Build stats pixel for Jetpack sites

jetpack-helper.php

@@ -9,6 +9,9 @@
  *
  **/
 function amp_jetpack_mods() {
+	if ( Jetpack::is_module_active( 'stats' ) ) {
+		add_action( 'amp_post_template_footer', 'jetpack_amp_add_stats_pixel' );
+	}
 	amp_jetpack_disable_sharing();
 	amp_jetpack_disable_related_posts();
 }
@@ -29,3 +32,38 @@ function amp_jetpack_disable_related_posts() {
 		remove_filter( 'the_content', array( $jprp, 'filter_add_target_to_dom' ), 40 );
 	}
 }
+
+function jetpack_amp_add_stats_pixel( $amp_template ) {
+	if ( ! has_action( 'wp_footer', 'stats_footer' ) ) {
+		return;
+	}
+	?>
+	<amp-pixel src="<?php echo esc_url( jetpack_amp_build_stats_pixel_url() ); ?>"></amp-pixel>
+	<?php
+}
+
+/**
+ * Generate the stats pixel.
+ *
+ * Looks something like:
+ *     https://pixel.wp.com/g.gif?v=ext&j=1%3A3.9.1&blog=1234&post=5678&tz=-4&srv=example.com&host=example.com&ref=&rand=0.4107963021218808
+ */
+function jetpack_amp_build_stats_pixel_url() {
+	if ( function_exists( 'stats_build_view_data' ) ) { // added in https://github.com/Automattic/jetpack/pull/3445
+		$data = stats_build_view_data();
+	} else {
+		$blog = Jetpack_Options::get_option( 'id' );
+		$tz = get_option( 'gmt_offset' );
+		$v = 'ext';
+		$blog_url = parse_url( site_url() );
+		$srv = $blog_url['host'];
+		$j = sprintf( '%s:%s', JETPACK__API_VERSION, JETPACK__VERSION );
+		$post = $wp_the_query->get_queried_object_id();
+		$data = compact( 'v', 'j', 'blog', 'post', 'tz', 'srv' );
+	}
+
+	$data['rand'] = 'RANDOM'; // amp placeholder
+	$data['ref'] = 'DOCUMENT_REFERRER'; // amp placeholder
+	$data = array_map( 'rawurlencode' , $data );
+	return add_query_arg( $data, 'https://pixel.wp.com/g.gif' );
+}