Facebook open graph and Twitter card add in functions.php

add-open-graph.php

function add_opengraph_markup() {
  if (is_single()) {
    global $post;
    if(get_the_post_thumbnail($post->ID, 'thumbnail')) {
      $thumbnail_id = get_post_thumbnail_id($post->ID);
      $thumbnail_object = get_post($thumbnail_id);
      $image = $thumbnail_object->guid;
    } else {
      // set default image
      $image = ''; //
    }
    //$description = get_bloginfo('description');
    $description = substr(strip_tags($post->post_content),0,200) . '...';
?>
<meta property="og:title" content="<?php the_title(); ?>" />
<meta property="og:type" content="article" />
<meta property="og:image" content="<?=$image?>" />
<meta property="og:url" content="<?php the_permalink(); ?>" />
<meta property="og:description" content="<?=$description?>" />
<meta property="og:site_name" content="<?=get_bloginfo('name')?>" />
<?php
  }
}
add_action('wp_head', 'add_opengraph_markup');

add-twitter-card.php

function add_opengraph_markup() {
  if (is_single()) {
    global $post;
    $image = get_image(get_field('main_image'),'692x410');
    $description = substr(strip_tags($post->post_content),0,200) . '...';
?>
<meta property="og:title" content="<?php the_title(); ?>" />
<meta property="og:type" content="article" />
<meta property="og:image:url" content="<?=$image?>" />
<meta property="og:url" content="<?php the_permalink(); ?>" />
<meta property="og:description" content="<?=$description?>" />
<meta property="og:site_name" content="<?=get_bloginfo('name')?>" />

<meta name="twitter:card" content="summary_large_image">
<meta name="twitter:site" content="@fathomjournal">
<meta name="twitter:title" content="<?php the_title(); ?>">
<meta name="twitter:description" content="<?=$description?>">
<meta name="twitter:image" content="<?=$image?>">
<?php
  }
}
add_action('wp_head', 'add_opengraph_markup');