ページングデータの取得

  score   ：   cursor->score 【  】 length   
   *
   *      ：
   *          ，      ，      
   *
   * User: xjyin
   * Date: 15/11/5
   * Time:   7:45
   */

  class Cursor {

      private $member;

      private $score;
  }

  abstract class CursorTimelineGetter {

      private $cursor;

      private $length;

      function _construct($cursor, $length) {
          $this->cursor = $cursor;
          $this->length = $length;
      }

      //      cursor array,        $length
      abstract protected function getFromCache($cursor, $length);

      //      cursor array,        $length
      abstract protected function getFromDB($cursor, $length);

      //                 , dbResults  cursor  array
      abstract protected function saveToCache($dbResults);

      //            ，          
      //         zAdd(key, map)   ，        member  zAdd
      abstract protected function patchToCache($cursor);

      public function exec() {
          $cacheResults = $this->getFromCache($this->cursor, $this->length);
          if(!$cacheResults) {
              $cacheResults = array();
          }
          //                ，     
          if(count($cacheResults) >= $this->length) {
              return $cacheResults;
          }
          //         ，          
          $lengthFromDB = $this->length - count($cacheResults);
          $cursorFromDb = null;
          //              ，   cursor      db  cache ，      
          //              ，       ，     patchToCache
          if (count($cacheResults) <= 0) {
              $this->patchToCache($this->cursor);
              $cursorFromDb = $this->cursor;
          }
          else {
              $cursorFromDb = $cacheResults[count($cacheResults) - 1];
          }
          $dbResults = $this->getFromDB($cursorFromDb, $lengthFromDB);
          if(!$dbResults or count($dbResults) == 0) {
              return $cacheResults;
          }
          $this->saveToCache($dbResults);
          return array_merge($cacheResults, $dbResults);
      }
  }