query_args_adjust', 11 );