Find and replace absolute Drupal 6 URLS with aliases so that Migrate module and redirect them

RewriteAbsoluteURLAsAlias.php

<?php 
/**
 * Helper class to pass parameters to callback function within preg_replace_callback
 * to replace absolute D6 urls with D6 aliases
 */

class InternalLinksConverter {
  function replace($matches) {
    if (isset($this->link_aliases)) {
      $link_aliases = $this->link_aliases;
    }
    $first_delimeter = isset($matches[0]) ? $matches[0] : '';
    $slug = isset($matches[3]) ? $matches[3] : '';
    $link_alias = isset($link_aliases[$slug]) ? $link_aliases[$slug] : '';
    // hashtag is not exists - show without link
    if (empty($link_alias)) {
      return $first_delimeter;
      // Log error
    }
    return $link_alias;
  }
}

/**
 * Helper function to Create and return comma separated string of slugs related to entities
 * (/node/nid or /taxonomy/term or user/)
 *
 * @param string $text of the body field
 * @param boolean $is_string_return
 * @param boolean $capture_position
 * @return string or array $result of any discovered permalinks ($slug) found
 *
 */

function ParseBodyLinks($text, $is_string_return = TRUE, $capture_position = FALSE) {
  // capture_position == PREG_OFFSET_CAPTURE;
  // save position
  $flag = $capture_position ? PREG_OFFSET_CAPTURE : PREG_PATTERN_ORDER;

  $links_list = array();
  $pattern = "/((http|https):\/\/www\.website\.com\/)?(node\/\w+|taxonomy\/term\/\w+|user\/\w+)/";
  // add <htest> to process first #hastag - string beginning
  preg_match_all($pattern, '<test>'.$text.'<test>', $links_list, $flag);
  // no hashtags has been found
  if (isset($links_list[0]) && !sizeof($links_list[0])) {
    if ($is_string_return) {
      return '';
    }
    return array();
  }
  // save position
  if ($capture_position) {
    foreach ($links_list[1] as $key => $data) {
      // array[position] = link
      $result[$data[1]] = strtolower($data[0]);
    }
  } else {
    // assign the node id to the array
    foreach ($links_list[3] as $key => $slug) {
      $links_list[3][$key] = $slug;
    }
    // implode and return
    if ($is_string_return) {
      $result = implode(',', $links_list[3]);
    } else {
      $result = $links_list[3];
    }
  }
  if (isset($result)) {
    return $result;
  }
  else return '';
}


/**
   * Helper function to check the permalink slug and return the
   * path alias if available
   *
   * @param array $slugs, should be string values
   * @return array - aliases of each permalink
   *
   */
protected  function GetD6Aliases($slugs) {
  $aliases = array();
  foreach ($slugs as $slug) {
    $query = Database::getConnection('default',
      $this->arguments['source_connection'])
      ->select('url_alias', 'ua')
      ->fields('ua')
      ->condition('ua.src', $slug, '=');
    $results = $query->execute();
      foreach ($results as $result) {
        $aliases[$result->src] = $result->dst;
      }
    }
  if (!empty($aliases)) {
    return $aliases;
  }
  else {
    return '';
  }
}

  /**
   * Helper function to check send the body field for parsing in
   * a custom helper function and to return the aliases for any
   * discovered permalink paths and replace this path in the link
   *
   * @param string $text of the body field
   * @return string $text of the body field with permalinks
   * replaced, if found
   *
   */
 protected function ProcessBodyLinks($text) {
   // Send to helper function to parse links and identify node id
    $slugs = ParseBodyLinks($text, FALSE);

   // No internal links found in text return original text
    if (!sizeof($slugs)) { return $text; }
    $link_aliases = $this->GetD6Aliases($slugs);

   // No aliases found return original text
    if (!sizeof($link_aliases)) { return $text; }

    // Create a class to pass parameters and have replace logic
    $replace_parameter = new InternalLinksConverter;
    $replace_parameter->link_aliases = $link_aliases;
    // Replace the absolute url with the alias
    $pattern = "/((http|https):\/\/www\.website\.com\/)?(node\/\w+|taxonomy\/term\/\w+|user\/\w+)/";
    $text = preg_replace_callback($pattern, array(&$replace_parameter, 'replace'), $text);

    return $text;
  }