flutter_application_1/lib/main.dart

import 'package:flutter/material.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter_localizations/flutter_localizations.dart';
import 'package:flutter_gen/gen_l10n/app_localizations.dart';
import 'package:flutter_application_1/calculator.dart';
import 'package:flutter_application_1/enums.dart';
import 'package:flutter_application_1/utils.dart';
import 'package:flutter_application_1/widgets/input_widget.dart';
import 'package:flutter_application_1/widgets/interval_widget.dart';
import 'package:flutter_application_1/widgets/result_widget.dart';
import 'package:flutter_application_1/widgets/error_widget.dart';
import 'package:flutter_application_1/widgets/language_switcher_widget.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatefulWidget {
  const MyApp({super.key});

  @override
  MyAppState createState() => MyAppState();
}

class MyAppState extends State<MyApp> {
  Locale _locale = const Locale('de'); // Standard-Locale

  void _changeLanguage(Locale locale) {
    setState(() {
      _locale = locale;
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Compound interest calculator',
      localizationsDelegates: const [
        AppLocalizations.delegate,
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
        GlobalCupertinoLocalizations.delegate,
      ],
      supportedLocales: const [
        Locale('en'), // English
        Locale('de'), // Deutsch
      ],
      locale: _locale,
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: CupertinoColors.white, background: CupertinoColors.white),
        useMaterial3: true,
      ),
      home: MyHomePage(
        title: 'Compound interest calculator',
        onLocaleChanged: _changeLanguage, // Übergibt die Sprachwechsel-Funktion an die Startseite
      ),
      debugShowCheckedModeBanner: false,
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title, required this.onLocaleChanged});
  final String title;
  final Function(Locale) onLocaleChanged;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  // Controller und Fokus-Knoten für die Eingabefelder
  final TextEditingController _initialCapitalController = TextEditingController();
  final TextEditingController _monthlySavingsRateController = TextEditingController();
  final TextEditingController _interestRateController = TextEditingController();
  final TextEditingController _timeController = TextEditingController();
  final FocusNode _initialCapitalFocusNode = FocusNode();
  final FocusNode _monthlySavingsRateFocusNode = FocusNode();
  final FocusNode _interestRateFocusNode = FocusNode();
  final FocusNode _timeFocusNode = FocusNode();

  // Zustandsvariablen für die Validierung der Eingaben
  bool _isInitialCapitalEntered = false;
  bool _isMonthlySavingsRateEntered = false;
  bool _isInterestRateEntered = false;
  bool _isTimeEntered = false;

  @override
  void initState() {
    super.initState();

    // Listener für die Eingabefelder, um die Validierung durchzuführen und Standardwerte wiederherzustellen
    _initialCapitalController.addListener(() {
      setState(() {
        _isInitialCapitalEntered = _initialCapitalController.text.isNotEmpty &&
            isNumeric(_initialCapitalController.text);
        restoreDefaultValuesIfEmpty(_initialCapitalController);
      });
    });

    _monthlySavingsRateController.addListener(() {
      setState(() {
        _isMonthlySavingsRateEntered = _monthlySavingsRateController.text.isNotEmpty &&
            isNumeric(_monthlySavingsRateController.text);
        restoreDefaultValuesIfEmpty(_monthlySavingsRateController);
      });
    });

    _interestRateController.addListener(() {
      setState(() {
        _isInterestRateEntered = _interestRateController.text.isNotEmpty &&
            isNumeric(_interestRateController.text);
        restoreDefaultValuesIfEmpty(_interestRateController);
      });
    });

    _timeController.addListener(() {
      setState(() {
        _isTimeEntered = _timeController.text.isNotEmpty &&
            isNumeric(_timeController.text);
        restoreDefaultValuesIfEmpty(_timeController);
      });
    });

    // Listener für die Fokus-Knoten, um die Eingabe zu runden, wenn der Fokus verloren geht
    _initialCapitalFocusNode.addListener(() {
      if (!_initialCapitalFocusNode.hasFocus) {
        roundToInteger(_initialCapitalController);
      }
    });

    _monthlySavingsRateFocusNode.addListener(() {
      if (!_monthlySavingsRateFocusNode.hasFocus) {
        roundToInteger(_monthlySavingsRateController);
      }
    });

    _interestRateFocusNode.addListener(() {
      if (!_interestRateFocusNode.hasFocus) {
        roundToInteger(_interestRateController);
      }
    });

    _timeFocusNode.addListener(() {
      if (!_timeFocusNode.hasFocus) {
        roundToInteger(_timeController);
      }
    });

    // Setzen von Beispielwerten für die Eingabefelder
    _initialCapitalController.text = '1000';
    _monthlySavingsRateController.text = '50';
    _interestRateController.text = '5';
    _timeController.text = '10';
  }

  double _initialCapital = 0.0; // Das anfängliche Kapital
  double _monthlySavingsRate = 0.0; // Der monatliche Sparbetrag
  double _interestRate = 0.0; // Der jährliche Zinssatz
  double _time = 0.0; // Der Anlagezeitraum in Jahren
  double _investedMoney = 0.0; // Das investierte Geld
  final List<double> _investedMoneyList = []; // Liste, die das investierte Geld pro Jahr speichert
  PayoutInterval _payoutInterval = PayoutInterval.yearly; // Das Auszahlungsintervall (jährlich oder monatlich)
  double _compoundInterest = 0.0; // Der Zinseszins
  final List<double> _compoundInterestList = []; // Liste, die den Zinseszins pro Jahr speichert

  // Methoden zum Festlegen der Werte aus den Eingabefeldern
  void setInitialCapital() {
    setState(() {
      _initialCapital = double.parse(_initialCapitalController.text);
    });
  }

  void setMonthlySavingsRate() {
    setState(() {
      _monthlySavingsRate = double.parse(_monthlySavingsRateController.text);
    });
  }

  void setInterestRate() {
    setState(() {
      _interestRate = double.parse(_interestRateController.text);
    });
  }

  void setTime() {
    setState(() {
      _time = double.parse(_timeController.text);
    });
  }

  CalculationPerformed _isCalculated = CalculationPerformed.noFirstTimeItLoaded;

  @override
  Widget build(BuildContext context) {
    final localizations = AppLocalizations.of(context)!;

    return Scaffold(
      body: SafeArea(
        child: Stack(
          children: [
            SingleChildScrollView(
              physics: const BouncingScrollPhysics(),
              child: Padding(
                padding: const EdgeInsets.all(20.0),
                child: Column(
                  crossAxisAlignment: CrossAxisAlignment.stretch,
                  children: <Widget>[
                    InputWidget(
                      label: localizations.initial_capital,
                      controller: _initialCapitalController,
                      focusNode: _initialCapitalFocusNode,
                      isValid: _isInitialCapitalEntered,
                      suffixText: localizations.currency,
                      tooltipText: localizations.initial_capital_tooltiptext
                    ),
                    InputWidget(
                      label: localizations.monthly_savings_rate,
                      controller: _monthlySavingsRateController,
                      focusNode: _monthlySavingsRateFocusNode,
                      isValid: _isMonthlySavingsRateEntered,
                      suffixText: localizations.currency,
                      tooltipText: localizations.monthly_savings_rate_tooltiptext
                    ),
                    InputWidget(
                      label: localizations.interest_rate,
                      controller: _interestRateController,
                      focusNode: _interestRateFocusNode,
                      isValid: _isInterestRateEntered,
                      suffixText: '%',
                      tooltipText: localizations.interest_rate_tooltiptext
                    ),
                    InputWidget(
                      label: localizations.investment_period,
                      controller: _timeController,
                      focusNode: _timeFocusNode,
                      isValid: _isTimeEntered,
                      suffixText: localizations.years,
                      tooltipText: localizations.investment_period_tooltiptext
                    ),
                    IntervalWidget(
                      selectedInterval: _payoutInterval == PayoutInterval.yearly ? localizations.yearly : localizations.monthly,
                      onChanged: (newInterval) {
                        setState(() {
                          _payoutInterval = newInterval == localizations.yearly ? PayoutInterval.yearly : PayoutInterval.monthly;
                        });
                      },
                    ),
                    ElevatedButton(
                      onPressed: () {
                        if (_isInitialCapitalEntered &&
                          _isMonthlySavingsRateEntered &&
                          _isInterestRateEntered &&
                          _isTimeEntered) {
                          setInitialCapital();
                          setMonthlySavingsRate();
                          setInterestRate();
                          setTime();
                          _investedMoney = calculateInvestedMoney(_initialCapital, _monthlySavingsRate, _time, _investedMoneyList);
                          _compoundInterest = calculateCompoundInterest(
                            _initialCapital,
                            _monthlySavingsRate,
                            _interestRate,
                            _time,
                            _payoutInterval,
                            _investedMoneyList,
                            _compoundInterestList
                        );
                        _isCalculated = CalculationPerformed.yes;
                        } else {
                          _isCalculated = CalculationPerformed.no;
                        }
                        setState(() {});
                      },
                      style: ButtonStyle(
                        backgroundColor: MaterialStateProperty.all<Color>(CupertinoColors.black),
                        foregroundColor: MaterialStateProperty.all<Color>(CupertinoColors.white),
                        shape: MaterialStateProperty.all<RoundedRectangleBorder>(
                          RoundedRectangleBorder(
                            borderRadius: BorderRadius.circular(5),
                          ),
                        ),
                      ),
                      child: Text(
                        localizations.calculate,
                        style: const TextStyle(
                          fontWeight: FontWeight.bold,
                        ),
                      ),
                    ),
                    const SizedBox(height: 20),
                    if(_isCalculated == CalculationPerformed.yes)
                      ResultWidget( 
                        compoundInterest: _compoundInterest.toStringAsFixed(0),
                        investedMoney: _investedMoney.toStringAsFixed(0),
                        time: _time.toStringAsFixed(0),
                        monthlySavingsRate: _monthlySavingsRate.toStringAsFixed(0),
                        interestRate: _interestRate.toStringAsFixed(0),
                        payoutInterval: _payoutInterval,
                        investedMoneyList: _investedMoneyList,
                        compoundInterestList: _compoundInterestList,
                      ),
                    if(_isCalculated == CalculationPerformed.no)
                      ErrWidget(
                        errorMessage: localizations.invalid_input,
                      ),
                  ],
                ),
              ),
            ),
            Positioned(
              top: MediaQuery.of(context).size.height / 2 - 20,
              right: 10,
              child: LanguageSwitcher(
                currentLocale: Localizations.localeOf(context),
                onLocaleChanged: widget.onLocaleChanged,
              ),
            ),
          ],
        ),
      ),
    );
  }
}