Implement fetched posts count tracking for catching gaps in cached postsHEADmain

1 files changed, 17 insertions, 3 deletions

diff --git a/main.go b/main.go
index 85c8712..6fb7bcf 100644
--- a/main.go
+++ b/main.go
@@ -373,14 +373,28 @@ func postsHandler(w http.ResponseWriter, r *http.Request) {
 	}
 	config.Logger.Debug("posts ready", "count", len(posts))
 
-	// background refetch if cache is running low
+	// background refetch if cache is running low or has developed a gap
 	oldestSent, hasOldest := config.Cache.GetOldestSent(session.DID)
 	if !hasOldest || len(posts) > 0 {
 		oldest := posts[len(posts)-1].CreatedAt
 		count, _ := config.Cache.CountPostsOlderThan(session.DID, oldest)
 		cursor, hasCursor := config.Cache.GetCursor(session.DID)
-		config.Logger.Debug("refetch check", "count", count, "pageSize", config.PageSize, "hasCursor", hasCursor, "oldest", oldest)
-		if count < config.PageSize && hasCursor {
+
+		// skip right after a fresh fetch; expected count was just reset to match it
+		hasGap := false
+		if len(cached) > 0 {
+			if expectedCount, hasExpected := config.Cache.GetPostCount(session.DID); hasExpected {
+				hasGap = len(cached) < expectedCount
+			}
+		}
+
+		config.Logger.Debug("refetch check", "count", count, "pageSize", config.PageSize, "hasCursor", hasCursor, "oldest", oldest, "hasGap", hasGap)
+
+		switch {
+		case hasGap:
+			sessionCopy := session.Copy()
+			go fetchers.FetchAppBskyFeedPostsWithCursor(config, sessionCopy.DID, sessionCopy.PDS, sessionCopy, "")
+		case count < config.PageSize && hasCursor:
 			sessionCopy := session.Copy()
 			go fetchers.FetchAppBskyFeedPostsWithCursor(config, sessionCopy.DID, sessionCopy.PDS, sessionCopy, cursor)
 		}