session_shells/ermine/shell/lib/src/widgets/story/clusters.dart

// Copyright 2019 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/material.dart';

import '../../models/app_model.dart';
import '../../utils/styles.dart';
import 'cluster.dart';

/// Defines a [PageView] to hold a [Cluster] widget per screen.
class Clusters extends StatelessWidget {
  final AppModel model;

  const Clusters({this.model});

  @override
  Widget build(BuildContext context) {
    final clustersModel = model.clustersModel;
    final currentCluster = clustersModel.currentCluster.value;
    final pageController = PageController(
      initialPage: currentCluster == null
          ? 0
          : clustersModel.clusters.indexOf(currentCluster),
    );
    clustersModel.currentCluster.addListener(() {
      if (pageController.hasClients) {
        int index =
            clustersModel.clusters.indexOf(clustersModel.currentCluster.value);
        if (index != pageController.page) {
          if (clustersModel.clusters[index].isEmpty &&
              clustersModel.clusters[pageController.page.toInt()].isEmpty) {
            pageController.jumpToPage(index);
          } else {
            pageController.animateToPage(
              index,
              duration: Duration(milliseconds: 200),
              curve: Curves.easeOut,
            );
          }
        }
      }
    });
    return AnimatedBuilder(
      animation: Listenable.merge([
        model.overviewVisibility,
        clustersModel.fullscreenStoryNotifier,
      ]),
      child: AnimatedBuilder(
        animation: clustersModel,
        builder: (context, child) => Stack(
          children: <Widget>[
            Positioned.fill(
              child: Container(
                color: ErmineStyle.kBackgroundColor,
                child: PageView.builder(
                  controller: pageController,
                  scrollDirection: Axis.horizontal,
                  itemCount: clustersModel.clusters.length,
                  itemBuilder: (context, index) {
                    final cluster = clustersModel.clusters[index];
                    return Cluster(model: cluster);
                  },
                ),
              ),
            ),
          ],
        ),
      ),
      builder: (context, child) => Offstage(
        offstage: model.isFullscreen || model.overviewVisibility.value,
        child: child,
      ),
    );
  }
}