if location is not available, keep last map position across app restarts

addresses #191

app/src/main/java/net/vonforst/evmap/fragment/MapFragment.kt

@@ -1038,9 +1038,12 @@ class MapFragment : Fragment(), OnMapReadyCallback, MapsActivity.FragmentCallbac
             positionSet = true
         }
         if (!positionSet) {
-            // center the camera on Europe
+            // use position saved in preferences, fall back to default (Europe)
             val cameraUpdate =
-                map.cameraUpdateFactory.newLatLngZoom(LatLng(50.113388, 9.252536), 3.5f)
+                map.cameraUpdateFactory.newLatLngZoom(
+                    prefs.currentMapLocation,
+                    prefs.currentMapZoom
+                )
             map.moveCamera(cameraUpdate)
         }
 
@@ -1378,6 +1381,10 @@ class MapFragment : Fragment(), OnMapReadyCallback, MapsActivity.FragmentCallbac
     override fun onPause() {
         super.onPause()
         removeLocationUpdates()
+        vm.mapPosition.value?.let {
+            prefs.currentMapLocation = it.bounds.center
+            prefs.currentMapZoom = it.zoom
+        }
     }
 
     override fun onDestroy() {

app/src/main/java/net/vonforst/evmap/storage/PreferenceDataSource.kt

@@ -1,6 +1,8 @@
 package net.vonforst.evmap.storage
 
 import android.content.Context
+import android.content.SharedPreferences
+import android.content.SharedPreferences.Editor
 import androidx.preference.PreferenceManager
 import com.car2go.maps.AnyMap
 import com.car2go.maps.model.LatLng
@@ -224,21 +226,9 @@ class PreferenceDataSource(val context: Context) {
         }
 
     var placeSearchResultAndroidAuto: LatLng?
-        get() = if (sp.contains("place_search_result_android_auto_lat")) {
-            LatLng(
-                Double.fromBits(sp.getLong("place_search_result_android_auto_lat", 0L)),
-                Double.fromBits(sp.getLong("place_search_result_android_auto_lng", 0L))
-            )
-        } else null
+        get() = sp.getLatLng("place_search_result_android_auto")
         set(value) {
-            if (value == null) {
-                sp.edit().remove("place_search_result_android_auto_lat")
-                    .remove("place_search_result_android_auto_lng").apply()
-            } else {
-                sp.edit().putLong("place_search_result_android_auto_lat", value.latitude.toBits())
-                    .putLong("place_search_result_android_auto_lng", value.longitude.toBits())
-                    .apply()
-            }
+            sp.edit().putLatLng("place_search_result_android_auto", value).apply()
         }
 
     var placeSearchResultAndroidAutoName: String?
@@ -264,4 +254,35 @@ class PreferenceDataSource(val context: Context) {
 
     val mapScale: String
         get() = sp.getString("map_scale", null) ?: "both"
-}
+
+    var currentMapLocation: LatLng
+        get() = sp.getLatLng("current_map_location") ?: LatLng(50.113388, 9.252536)
+        set(value) {
+            sp.edit().putLatLng("current_map_location", value).apply()
+        }
+
+    var currentMapZoom: Float
+        get() = sp.getFloat("current_map_zoom", 3.5f)
+        set(value) {
+            sp.edit().putFloat("current_map_zoom", value).apply()
+        }
+}
+
+fun SharedPreferences.getLatLng(key: String): LatLng? =
+    if (contains("${key}_lat") && contains("${key}_lng")) {
+        LatLng(
+            Double.fromBits(getLong("${key}_lat", 0L)),
+            Double.fromBits(getLong("${key}_lng", 0L))
+        )
+    } else null
+
+fun Editor.putLatLng(key: String, value: LatLng?): Editor {
+    if (value == null) {
+        remove("${key}_lat")
+        remove("${key}_lng")
+    } else {
+        putLong("${key}_lat", value.latitude.toBits())
+        putLong("${key}_lng", value.longitude.toBits())
+    }
+    return this
+}