Keep a just-read article visible (and Previous-reachable) until the next fetch

The Unread/Older views are live Room Flow queries filtered on
isRead = 0, so marking an article read (which only happens on
Next/Previous, not on open) makes it vanish from the list the instant
Room re-emits -- mid-scroll, or from underneath the reader's own
Previous button, which re-queries this same flow to find its
neighbors. Concretely: Next from C to D marks C read and prunes it
from the live list; Previous from D then can't find C anymore, and
jumps past it to whatever was unread before C. A misclick or the
in-flight prune could cost you the article you meant to keep reading.

Adds ArticleEntity.readAt (set whenever isRead flips true, cleared on
explicit "mark unread"); observeUnread/observeOlderUnread now match
"isRead = 0 OR readAt >= sinceFetch", where sinceFetch is
Settings.lastFetchAt -- the same durable signal the new-articles
snackbar already uses. A read article now lingers (shown dimmed via
the existing showReadState styling) until the next real fetch
actually completes, not the next DB write, and Previous/Next read from
the same still-inclusive query so stepping back to what you just read
finds it right where it was.

1 files changed, 26 insertions, 13 deletions

diff --git a/app/src/main/java/org/terst/feedreader/data/Daos.kt b/app/src/main/java/org/terst/feedreader/data/Daos.kt
index ecaac43..20632f8 100644
--- a/app/src/main/java/org/terst/feedreader/data/Daos.kt
+++ b/app/src/main/java/org/terst/feedreader/data/Daos.kt
@@ -107,21 +107,30 @@ interface ArticleDao {
     // MainActivity) so a backlog of hundreds of older unread items doesn't bury
     // what's actually new. Undated articles (publishedAt failed to parse) are kept
     // here rather than silently dropped from both views.
+    //
+    // "isRead = 0 OR readAt >= sinceFetch" (not just "isRead = 0"): a just-read article
+    // stays in this view until the NEXT fetch completes, not the instant it's marked
+    // read. Without this, Room's live Flow re-emits the moment isRead flips, so (a) a
+    // read row vanishes out from under you mid-scroll, and (b) the reader's Previous
+    // button -- which re-queries this same flow to find its neighbors -- can no longer
+    // find the article you just came from, since Next already marked it read a moment
+    // earlier. sinceFetch is Settings.lastFetchAt, the same durable "when did a fetch
+    // last finish" signal the new-articles snackbar already uses.
     @Query(
         "SELECT $ARTICLE_LIST_COLUMNS FROM $ARTICLE_LIST_FROM " +
-            "WHERE articles.isRead = 0 AND (articles.publishedAt IS NULL OR articles.publishedAt >= :cutoff) " +
+            "WHERE (articles.isRead = 0 OR articles.readAt >= :sinceFetch) AND (articles.publishedAt IS NULL OR articles.publishedAt >= :cutoff) " +
             "ORDER BY articles.publishedAt DESC"
     )
-    fun observeUnread(cutoff: Long): Flow<List<ArticleListItem>>
+    fun observeUnread(cutoff: Long, sinceFetch: Long): Flow<List<ArticleListItem>>
 
     // The rest of the unread backlog, older than the cutoff -- its own view rather
-    // than mixed into the main one.
+    // than mixed into the main one. See observeUnread for why sinceFetch is here.
     @Query(
         "SELECT $ARTICLE_LIST_COLUMNS FROM $ARTICLE_LIST_FROM " +
-            "WHERE articles.isRead = 0 AND articles.publishedAt IS NOT NULL AND articles.publishedAt < :cutoff " +
+            "WHERE (articles.isRead = 0 OR articles.readAt >= :sinceFetch) AND articles.publishedAt IS NOT NULL AND articles.publishedAt < :cutoff " +
             "ORDER BY articles.publishedAt DESC"
     )
-    fun observeOlderUnread(cutoff: Long): Flow<List<ArticleListItem>>
+    fun observeOlderUnread(cutoff: Long, sinceFetch: Long): Flow<List<ArticleListItem>>
 
     @Query("SELECT COUNT(*) FROM articles WHERE isRead = 0 AND (publishedAt IS NULL OR publishedAt >= :cutoff)")
     fun observeUnreadCount(cutoff: Long): Flow<Int>
@@ -157,16 +166,20 @@ interface ArticleDao {
     @Insert(onConflict = OnConflictStrategy.REPLACE)
     suspend fun upsert(article: ArticleEntity)
 
-    @Query("UPDATE articles SET isRead = :read WHERE id = :id")
-    suspend fun setRead(id: String, read: Boolean)
+    // readAt is caller-supplied (not CURRENT_TIMESTAMP in SQL) so it's directly comparable
+    // to Settings.lastFetchAt, which is also a Kotlin System.currentTimeMillis() epoch
+    // value, not a SQLite datetime string. Pass null when read=false (explicit "mark
+    // unread") so a stale readAt can't linger on a row that's unread again.
+    @Query("UPDATE articles SET isRead = :read, readAt = :readAt WHERE id = :id")
+    suspend fun setRead(id: String, read: Boolean, readAt: Long?)
 
     // Explicit bulk action ("mark read from here") -- batched per confirmed tap,
     // never called implicitly (e.g. by scrolling).
-    @Query("UPDATE articles SET isRead = 1 WHERE id IN (:ids)")
-    suspend fun markReadBatch(ids: List<String>)
+    @Query("UPDATE articles SET isRead = 1, readAt = :readAt WHERE id IN (:ids)")
+    suspend fun markReadBatch(ids: List<String>, readAt: Long)
 
-    @Query("UPDATE articles SET isRead = 1 WHERE feedId = :feedId")
-    suspend fun markAllReadForFeed(feedId: String)
+    @Query("UPDATE articles SET isRead = 1, readAt = :readAt WHERE feedId = :feedId")
+    suspend fun markAllReadForFeed(feedId: String, readAt: Long)
 
     // Run when unsubscribing from a feed. Saved articles are deliberately kept
     // regardless (isSaved is a separate, durable "keep forever" concept,
@@ -196,8 +209,8 @@ interface ArticleDao {
 // and SQLite has a hard per-statement limit on bound variables (historically 999 on many
 // Android SQLite builds). Chunking well under any realistic limit means this can't throw
 // "too many SQL variables" and crash on an otherwise routine bulk mark-read tap.
-suspend fun ArticleDao.markReadBatchChunked(ids: List<String>) {
-    ids.chunked(500).forEach { chunk -> markReadBatch(chunk) }
+suspend fun ArticleDao.markReadBatchChunked(ids: List<String>, readAt: Long = System.currentTimeMillis()) {
+    ids.chunked(500).forEach { chunk -> markReadBatch(chunk, readAt) }
 }
 
 @Dao