Checks content for video and audio links to add as enclosures.

Will not add enclosures that have already been added and will
remove enclosures that are no longer in the post. This is called as
pingbacks and trackbacks.

function do_enclose( $content, $post ) {
	global $wpdb;

	// @todo Tidy this code and make the debug code optional.
	include_once ABSPATH . WPINC . '/class-IXR.php';

	$post = get_post( $post );
	if ( ! $post ) {
		return false;
	}

	if ( null === $content ) {
		$content = $post->post_content;
	}

	$post_links = array();

	$pung = get_enclosed( $post->ID );

	$post_links_temp = wp_extract_urls( $content );

	foreach ( $pung as $link_test ) {
		// Link is no longer in post.
		if ( ! in_array( $link_test, $post_links_temp, true ) ) {
			$mids = $wpdb->get_col( $wpdb->prepare( "SELECT meta_id FROM $wpdb->postmeta WHERE post_id = %d AND meta_key = 'enclosure' AND meta_value LIKE %s", $post->ID, $wpdb->esc_like( $link_test ) . '%' ) );
			foreach ( $mids as $mid ) {
				delete_metadata_by_mid( 'post', $mid );
			}
		}
	}

	foreach ( (array) $post_links_temp as $link_test ) {
		// If we haven't pung it already.
		if ( ! in_array( $link_test, $pung, true ) ) {
			$test = parse_url( $link_test );
			if ( false === $test ) {
				continue;
			}
			if ( isset( $test['query'] ) ) {
				$post_links[] = $link_test;
			} elseif ( isset( $test['path'] ) && ( '/' !== $test['path'] ) && ( '' !== $test['path'] ) ) {
				$post_links[] = $link_test;
			}
		}
	}

	/**
	 * Filters the list of enclosure links before querying the database.
	 *
	 * Allows for the addition and/or removal of potential enclosures to save
	 * to postmeta before checking the database for existing enclosures.
	 *
	 * @since 4.4.0
	 *
	 * @param string[] $post_links An array of enclosure links.
	 * @param int      $post_ID    Post ID.
	 */
	$post_links = apply_filters( 'enclosure_links', $post_links, $post->ID );

	foreach ( (array) $post_links as $url ) {
		$url = strip_fragment_from_url( $url );

		if ( '' !== $url && ! $wpdb->get_var( $wpdb->prepare( "SELECT post_id FROM $wpdb->postmeta WHERE post_id = %d AND meta_key = 'enclosure' AND meta_value LIKE %s", $post->ID, $wpdb->esc_like( $url ) . '%' ) ) ) {

			$headers = wp_get_http_headers( $url );
			if ( $headers ) {
				$len           = isset( $headers['content-length'] ) ? (int) $headers['content-length'] : 0;
				$type          = isset( $headers['content-type'] ) ? $headers['content-type'] : '';
				$allowed_types = array( 'video', 'audio' );

				// Check to see if we can figure out the mime type from the extension.
				$url_parts = parse_url( $url );
				if ( false !== $url_parts && ! empty( $url_parts['path'] ) ) {
					$extension = pathinfo( $url_parts['path'], PATHINFO_EXTENSION );
					if ( ! empty( $extension ) ) {
						foreach ( wp_get_mime_types() as $exts => $mime ) {
							if ( preg_match( '!^(' . $exts . ')$!i', $extension ) ) {
								$type = $mime;
								break;
							}
						}
					}
				}

				if ( in_array( substr( $type, 0, strpos( $type, '/' ) ), $allowed_types, true ) ) {
					add_post_meta( $post->ID, 'enclosure', "$urln$lenn$mimen" );
				}
			}
		}
	}
}