import 'package:flutter/material.dart';
import 'package:flutter_markdown/flutter_markdown.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

import '../../core/exceptions.dart';
import '../../data/models/message.dart';
import '../../providers/chat_provider.dart';

class ChatScreen extends ConsumerStatefulWidget {
  final int conversationId;
  const ChatScreen({super.key, required this.conversationId});

  @override
  ConsumerState<ChatScreen> createState() => _ChatScreenState();
}

class _ChatScreenState extends ConsumerState<ChatScreen> {
  final _controller = TextEditingController();
  final _scrollController = ScrollController();

  @override
  void dispose() {
    _controller.dispose();
    _scrollController.dispose();
    super.dispose();
  }

  void _scrollToBottom() {
    WidgetsBinding.instance.addPostFrameCallback((_) {
      if (_scrollController.hasClients) {
        _scrollController.animateTo(
          _scrollController.position.maxScrollExtent,
          duration: const Duration(milliseconds: 200),
          curve: Curves.easeOut,
        );
      }
    });
  }

  Future<void> _send() async {
    final text = _controller.text.trim();
    if (text.isEmpty) return;
    _controller.clear();
    try {
      await ref
          .read(messagesProvider(widget.conversationId).notifier)
          .sendMessage(text);
    } on AppException catch (e) {
      if (mounted) {
        ScaffoldMessenger.of(context)
            .showSnackBar(SnackBar(content: Text(e.message)));
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    final messagesAsync = ref.watch(messagesProvider(widget.conversationId));
    final isStreaming = ref.watch(isStreamingProvider(widget.conversationId));

    // Scroll when messages change
    ref.listen(messagesProvider(widget.conversationId), (_, _) {
      _scrollToBottom();
    });

    return Scaffold(
      appBar: AppBar(title: const Text('Chat')),
      body: Column(
        children: [
          Expanded(
            child: messagesAsync.when(
              loading: () =>
                  const Center(child: CircularProgressIndicator()),
              error: (e, _) => Center(child: Text('Error: $e')),
              data: (messages) {
                if (messages.isEmpty) {
                  return const Center(
                      child: Text('Send a message to start.'));
                }
                return ListView.builder(
                  controller: _scrollController,
                  padding: const EdgeInsets.symmetric(
                      horizontal: 8, vertical: 12),
                  itemCount: messages.length,
                  itemBuilder: (context, i) =>
                      _MessageBubble(message: messages[i]),
                );
              },
            ),
          ),
          const Divider(height: 1),
          SafeArea(
            child: Padding(
              padding:
                  const EdgeInsets.symmetric(horizontal: 8, vertical: 6),
              child: Row(
                children: [
                  Expanded(
                    child: TextField(
                      controller: _controller,
                      decoration: const InputDecoration(
                        hintText: 'Message...',
                        border: OutlineInputBorder(),
                        isDense: true,
                        contentPadding: EdgeInsets.symmetric(
                            horizontal: 12, vertical: 10),
                      ),
                      maxLines: 4,
                      minLines: 1,
                      textInputAction: TextInputAction.newline,
                      enabled: !isStreaming,
                    ),
                  ),
                  const SizedBox(width: 8),
                  IconButton.filled(
                    onPressed: isStreaming ? null : _send,
                    icon: isStreaming
                        ? const SizedBox(
                            width: 20,
                            height: 20,
                            child:
                                CircularProgressIndicator(strokeWidth: 2),
                          )
                        : const Icon(Icons.send),
                  ),
                ],
              ),
            ),
          ),
        ],
      ),
    );
  }
}

class _MessageBubble extends StatelessWidget {
  final Message message;
  const _MessageBubble({required this.message});

  @override
  Widget build(BuildContext context) {
    final isUser = message.role == MessageRole.user;
    final scheme = Theme.of(context).colorScheme;

    return Align(
      alignment: isUser ? Alignment.centerRight : Alignment.centerLeft,
      child: Container(
        constraints: BoxConstraints(
          maxWidth: MediaQuery.of(context).size.width * 0.8,
        ),
        margin: const EdgeInsets.symmetric(vertical: 4),
        padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 8),
        decoration: BoxDecoration(
          color: isUser ? scheme.primary : scheme.surfaceContainerHighest,
          borderRadius: BorderRadius.only(
            topLeft: const Radius.circular(16),
            topRight: const Radius.circular(16),
            bottomLeft: Radius.circular(isUser ? 16 : 4),
            bottomRight: Radius.circular(isUser ? 4 : 16),
          ),
        ),
        child: isUser
            ? Text(
                message.content,
                style: TextStyle(color: scheme.onPrimary),
              )
            : MarkdownBody(
                data: message.content.isEmpty ? '...' : message.content,
                styleSheet: MarkdownStyleSheet.fromTheme(Theme.of(context)),
              ),
      ),
    );
  }
}