Save Jetpack "Site Stats" Pageviews as Post Meta

ac-ajax-save-views.php

<?php
/**
 * Save Jetpack views as post meta: Process Ajax request
 * 
 */
add_action( 'wp_ajax_save_views',        'ac_ajax_save_views' );
add_action( 'wp_ajax_nopriv_save_views', 'ac_ajax_save_views' );

function ac_ajax_save_views() {

	// Verify nonce
	if ( ! wp_verify_nonce( $_POST['nonce'], 'ac-save-views-' . $_POST['post_id'] ) ) {
		wp_die();
	}

	// Arguments for API call
	// @link: https://stats.wordpress.com/csv.php
	$args = array(
		'days'    => rand( 100 * 365, getrandmax() ), // To reliably bust cache: random number of days between 36,500 (~100 years in days) and max random number
		'post_id' => $_POST['post_id'],
	);

	// Make API call
	$stats = stats_get_csv( 'postviews', $args );

	// Get current view count
	$current_views = get_post_meta( $_POST['post_id'], 'views', true );

	// Make sure new view count is greater than current view count (b/c if not, then something went wrong)
	if ( isset( $stats[0]['views'] ) && (int) $stats[0]['views'] > (int) $current_views ) {

		// Save views
		update_post_meta( $_POST['post_id'], 'views', (int) $stats['0']['views'] );

	}

	// Set transient (so that we do not bombard the service w/ API calls)
	set_transient( 'ac_view_counter_' . $_POST['post_id'], 1, 4 * HOUR_IN_SECONDS ); // Adjust transient time, if desired (here: 4 hours between API calls [which seems sensible])

	wp_die(); // "this is required to terminate immediately and return a proper response"

}

ac-enqueue-scripts-save-views.php

<?php
/**
 * Save Jetpack views as post meta: Enqueue script to trigger API call (via Ajax request)
 * 
 */
add_action( 'wp_enqueue_scripts', 'ac_enqueue_scripts_save_views' );

function ac_enqueue_scripts_save_views() {

	// Bail: Not using Jetpack site stats
	if ( ! function_exists( 'stats_get_csv' ) ) return;

	// Bail: Not singular and specified post type(s)
	$post_types = array(
		'post', // Include other post types in array, if desired
	);
	if ( ! is_singular( $post_types ) ) return;

	// Bail: Transient not expired
	if ( false !== get_transient( 'ac_view_counter_' . get_the_ID() ) ) return;

	// Script
	wp_enqueue_script(
		'ac-ajax-save-views',
		get_stylesheet_directory_uri() . '/lib/js/ac.ajax-save-views.min.js', // Verify path to file
		array( 'jquery' ),
		CHILD_THEME_VERSION,
		true
	);
	
	// Localization
	$data = array(
		'ajax_url' => admin_url( 'admin-ajax.php' ),
		'post_id'  => get_the_ID(),
		'nonce'    => wp_create_nonce( 'ac-save-views-' . get_the_ID() ),
	);
	wp_localize_script( 'ac-ajax-save-views', 'save_views', $data );

}

ac.ajax-save-views.js

jQuery(document).ready(function(e) {
	e.ajax({
		method: "POST",
		url: save_views.ajax_url,
		data: {
			post_id: save_views.post_id,
			nonce: save_views.nonce,
			action: "save_views"
		}
	});
});