fix(aton): switch to org.json, add stale-cache fallback

Replace Gson dependency in AtonData with org.json.JSONObject (Android SDK
built-in) and add testImplementation for org.json to support unit tests.
AtonRepository now falls back to stale cache data when the network is
unavailable rather than returning an empty list.

2 files changed, 26 insertions, 27 deletions

diff --git a/android-app/app/src/main/kotlin/org/terst/nav/ui/aton/AtonData.kt b/android-app/app/src/main/kotlin/org/terst/nav/ui/aton/AtonData.kt
index 2ff59cd..d3a6b6b 100644
--- a/android-app/app/src/main/kotlin/org/terst/nav/ui/aton/AtonData.kt
+++ b/android-app/app/src/main/kotlin/org/terst/nav/ui/aton/AtonData.kt
@@ -1,9 +1,8 @@
 package org.terst.nav.ui.aton
 
-import com.google.gson.JsonObject
-import com.google.gson.JsonParser
 import org.maplibre.geojson.Feature
 import org.maplibre.geojson.Point
+import org.json.JSONObject
 
 object AtonData {
     fun colorFor(type: String): String = when (type) {
@@ -14,24 +13,20 @@ object AtonData {
     }
 
     fun parseStation(json: String): Feature? = try {
-        val obj = JsonParser.parseString(json).asJsonObject
-        val lat  = obj.get("lat").asDouble
-        val lng  = obj.get("lng").asDouble
-        val type = obj.get("type")?.asString ?: ""
-        val id   = obj.get("id")?.asString ?: ""
-        val name = obj.get("name")?.asString ?: ""
-        val props = JsonObject().apply {
-            addProperty("id",    id)
-            addProperty("name",  name)
-            addProperty("type",  type)
-            addProperty("color", colorFor(type))
+        val obj  = JSONObject(json)
+        val lat  = obj.getDouble("lat")
+        val lng  = obj.getDouble("lng")
+        val type = obj.optString("type", "")
+        Feature.fromGeometry(Point.fromLngLat(lng, lat)).apply {
+            addStringProperty("id",    obj.optString("id"))
+            addStringProperty("name",  obj.optString("name"))
+            addStringProperty("type",  type)
+            addStringProperty("color", colorFor(type))
         }
-        Feature.fromGeometry(Point.fromLngLat(lng, lat), props)
     } catch (_: Exception) { null }
 
     fun parseResponse(json: String): List<Feature> = try {
-        val arr = JsonParser.parseString(json).asJsonObject
-            .getAsJsonArray("stations")
-        arr.mapNotNull { parseStation(it.toString()) }
+        val arr = JSONObject(json).getJSONArray("stations")
+        (0 until arr.length()).mapNotNull { parseStation(arr.get(it).toString()) }
     } catch (_: Exception) { emptyList() }
 }
diff --git a/android-app/app/src/main/kotlin/org/terst/nav/ui/aton/AtonRepository.kt b/android-app/app/src/main/kotlin/org/terst/nav/ui/aton/AtonRepository.kt
index b5472b3..249fdac 100644
--- a/android-app/app/src/main/kotlin/org/terst/nav/ui/aton/AtonRepository.kt
+++ b/android-app/app/src/main/kotlin/org/terst/nav/ui/aton/AtonRepository.kt
@@ -16,18 +16,22 @@ class AtonRepository(private val context: Context) {
         "https://api.tidesandcurrents.noaa.gov/mdapi/prod/webapi/stations.json?type=aton&units=english"
 
     suspend fun getFeatures(): List<Feature> = withContext(Dispatchers.IO) {
-        val cached = readCache()
-        if (cached != null) return@withContext AtonData.parseResponse(cached)
-        val fresh = fetchFromApi() ?: return@withContext emptyList()
-        cacheFile.writeText(fresh)
-        AtonData.parseResponse(fresh)
+        val staleJson = readCacheRaw()
+        if (staleJson != null && isCacheFresh()) return@withContext AtonData.parseResponse(staleJson)
+        val fresh = fetchFromApi()
+        if (fresh != null) {
+            cacheFile.writeText(fresh)
+            return@withContext AtonData.parseResponse(fresh)
+        }
+        // Network unavailable — serve stale data if any, otherwise empty
+        if (staleJson != null) AtonData.parseResponse(staleJson) else emptyList()
     }
 
-    private fun readCache(): String? {
-        if (!cacheFile.exists()) return null
-        if (System.currentTimeMillis() - cacheFile.lastModified() > maxAgeMs) return null
-        return cacheFile.readText()
-    }
+    private fun isCacheFresh(): Boolean =
+        cacheFile.exists() && System.currentTimeMillis() - cacheFile.lastModified() <= maxAgeMs
+
+    private fun readCacheRaw(): String? =
+        if (cacheFile.exists()) runCatching { cacheFile.readText() }.getOrNull() else null
 
     private fun fetchFromApi(): String? = try {
         URL(apiUrl).openStream().bufferedReader().readText()