task_06.dart

// Copyright 2018 The Chromium 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 'package:meta/meta.dart';

import 'unit.dart';

const _padding = EdgeInsets.all(16.0);

/// [ConverterRoute] where users can input amounts to convert in one [Unit]
/// and retrieve the conversion in another [Unit] for a specific [Category].
///
/// While it is named ConverterRoute, a more apt name would be ConverterScreen,
/// because it is responsible for the UI at the route's destination.
class ConverterRoute extends StatefulWidget {
  /// This [Category]'s name.
  final String name;

  /// Color for this [Category].
  final Color color;

  /// Units for this [Category].
  final List<Unit> units;

  /// This [ConverterRoute] requires the name, color, and units to not be null.
  const ConverterRoute({
    @required this.name,
    @required this.color,
    @required this.units,
  })  : assert(name != null),
        assert(color != null),
        assert(units != null);

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

class _ConverterRouteState extends State<ConverterRoute> {
  // TODO: Set some variables, such as for keeping track of the user's input
  // value and units
  List<DropdownMenuItem> unitsDropDownItems = List();
  Unit fromUnit; // unit di partenza
  Unit toUnit; // unit d'arrivo
  double inputValue; // valore immesso 
  String covertedValue; // valore convertito

  @override
  void initState() {
    for (var u in widget.units){
      unitsDropDownItems.add(DropdownMenuItem(
          child: Text(u.name),
          value: u,
      ));
      super.initState();
    }
  } // TODO: Determine whether you need to override anything, such as initState()
  

  // TODO: Add other helper functions. We've given you one, _format()

  /// Clean up conversion; trim trailing zeros, e.g. 5.500 -> 5.5, 10.0 -> 10
  String _format(double conversion) {
    var outputNum = conversion.toStringAsPrecision(7);
    if (outputNum.contains('.') && outputNum.endsWith('0')) {
      var i = outputNum.length - 1;
      while (outputNum[i] == '0') {
        i -= 1;
      }
      outputNum = outputNum.substring(0, i + 1);
    }
    if (outputNum.endsWith('.')) {
      return outputNum.substring(0, outputNum.length - 1);
    }
    return outputNum;
  }

  @override
  Widget build(BuildContext context) {
    // TODO: Create the 'input' group of widgets. This is a Column that
    // includes the input value, and 'from' unit [Dropdown].
    var input = Column(
      children: <Widget>[
        TextField(),
        DropdownButton(
            items: null,
            onChanged: null,
            value: null,
        )
      ],
    );

    // TODO: Create a compare arrows icon.

    // TODO: Create the 'output' group of widgets. This is a Column that
    // includes the output value, and 'to' unit [Dropdown].

    // TODO: Return the input, arrows, and output widgets, wrapped in a Column.

    // TODO: Delete the below placeholder code.
    final unitWidgets = widget.units.map((Unit unit) {
      return Container(
        color: widget.color,
        margin: EdgeInsets.all(8.0),
        padding: EdgeInsets.all(16.0),
        child: Column(
          children: <Widget>[
            Text(
              unit.name,
              style: Theme.of(context).textTheme.headline,
            ),
            Text(
              'Conversion: ${unit.conversion}',
              style: Theme.of(context).textTheme.subhead,
            ),
          ],
        ),
      );
    }).toList();

    return ListView(
      children: unitWidgets,
    );
  }
}