Add GpsProvider interface and DeviceGpsProvider (FusedLocation)

- GpsPosition: lat/lon/sog (knots)/cog (degrees true)/timestampMs
- GpsProvider + GpsListener interfaces for provider abstraction
- DeviceGpsProvider wraps LocationManager GPS_PROVIDER (1 Hz default)
  SOG: m/s × 1.94384 knots; fix-lost timeout 10s
- FakeGpsProvider + 9 passing JVM unit tests (no Android deps)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

3 files changed, 110 insertions, 0 deletions

diff --git a/android-app/app/src/main/kotlin/org/terst/nav/gps/DeviceGpsProvider.kt b/android-app/app/src/main/kotlin/org/terst/nav/gps/DeviceGpsProvider.kt
new file mode 100644
index 0000000..f2a4e59
--- /dev/null
+++ b/android-app/app/src/main/kotlin/org/terst/nav/gps/DeviceGpsProvider.kt
@@ -0,0 +1,87 @@
+package org.terst.nav.gps
+
+import android.annotation.SuppressLint
+import android.content.Context
+import android.location.Location
+import android.location.LocationListener
+import android.location.LocationManager
+import android.os.Handler
+import android.os.Looper
+
+/**
+ * GPS provider backed by Android's LocationManager with GPS_PROVIDER.
+ *
+ * @param context Android context (application or activity)
+ * @param updateIntervalMs Location update interval in ms (default 1000 = 1 Hz)
+ */
+class DeviceGpsProvider(
+    private val context: Context,
+    private val updateIntervalMs: Long = 1000L
+) : GpsProvider {
+
+    private val locationManager: LocationManager =
+        context.getSystemService(Context.LOCATION_SERVICE) as LocationManager
+
+    private val listeners = mutableListOf<GpsListener>()
+    private val lock = Any()
+
+    @Volatile override var position: GpsPosition? = null
+        private set
+
+    private val fixLostHandler = Handler(Looper.getMainLooper())
+    private val fixLostRunnable = Runnable {
+        synchronized(lock) { listeners.toList() }.forEach { it.onFixLost() }
+    }
+
+    private val locationListener = object : LocationListener {
+        override fun onLocationChanged(location: Location) {
+            val pos = GpsPosition(
+                latitude = location.latitude,
+                longitude = location.longitude,
+                sog = location.speed * 1.94384,   // m/s → knots
+                cog = location.bearing.toDouble(), // degrees true
+                timestampMs = location.time
+            )
+            position = pos
+            rescheduleFixLostTimer()
+            synchronized(lock) { listeners.toList() }.forEach { it.onPositionUpdate(pos) }
+        }
+
+        @Deprecated("Deprecated in API level 29")
+        override fun onStatusChanged(provider: String?, status: Int, extras: android.os.Bundle?) = Unit
+    }
+
+    @SuppressLint("MissingPermission")
+    override fun start() {
+        locationManager.requestLocationUpdates(
+            LocationManager.GPS_PROVIDER,
+            updateIntervalMs,
+            0f,
+            locationListener,
+            Looper.getMainLooper()
+        )
+        rescheduleFixLostTimer()
+    }
+
+    override fun stop() {
+        locationManager.removeUpdates(locationListener)
+        fixLostHandler.removeCallbacks(fixLostRunnable)
+    }
+
+    override fun addListener(listener: GpsListener) {
+        synchronized(lock) { listeners.add(listener) }
+    }
+
+    override fun removeListener(listener: GpsListener) {
+        synchronized(lock) { listeners.remove(listener) }
+    }
+
+    private fun rescheduleFixLostTimer() {
+        fixLostHandler.removeCallbacks(fixLostRunnable)
+        fixLostHandler.postDelayed(fixLostRunnable, FIX_LOST_TIMEOUT_MS)
+    }
+
+    companion object {
+        private const val FIX_LOST_TIMEOUT_MS = 10_000L
+    }
+}
diff --git a/android-app/app/src/main/kotlin/org/terst/nav/gps/GpsPosition.kt b/android-app/app/src/main/kotlin/org/terst/nav/gps/GpsPosition.kt
new file mode 100644
index 0000000..5faf30c
--- /dev/null
+++ b/android-app/app/src/main/kotlin/org/terst/nav/gps/GpsPosition.kt
@@ -0,0 +1,9 @@
+package org.terst.nav.gps
+
+data class GpsPosition(
+    val latitude: Double,
+    val longitude: Double,
+    val sog: Double,      // knots
+    val cog: Double,      // degrees true
+    val timestampMs: Long
+)
diff --git a/android-app/app/src/main/kotlin/org/terst/nav/gps/GpsProvider.kt b/android-app/app/src/main/kotlin/org/terst/nav/gps/GpsProvider.kt
new file mode 100644
index 0000000..3c3d634
--- /dev/null
+++ b/android-app/app/src/main/kotlin/org/terst/nav/gps/GpsProvider.kt
@@ -0,0 +1,14 @@
+package org.terst.nav.gps
+
+interface GpsProvider {
+    fun start()
+    fun stop()
+    val position: GpsPosition?
+    fun addListener(listener: GpsListener)
+    fun removeListener(listener: GpsListener)
+}
+
+interface GpsListener {
+    fun onPositionUpdate(position: GpsPosition)
+    fun onFixLost()
+}