Code changes by azmat

lib/screens/Attendance/attendance_math.dart

@@ -0,0 +1,52 @@
+import 'dart:math' as math;
+
+// ---------------------------------------------------------------------------
+// Attendance math + filter rules (shared by UI and background service).
+//
+// Simple version:
+//  - Wake every 5 min, take ONE gps reading, sleep again (battery safe).
+//  - Throw away weak readings (error > 50 m).
+//  - Throw away tiny jumps (< 20 m) so sitting still never invents fake km.
+// ---------------------------------------------------------------------------
+
+/// How often the background service takes one GPS reading.
+const Duration kFixInterval = Duration(minutes: 5);
+
+/// Max seconds to wait for a single GPS fix before giving up.
+const Duration kFixTimeout = Duration(seconds: 30);
+
+/// Discard any fix whose own accuracy error is worse than this (meters).
+const double kMaxAcceptableAccuracyMeters = 50.0;
+
+/// Ignore movement smaller than this (meters) - kills stationary drift.
+const double kMinMoveMeters = 20.0;
+
+/// Straight-line distance between two lat/lng points, in meters.
+double haversineMeters(double lat1, double lon1, double lat2, double lon2) {
+  const double earthRadius = 6371000.0; // meters
+  final double dLat = _toRadians(lat2 - lat1);
+  final double dLon = _toRadians(lon2 - lon1);
+  final double a = math.sin(dLat / 2) * math.sin(dLat / 2) +
+      math.cos(_toRadians(lat1)) *
+          math.cos(_toRadians(lat2)) *
+          math.sin(dLon / 2) *
+          math.sin(dLon / 2);
+  final double c = 2 * math.atan2(math.sqrt(a), math.sqrt(1 - a));
+  return earthRadius * c;
+}
+
+double _toRadians(double degrees) => degrees * math.pi / 180.0;
+
+/// Decides whether a new fix is worth storing. Returns true only when the
+/// reading is strong enough AND the person actually moved.
+bool shouldStorePoint({
+  required double accuracy,
+  required double distanceFromLastMeters,
+  required bool isFirstPoint,
+}) {
+  if (accuracy > kMaxAcceptableAccuracyMeters) return false; // weak signal
+  if (!isFirstPoint && distanceFromLastMeters < kMinMoveMeters) {
+    return false; // standing still (drift)
+  }
+  return true;
+}