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/geo.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 '../places/location_flow.dart';
import '../places/location_service.dart';
import '../places/map_target.dart';
import '../places/places_screen.dart';
import '../places/saved_place.dart';
import '../places/saved_places.dart';
import '../places/search_screen.dart';
import '../settings/settings_screen.dart';
import '../timeline/data_age_banner.dart';
import '../timeline/radar_timeline.dart';
import '../timeline/timeline_bar.dart';
import 'map_overlay_controls.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);

    // No app bar. Its title was just the app name, which the launcher already
    // shows, and its one action now lives over the map with the other controls.
    // The map runs full-bleed to the top; the overlaid controls carry their own
    // SafeArea.
    return Scaffold(
      body: switch (region) {
        AsyncData(:final value) => _MapBody(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 _MapBody extends ConsumerWidget {
  const _MapBody({required this.region});

  final RegionConfig region;

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

    return Column(
      children: [
        if (Env.isDemoMode)
          SafeArea(
            bottom: false,
            child: MaterialBanner(
              content: Text(l10n.demoModeBanner),
              actions: const [SizedBox.shrink()],
            ),
          ),
        Expanded(
          child: _RegionMap(region: region, style: style),
        ),
        const DataAgeBanner(),
        const TimelineBar(),
      ],
    );
  }
}

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> {
  /// Close enough to read a town and its surroundings, wide enough to see
  /// weather arriving from the next valley.
  static const double placeZoom = 9.5;

  MapLibreMapController? _controller;
  RadarOverlay? _overlay;
  AppLifecycleListener? _lifecycle;

  /// Whether the map may draw the blue dot.
  ///
  /// Turning it on without permission makes the native layer complain, so it
  /// waits until permission is actually held.
  bool _locationEnabled = false;

  /// Guards against a frame that finished loading after the playhead moved on.
  int _requestId = 0;

  @override
  void initState() {
    super.initState();
    _lifecycle = AppLifecycleListener(
      onPause: () =>
          ref.read(radarTimelineProvider.notifier).onAppBackgrounded(),
    );
    unawaited(_syncLocationAvailability());
  }

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

  Future<void> _syncLocationAvailability() async {
    final availability = await ref.read(locationServiceProvider).availability();
    if (!mounted) return;
    setState(
      () => _locationEnabled = availability == LocationAvailability.granted,
    );
  }

  // --- camera ---------------------------------------------------------------

  Future<void> _frameRegion() async {
    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,
      ),
    );
  }

  Future<void> _centreOn(GeoPoint point, {double? zoom}) async {
    await _controller?.animateCamera(
      zoom == null
          ? CameraUpdate.newLatLng(LatLng(point.latitude, point.longitude))
          : CameraUpdate.newLatLngZoom(
              LatLng(point.latitude, point.longitude),
              zoom,
            ),
    );
  }

  /// Puts the camera where the current target says it should be.
  Future<void> _applyTarget(MapTarget target) async {
    switch (target) {
      case FollowUser():
        // The native tracking mode does the following; nothing to animate.
        break;
      case PlaceTarget(:final place):
        await _centreOn(place.point, zoom: placeZoom);
      case FreeTarget():
        await _frameRegion();
    }
  }

  // --- actions --------------------------------------------------------------

  /// Asks for permission, then starts following.
  Future<void> _requestFollow() async {
    final point = await requestPosition(context, ref);
    if (!mounted) return;

    if (point == null) {
      // requestPosition has already explained why it could not.
      await _syncLocationAvailability();
      return;
    }

    if (!widget.region.bounds.contains(point)) {
      // Worth following anyway — someone may be travelling into the region —
      // but they should know why the map looks empty.
      ScaffoldMessenger.of(context).showSnackBar(
        SnackBar(
          content: Text(AppLocalizations.of(context).locationOutsideRegion),
        ),
      );
    }

    setState(() => _locationEnabled = true);
    await ref.read(mapTargetProvider.notifier).select(const FollowUser());
    if (mounted) await _centreOn(point, zoom: placeZoom);
  }

  Future<void> _openSearch() async {
    final result = await Navigator.of(context).push<SearchResult>(
      MaterialPageRoute<SearchResult>(builder: (_) => const SearchScreen()),
    );
    if (result == null || !mounted) return;

    // A searched point is somewhere the user is looking, not somewhere they
    // have committed to, so it moves the camera without becoming the target.
    // Saving it is one tap away if they want it to stick.
    await ref.read(mapTargetProvider.notifier).select(const FreeTarget());
    await _centreOn(result.point, zoom: placeZoom);
    if (!mounted) return;

    final l10n = AppLocalizations.of(context);
    ScaffoldMessenger.of(context).showSnackBar(
      SnackBar(
        content: Text(result.label),
        action: SnackBarAction(
          label: l10n.mapSaveThisPoint,
          onPressed: () => unawaited(_savePoint(result)),
        ),
      ),
    );
  }

  Future<void> _savePoint(SearchResult result) async {
    try {
      final place = await ref
          .read(savedPlacesProvider.notifier)
          .add(name: result.label, point: result.point);
      if (!mounted) return;
      await ref.read(mapTargetProvider.notifier).select(PlaceTarget(place));
    } on SavedPlaceException catch (error) {
      if (!mounted) return;
      ScaffoldMessenger.of(context).showSnackBar(
        SnackBar(
          content: Text(messageFor(AppLocalizations.of(context), error)),
        ),
      );
    }
  }

  Future<void> _openPlaces() async {
    final target = _controller?.cameraPosition?.target;
    final centre = target == null
        ? widget.region.map.center
        : GeoPoint(target.longitude, target.latitude);

    final chosen = await Navigator.of(context).push<SavedPlace>(
      MaterialPageRoute<SavedPlace>(
        builder: (_) => PlacesScreen(mapCentre: centre),
      ),
    );
    if (chosen == null || !mounted) return;
    await ref.read(mapTargetProvider.notifier).select(PlaceTarget(chosen));
  }

  /// Puts the camera back on whatever is being followed.
  Future<void> _recentre() async {
    final target = ref.read(mapTargetProvider);
    if (target is FollowUser) {
      // Re-asserting the tracking mode is what pulls the camera back to the
      // blue dot after the user has panned away from it.
      await _controller?.updateMyLocationTrackingMode(
        MyLocationTrackingMode.tracking,
      );
      return;
    }
    await _applyTarget(target);
  }

  // --- map lifecycle --------------------------------------------------------

  Future<void> _onMapCreated(MapLibreMapController controller) async {
    _controller = controller;
    await _applyTarget(ref.read(mapTargetProvider));
  }

  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);
      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 is a worse answer.
    }
  }

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

    final target = ref.watch(mapTargetProvider);
    final manifest = ref.watch(
      radarTimelineProvider.select((state) => state.manifest),
    );
    final centre = widget.region.map.center;
    final zoom = widget.region.map.zoom;
    final bounds = widget.region.bounds;

    return Stack(
      children: [
        Positioned.fill(
          child: MapLibreMap(
            styleString: widget.style.styleString,
            onMapCreated: _onMapCreated,
            onStyleLoadedCallback: () => unawaited(_onStyleLoaded()),
            // Without this the controller's cameraPosition stays null, and
            // "save the map centre" silently saves the region default instead
            // of what the user is actually looking at.
            trackCameraPosition: true,
            initialCameraPosition: CameraPosition(
              target: LatLng(centre.latitude, centre.longitude),
              zoom: zoom.initial,
            ),
            minMaxZoomPreference: MinMaxZoomPreference(zoom.min, zoom.max),
            cameraTargetBounds: CameraTargetBounds(
              LatLngBounds(
                southwest: LatLng(bounds.south, bounds.west),
                northeast: LatLng(bounds.north, bounds.east),
              ),
            ),
            // Top right: the bottom-right corner now holds our own control
            // column, and the plugin's button was landing underneath it.
            attributionButtonPosition: AttributionButtonPosition.topRight,
            compassEnabled: false,
            rotateGesturesEnabled: false,
            tiltGesturesEnabled: false,
            myLocationEnabled: _locationEnabled,
            myLocationTrackingMode: target is FollowUser
                ? MyLocationTrackingMode.tracking
                : MyLocationTrackingMode.none,
            // Dragging the map while it is chasing the user means "let me look
            // over here". The camera stops following, but what the app reopens
            // on is left alone: that is a different decision.
            onCameraTrackingDismissed: () =>
                ref.read(mapTargetProvider.notifier).releaseFollow(),
          ),
        ),

        Positioned(
          left: 12,
          right: 12,
          top: 12,
          child: SafeArea(
            bottom: false,
            child: Align(
              alignment: Alignment.topCenter,
              child: TargetSelector(
                region: widget.region,
                onFollowRequested: () => unawaited(_requestFollow()),
                onSearch: () => unawaited(_openSearch()),
                onManagePlaces: () => unawaited(_openPlaces()),
              ),
            ),
          ),
        ),

        if (manifest != null)
          Positioned(
            left: 12,
            bottom: 12,
            child: _RadarLegend(legend: manifest.legend),
          ),

        Positioned(
          right: 12,
          bottom: 12,
          child: MapActionButtons(
            onSettings: () => Navigator.of(context).push(
              MaterialPageRoute<void>(builder: (_) => const SettingsScreen()),
            ),
            onSearch: () => unawaited(_openSearch()),
            onRecentre: () => unawaited(_recentre()),
          ),
        ),
      ],
    );
  }
}

/// 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,
                ),
              ],
            ),
          ],
        ),
      ),
    );
  }
}