/// Where map tiles come from, what must be credited, and any key needed to ask
/// for them.
///
/// This is the **only** place a tile URL, an attribution string or a map API
/// key exists. No widget builds a URL; screens ask for a style and get back
/// whatever the configured provider serves. Swapping CARTO for MapTiler, for a
/// keyed CARTO plan, or for self-hosted tiles is a build flag or one entry in
/// [MapTileProvider.presets] — no map screen changes.
///
/// Deliberately free of Flutter imports so the choice of provider is testable
/// as plain data. `lib/ui/widgets/map_tiles.dart` turns it into a `TileLayer`.
library;

/// The two cartographies the app uses.
enum DmMapStyle {
  /// Streets, labels and landmarks. The pickup map, where the customer is
  /// looking for their own door.
  streets,

  /// Quieter, near-monochrome. The route map, where the line is the subject
  /// and the basemap is context.
  muted,
}

/// A raster tile source: its URL templates, its credit line, and its key.
class MapTileProvider {
  const MapTileProvider({
    required this.id,
    required this.name,
    required this.templates,
    required this.attribution,
    this.attributionUrl = osmCopyright,
    this.subdomains = const <String>[],
    this.keyParam,
    this.apiKey = '',
    this.requiresKey = false,
    this.maxNativeZoom = 20,
    this.retina = true,
  });

  /// Stable id, also what `DM_MAP_PROVIDER` selects.
  final String id;

  /// Human name, for the "map source" line in diagnostics.
  final String name;

  /// One URL template per style. `{s}` `{z}` `{x}` `{y}` `{r}` as flutter_map
  /// expects; the key is appended by [urlFor], never written into a template.
  final Map<DmMapStyle, String> templates;

  /// The credit line that must stay visible on every map using this source.
  final String attribution;

  /// Where the attribution links, for the licence.
  final String attributionUrl;

  /// Tile host shards, when the provider uses them.
  final List<String> subdomains;

  /// Query parameter the key travels in — `api_key` for CARTO and Stadia,
  /// `key` for MapTiler. Null when the provider takes no key.
  final String? keyParam;

  /// The key itself. Supplied at build time, never committed.
  final String apiKey;

  /// True when the provider serves nothing without a key, so a missing key is
  /// a misconfiguration rather than a downgrade.
  final bool requiresKey;

  final int maxNativeZoom;

  /// Whether the provider serves `@2x` tiles for the `{r}` placeholder.
  final bool retina;

  static const osmCopyright = 'https://www.openstreetmap.org/copyright';

  bool get hasKey => apiKey.isNotEmpty;

  /// False when this provider cannot serve a tile as configured.
  bool get usable => !requiresKey || hasKey;

  /// The template for [style], with the key appended when there is one.
  String urlFor(DmMapStyle style) {
    final template = templates[style] ?? templates[DmMapStyle.streets]!;
    if (!hasKey || keyParam == null) return template;
    final separator = template.contains('?') ? '&' : '?';
    return '$template$separator$keyParam=$apiKey';
  }

  MapTileProvider withKey(String key) => MapTileProvider(
    id: id,
    name: name,
    templates: templates,
    attribution: attribution,
    attributionUrl: attributionUrl,
    subdomains: subdomains,
    keyParam: keyParam,
    apiKey: key,
    requiresKey: requiresKey,
    maxNativeZoom: maxNativeZoom,
    retina: retina,
  );

  // ------------------------------------------------------------- presets

  /// CARTO's basemaps over OpenStreetMap data. The development default:
  /// warm, legible, and usable without an account.
  ///
  /// Anonymous use is **not** a production contract. CARTO issues API keys for
  /// application use — set `DM_MAP_KEY` and it travels as `api_key` on every
  /// tile request, no other change required.
  static const carto = MapTileProvider(
    id: 'carto',
    name: 'CARTO basemaps (OpenStreetMap data)',
    templates: {
      DmMapStyle.streets:
          'https://{s}.basemaps.cartocdn.com/rastertiles/voyager/{z}/{x}/{y}{r}.png',
      DmMapStyle.muted:
          'https://{s}.basemaps.cartocdn.com/rastertiles/light_all/{z}/{x}/{y}{r}.png',
    },
    attribution: '© OpenStreetMap contributors · © CARTO',
    subdomains: ['a', 'b', 'c', 'd'],
    keyParam: 'api_key',
  );

  /// OpenStreetMap's own tile servers.
  ///
  /// Their usage policy does not permit a distributed app to lean on these —
  /// present for local development and as a last-resort fallback only.
  static const osm = MapTileProvider(
    id: 'osm',
    name: 'OpenStreetMap standard tiles',
    templates: {
      DmMapStyle.streets: 'https://tile.openstreetmap.org/{z}/{x}/{y}.png',
      DmMapStyle.muted: 'https://tile.openstreetmap.org/{z}/{x}/{y}.png',
    },
    attribution: '© OpenStreetMap contributors',
    maxNativeZoom: 19,
    retina: false,
  );

  /// MapTiler — a commercial provider with an India-usable free tier.
  static const maptiler = MapTileProvider(
    id: 'maptiler',
    name: 'MapTiler',
    templates: {
      DmMapStyle.streets:
          'https://api.maptiler.com/maps/streets-v2/{z}/{x}/{y}{r}.png',
      DmMapStyle.muted:
          'https://api.maptiler.com/maps/dataviz-light/{z}/{x}/{y}{r}.png',
    },
    attribution: '© MapTiler · © OpenStreetMap contributors',
    keyParam: 'key',
    requiresKey: true,
  );

  /// Stadia Maps, serving OpenStreetMap-derived styles.
  static const stadia = MapTileProvider(
    id: 'stadia',
    name: 'Stadia Maps',
    templates: {
      DmMapStyle.streets:
          'https://tiles.stadiamaps.com/tiles/osm_bright/{z}/{x}/{y}{r}.png',
      DmMapStyle.muted:
          'https://tiles.stadiamaps.com/tiles/alidade_smooth/{z}/{x}/{y}{r}.png',
    },
    attribution: '© Stadia Maps · © OpenStreetMap contributors',
    keyParam: 'api_key',
    requiresKey: true,
  );

  /// Everything that ships with the app, by id.
  static const Map<String, MapTileProvider> presets = {
    'carto': carto,
    'osm': osm,
    'maptiler': maptiler,
    'stadia': stadia,
  };
}

/// The resolved map configuration for this build.
///
/// Read once at startup from `--dart-define`s; [instance] is assignable so a
/// test or a staging build can substitute one without touching a screen.
class DmMapConfig {
  const DmMapConfig({
    required this.provider,
    required this.userAgent,
    this.warning,
  });

  final MapTileProvider provider;

  /// Sent as the `User-Agent` on every tile request, so the provider can
  /// identify and rate-limit the app properly rather than seeing raw traffic.
  final String userAgent;

  /// Set when the requested configuration could not be honoured — surfaced in
  /// debug diagnostics rather than silently swallowed.
  final String? warning;

  /// Swappable for tests and staging.
  static DmMapConfig instance = DmMapConfig.fromEnvironment();

  /// The bundle id, which is also what identifies us to a tile provider.
  static const packageName = 'in.doormile.customer';

  // ---- build-time configuration -------------------------------------------
  //
  //   flutter run \
  //     --dart-define=DM_MAP_PROVIDER=maptiler \
  //     --dart-define=DM_MAP_KEY=xxxxxxxx
  //
  //   flutter build appbundle \
  //     --dart-define=DM_MAP_PROVIDER=carto \
  //     --dart-define=DM_MAP_KEY=$CARTO_API_KEY
  //
  //   # a fully custom or self-hosted style
  //   flutter run \
  //     --dart-define=DM_MAP_PROVIDER=custom \
  //     --dart-define=DM_MAP_URL=https://tiles.doormile.in/streets/{z}/{x}/{y}.png \
  //     --dart-define=DM_MAP_URL_MUTED=https://tiles.doormile.in/light/{z}/{x}/{y}.png \
  //     --dart-define=DM_MAP_ATTRIBUTION='© Doormile · © OpenStreetMap contributors'

  static const _provider = String.fromEnvironment('DM_MAP_PROVIDER');
  static const _key = String.fromEnvironment('DM_MAP_KEY');
  static const _url = String.fromEnvironment('DM_MAP_URL');
  static const _urlMuted = String.fromEnvironment('DM_MAP_URL_MUTED');
  static const _subdomains = String.fromEnvironment('DM_MAP_SUBDOMAINS');
  static const _attribution = String.fromEnvironment('DM_MAP_ATTRIBUTION');
  static const _attributionUrl = String.fromEnvironment('DM_MAP_ATTRIBUTION_URL');
  static const _maxZoom = int.fromEnvironment('DM_MAP_MAX_ZOOM', defaultValue: 0);
  static const _appVersion = String.fromEnvironment(
    'DM_APP_VERSION',
    defaultValue: '1.0.0',
  );

  factory DmMapConfig.fromEnvironment() {
    final id = _provider.isEmpty ? 'carto' : _provider;
    String? warning;

    MapTileProvider provider;
    if (id == 'custom') {
      if (_url.isEmpty) {
        provider = MapTileProvider.carto;
        warning =
            'DM_MAP_PROVIDER=custom needs DM_MAP_URL; fell back to CARTO.';
      } else {
        provider = MapTileProvider(
          id: 'custom',
          name: 'Custom tile source',
          templates: {
            DmMapStyle.streets: _url,
            DmMapStyle.muted: _urlMuted.isEmpty ? _url : _urlMuted,
          },
          attribution: _attribution.isEmpty
              ? '© OpenStreetMap contributors'
              : _attribution,
          attributionUrl: _attributionUrl.isEmpty
              ? MapTileProvider.osmCopyright
              : _attributionUrl,
          subdomains: _subdomains.isEmpty
              ? const []
              : _subdomains.split(',').map((s) => s.trim()).toList(),
          maxNativeZoom: _maxZoom == 0 ? 20 : _maxZoom,
          retina: _url.contains('{r}'),
        );
      }
    } else {
      provider = MapTileProvider.presets[id] ?? MapTileProvider.carto;
      if (!MapTileProvider.presets.containsKey(id)) {
        warning = 'Unknown DM_MAP_PROVIDER "$id"; fell back to CARTO.';
      }
    }

    if (_key.isNotEmpty) provider = provider.withKey(_key);

    // A keyed provider with no key would render nothing at all. Better a
    // downgraded map than a grey rectangle in a customer's hands.
    if (!provider.usable) {
      warning =
          '${provider.name} needs DM_MAP_KEY; fell back to CARTO for this build.';
      provider = MapTileProvider.carto;
      if (_key.isNotEmpty) provider = provider.withKey(_key);
    }

    return DmMapConfig(
      provider: provider,
      userAgent: 'Doormile/$_appVersion ($packageName)',
      warning: warning,
    );
  }

  String urlFor(DmMapStyle style) => provider.urlFor(style);

  String get attribution => provider.attribution;
  String get attributionUrl => provider.attributionUrl;
  List<String> get subdomains => provider.subdomains;
  int get maxNativeZoom => provider.maxNativeZoom;
  bool get retina => provider.retina;

  /// One line for a diagnostics screen or a log at startup.
  String get describe =>
      '${provider.name}${provider.hasKey ? ' (keyed)' : ' (anonymous)'}';
}