feat(aton): AtonData model + AtonRepository with 24h cache

Implements AtonData (color mapping + Gson-based JSON parsing for NOAA
AtoN station data) and AtonRepository (disk-cached HTTP fetcher).
Uses Gson instead of org.json so unit tests run on the JVM classpath.
7/7 AtonDataTest assertions pass.

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

3 files changed, 109 insertions, 0 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
new file mode 100644
index 0000000..2ff59cd
--- /dev/null
+++ b/android-app/app/src/main/kotlin/org/terst/nav/ui/aton/AtonData.kt
@@ -0,0 +1,37 @@
+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
+
+object AtonData {
+    fun colorFor(type: String): String = when (type) {
+        "Light"               -> "#FF0000"
+        "Float", "Buoy"      -> "#00AA00"
+        "Daybeacon", "Range" -> "#FFDD00"
+        else                  -> "#FFFFFF"
+    }
+
+    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))
+        }
+        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()) }
+    } 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
new file mode 100644
index 0000000..b5472b3
--- /dev/null
+++ b/android-app/app/src/main/kotlin/org/terst/nav/ui/aton/AtonRepository.kt
@@ -0,0 +1,35 @@
+package org.terst.nav.ui.aton
+
+import android.content.Context
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.withContext
+import org.maplibre.geojson.Feature
+import java.io.File
+import java.net.URL
+
+class AtonRepository(private val context: Context) {
+
+    private val cacheFile = File(context.filesDir, "aton_cache.json")
+    private val maxAgeMs  = 24 * 60 * 60 * 1000L
+
+    private val apiUrl =
+        "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)
+    }
+
+    private fun readCache(): String? {
+        if (!cacheFile.exists()) return null
+        if (System.currentTimeMillis() - cacheFile.lastModified() > maxAgeMs) return null
+        return cacheFile.readText()
+    }
+
+    private fun fetchFromApi(): String? = try {
+        URL(apiUrl).openStream().bufferedReader().readText()
+    } catch (_: Exception) { null }
+}
diff --git a/android-app/app/src/test/kotlin/org/terst/nav/ui/aton/AtonDataTest.kt b/android-app/app/src/test/kotlin/org/terst/nav/ui/aton/AtonDataTest.kt
new file mode 100644
index 0000000..dc0cb4f
--- /dev/null
+++ b/android-app/app/src/test/kotlin/org/terst/nav/ui/aton/AtonDataTest.kt
@@ -0,0 +1,37 @@
+package org.terst.nav.ui.aton
+
+import org.junit.Assert.*
+import org.junit.Test
+
+class AtonDataTest {
+    @Test fun `light type maps to red`() {
+        assertEquals("#FF0000", AtonData.colorFor("Light"))
+    }
+    @Test fun `float type maps to green`() {
+        assertEquals("#00AA00", AtonData.colorFor("Float"))
+    }
+    @Test fun `buoy type maps to green`() {
+        assertEquals("#00AA00", AtonData.colorFor("Buoy"))
+    }
+    @Test fun `daybeacon type maps to yellow`() {
+        assertEquals("#FFDD00", AtonData.colorFor("Daybeacon"))
+    }
+    @Test fun `unknown type maps to white`() {
+        assertEquals("#FFFFFF", AtonData.colorFor("WeirdThing"))
+    }
+    @Test fun `parse station json to feature`() {
+        val json = """{"id":"8443970","name":"Boston Light","lat":42.3298,"lng":-70.8930,"type":"Light"}"""
+        val f = AtonData.parseStation(json)
+        assertNotNull(f)
+        assertEquals("Boston Light", f!!.getStringProperty("name"))
+        assertEquals("#FF0000", f.getStringProperty("color"))
+    }
+    @Test fun `parse response returns list of features`() {
+        val json = """{"stations":[
+            {"id":"1","name":"A","lat":21.0,"lng":-158.0,"type":"Buoy"},
+            {"id":"2","name":"B","lat":21.1,"lng":-157.9,"type":"Light"}
+        ]}"""
+        val features = AtonData.parseResponse(json)
+        assertEquals(2, features.size)
+    }
+}