calorimeter/lib/perdate/perdate_pageview.dart

import 'package:calorimeter/perdate/perdate_widget.dart';
import 'package:flutter/material.dart';

class PerDatePageview extends StatefulWidget {
  // this is the date for which the PerDate widget will be shown on screen
  // left of it will be yesterday's PerDate widget
  // right of it will be tomorrow's PerDate widget
  final DateTime initalDate;
  const PerDatePageview({required this.initalDate, super.key});

  @override
  State<PerDatePageview> createState() => _PerDatePageviewState();
}

class _PerDatePageviewState extends State<PerDatePageview> {
  late PageController pageController;
  late DateTime displayedDate;
  late List<int> visitedIndexes = [];
  final int initialOffset = 36500000;

  //TODO: that is just ugly
  bool backButtonWasPressed = false;

  @override
  void initState() {
    super.initState();
    pageController = PageController(initialPage: initialOffset);
    displayedDate = widget.initalDate;
    visitedIndexes.add(initialOffset);
  }

  @override
  Widget build(BuildContext context) {
    return BackButtonListener(
      onBackButtonPressed: () async {
        if (visitedIndexes.length == 1) {
          return false;
        }

        visitedIndexes.removeLast();

        backButtonWasPressed = true;
        pageController.jumpToPage(visitedIndexes.last);

        return true;
      },
      child: PageView.builder(
          reverse: true,
          controller: pageController,
          onPageChanged: (value) {
            if (backButtonWasPressed) {
              backButtonWasPressed = false;
              return;
            }

            visitedIndexes.add(value);
          },
          itemBuilder: (context, index) {
            var dateToBuildWidgetFor =
                displayedDate.subtract(Duration(days: index - initialOffset));

            return PerDateWidget(
                key: ValueKey(dateToBuildWidgetFor.toString()),
                date: dateToBuildWidgetFor,
                onDateSelected: (dateSelected) {
                  if (dateSelected == null) return;

                  var diff = dateSelected.difference(dateToBuildWidgetFor);
                  var newIndex = index - diff.inDays;

                  pageController.jumpToPage(newIndex);
                });
          }),
    );
  }
}