fcs/lib/helpers/pagination.dart

import 'dart:async';

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:logging/logging.dart';

/*
 * Pagination load data in page 
 */
class Pagination {
  final log = Logger('PaginationModel');

  final int rowPerLoad;
  DocumentSnapshot prev;
  bool ended = false;

  Query pageQuery;

  Pagination(Query pageQuery, {this.rowPerLoad = 20}) {
    this.pageQuery = pageQuery;
    initData();
  }

  void initData() async {
    _clearState();
    load();
  }

  void _clearState() {
    prev = null;
    ended = false;
    if (controller != null) controller.close();
  }

  StreamController<DocumentSnapshot> controller;
  Stream<DocumentSnapshot> get stream {
    if (controller != null) {
      controller.close();
    }
    controller = StreamController<DocumentSnapshot>(onCancel: _clearState);
    return controller.stream;
  }

  void close() {
    _clearState();
  }

  Future<bool> load() async {
    Query _query =
        prev != null ? pageQuery.startAfterDocument(prev) : pageQuery;
    try {
      await _query
          .limit(rowPerLoad)
          .getDocuments(source: Source.server)
          .then((QuerySnapshot snapshot) {
        int count = snapshot.documents.length;
        ended = count < rowPerLoad;
        prev = count > 0 ? snapshot.documents[count - 1] : prev;
        snapshot.documents.forEach((e) {
          controller.add(e);
        });
        if (ended) {
          controller.add(null);
        }
      });
    } catch (e) {
      log.warning("Error!! $e");
    }
    return ended;
  }
}