doormile_milderapp/lib/utils/external_navigation.dart

import 'package:flutter/foundation.dart';
import 'package:url_launcher/url_launcher.dart';

/// Hands a destination to the phone's own maps app.
///
/// Native intent first, web as the fallback, so a rider gets the same app
/// whichever control in Miler he presses. Three screens had their own copy of
/// these two URLs — a route row, a map screen and a confirmation sheet — which
/// is three chances for one of them to open a different app, or the wrong
/// scheme, on the one action a rider takes at every single stop.
///
/// Silent on failure by design: there is nothing useful to say to a rider whose
/// phone has no maps application, and the screen he pressed from still has the
/// address on it.
Future<void> openExternalNavigation(double lat, double lng) async {
  try {
    final native = Uri.parse('google.navigation:q=$lat,$lng&mode=d');
    if (await launchUrl(native, mode: LaunchMode.externalApplication)) return;
  } catch (_) {
    // Falls through to the web URL below — a device with no navigation intent
    // handler is the normal case on iOS, not an error.
  }
  try {
    await launchUrl(
      Uri.parse(
        'https://www.google.com/maps/dir/?api=1'
        '&destination=$lat,$lng&travelmode=driving',
      ),
      mode: LaunchMode.externalApplication,
    );
  } catch (e) {
    debugPrint('[NAV] could not open maps: $e');
  }
}