feat: cache AMSAT status while app is foreground

app/src/main/java/com/rtbishop/look4sat/MainApplication.kt

@@ -17,7 +17,10 @@
  */
 package com.rtbishop.look4sat
 
+import android.app.Activity
 import android.app.Application
+import android.app.Application.ActivityLifecycleCallbacks
+import android.os.Bundle
 import com.rtbishop.look4sat.core.data.injection.MainContainer
 import com.rtbishop.look4sat.core.domain.repository.IContainerProvider
 import com.rtbishop.look4sat.core.domain.repository.IMainContainer
@@ -35,12 +38,34 @@ class MainApplication : Application(), IContainerProvider {
     override fun onCreate() {
         super.onCreate()
         container = MainContainer(this)
+        clearAmSatCacheOnAppBackground()
         // trigger automatic update every 48 hours
         container.appScope.launch { checkAutoUpdate() }
         // load satellite data on every app start
         container.appScope.launch { container.satelliteRepo.initRepository() }
     }
 
+    private fun clearAmSatCacheOnAppBackground() {
+        registerActivityLifecycleCallbacks(object : ActivityLifecycleCallbacks {
+            private var startedActivityCount = 0
+
+            override fun onActivityStarted(activity: Activity) {
+                startedActivityCount += 1
+            }
+
+            override fun onActivityStopped(activity: Activity) {
+                startedActivityCount = (startedActivityCount - 1).coerceAtLeast(0)
+                if (startedActivityCount == 0) container.amSatRepo.clearStatusCache()
+            }
+
+            override fun onActivityCreated(activity: Activity, savedInstanceState: Bundle?) = Unit
+            override fun onActivityResumed(activity: Activity) = Unit
+            override fun onActivityPaused(activity: Activity) = Unit
+            override fun onActivitySaveInstanceState(activity: Activity, outState: Bundle) = Unit
+            override fun onActivityDestroyed(activity: Activity) = Unit
+        })
+    }
+
     private suspend fun checkAutoUpdate(timeNow: Long = System.currentTimeMillis()) {
         if (container.settingsRepo.otherSettings.value.stateOfAutoUpdate) {
             val timeDelta = timeNow - container.settingsRepo.databaseState.value.updateTimestamp

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
@@ -31,11 +32,25 @@ 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) {
+    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.
@@ -50,7 +65,17 @@ class AmSatRepository(private val remoteSource: IRemoteSource) : IAmSatRepositor
 
             val statuses = buildStatuses(names, reports, nowSec)
             val reportMap = reports.associate { it.id to toSatReport(it) }
-        SatStatusPage(System.currentTimeMillis(), statuses, reportMap)
+            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
+}

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/repository/IAmSatRepository.kt

@@ -6,8 +6,14 @@ import com.rtbishop.look4sat.core.domain.model.SatStatusPage
 
 /** AMSAT satellite status data source */
 interface IAmSatRepository {
-    /** Fetch and parse the AMSAT status page; null on failure */
-    suspend fun fetchStatus(): SatStatusPage?
+    /** Cached AMSAT status page for the current foreground session, if any. */
+    fun getCachedStatus(): SatStatusPage?
+
+    /** Fetch and parse the AMSAT status page; null on failure. */
+    suspend fun fetchStatus(forceRefresh: Boolean = false): SatStatusPage?
+
+    /** Clear the foreground-session status cache. */
+    fun clearStatusCache()
 
     /** Submit a public AMSAT satellite status report. */
     suspend fun submitReport(submission: AmSatReportSubmission): AmSatReportSubmitResult

feature/status/src/main/java/com/rtbishop/look4sat/feature/status/SatStatusScreen.kt

@@ -32,6 +32,7 @@ import androidx.compose.material3.OutlinedTextField
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.DisposableEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
@@ -50,6 +51,9 @@ import androidx.compose.ui.text.style.TextOverflow
 import androidx.compose.ui.unit.Dp
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
+import androidx.lifecycle.Lifecycle
+import androidx.lifecycle.LifecycleEventObserver
+import androidx.lifecycle.compose.LocalLifecycleOwner
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.lifecycle.viewmodel.compose.viewModel
 import com.rtbishop.look4sat.core.domain.model.SatDay
@@ -106,7 +110,22 @@ fun SatStatusDestination() {
     val context = LocalContext.current
     val container = (context.applicationContext as IContainerProvider).getMainContainer()
     val viewModel: SatStatusViewModel = viewModel(factory = SatStatusViewModel.factory(container))
+    val lifecycleOwner = LocalLifecycleOwner.current
     val uiState by viewModel.uiState.collectAsStateWithLifecycle()
+    DisposableEffect(lifecycleOwner, viewModel) {
+        var skipInitialStart = true
+        val observer = LifecycleEventObserver { _, event ->
+            if (event == Lifecycle.Event.ON_START) {
+                if (skipInitialStart) {
+                    skipInitialStart = false
+                } else {
+                    viewModel.fetch()
+                }
+            }
+        }
+        lifecycleOwner.lifecycle.addObserver(observer)
+        onDispose { lifecycleOwner.lifecycle.removeObserver(observer) }
+    }
     SatStatusScreen(
         uiState = uiState,
         refresh = viewModel::refresh,

feature/status/src/main/java/com/rtbishop/look4sat/feature/status/SatStatusViewModel.kt

@@ -7,6 +7,7 @@ import androidx.lifecycle.viewmodel.viewModelFactory
 import com.rtbishop.look4sat.core.domain.model.AmSatReportSubmission
 import com.rtbishop.look4sat.core.domain.model.SatReport
 import com.rtbishop.look4sat.core.domain.model.SatStatus
+import com.rtbishop.look4sat.core.domain.model.SatStatusPage
 import com.rtbishop.look4sat.core.domain.repository.IAmSatRepository
 import com.rtbishop.look4sat.core.domain.repository.IMainContainer
 import com.rtbishop.look4sat.core.domain.repository.ISettingsRepo
@@ -51,28 +52,25 @@ class SatStatusViewModel(
     private val settingsRepo: ISettingsRepo
 ) : ViewModel() {
 
-    private val _uiState = MutableStateFlow(SatStatusUiState(isLoading = true))
+    private val cachedStatusPage = amSatRepo.getCachedStatus()
+    private val _uiState = MutableStateFlow(cachedStatusPage?.toUiState() ?: SatStatusUiState(isLoading = true))
     val uiState: StateFlow<SatStatusUiState> = _uiState
 
     init {
-        fetch()
+        if (cachedStatusPage == null) fetch()
     }
 
     fun fetch() {
+        amSatRepo.getCachedStatus()?.let { page ->
+            applyStatusPage(page)
+            return
+        }
         viewModelScope.launch {
             _uiState.update { it.copy(isLoading = true, error = null) }
             try {
                 val page = amSatRepo.fetchStatus()
                 if (page != null && page.statuses.isNotEmpty()) {
-                    _uiState.update {
-                        it.copy(
-                            isLoading = false,
-                            isRefreshing = false,
-                            statuses = page.statuses,
-                            reports = page.reports,
-                            fetchedAtUtcMs = page.fetchedAtUtcMs
-                        )
-                    }
+                    applyStatusPage(page)
                 } else {
                     _uiState.update {
                         it.copy(isLoading = false, isRefreshing = false, error = "fetch_failed")
@@ -91,16 +89,9 @@ class SatStatusViewModel(
         _uiState.update { it.copy(isRefreshing = true, error = null) }
         viewModelScope.launch {
             try {
-                val page = amSatRepo.fetchStatus()
+                val page = amSatRepo.fetchStatus(forceRefresh = true)
                 if (page != null && page.statuses.isNotEmpty()) {
-                    _uiState.update {
-                        it.copy(
-                            isRefreshing = false,
-                            statuses = page.statuses,
-                            reports = page.reports,
-                            fetchedAtUtcMs = page.fetchedAtUtcMs
-                        )
-                    }
+                    applyStatusPage(page)
                 } else {
                     _uiState.update { it.copy(isRefreshing = false, error = "fetch_failed") }
                 }
@@ -110,6 +101,19 @@ class SatStatusViewModel(
         }
     }
 
+    private fun applyStatusPage(page: SatStatusPage) {
+        _uiState.update {
+            it.copy(
+                isLoading = false,
+                isRefreshing = false,
+                statuses = page.statuses,
+                reports = page.reports,
+                fetchedAtUtcMs = page.fetchedAtUtcMs,
+                error = null
+            )
+        }
+    }
+
     fun toggleUploadPanel() {
         val storedCallsign = settingsRepo.getAmSatCallsign()
         val defaultGrid = defaultGridSquare()
@@ -275,6 +279,12 @@ class SatStatusViewModel(
     }
 }
 
+private fun SatStatusPage.toUiState() = SatStatusUiState(
+    statuses = statuses,
+    reports = reports,
+    fetchedAtUtcMs = fetchedAtUtcMs
+)
+
 private data class PreparedUpload(
     val report: String,
     val callsign: String,

gradle/libs.versions.toml

@@ -1,8 +1,8 @@
 [versions]
 #noinspection UnusedVersionCatalogEntry
-appVersionCode = "447"
+appVersionCode = "448"
 #noinspection UnusedVersionCatalogEntry
-appVersionName = "4.4.6-ba7opf.3"
+appVersionName = "4.4.6-ba7opf.4"
 #noinspection UnusedVersionCatalogEntry
 compileSdk = "37"
 #noinspection UnusedVersionCatalogEntry