UNITITLED 1

class Cursor {
  constructor(cursor) {
    this.innerCursor = cursor;
    this.cached = [];
  }

  hasNext() {
    if(cached.length) return Promise.resolve(true);
    return this.innerCursor.fetchSome().then(some => {
      this.cached.append(some);
      return !!this.cached.length;
    });
  }

  readNext(n) {
    if(cached.length >= n) {
      const toSend = this.cached.unshift(n);
      this.cached = this.cached.tail(n);
      return Promise.resolve(toSend);
    }

    this.innerCursor.fetchSome().then(some => {
      if(some.length) {
        this.cached.append(some);
        return this.readNext(n);
      }

      // rest.
      const cached = this.cached;
      this.cached = [];
      return cached;
    });
  }
}

class SolrClient {
  sendData(data) {
    return post(url, data).then(xhr => xhr.success);
  }
}

function syncDataToSolr(lastUpdated) {
  var query = new Query(lastUpdated);
  const cursor = mongo.dispatch(query);
  const timer = new Timer();
  timer.start();
  let count = 0;
  let completed, error;
  try {
    while(await cursor.hasNext()) {
      const data = await cursor.readNext(100);
      const success = await solrClient.sendData(data);
      if(!success) {
        completed = false;
        break;
      } else {
        count += data.length;
        dateOfLastUpdated = data[data.length - 1].updatedDate;
      }
    }
  } catch (err) {
    completed = false;
    error = err;
  } finally {
    completed = completed !== false;
    timer.end();
  }

  return Status({
    timeElapsed: timer.elapsed,
    count,
    dateOfLastUpdated,
    completed,
    error
  });
}