feat: cache AMSAT status while app is foreground

core/data/src/main/java/com/rtbishop/look4sat/core/data/repository/AmSatRepository.kt

@@ -10,6 +10,7 @@ import com.rtbishop.look4sat.core.domain.model.SatStatusPage
 import com.rtbishop.look4sat.core.domain.repository.IAmSatRepository
 import com.rtbishop.look4sat.core.domain.source.IRemoteSource
 import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.withContext
 import org.json.JSONObject
 import java.text.SimpleDateFormat
@@ -31,26 +32,50 @@ private data class ApiReport(
 /** AMSAT status repository using RemoteSource (Clean Architecture: data layer handles HTTP). */
 class AmSatRepository(private val remoteSource: IRemoteSource) : IAmSatRepository {
 
+    private val statusCacheMutex = Mutex()
+
+    @Volatile
+    private var statusCache: SatStatusPage? = null
+
+    @Volatile
+    private var cacheGeneration = 0
+
     private val isoUtcFormat = SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'", Locale.US).apply {
         timeZone = TimeZone.getTimeZone("UTC")
     }
 
-    override suspend fun fetchStatus(): SatStatusPage? = withContext(Dispatchers.IO) {
-        val nowSec = System.currentTimeMillis() / 1000
-        val catalogJson = remoteSource.getAmSatCatalog() ?: return@withContext null
-        // 72h = 3 days; API hard cap is limit=500 regardless of what we send.
-        // 500 records across ~100 catalog satellites ≈ ~1-5 reports/satellite/day — enough for 3 days.
-        // Upgrade path: paginate or request AMSAT to raise the cap if catalog grows beyond ~200 sats.
-        val reportsJson = remoteSource.getAmSatReports(hours = 72, limit = 500) ?: return@withContext null
-        
-        val names = parseCatalog(catalogJson)
-        val reports = parseReports(reportsJson)
-        
-        if (names.isEmpty() && reports.isEmpty()) return@withContext null
-        
-        val statuses = buildStatuses(names, reports, nowSec)
-        val reportMap = reports.associate { it.id to toSatReport(it) }
-        SatStatusPage(System.currentTimeMillis(), statuses, reportMap)
+    override fun getCachedStatus(): SatStatusPage? = statusCache
+
+    override suspend fun fetchStatus(forceRefresh: Boolean): SatStatusPage? = withContext(Dispatchers.IO) {
+        statusCacheMutex.lock()
+        try {
+            if (!forceRefresh) statusCache?.let { return@withContext it }
+            val generation = cacheGeneration
+            val nowSec = System.currentTimeMillis() / 1000
+            val catalogJson = remoteSource.getAmSatCatalog() ?: return@withContext null
+            // 72h = 3 days; API hard cap is limit=500 regardless of what we send.
+            // 500 records across ~100 catalog satellites ≈ ~1-5 reports/satellite/day — enough for 3 days.
+            // Upgrade path: paginate or request AMSAT to raise the cap if catalog grows beyond ~200 sats.
+            val reportsJson = remoteSource.getAmSatReports(hours = 72, limit = 500) ?: return@withContext null
+
+            val names = parseCatalog(catalogJson)
+            val reports = parseReports(reportsJson)
+
+            if (names.isEmpty() && reports.isEmpty()) return@withContext null
+
+            val statuses = buildStatuses(names, reports, nowSec)
+            val reportMap = reports.associate { it.id to toSatReport(it) }
+            SatStatusPage(System.currentTimeMillis(), statuses, reportMap).also { page ->
+                if (generation == cacheGeneration) statusCache = page
+            }
+        } finally {
+            statusCacheMutex.unlock()
+        }
+    }
+
+    override fun clearStatusCache() {
+        statusCache = null
+        cacheGeneration += 1
     }
 
     override suspend fun submitReport(submission: AmSatReportSubmission): AmSatReportSubmitResult = withContext(Dispatchers.IO) {

core/data/src/test/java/com/rtbishop/look4sat/core/data/repository/AmSatRepositoryTest.kt

@@ -0,0 +1,87 @@
+package com.rtbishop.look4sat.core.data.repository
+
+import com.rtbishop.look4sat.core.domain.model.SatStatus
+import com.rtbishop.look4sat.core.domain.model.SatStatusPage
+import com.rtbishop.look4sat.core.domain.source.IRemoteSource
+import kotlinx.coroutines.test.runTest
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Assert.assertSame
+import org.junit.Test
+import java.io.InputStream
+
+class AmSatRepositoryTest {
+
+    @Test
+    fun fetchStatusReturnsSeededCacheUntilCacheIsCleared() = runTest {
+        val remoteSource = FakeAmSatRemoteSource()
+        val repository = AmSatRepository(remoteSource)
+        val cachedPage = SatStatusPage(
+            fetchedAtUtcMs = 123L,
+            statuses = listOf(SatStatus(name = "AO-7", days = emptyList())),
+            reports = emptyMap()
+        )
+        repository.seedStatusCache(cachedPage)
+
+        val firstPage = repository.fetchStatus()
+        val secondPage = repository.fetchStatus()
+
+        assertSame(cachedPage, firstPage)
+        assertSame(cachedPage, secondPage)
+        assertSame(cachedPage, repository.getCachedStatus())
+        assertEquals(0, remoteSource.catalogRequests)
+        assertEquals(0, remoteSource.reportRequests)
+
+        repository.clearStatusCache()
+        assertNull(repository.getCachedStatus())
+        repository.fetchStatus()
+
+        assertEquals(1, remoteSource.catalogRequests)
+        assertEquals(1, remoteSource.reportRequests)
+    }
+
+    @Test
+    fun forceRefreshBypassesCachedPage() = runTest {
+        val remoteSource = FakeAmSatRemoteSource()
+        val repository = AmSatRepository(remoteSource)
+        repository.seedStatusCache(
+            SatStatusPage(
+                fetchedAtUtcMs = 123L,
+                statuses = listOf(SatStatus(name = "AO-7", days = emptyList())),
+                reports = emptyMap()
+            )
+        )
+
+        repository.fetchStatus(forceRefresh = true)
+
+        assertEquals(1, remoteSource.catalogRequests)
+        assertEquals(1, remoteSource.reportRequests)
+    }
+}
+
+private fun AmSatRepository.seedStatusCache(page: SatStatusPage) {
+    val cacheField = AmSatRepository::class.java.getDeclaredField("statusCache")
+    cacheField.isAccessible = true
+    cacheField.set(this, page)
+}
+
+private class FakeAmSatRemoteSource : IRemoteSource {
+    var catalogRequests = 0
+    var reportRequests = 0
+
+    override suspend fun getFileStream(uri: String): InputStream? = null
+
+    override suspend fun getNetworkStream(url: String): InputStream? = null
+
+    override suspend fun getAmSatCatalog(): String? {
+        catalogRequests += 1
+        return """{"data":[{"name":"AO-7"}]}"""
+    }
+
+    override suspend fun getAmSatReports(hours: Int, limit: Int): String? {
+        reportRequests += 1
+        return """{"data":[]}"""
+    }
+
+    override suspend fun submitAmSatReport(payloadJson: String): Pair<Int, String>? = null
+}