Publish Posts to Multiple Blogs in WordPress Multisite

add_action( 'save_post', 'misha_post_to_all_sites', 20, 2 );

function misha_post_to_all_sites( $original_post_id, $original_post ){

	// do not publish revisions
	if( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
		return $original_post_id;
	}

	// actually we need only "publish" status
	if( 'publish' !== get_post_status( $original_post ) ) {
		return $original_post_id;
	}

	// prevent "Fatal error: Maximum function nesting level reached"
	remove_action( 'save_post', __FUNCTION__ );

	// here you have to specify blog IDs where you would like to publish the posts
	$blog_ids = array( 2, 3 );

	// let's get this post data as an array
	$post_data = array(
		'post_author' => $original_post->post_author,
		'post_date' => $original_post->post_date,
		'post_modified' => $original_post->post_modified,
		'post_content' => $original_post->post_content,
		'post_title' => $original_post->post_title,
		'post_excerpt' => $original_post->post_excerpt,
		'post_status' => 'publish',
		'post_name' => $original_post->post_name,
		'post_type' => $original_post->post_type,
	);


	// terms and post meta as well
	$post_terms = wp_get_object_terms( $original_post_id, 'category', array( 'fields' => 'slugs' ) );
	$post_meta = get_post_custom( $original_post_id );

	foreach( $blog_ids as $blog_id ) {

		switch_to_blog( $blog_id );

		// if post with the same slug exists, do nothing
		if( get_posts( array( 'name' => $post_data[ 'post_name' ], 'post_type' => $post_data[ 'post_type' ], 'post_status' => 'publish' ) ) ) {
			restore_current_blog();
			continue;
		}

		$inserted_post_id = wp_insert_post( $post_data );

		wp_set_object_terms( $inserted_post_id, $post_terms, 'category', false );
		
		foreach ( $post_meta as $meta_key => $meta_values) {
			// we do not need these redirects
			if( '_wp_old_slug' === $meta_key ) {
				continue;
			}
			foreach ( $meta_values as $meta_value ) {
				add_post_meta( $inserted_post_id, $meta_key, $meta_value );
			}
		}
		
		restore_current_blog();

	}

}