Add night vision mode toggle

Single-tap moon FAB (stacked below layers FAB) toggles red-on-black
night vision mode. NightVision theme now has a full M3 color palette
(surface, surfaceVariant, outline, secondary, error) all in dark red
tones. Screen brightness is set to 30% in night mode and restored to
system default on exit. State persists across sessions; recreate()
applies the theme switch cleanly.

https://claude.ai/code/session_01KXYBuAHZkvv63DeUG6XaZD

1 files changed, 21 insertions, 0 deletions

diff --git a/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt b/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt
index da887f4..69ca666 100644
--- a/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt
+++ b/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt
@@ -54,6 +54,7 @@ import org.terst.nav.ui.safety.SafetyFragment
 import org.terst.nav.ui.vessel.VesselRegistryFragment
 import org.terst.nav.ui.voicelog.VoiceLogFragment
 import java.util.*
+import android.view.WindowManager
 import org.terst.nav.data.model.MarineConditions
 import org.terst.nav.safety.AnchorWatchState
 
@@ -61,6 +62,11 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
 
     private val featureFlags get() = (application as NavApplication).featureFlags
 
+    private val nightModePrefs by lazy { getSharedPreferences("night_mode", MODE_PRIVATE) }
+    private var isNightMode: Boolean
+        get() = nightModePrefs.getBoolean("enabled", false)
+        set(v) { nightModePrefs.edit().putBoolean("enabled", v).apply() }
+
     private var mapView: MapView? = null
     private var mobHandler: MobHandler? = null
     private var instrumentHandler: InstrumentHandler? = null
@@ -75,6 +81,7 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
     private lateinit var fragmentContainer: FrameLayout
     private lateinit var fabRecordTrack: FloatingActionButton
     private lateinit var fabLayers: FloatingActionButton
+    private lateinit var fabNightMode: FloatingActionButton
     private lateinit var fabRecenter: MaterialButton
     private lateinit var bottomSheet: CardView
     private lateinit var bottomNav: BottomNavigationView
@@ -134,6 +141,7 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
     }
 
     override fun onCreate(savedInstanceState: Bundle?) {
+        if (isNightMode) setTheme(R.style.Theme_Nav_NightVision)
         super.onCreate(savedInstanceState)
         MapLibre.getInstance(this)
         setContentView(R.layout.activity_main)
@@ -200,10 +208,17 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
         fragmentContainer = findViewById(R.id.fragment_container)
         fabRecordTrack = findViewById(R.id.fab_record_track)
         fabLayers = findViewById(R.id.fab_layers)
+        fabNightMode = findViewById(R.id.fab_night_mode)
         fabRecenter = findViewById(R.id.fab_recenter)
         fabLayers.setOnClickListener {
             buildLayerPickerSheet().show(supportFragmentManager, "layer_picker")
         }
+        fabNightMode.setOnClickListener {
+            isNightMode = !isNightMode
+            applyScreenBrightness()
+            recreate()
+        }
+        applyScreenBrightness()
         bottomSheet = findViewById(R.id.instrument_bottom_sheet)
         bottomNav = findViewById(R.id.bottom_navigation)
         mapCrosshair = findViewById(R.id.map_crosshair)
@@ -307,6 +322,12 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
     }
 
     /** Updates all static unit label TextViews to match current [unitPrefs]. */
+    private fun applyScreenBrightness() {
+        val lp = window.attributes
+        lp.screenBrightness = if (isNightMode) 0.3f else WindowManager.LayoutParams.BRIGHTNESS_OVERRIDE_NONE
+        window.attributes = lp
+    }
+
     private fun applyUnitLabels() {
         unitHudSog.text   = unitPrefs.speedUnitLabel()
         unitHudBsp.text   = unitPrefs.speedUnitLabel()