dev mode, imperial units incl. custom scalebar

lib/services/distance_service.dart

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+import '../state/settings_state.dart';
+
+/// Service for distance unit conversions and formatting
+/// 
+/// Follows brutalist principles: simple, explicit conversions without fancy abstractions.
+/// All APIs work in metric units (meters/km), this service only handles display formatting.
+class DistanceService {
+  // Conversion constants
+  static const double _metersToFeet = 3.28084;
+  static const double _metersToMiles = 0.000621371;
+  static const double _kmToMiles = 0.621371;
+
+  /// Format distance for display based on unit preference
+  /// 
+  /// For metric: uses meters for < 1000m, kilometers for >= 1000m
+  /// For imperial: uses feet for < 5280ft (1 mile), miles for >= 5280ft
+  static String formatDistance(double distanceInMeters, DistanceUnit unit) {
+    switch (unit) {
+      case DistanceUnit.metric:
+        if (distanceInMeters < 1000) {
+          return '${distanceInMeters.round()} m';
+        } else {
+          return '${(distanceInMeters / 1000).toStringAsFixed(1)} km';
+        }
+      
+      case DistanceUnit.imperial:
+        final distanceInFeet = distanceInMeters * _metersToFeet;
+        if (distanceInFeet < 5280) {
+          return '${distanceInFeet.round()} ft';
+        } else {
+          final distanceInMiles = distanceInMeters * _metersToMiles;
+          return '${distanceInMiles.toStringAsFixed(1)} mi';
+        }
+    }
+  }
+
+  /// Format large distances (like route distances) for display
+  /// 
+  /// Always uses the larger unit (km/miles) for routes
+  static String formatRouteDistance(double distanceInMeters, DistanceUnit unit) {
+    switch (unit) {
+      case DistanceUnit.metric:
+        return '${(distanceInMeters / 1000).toStringAsFixed(1)} km';
+      
+      case DistanceUnit.imperial:
+        final distanceInMiles = distanceInMeters * _metersToMiles;
+        return '${distanceInMiles.toStringAsFixed(1)} mi';
+    }
+  }
+
+  /// Get the unit suffix for small distances (used in form fields, etc.)
+  static String getSmallDistanceUnit(DistanceUnit unit) {
+    switch (unit) {
+      case DistanceUnit.metric:
+        return 'm';
+      case DistanceUnit.imperial:
+        return 'ft';
+    }
+  }
+
+  /// Convert displayed distance value back to meters for API usage
+  /// 
+  /// This is for form fields where users enter values in their preferred units
+  static double convertToMeters(double value, DistanceUnit unit, {bool isSmallDistance = true}) {
+    switch (unit) {
+      case DistanceUnit.metric:
+        return isSmallDistance ? value : value * 1000; // m or km to m
+      
+      case DistanceUnit.imperial:
+        if (isSmallDistance) {
+          return value / _metersToFeet; // ft to m
+        } else {
+          return value / _metersToMiles; // miles to m
+        }
+    }
+  }
+
+  /// Convert meters to the preferred small distance unit for form display
+  static double convertFromMeters(double meters, DistanceUnit unit) {
+    switch (unit) {
+      case DistanceUnit.metric:
+        return meters;
+      
+      case DistanceUnit.imperial:
+        return meters * _metersToFeet;
+    }
+  }
+}