Concurrent feed fetching with durable fetch-result tracking

Feeds are fetched with bounded concurrency (semaphore of 8) instead of
strictly sequentially -- with 100+ subscriptions, one slow/stalling
server no longer delays every feed queued behind it. A process-local
mutex prevents the periodic and manual/alarm-triggered one-time
fetches (two different WorkManager unique-work names, so its own dedup
doesn't cover this) from ever running concurrently and racing writes
to the same feed rows.

Settings.recordFetchResult persists lastFetchAt/lastFetchNewArticles
on every run, not derived from WorkInfo.State -- a PeriodicWorkRequest
cycles back to ENQUEUED after every successful run and never reaches
SUCCEEDED, so anything watching for that only ever saw manual fetches.
ArticleListScreen surfaces this as a "N new articles" snackbar
(acknowledged durably, so returning to the screen doesn't re-show it)
and computes live "Checking feed X of Y" progress from the worker's
tagged WorkInfo, scoped to the Unread/Older views that actually
aggregate every subscription.

1 files changed, 33 insertions, 0 deletions

diff --git a/app/src/main/java/org/terst/feedreader/data/Settings.kt b/app/src/main/java/org/terst/feedreader/data/Settings.kt
index b4af70e..ce05974 100644
--- a/app/src/main/java/org/terst/feedreader/data/Settings.kt
+++ b/app/src/main/java/org/terst/feedreader/data/Settings.kt
@@ -2,6 +2,8 @@ package org.terst.feedreader.data
 
 import android.content.Context
 import androidx.datastore.preferences.core.edit
+import androidx.datastore.preferences.core.intPreferencesKey
+import androidx.datastore.preferences.core.longPreferencesKey
 import androidx.datastore.preferences.core.stringPreferencesKey
 import androidx.datastore.preferences.preferencesDataStore
 import kotlinx.coroutines.flow.Flow
@@ -13,6 +15,9 @@ val Context.settingsDataStore by preferencesDataStore(name = "settings")
 private object SettingsKeys {
     val STASH_BASE_URL = stringPreferencesKey("stash_base_url")
     val STASH_API_KEY = stringPreferencesKey("stash_api_key")
+    val LAST_FETCH_AT = longPreferencesKey("last_fetch_at")
+    val LAST_FETCH_NEW_ARTICLES = intPreferencesKey("last_fetch_new_articles")
+    val LAST_ACKNOWLEDGED_FETCH_AT = longPreferencesKey("last_acknowledged_fetch_at")
 }
 
 /** Stash connection settings, configured on the Settings screen. Both blank until set. */
@@ -31,4 +36,32 @@ class Settings(private val context: Context) {
             prefs[SettingsKeys.STASH_API_KEY] = apiKey.trim()
         }
     }
+
+    // Durable record of "when did a feed fetch last finish, and with how many new
+    // articles" -- deliberately NOT derived from WorkManager's WorkInfo.State. A
+    // PeriodicWorkRequest's state cycles back to ENQUEUED after every successful run
+    // (it never settles on SUCCEEDED the way a one-time request does), so anything
+    // watching for SUCCEEDED only ever sees manual/alarm-triggered one-time fetches --
+    // the actual hourly background fetch is invisible to that approach. Writing the
+    // result here on every run (periodic or one-time alike) gives the UI one consistent
+    // signal regardless of which triggered it.
+    val lastFetchAt: Flow<Long> =
+        context.settingsDataStore.data.map { it[SettingsKeys.LAST_FETCH_AT] ?: 0L }
+    val lastFetchNewArticles: Flow<Int> =
+        context.settingsDataStore.data.map { it[SettingsKeys.LAST_FETCH_NEW_ARTICLES] ?: 0 }
+    val lastAcknowledgedFetchAt: Flow<Long> =
+        context.settingsDataStore.data.map { it[SettingsKeys.LAST_ACKNOWLEDGED_FETCH_AT] ?: 0L }
+
+    suspend fun recordFetchResult(newArticles: Int) {
+        context.settingsDataStore.edit { prefs ->
+            prefs[SettingsKeys.LAST_FETCH_AT] = System.currentTimeMillis()
+            prefs[SettingsKeys.LAST_FETCH_NEW_ARTICLES] = newArticles
+        }
+    }
+
+    // Persisted (not just in-memory Compose state) so that navigating away from a screen
+    // and back doesn't forget a fetch was already acknowledged and re-show its snackbar.
+    suspend fun acknowledgeFetch(at: Long) {
+        context.settingsDataStore.edit { prefs -> prefs[SettingsKeys.LAST_ACKNOWLEDGED_FETCH_AT] = at }
+    }
 }