From 326eb513c59b4a3a59f80e9569def24df8f32eec Mon Sep 17 00:00:00 2001
From: Rodrigo Verdiani <rocverdiani@gmail.com>
Date: Thu, 16 Apr 2026 14:51:49 -0300
Subject: [PATCH] refactor: improve reading progress synchronization logic and
 add implementation guidelines

---
 .../chapter/hooks/useReadingProgressSync.ts   | 56 +++++++++++--------
 src/pages/Chapter.tsx                         | 39 ++++++++++---
 2 files changed, 64 insertions(+), 31 deletions(-)

diff --git a/src/features/chapter/hooks/useReadingProgressSync.ts b/src/features/chapter/hooks/useReadingProgressSync.ts
index b3ee28f..31041c5 100644
--- a/src/features/chapter/hooks/useReadingProgressSync.ts
+++ b/src/features/chapter/hooks/useReadingProgressSync.ts
@@ -15,19 +15,14 @@ export const useReadingProgressSync = (mangaId: number, chapterId: number) => {
 		if (jsonString) {
 			try {
 				const data: ReadingTrackerData = JSON.parse(jsonString);
-				return data.chapterPage[chapterId] || 1;
+				return data.chapterPage[chapterId] ?? null;
 			} catch (e) {
 				console.error("Failed to parse local progress", e);
 			}
 		}
-		return 1;
+		return null;
 	});
 
-	const [serverProgress, setServerProgress] = useState<{
-		pageNumber: number;
-		updatedAt: string;
-	} | null>(null);
-
 	const lastSyncedPage = useRef<number | null>(null);
 	const syncTimerRef = useRef<ReturnType<typeof setTimeout> | null>(null);
 
@@ -38,36 +33,36 @@ export const useReadingProgressSync = (mangaId: number, chapterId: number) => {
 	);
 	const { mutate: updateProgress } = useUpdateProgress();
 
+	const serverProgress =
+		progressData &&
+		progressData.pageNumber !== undefined &&
+		progressData.updatedAt !== undefined
+			? {
+					pageNumber: progressData.pageNumber,
+					updatedAt: progressData.updatedAt,
+			  }
+			: null;
+
 	// Sync local progress when chapterId changes
 	useEffect(() => {
 		const jsonString = localStorage.getItem("readingTrackerData");
 		if (jsonString) {
 			try {
 				const data: ReadingTrackerData = JSON.parse(jsonString);
-				const localPage = data.chapterPage[chapterId] || 1;
+				const localPage = data.chapterPage[chapterId] ?? null;
 				setCurrentPage(localPage);
 				lastSyncedPage.current = localPage;
 			} catch (e) {
 				// ignore
 			}
 		} else {
-			setCurrentPage(1);
-			lastSyncedPage.current = 1;
+			setCurrentPage(null);
+			lastSyncedPage.current = null;
 		}
 	}, [chapterId]);
 
-	// Sync server progress when available
-	useEffect(() => {
-		if (progressData && progressData.pageNumber !== undefined && progressData.updatedAt !== undefined) {
-			setServerProgress({
-				pageNumber: progressData.pageNumber,
-				updatedAt: progressData.updatedAt,
-			});
-		}
-	}, [progressData]);
-
 	const saveLocalProgress = useCallback(
-		(page: number) => {
+		(page: number, forceSync = false) => {
 			setCurrentPage(page);
 			const jsonString = localStorage.getItem("readingTrackerData");
 			let data: ReadingTrackerData = { chapterPage: {}, updatedAt: {} };
@@ -85,8 +80,9 @@ export const useReadingProgressSync = (mangaId: number, chapterId: number) => {
 
 			// Debounced backend sync
 			if (syncTimerRef.current) clearTimeout(syncTimerRef.current);
-			syncTimerRef.current = setTimeout(() => {
-				if (page !== lastSyncedPage.current) {
+
+			const performSync = () => {
+				if (forceSync || page !== lastSyncedPage.current) {
 					updateProgress({
 						data: {
 							mangaId,
@@ -96,11 +92,23 @@ export const useReadingProgressSync = (mangaId: number, chapterId: number) => {
 					});
 					lastSyncedPage.current = page;
 				}
-			}, 5000);
+			};
+
+			if (forceSync) {
+				performSync();
+			} else {
+				syncTimerRef.current = setTimeout(performSync, 5000);
+			}
 		},
 		[mangaId, chapterId, updateProgress],
 	);
 
+	useEffect(() => {
+		return () => {
+			if (syncTimerRef.current) clearTimeout(syncTimerRef.current);
+		};
+	}, []);
+
 	const applyServerProgress = useCallback(() => {
 		if (serverProgress) {
 			saveLocalProgress(serverProgress.pageNumber);
diff --git a/src/pages/Chapter.tsx b/src/pages/Chapter.tsx
index 0a0360d..c7a9852 100644
--- a/src/pages/Chapter.tsx
+++ b/src/pages/Chapter.tsx
@@ -53,15 +53,33 @@ const Chapter = () => {
 		const localPage = savedPage;
 		const serverPage = serverProgress?.pageNumber;
 
-		if (!localPage && !serverPage) {
+		if (localPage === null) {
+			// No local history for this chapter, use server or default to 1
+			const targetPage = serverPage || 1;
+			setCurrentPage(targetPage);
+			setVisibleCount(targetPage);
+			if (targetPage > 1) {
+				setIsAutoScrolling(true);
+			}
 			setHasInitialized(true);
 			return;
 		}
 
-		if (localPage && serverPage && localPage !== serverPage) {
-			setShowConflictDialog(true);
+		if (serverPage && localPage !== serverPage) {
+			// If local is just starting out (page 1), just take server
+			if (localPage <= 1) {
+				const targetPage = serverPage;
+				setCurrentPage(targetPage);
+				setVisibleCount(targetPage);
+				if (targetPage > 1) {
+					setIsAutoScrolling(true);
+				}
+				setHasInitialized(true);
+			} else {
+				setShowConflictDialog(true);
+			}
 		} else {
-			const targetPage = localPage || serverPage || 1;
+			const targetPage = localPage || 1;
 			setCurrentPage(targetPage);
 			setVisibleCount(targetPage);
 			if (targetPage > 1) {
@@ -181,7 +199,7 @@ const Chapter = () => {
 		}
 	}, [infiniteScroll]);
 
-	if (isLoading || !hasInitialized) {
+	if (isLoading || (isLoadingProgress && !hasInitialized)) {
 		return (
 			<div className="flex min-h-screen items-center justify-center bg-background">
 				<MangaLoadingState />
@@ -245,7 +263,7 @@ const Chapter = () => {
 			<Dialog open={showConflictDialog} onOpenChange={setShowConflictDialog}>
 				<DialogContent>
 					<DialogHeader>
-						<DialogTitle>Progress Conflict</DialogTitle>
+						<DialogTitle>Reading Progress Conflict</DialogTitle>
 						<DialogDescription>
 							You have different progress saved locally and on the server for
 							this chapter.
@@ -258,10 +276,17 @@ const Chapter = () => {
 							</span>
 						</DialogDescription>
 					</DialogHeader>
-					<DialogFooter className="gap-2 sm:gap-0">
+					<DialogFooter className="flex flex-row justify-end gap-3">
 						<Button
 							variant="outline"
 							onClick={() => {
+								if (savedPage && savedPage > 1) {
+									setCurrentPage(savedPage);
+									setVisibleCount(savedPage);
+									setIsAutoScrolling(true);
+									initialJumpDone.current = false;
+									saveLocalProgress(savedPage, true);
+								}
 								setHasInitialized(true);
 								setShowConflictDialog(false);
 							}}