Fetch context surrounding a link

fetch_context.php

<?php
/**
 * Returns the text surrounding a (back)link. Very heavily inspired by
 * WordPress core.
 *
 * @link https://github.com/WordPress/WordPress/blob/1dcf3eef7a191bd0a6cd21d4382b8b5c5a25c886/wp-includes/class-wp-xmlrpc-server.php#L6929
 *
 * @param string $html   The remote page's source.
 * @param string $target The target URL.
 *
 * @return string        The excerpt, or an empty string if the target isn't found.
 */
function my_fetch_context( $html, $target ) {
  // Work around bug in `strip_tags()`.
  $html = str_replace( '<!DOC', '<DOC', $html );
  $html = preg_replace( '/[\r\n\t ]+/', ' ', $html );
  $html = preg_replace( '/<\/*(h1|h2|h3|h4|h5|h6|p|th|td|li|dt|dd|pre|caption|input|textarea|button|body)[^>]*>/', "\n\n", $html );

  // Remove all script and style tags, including their content.
  $html = preg_replace( '@<(script|style)[^>]*?>.*?</\\1>@si', '', $html );
  // Just keep the tag we need.
  $html = strip_tags( $html, '<a>' );

  $p = explode( "\n\n", $html );

  $preg_target = preg_quote( $target, '|' );

  foreach ( $p as $para ) {
    if ( strpos( $para, $target ) !== false ) {
      preg_match( '|<a[^>]+?' . $preg_target . '[^>]*>([^>]+?)</a>|', $para, $context );

      if ( empty( $context ) ) {
        // The URL isn't in a link context; keep looking.
        continue;
      }

      // We're going to use this fake tag to mark the context in a
      // bit. The marker is needed in case the link text appears more
      // than once in the paragraph.
      $excerpt = preg_replace( '|\</?wpcontext\>|', '', $para );

      // Prevent really long link text.
      if ( strlen( $context[1] ) > 100 ) {
        $context[1] = substr( $context[1], 0, 100 ) . '&#8230;';
      }

      $marker      = '<wpcontext>' . $context[1] . '</wpcontext>';  // Set up our marker.
      $excerpt     = str_replace( $context[0], $marker, $excerpt ); // Swap out the link for our marker.
      $excerpt     = strip_tags( $excerpt, '<wpcontext>' );         // Strip all tags but our context marker.
      $excerpt     = trim( $excerpt );
      $preg_marker = preg_quote( $marker, '|' );
      $excerpt     = preg_replace( "|.*?\s(.{0,100}$preg_marker.{0,100})\s.*|s", '$1', $excerpt );
      $excerpt     = strip_tags( $excerpt ); // Again, to remove the marker wrapper
      break;
    }
  }

  if ( empty( $context ) ) {
    // Link to target not found.
    return '';
  }

  return '[&#8230;] ' . esc_html( $excerpt ) . ' [&#8230;]';
}