opengraph-title'       => 'open_graph_title',
			'wpseo_opengraph-description' => 'open_graph_description',
			'wpseo_opengraph-image'       => 'open_graph_image',
			'wpseo_opengraph-image-id'    => 'open_graph_image_id',
			'wpseo_twitter-title'         => 'twitter_title',
			'wpseo_twitter-description'   => 'twitter_description',
			'wpseo_twitter-image'         => 'twitter_image',
			'wpseo_twitter-image-id'      => 'twitter_image_id',
		];
	}

	/**
	 * Retrieves a meta value from the given meta data.
	 *
	 * @param string $meta_key  The key to extract.
	 * @param array  $term_meta The meta data.
	 *
	 * @return null|string The meta value.
	 */
	protected function get_meta_value( $meta_key, $term_meta ) {
		if ( ! $term_meta || ! \array_key_exists( $meta_key, $term_meta ) ) {
			return null;
		}

		$value = $term_meta[ $meta_key ];
		if ( \is_string( $value ) && $value === '' ) {
			return null;
		}

		return $value;
	}

	/**
	 * Finds an alternative image for the social image.
	 *
	 * @param Indexable $indexable The indexable.
	 *
	 * @return array|bool False when not found, array with data when found.
	 */
	protected function find_alternative_image( Indexable $indexable ) {
		$content_image = $this->image->get_term_content_image( $indexable->object_id );
		if ( $content_image ) {
			return [
				'image'  => $content_image,
				'source' => 'first-content-image',
			];
		}

		return false;
	}
}