import 'dart:async';
import 'dart:math';
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

import '../../data/services/unsplash_service.dart';
import '../../providers.dart';

/// Renders a securely rotating background using Unsplash API.
class UnsplashBackground extends ConsumerStatefulWidget {
  const UnsplashBackground({super.key});

  @override
  ConsumerState<UnsplashBackground> createState() => _UnsplashBackgroundState();
}

class _UnsplashBackgroundState extends ConsumerState<UnsplashBackground> {
  final Random _rng = Random();
  List<String> _urls = [];
  int _currentIndex = 0;
  Timer? _rotationTimer;
  Timer? _keywordDebounceTimer;
  int _fetchNonce = 0;
  String? _lastKeyword;
  int? _lastRotationHours;
  bool? _lastUseUnsplash;

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

  void _initDataAndTimer() async {
    final settings = ref.read(settingsProvider);
    _lastKeyword = settings.unsplashKeyword;
    _lastRotationHours = settings.unsplashRotationHours;
    _lastUseUnsplash = settings.useUnsplashBackground;

    if (settings.useUnsplashBackground) {
      await _fetchImages(settings.unsplashKeyword, immediate: true);
    }
    _startTimer(settings.unsplashRotationHours);
  }

  Future<void> _fetchImages(String keyword, {bool immediate = false}) async {
    _keywordDebounceTimer?.cancel();
    Future<void> runFetch() async {
      if (!ref.read(settingsProvider).useUnsplashBackground) return;
      final requestId = ++_fetchNonce;
      final urls = await UnsplashService.instance.fetchLandscapeBackgrounds(
        keyword,
      );
      if (!mounted || requestId != _fetchNonce) return;
      if (urls.isNotEmpty) {
        urls.shuffle(_rng);
        setState(() {
          _urls = urls;
          _currentIndex = _rng.nextInt(_urls.length);
        });
      }
    }

    if (immediate) {
      await runFetch();
      return;
    }

    _keywordDebounceTimer = Timer(
      const Duration(milliseconds: 1200),
      () {
        unawaited(runFetch());
      },
    );
  }

  void _nextRandomImage() {
    if (_urls.isNotEmpty && mounted) {
      if (_urls.length <= 1) return;
      var nextIndex = _currentIndex;
      while (nextIndex == _currentIndex) {
        nextIndex = _rng.nextInt(_urls.length);
      }
      setState(() => _currentIndex = nextIndex);
    }
  }

  void _startTimer(int hours) {
    _rotationTimer?.cancel();
    if (hours <= 0) return;

    _rotationTimer = Timer.periodic(Duration(hours: hours), (_) {
      _nextRandomImage();
    });
  }

  @override
  void dispose() {
    _rotationTimer?.cancel();
    _keywordDebounceTimer?.cancel();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final settings = ref.watch(settingsProvider);

    // Watch for config changes
    if (settings.useUnsplashBackground != _lastUseUnsplash) {
      _lastUseUnsplash = settings.useUnsplashBackground;
      if (settings.useUnsplashBackground && _urls.isEmpty) {
        _fetchImages(settings.unsplashKeyword, immediate: true);
      }
    }

    if (settings.unsplashKeyword != _lastKeyword) {
      _lastKeyword = settings.unsplashKeyword;
      if (settings.useUnsplashBackground) {
        _fetchImages(settings.unsplashKeyword);
      }
    }

    if (settings.unsplashRotationHours != _lastRotationHours) {
      _lastRotationHours = settings.unsplashRotationHours;
      _startTimer(settings.unsplashRotationHours);
    }

    if (!settings.useUnsplashBackground || _urls.isEmpty) {
      return const SizedBox.shrink(); // Fallback to flat background handled underneath
    }

    return AnimatedSwitcher(
      duration: const Duration(seconds: 3),
      transitionBuilder: (child, animation) => FadeTransition(opacity: animation, child: child),
      child: Image.network(
        _urls[_currentIndex],
        key: ValueKey(_urls[_currentIndex]),
        fit: BoxFit.cover,
        width: double.infinity,
        height: double.infinity,
        // Soft opacity behind the MainScreen's dark glass vignette
        color: Colors.black.withValues(alpha: 0.5), 
        colorBlendMode: BlendMode.darken,
        errorBuilder: (_, __, ___) => const SizedBox.shrink(),
      ),
    );
  }
}