import 'dart:async';

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

import '../../core/config/env.dart';
import '../../core/region/region_config.dart';
import '../../core/region/region_repository.dart';
import '../../data/radar/radar_manifest.dart';
import '../../data/radar/radar_source.dart';
import '../../l10n/app_localizations.dart';
import '../timeline/data_age_banner.dart';
import '../timeline/radar_timeline.dart';
import '../timeline/timeline_bar.dart';
import 'attribution_bar.dart';
import 'map_style.dart';
import 'radar_overlay.dart';

/// The radar map: base map, animated precipitation overlay, timeline.
class RadarMapScreen extends ConsumerWidget {
  const RadarMapScreen({super.key});

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final l10n = AppLocalizations.of(context);
    final region = ref.watch(regionConfigProvider);

    return Scaffold(
      appBar: AppBar(title: Text(l10n.appTitle)),
      body: switch (region) {
        AsyncData(:final value) => _MapWithAttribution(region: value),
        AsyncError(:final error) => Center(
          child: Padding(
            padding: const EdgeInsets.all(24),
            child: Text('${l10n.dataUnavailable}\n$error'),
          ),
        ),
        _ => Center(child: Text(l10n.loading)),
      },
    );
  }
}

class _MapWithAttribution extends ConsumerWidget {
  const _MapWithAttribution({required this.region});

  final RegionConfig region;

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final l10n = AppLocalizations.of(context);
    final style = MapStyle.forRegion(region);
    final manifest = ref.watch(
      radarTimelineProvider.select((state) => state.manifest),
    );

    return Column(
      children: [
        if (Env.isDemoMode)
          MaterialBanner(
            content: Text(l10n.demoModeBanner),
            actions: const [SizedBox.shrink()],
          ),
        Expanded(
          child: Stack(
            children: [
              Positioned.fill(
                child: _RegionMap(region: region, style: style),
              ),
              if (manifest != null)
                Positioned(
                  left: 12,
                  bottom: 12,
                  child: _RadarLegend(legend: manifest.legend),
                ),
            ],
          ),
        ),
        const DataAgeBanner(),
        const TimelineBar(),
        // Outside the map rather than floating over it, so the credit can never
        // be occluded by a map control. SafeArea keeps it clear of the system
        // gesture bar as well — a credit sitting behind the navigation pill is
        // a credit that is not being displayed.
        SafeArea(
          top: false,
          child: AttributionBar(
            region: region,
            activeSourceIds: style.attributionIds,
            showBaseMapNotice: style.kind == BaseMapKind.offlineFallback,
            // The manifest carries the credit for the frames it indexes, which
            // is the whole point of it travelling with the data: whoever
            // published these frames says here who to credit for them.
            additionalCredits: <String>[
              if (manifest != null) manifest.attribution,
            ],
          ),
        ),
      ],
    );
  }
}

class _RegionMap extends ConsumerStatefulWidget {
  const _RegionMap({required this.region, required this.style});

  final RegionConfig region;
  final MapStyle style;

  @override
  ConsumerState<_RegionMap> createState() => _RegionMapState();
}

class _RegionMapState extends ConsumerState<_RegionMap> {
  MapLibreMapController? _controller;
  RadarOverlay? _overlay;
  AppLifecycleListener? _lifecycle;

  /// Guards against a frame that finished loading after the playhead moved on,
  /// which would briefly show the wrong image.
  int _requestId = 0;

  @override
  void initState() {
    super.initState();
    // Playback runs a timer and pushes a texture several times a second.
    // Behind another app there is no one watching, so it is pure battery.
    _lifecycle = AppLifecycleListener(
      onPause: () =>
          ref.read(radarTimelineProvider.notifier).onAppBackgrounded(),
    );
  }

  @override
  void dispose() {
    _lifecycle?.dispose();
    unawaited(_overlay?.detach());
    super.dispose();
  }

  /// Frames the whole region once the map is ready.
  ///
  /// The configured initial zoom is only a starting point: a single zoom number
  /// cannot fit the region on both a small phone and a tablet, and on a 411dp
  /// screen zoom 7.2 puts the viewport entirely inside the region, so the user
  /// sees a flat expanse with no border or outline to orient by. Fitting the
  /// bounds works on every screen size.
  Future<void> _onMapCreated(MapLibreMapController controller) async {
    _controller = controller;

    final bounds = widget.region.bounds;
    await controller.moveCamera(
      CameraUpdate.newLatLngBounds(
        LatLngBounds(
          southwest: LatLng(bounds.south, bounds.west),
          northeast: LatLng(bounds.north, bounds.east),
        ),
        left: 16,
        top: 16,
        right: 16,
        bottom: 16,
      ),
    );
  }

  /// Layers can only be added once the style exists, and the style is reloaded
  /// whenever it changes, so the overlay is rebuilt here rather than in
  /// [_onMapCreated].
  Future<void> _onStyleLoaded() async {
    final controller = _controller;
    if (controller == null) return;

    _overlay = RadarOverlay(map: controller, bounds: widget.region.bounds);
    await _showFrame(ref.read(radarTimelineProvider).currentFrame);
  }

  Future<void> _showFrame(RadarFrame? frame) async {
    final overlay = _overlay;
    if (overlay == null || frame == null) return;
    if (overlay.visiblePath == frame.path) return;

    final request = ++_requestId;
    try {
      final bytes = await ref
          .read(radarTimelineProvider.notifier)
          .bytesFor(frame);
      // Someone scrubbed while this was loading; that newer frame wins.
      if (!mounted || request != _requestId) return;
      await overlay.show(frame.path, bytes);
    } on RadarUnavailableException {
      // Hold the previous frame. A gap mid-timeline is normal while the worker
      // publishes, and blanking the map would be a worse answer than showing
      // the neighbouring minute.
    }
  }

  @override
  Widget build(BuildContext context) {
    ref.listen(
      radarTimelineProvider.select((state) => state.currentFrame),
      (_, frame) => unawaited(_showFrame(frame)),
    );

    final center = widget.region.map.center;
    final zoom = widget.region.map.zoom;
    final bounds = widget.region.bounds;

    return MapLibreMap(
      styleString: widget.style.styleString,
      onMapCreated: _onMapCreated,
      onStyleLoadedCallback: () => unawaited(_onStyleLoaded()),
      initialCameraPosition: CameraPosition(
        target: LatLng(center.latitude, center.longitude),
        zoom: zoom.initial,
      ),
      minMaxZoomPreference: MinMaxZoomPreference(zoom.min, zoom.max),
      // Panning is confined to the region: this app has data for Piedmont and
      // nowhere else, so letting the user drift away would only ever show an
      // empty map.
      cameraTargetBounds: CameraTargetBounds(
        LatLngBounds(
          southwest: LatLng(bounds.south, bounds.west),
          northeast: LatLng(bounds.north, bounds.east),
        ),
      ),
      // Kept enabled on top of our own attribution bar: some tile providers
      // require the plugin's own attribution control, and a duplicated credit
      // is harmless where a missing one is a licence breach.
      attributionButtonPosition: AttributionButtonPosition.bottomRight,
      compassEnabled: false,
      rotateGesturesEnabled: false,
      tiltGesturesEnabled: false,
      myLocationEnabled: false,
    );
  }
}

/// The colour ramp for the frames currently on screen.
///
/// Built from the manifest rather than from a constant: the worker chose these
/// colours when it rendered the PNGs, so anything hardcoded here could drift
/// and mislabel the intensities the reader is looking at.
class _RadarLegend extends StatelessWidget {
  const _RadarLegend({required this.legend});

  final RadarLegend legend;

  @override
  Widget build(BuildContext context) {
    final l10n = AppLocalizations.of(context);
    final theme = Theme.of(context);

    return DecoratedBox(
      decoration: BoxDecoration(
        color: theme.colorScheme.surface.withValues(alpha: 0.85),
        borderRadius: BorderRadius.circular(8),
      ),
      child: Padding(
        padding: const EdgeInsets.symmetric(horizontal: 10, vertical: 8),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          mainAxisSize: MainAxisSize.min,
          children: [
            Text(
              l10n.radarLegendUnit(legend.unit),
              style: theme.textTheme.labelSmall,
            ),
            const SizedBox(height: 6),
            Row(
              mainAxisSize: MainAxisSize.min,
              children: [
                for (final stop in legend.stops)
                  Container(width: 14, height: 12, color: stop.color),
              ],
            ),
            const SizedBox(height: 2),
            Row(
              mainAxisSize: MainAxisSize.min,
              children: [
                Text(
                  '${legend.stops.first.value.toInt()}',
                  style: theme.textTheme.labelSmall,
                ),
                SizedBox(width: 14.0 * legend.stops.length - 28),
                Text(
                  '${legend.stops.last.value.toInt()}',
                  style: theme.textTheme.labelSmall,
                ),
              ],
            ),
          ],
        ),
      ),
    );
  }
}