import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:supabase_flutter/supabase_flutter.dart' show AuthException;

import '../controllers/auth_controller.dart';

/// Which authentication flow is currently executing, so the relevant button
/// can render a spinner while the request is in flight.
enum _AuthAction { google, apple, microsoft, magicLink }

/// Passwordless sign-in surface: federated OAuth (Google, Apple, Microsoft)
/// and email magic links. Wired to [authControllerProvider] for execution and
/// progress/error feedback.
class LoginScreen extends ConsumerStatefulWidget {
  const LoginScreen({super.key});

  @override
  ConsumerState<LoginScreen> createState() => _LoginScreenState();
}

class _LoginScreenState extends ConsumerState<LoginScreen> {
  final TextEditingController _emailController = TextEditingController();

  /// The action currently awaiting completion, or `null` when idle.
  _AuthAction? _pendingAction;

  static final RegExp _emailPattern = RegExp(
    r"^[A-Za-z0-9._%+\-]+@[A-Za-z0-9.\-]+\.[A-Za-z]{2,}$",
  );

  @override
  void dispose() {
    _emailController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    // The controller records failures in its AsyncValue state instead of
    // throwing, so a single listener surfaces every flow's error feedback.
    ref.listen<AsyncValue<void>>(authControllerProvider, (previous, next) {
      final error = next.error;
      if (error == null) return;
      _showSnack(_messageFor(error), isError: true);
    });

    final isBusy = ref.watch(authControllerProvider).isLoading;

    return Scaffold(
      body: Center(
        child: SingleChildScrollView(
          child: ConstrainedBox(
            constraints: const BoxConstraints(maxWidth: 400),
            child: Padding(
              padding: const EdgeInsets.all(24.0),
              child: Column(
                mainAxisSize: MainAxisSize.min,
                mainAxisAlignment: MainAxisAlignment.center,
                crossAxisAlignment: CrossAxisAlignment.stretch,
                children: [
                  const Icon(Icons.health_and_safety,
                      size: 64, color: Colors.teal),
                  const SizedBox(height: 16),
                  const Text(
                    'GLP-1 Companion',
                    textAlign: TextAlign.center,
                    style: TextStyle(fontSize: 24, fontWeight: FontWeight.bold),
                  ),
                  const SizedBox(height: 8),
                  const Text(
                    'Passwordless & Biometric Sign In',
                    textAlign: TextAlign.center,
                    style: TextStyle(color: Colors.grey),
                  ),
                  const SizedBox(height: 32),
                  _oauthButton(_AuthAction.google, Icons.g_mobiledata,
                      'Continue with Google'),
                  const SizedBox(height: 12),
                  _oauthButton(
                      _AuthAction.apple, Icons.apple, 'Continue with Apple'),
                  const SizedBox(height: 12),
                  _oauthButton(_AuthAction.microsoft, Icons.window,
                      'Continue with Microsoft'),
                  const SizedBox(height: 24),
                  const Row(
                    children: [
                      Expanded(child: Divider()),
                      Padding(
                        padding: EdgeInsets.symmetric(horizontal: 8.0),
                        child: Text('OR'),
                      ),
                      Expanded(child: Divider()),
                    ],
                  ),
                  const SizedBox(height: 24),
                  TextField(
                    controller: _emailController,
                    enabled: !isBusy,
                    keyboardType: TextInputType.emailAddress,
                    autofillHints: const [AutofillHints.email],
                    decoration: const InputDecoration(
                      labelText: 'Email Address',
                      border: OutlineInputBorder(),
                      prefixIcon: Icon(Icons.email_outlined),
                    ),
                  ),
                  const SizedBox(height: 12),
                  FilledButton(
                    onPressed: isBusy ? null : _sendMagicLink,
                    child: _pendingAction == _AuthAction.magicLink
                        ? const SizedBox(
                            height: 20,
                            width: 20,
                            child: CircularProgressIndicator(strokeWidth: 2),
                          )
                        : const Text('Send Magic Link'),
                  ),
                ],
              ),
            ),
          ),
        ),
      ),
    );
  }

  /// Builds an OAuth button bound to [action]; disabled while any flow runs
  /// and swapped for a spinner while [action] itself is executing.
  Widget _oauthButton(_AuthAction action, IconData icon, String label) {
    final isBusy = ref.watch(authControllerProvider).isLoading;
    return ElevatedButton.icon(
      onPressed: isBusy ? null : () => _start(action, _runnerFor(action)),
      icon: _pendingAction == action
          ? const SizedBox(
              height: 16,
              width: 16,
              child: CircularProgressIndicator(strokeWidth: 2),
            )
          : Icon(icon),
      label: Text(label),
    );
  }

  /// Resolves the controller method backing [action].
  Future<void> Function() _runnerFor(_AuthAction action) {
    final notifier = ref.read(authControllerProvider.notifier);
    return switch (action) {
      _AuthAction.google => notifier.signInWithGoogle,
      _AuthAction.apple => notifier.signInWithApple,
      _AuthAction.microsoft => notifier.signInWithMicrosoft,
      _AuthAction.magicLink =>
        () => notifier.signInWithMagicLink(_emailController.text.trim()),
    };
  }

  /// Runs [execute] while marking [action] as pending.
  ///
  /// A completed flow without a recorded error counts as success; optional
  /// [successMessage] is surfaced via SnackBar. Errors are reported by the
  /// listener in [build], so they are not repeated here.
  Future<void> _start(
    _AuthAction action,
    Future<void> Function() execute, {
    String? successMessage,
  }) async {
    if (_pendingAction != null) return;
    setState(() => _pendingAction = action);
    try {
      await execute();
      if (!mounted) return;
      final result = ref.read(authControllerProvider);
      if (!result.hasError && successMessage != null) {
        _showSnack(successMessage);
      }
    } finally {
      if (mounted) setState(() => _pendingAction = null);
    }
  }

  Future<void> _sendMagicLink() async {
    final email = _emailController.text.trim();
    if (!_emailPattern.hasMatch(email)) {
      _showSnack(
        'Enter a valid email address to receive a magic link.',
        isError: true,
      );
      return;
    }
    await _start(
      _AuthAction.magicLink,
      _runnerFor(_AuthAction.magicLink),
      successMessage:
          'Magic link sent to $email. Check your inbox to finish signing in.',
    );
  }

  void _showSnack(String message, {bool isError = false}) {
    if (!mounted) return;
    final messenger = ScaffoldMessenger.of(context);
    messenger
      ..hideCurrentSnackBar()
      ..showSnackBar(
        SnackBar(
          content: Text(message),
          backgroundColor: isError ? Theme.of(context).colorScheme.error : null,
        ),
      );
  }

  String _messageFor(Object error) {
    if (error is AuthException) return error.message;
    return 'Authentication failed. Please try again.';
  }

}