feat: ui rework and gear generator

test/model/gear_configurator_test.dart

@@ -0,0 +1,72 @@
+import 'package:abawo_bt_app/model/gear_configurator.dart';
+import 'package:abawo_bt_app/model/gear_ratio_codec.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('gear ratio codec', () {
+    test('maps one byte across the configured drivetrain range', () {
+      expect(decodeGearRatioByte(1), gearRatioMin);
+      expect(decodeGearRatioByte(255), gearRatioMax);
+      expect(encodeGearRatioByte(0), 0);
+      expect(encodeGearRatioByte(gearRatioMax + 1), 255);
+    });
+
+    test('quantizes ratios through the byte encoding', () {
+      final quantized = quantizeGearRatio(50 / 11);
+
+      expect(quantized, closeTo(4.55, 0.02));
+      expect(encodeGearRatioByte(quantized), encodeGearRatioByte(50 / 11));
+    });
+  });
+
+  group('calculateGearRatios', () {
+    test('keep all deduplicates and sorts ascending', () {
+      final result = calculateGearRatios(
+        chainrings: [40, 20],
+        sprockets: [20, 10],
+        mode: GearRetentionMode.keepAll,
+      );
+
+      expect(result.ratios, orderedEquals(result.ratios.toList()..sort()));
+      expect(result.ratios.length, 3);
+      expect(result.duplicateCount, 1);
+    });
+
+    test('keep highest drops lower overlapping larger-chainring ratios', () {
+      final result = calculateGearRatios(
+        chainrings: [30, 50],
+        sprockets: [10, 20, 30],
+        mode: GearRetentionMode.keepHighest,
+      );
+
+      expect(result.ratios.first, closeTo(1, 0.02));
+      expect(result.ratios.last, closeTo(5, 0.02));
+      expect(result.ratios.length, 4);
+      expect(result.ratios.where((ratio) => ratio < 1).length, 0);
+    });
+
+    test('discard ratios outside the one-byte range', () {
+      final result = calculateGearRatios(
+        chainrings: [20, 60],
+        sprockets: [5, 100],
+        mode: GearRetentionMode.keepAll,
+      );
+
+      expect(result.discardedBelowRange, 1);
+      expect(result.discardedAboveRange, 1);
+      expect(result.ratios.length, 2);
+    });
+
+    test('truncates to the configured maximum', () {
+      final result = calculateGearRatios(
+        chainrings: [30, 40, 50],
+        sprockets: [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21],
+        mode: GearRetentionMode.keepAll,
+        maxRatios: 8,
+      );
+
+      expect(result.ratios.length, 8);
+      expect(result.truncatedCount, greaterThan(0));
+    });
+  });
+}