main.dart

import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/cupertino.dart';

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

final ThemeData kIOSTheme = ThemeData(
  primaryColor: Colors.grey[100],
  primarySwatch: Colors.orange,
);

final ThemeData kDefaultTheme = ThemeData(
  colorScheme: ColorScheme.fromSwatch(primarySwatch: Colors.purple)
      .copyWith(secondary: Colors.orangeAccent[700]),
);

String _name = 'Arunima';

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'FriendlyChat',
      theme: (defaultTargetPlatform == TargetPlatform.iOS)
          ? kIOSTheme
          : kDefaultTheme,
      home: const ChatScreen(),
    );
  }
}

class ChatMessage extends StatelessWidget {
  const ChatMessage(
      {required this.text, required this.animationController, Key? key})
      : super(key: key);
  final String text;
  final AnimationController animationController;

  @override
  Widget build(BuildContext context) {
    return SizeTransition(
      sizeFactor:
          CurvedAnimation(parent: animationController, curve: Curves.easeOut),
      axisAlignment: 0.0,
      child: Container(
        margin: const EdgeInsets.symmetric(vertical: 10.0),
        child: Row(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            Container(
              margin: const EdgeInsets.only(right: 16.0),
              child: CircleAvatar(child: Text(_name[0])),
            ),
            Expanded(
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  Text(_name, style: Theme.of(context).textTheme.headline4),
                  Container(
                    margin: const EdgeInsets.only(top: 5.0),
                    child: Text(text),
                  ),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }
}

class ChatScreen extends StatefulWidget {
  const ChatScreen({Key? key}) : super(key: key);

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

class _ChatScreenState extends State<ChatScreen> with TickerProviderStateMixin {
  final List<ChatMessage> _messages = [];
  final _textController = TextEditingController();
  final FocusNode _focusNode = FocusNode();
  bool _isComposing = false;

  @override
  void dispose() {
    for (var message in _messages) {
      message.animationController.dispose();
    }
    super.dispose();
  }

  void _handleSubmitted(String text) {
    _textController.clear();
    setState(() {
      _isComposing = false;
    });
    var message = ChatMessage(
      text: text,
      animationController: AnimationController(
        duration: const Duration(milliseconds: 700),
        vsync: this,
      ),
    );
    setState(() {
      _messages.insert(0, message);
    });
    _focusNode.requestFocus();
    message.animationController.forward();
  }

  Widget _buildTextComposer() {
    return IconTheme(
      data: IconThemeData(color: Theme.of(context).colorScheme.secondary),
      child: Container(
        margin: const EdgeInsets.symmetric(horizontal: 8.0),
        child: Row(
          children: [
            Flexible(
              child: TextField(
                controller: _textController,
                onChanged: (text) {
                  setState(() {
                    _isComposing = text.isNotEmpty;
                  });
                },
                onSubmitted: _isComposing ? _handleSubmitted : null,
                decoration:
                    const InputDecoration.collapsed(hintText: 'Send a message'),
                focusNode: _focusNode,
              ),
            ),
            Container(
                margin: const EdgeInsets.symmetric(horizontal: 4.0),
                child: Theme.of(context).platform == TargetPlatform.iOS
                    ? CupertinoButton(
                        child: const Text('Send'),
                        onPressed: _isComposing
                            ? () => _handleSubmitted(_textController.text)
                            : null,
                      )
                    : IconButton(
                        icon: const Icon(Icons.send),
                        onPressed: _isComposing
                            ? () => _handleSubmitted(_textController.text)
                            : null,
                      )),
          ],
        ),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('FriendlyChat'),
        elevation: Theme.of(context).platform == TargetPlatform.iOS ? 0.0 : 4.0,
      ),
      body: Container(
        child: Column(
          children: [
            Flexible(
              child: ListView.builder(
                padding: const EdgeInsets.all(8.0),
                reverse: true,
                itemBuilder: (_, index) => _messages[index],
                itemCount: _messages.length,
              ),
            ),
            const Divider(
              height: 1.0,
            ),
            Container(
              decoration: BoxDecoration(color: Theme.of(context).cardColor),
              child: _buildTextComposer(),
            ),
          ],
        ),
        decoration: Theme.of(context).platform == TargetPlatform.iOS
            ? BoxDecoration(
                border: Border(
                  top: BorderSide(color: Colors.grey[200]!),
                ),
              )
            : null,
      ),
    );
  }
}