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test/utils/fast_gps_packet_test.dart

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+import 'dart:typed_data';
+import 'dart:math' as math;
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:meshcore_sar_app/utils/fast_gps_packet.dart';
+
+void main() {
+  group('FastGpsPacket', () {
+    test('encodes and parses a valid packet', () {
+      final packet = FastGpsPacket(
+        senderKey6: 'aabbccddeeff',
+        latitude: 46.0569,
+        longitude: 14.5058,
+        timestampSeconds: 1700000000,
+      );
+
+      final encoded = packet.encodeBinary();
+      final parsed = FastGpsPacket.tryParseBinary(encoded);
+
+      expect(parsed, isNotNull);
+      expect(parsed!.senderKey6, equals('aabbccddeeff'));
+      expect(parsed.latitude, closeTo(46.0569, 0.000001));
+      expect(parsed.longitude, closeTo(14.5058, 0.000001));
+      expect(parsed.timestampSeconds, equals(1700000000));
+    });
+
+    test('supports negative coordinates', () {
+      final packet = FastGpsPacket(
+        senderKey6: '001122334455',
+        latitude: -33.8688,
+        longitude: -151.2093,
+        timestampSeconds: 42,
+      );
+
+      final parsed = FastGpsPacket.tryParseBinary(packet.encodeBinary());
+      expect(parsed, isNotNull);
+      expect(parsed!.latitude, closeTo(-33.8688, 0.000001));
+      expect(parsed.longitude, closeTo(-151.2093, 0.000001));
+    });
+
+    test('rejects malformed payloads', () {
+      expect(
+        FastGpsPacket.tryParseBinary(Uint8List.fromList([0x47, 0x01])),
+        isNull,
+      );
+      expect(
+        FastGpsPacket.tryParseBinary(
+          Uint8List.fromList(List<int>.filled(19, 0)..[0] = 0x48),
+        ),
+        isNull,
+      );
+    });
+
+    test('rejects invalid coordinate ranges', () {
+      final payload = Uint8List(19);
+      payload[0] = FastGpsPacket.magic;
+      payload.setRange(1, 7, [0, 1, 2, 3, 4, 5]);
+      final data = ByteData.sublistView(payload);
+      data.setInt32(
+        7,
+        (91.0 * FastGpsPacket.coordinateScale).round(),
+        Endian.little,
+      );
+      data.setInt32(
+        11,
+        (14.5 * FastGpsPacket.coordinateScale).round(),
+        Endian.little,
+      );
+      data.setUint32(15, 1, Endian.little);
+
+      expect(FastGpsPacket.tryParseBinary(payload), isNull);
+    });
+
+    test('preserves at least meter accuracy', () {
+      const latitude = 46.0569123;
+      const longitude = 14.5058123;
+      final packet = FastGpsPacket(
+        senderKey6: 'aabbccddeeff',
+        latitude: latitude,
+        longitude: longitude,
+        timestampSeconds: 1700000000,
+      );
+
+      final parsed = FastGpsPacket.tryParseBinary(packet.encodeBinary());
+      expect(parsed, isNotNull);
+
+      final latMeters = (parsed!.latitude - latitude).abs() * 111320.0;
+      final lonMeters =
+          (parsed.longitude - longitude).abs() *
+          111320.0 *
+          math.cos(latitude * math.pi / 180.0);
+
+      expect(latMeters, lessThan(1.0));
+      expect(lonMeters, lessThan(1.0));
+    });
+  });
+}