feat: offline GRIB staleness checker, ViewModel integration, and UI badge

- Add GribRegion, GribFile data models and GribFileManager interface
- Add InMemoryGribFileManager for testing and default use
- Add GribStalenessChecker with FreshnessResult sealed class (Fresh/Stale/NoData)
- Integrate weatherStaleness StateFlow into MainViewModel (checked after loadWeather)
- Add yellow staleness banner TextView to fragment_map.xml
- Wire staleness banner in MapFragment (shown on Stale, hidden on Fresh/NoData)
- Add GribStalenessCheckerTest (4 TDD tests)

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

1 files changed, 91 insertions, 0 deletions

diff --git a/android-app/app/src/test/kotlin/com/example/androidapp/data/weather/GribStalenessCheckerTest.kt b/android-app/app/src/test/kotlin/com/example/androidapp/data/weather/GribStalenessCheckerTest.kt
new file mode 100644
index 0000000..535e46a
--- /dev/null
+++ b/android-app/app/src/test/kotlin/com/example/androidapp/data/weather/GribStalenessCheckerTest.kt
@@ -0,0 +1,91 @@
+package com.example.androidapp.data.weather
+
+import com.example.androidapp.data.model.GribFile
+import com.example.androidapp.data.model.GribRegion
+import com.example.androidapp.data.storage.InMemoryGribFileManager
+import org.junit.Assert.*
+import org.junit.Before
+import org.junit.Test
+import java.time.Instant
+
+class GribStalenessCheckerTest {
+
+    private lateinit var manager: InMemoryGribFileManager
+    private lateinit var checker: GribStalenessChecker
+    private val region = GribRegion("test", 35.0, 40.0, -125.0, -120.0)
+
+    @Before
+    fun setUp() {
+        manager = InMemoryGribFileManager()
+        checker = GribStalenessChecker(manager)
+    }
+
+    private fun makeFile(
+        modelRunTime: Instant,
+        forecastHours: Int,
+        downloadedAt: Instant = modelRunTime
+    ) = GribFile(
+        region = region,
+        modelRunTime = modelRunTime,
+        forecastHours = forecastHours,
+        downloadedAt = downloadedAt,
+        filePath = "/tmp/test.grib",
+        sizeBytes = 1024L
+    )
+
+    @Test
+    fun `check_returnsFresh_whenFileIsNotStale`() {
+        val now = Instant.parse("2026-03-16T12:00:00Z")
+        // model run at 06:00, 24h forecast → valid until 06:00 next day, well beyond now
+        val file = makeFile(
+            modelRunTime = Instant.parse("2026-03-16T06:00:00Z"),
+            forecastHours = 24,
+            downloadedAt = Instant.parse("2026-03-16T07:00:00Z")
+        )
+        manager.saveMetadata(file)
+
+        val result = checker.check(region, now)
+
+        assertTrue("Expected Fresh but got $result", result is FreshnessResult.Fresh)
+    }
+
+    @Test
+    fun `check_returnsStale_whenFileIsExpired`() {
+        val now = Instant.parse("2026-03-16T20:00:00Z")
+        // model run at 06:00, 6h forecast → valid until 12:00; now is 8h after that
+        val file = makeFile(
+            modelRunTime = Instant.parse("2026-03-16T06:00:00Z"),
+            forecastHours = 6,
+            downloadedAt = Instant.parse("2026-03-16T07:00:00Z")
+        )
+        manager.saveMetadata(file)
+
+        val result = checker.check(region, now)
+
+        assertTrue("Expected Stale but got $result", result is FreshnessResult.Stale)
+        val stale = result as FreshnessResult.Stale
+        assertTrue("Message should contain hours outdated", stale.message.contains("8h"))
+        assertEquals(file, stale.file)
+    }
+
+    @Test
+    fun `check_returnsNoData_whenNoFilesForRegion`() {
+        val otherRegion = GribRegion("other", 50.0, 55.0, -10.0, 0.0)
+        val file = makeFile(
+            modelRunTime = Instant.parse("2026-03-16T06:00:00Z"),
+            forecastHours = 24
+        )
+        manager.saveMetadata(file)
+
+        val result = checker.check(otherRegion, Instant.parse("2026-03-16T12:00:00Z"))
+
+        assertEquals(FreshnessResult.NoData, result)
+    }
+
+    @Test
+    fun `check_returnsNoData_whenManagerEmpty`() {
+        val result = checker.check(region, Instant.now())
+
+        assertEquals(FreshnessResult.NoData, result)
+    }
+}