Reapply "Fixed Preset on offgrid repeat toggle enhancemet #183"

This reverts commit 758619bbaa6ce5895c7146bbfc3b89054e759527.

lib/screens/settings_screen.dart

@@ -1088,6 +1088,7 @@ class _RadioSettingsDialogState extends State<_RadioSettingsDialog> {
   LoRaCodingRate _codingRate = LoRaCodingRate.cr4_5;
   final _txPowerController = TextEditingController(text: '20');
   bool _clientRepeat = false;
+  int? _selectedPresetIndex;
 
   @override
   void initState() {
@@ -1139,6 +1140,7 @@ class _RadioSettingsDialogState extends State<_RadioSettingsDialog> {
     }
 
     _clientRepeat = widget.connector.clientRepeat ?? false;
+    _selectedPresetIndex = _findMatchingPresetIndex();
   }
 
   @override
@@ -1158,6 +1160,55 @@ class _RadioSettingsDialogState extends State<_RadioSettingsDialog> {
     });
   }
 
+  int? _findMatchingPresetIndex() {
+    final freqMHz = double.tryParse(_frequencyController.text);
+    final txPower = int.tryParse(_txPowerController.text);
+    if (freqMHz == null || txPower == null) return null;
+
+    const epsilon = 0.001;
+    for (var i = 0; i < RadioSettings.presets.length; i++) {
+      final preset = RadioSettings.presets[i].$2;
+      if ((preset.frequencyMHz - freqMHz).abs() < epsilon &&
+          preset.bandwidth == _bandwidth &&
+          preset.spreadingFactor == _spreadingFactor &&
+          preset.codingRate == _codingRate &&
+          preset.txPowerDbm == txPower) {
+        return i;
+      }
+    }
+    return null;
+  }
+
+  double _offGridFrequencyForBaseFrequency(double baseFrequencyMHz) {
+    if (baseFrequencyMHz < 500) return 433.0;
+    if (baseFrequencyMHz < 900) return 869.0;
+    return 918.0;
+  }
+
+  double _normalFrequencyForBand(double frequencyMHz) {
+    if (frequencyMHz < 500) return 433.650;
+    if (frequencyMHz < 900) return 869.432;
+    return 915.8;
+  }
+
+  void _handleClientRepeatChanged(bool enabled) {
+    setState(() {
+      _clientRepeat = enabled;
+
+      final baseFrequencyMHz = _selectedPresetIndex != null
+          ? RadioSettings.presets[_selectedPresetIndex!].$2.frequencyMHz
+          : (double.tryParse(_frequencyController.text) ?? 915.0);
+
+      final nextFrequencyMHz = enabled
+          ? _offGridFrequencyForBaseFrequency(baseFrequencyMHz)
+          : (_selectedPresetIndex != null
+                ? RadioSettings.presets[_selectedPresetIndex!].$2.frequencyMHz
+                : _normalFrequencyForBand(baseFrequencyMHz));
+
+      _frequencyController.text = nextFrequencyMHz.toStringAsFixed(3);
+    });
+  }
+
   Future<void> _saveSettings() async {
     final l10n = context.l10n;
     final freqMHz = double.tryParse(_frequencyController.text);
@@ -1250,6 +1301,7 @@ class _RadioSettingsDialogState extends State<_RadioSettingsDialog> {
           crossAxisAlignment: CrossAxisAlignment.start,
           children: [
             DropdownButtonFormField<int>(
+              initialValue: _selectedPresetIndex,
               decoration: InputDecoration(
                 labelText: l10n.settings_presets,
                 border: const OutlineInputBorder(),
@@ -1263,6 +1315,7 @@ class _RadioSettingsDialogState extends State<_RadioSettingsDialog> {
               ],
               onChanged: (index) {
                 if (index != null) {
+                  _selectedPresetIndex = index;
                   _applyPreset(RadioSettings.presets[index].$2);
                 }
               },
@@ -1345,7 +1398,7 @@ class _RadioSettingsDialogState extends State<_RadioSettingsDialog> {
                 title: Text(l10n.settings_clientRepeat),
                 subtitle: Text(l10n.settings_clientRepeatSubtitle),
                 value: _clientRepeat,
-                onChanged: (value) => setState(() => _clientRepeat = value),
+                onChanged: _handleClientRepeatChanged,
                 contentPadding: EdgeInsets.zero,
               ),
             ],