Make backup status reconciliation memory-safe

Replace full [PhotoAsset] array enumeration with PHFetchResult batch
enumeration (autoreleasepool + Task.yield per batch) to keep memory
bounded during reconciliation. Introduce ManifestIndex with two O(1)
Set<String> lookups (localIdentifier + lowercased filename) instead of
O(n×m) linear scans. Scope manifest Data+struct inside buildManifestIndex
so they are released by ARC before the comparison loop begins. Add
UIApplication.didReceiveMemoryWarningNotification handler to cancel
in-flight tasks under memory pressure. Separate debounceTask from
refreshTask to avoid cancelling long-running reconciles on every photo
library event. fetchResultForReconciliation returns PHFetchResult
directly — no [PhotoAsset] array is ever allocated during reconciliation.

Co-Authored-By: Kutesir <kutesir@provoc.ug>
Co-Authored-By: Sentry <sentry@provoc.ug>

Core/Models/BackupManifest.swift

@@ -1,4 +1,54 @@
 import Foundation
+import Photos
+
+// MARK: — ManifestIndex
+// Lightweight comparison structure — two Sets for O(1) lookups.
+// Built from BackupManifest and then the manifest is released.
+struct ManifestIndex {
+    let localIdentifiers: Set<String>    // PHAsset.localIdentifier (primary key)
+    let lowercasedFilenames: Set<String> // filename fallback for legacy/bootstrap entries
+    let totalCount: Int                  // non-hidden file count for NAS Archive stat
+
+    var isFilenameOnly: Bool { localIdentifiers.isEmpty }
+
+    func matches(localIdentifier id: String) -> Bool {
+        !id.isEmpty && localIdentifiers.contains(id)
+    }
+
+    func matches(filename: String) -> Bool {
+        lowercasedFilenames.contains(filename.lowercased())
+    }
+
+    // Build from decoded manifest — manifest released by caller after this returns
+    init(manifest: BackupManifest) {
+        var ids   = Set<String>(minimumCapacity: manifest.entries.count)
+        var names = Set<String>(minimumCapacity: manifest.entries.count)
+        var count = 0
+        for entry in manifest.entries {
+            if !entry.filename.hasPrefix(".") { count += 1 }
+            if !entry.localIdentifier.isEmpty { ids.insert(entry.localIdentifier) }
+            names.insert(entry.filename.lowercased())
+        }
+        self.localIdentifiers   = ids
+        self.lowercasedFilenames = names
+        self.totalCount = count
+    }
+
+    // Build from NAS directory listing (bootstrap — no localIdentifiers known)
+    init(nasListing items: [NASItem]) {
+        var names = Set<String>()
+        var count = 0
+        for item in items where !item.isDirectory && item.name != BackupManifest.remoteFilename {
+            if !item.name.hasPrefix(".") { count += 1 }
+            names.insert(item.name.lowercased())
+        }
+        self.localIdentifiers   = []
+        self.lowercasedFilenames = names
+        self.totalCount = count
+    }
+}
+
+// MARK: — ManifestEntry
 
 struct ManifestEntry: Codable {
     let localIdentifier: String   // PHAsset.localIdentifier — primary key

Services/BackupStatusService.swift

@@ -1,5 +1,9 @@
 import Foundation
 import Photos
+import UIKit
+import os.log
+
+private let log = Logger(subsystem: "com.albert.nasbackup", category: "BackupStatus")
 
 @MainActor
 final class BackupStatusService: NSObject, ObservableObject {
@@ -11,45 +15,85 @@ final class BackupStatusService: NSObject, ObservableObject {
 
     private let photoService = PhotoLibraryService()
     private let cacheKey = "backupStatusSnapshot_v2"
+
+    // One active reconciliation task at a time — cancelled before starting a new one
     private var refreshTask: Task<Void, Never>?
+    // Separate debounce task for photo library change events
+    private var debounceTask: Task<Void, Never>?
+
     private var lastFullRefresh: Date?
+    private static let debounceInterval: TimeInterval = 4      // seconds before photo-change refresh runs
+    private static let minRefreshInterval: TimeInterval = 30   // minimum between full NAS reconciliations
+
+    // MARK: — Init
 
     private override init() {
         super.init()
         loadCachedSnapshot()
         PHPhotoLibrary.shared().register(self)
+        NotificationCenter.default.addObserver(
+            self,
+            selector: #selector(handleMemoryWarning),
+            name: UIApplication.didReceiveMemoryWarningNotification,
+            object: nil
+        )
     }
 
-    // MARK: — Public
+    deinit {
+        PHPhotoLibrary.shared().unregisterChangeObserver(self)
+        NotificationCenter.default.removeObserver(self)
+    }
 
-    /// Trigger a full reconciliation. `force: true` bypasses the 30-second debounce.
+    @objc private func handleMemoryWarning() {
+        log.warning("Memory warning — cancelling in-flight refresh")
+        cancelAll()
+        isRefreshing = false
+    }
+
+    // MARK: — Public API
+
+    /// Start a reconciliation. `force: true` bypasses the minimum refresh interval.
     func refresh(force: Bool = false) {
-        refreshTask?.cancel()
+        cancelAll()
         refreshTask = Task { [weak self] in
             await self?.performRefresh(force: force)
         }
     }
 
-    /// Called by BackupEngine after a completed run.
-    /// Applies an optimistic update immediately, then writes the manifest and reconciles in background.
+    /// Called by BackupEngine after a completed run with newly uploaded entries.
+    /// Applies an optimistic count update, writes the manifest in background, then reconciles.
     func refreshAfterBackup(entries: [ManifestEntry], connection: NASConnection) {
         let uploaded = entries.count
         snapshot.alreadySafe = min(snapshot.phoneTotal, snapshot.alreadySafe + uploaded)
         snapshot.nasArchiveTotal += uploaded
         saveSnapshot()
+        log.info("Post-backup optimistic update: +\(uploaded) safe")
+        // Write manifest then force reconcile (entries captured only briefly)
         Task {
             await writeManifest(entries: entries, connection: connection)
             refresh(force: true)
         }
     }
 
-    // MARK: — Core refresh
+    // MARK: — Refresh lifecycle
+
+    private func cancelAll() {
+        refreshTask?.cancel()
+        refreshTask = nil
+        debounceTask?.cancel()
+        debounceTask = nil
+    }
 
     private func performRefresh(force: Bool) async {
-        guard !isRefreshing else { return }
+        guard !isRefreshing else {
+            log.debug("Refresh skipped — already in progress")
+            return
+        }
 
-        // Debounce: non-forced refreshes skip the NAS round-trip if we just reconciled
-        if !force, let last = lastFullRefresh, Date().timeIntervalSince(last) < 30 {
+        // Minimum interval guard (skip NAS round-trip if recently refreshed)
+        if !force, let last = lastFullRefresh,
+           Date().timeIntervalSince(last) < Self.minRefreshInterval {
+            log.debug("Refresh debounced — updating phone count only")
             updatePhoneCountOnly()
             return
         }
@@ -57,14 +101,16 @@ final class BackupStatusService: NSObject, ObservableObject {
         lastFullRefresh = Date()
         isRefreshing = true
         refreshError = nil
+        log.info("Refresh started (force=\(force))")
 
         do {
             try await reconcile()
+            log.info("Refresh completed — phone=\(self.snapshot.phoneTotal) safe=\(self.snapshot.alreadySafe)")
         } catch is CancellationError {
-            // Swallow — a newer refresh superseded this one
+            log.info("Refresh cancelled")
         } catch {
+            log.error("Refresh failed: \(error.localizedDescription)")
             refreshError = error.localizedDescription
-            // Keep last cached numbers; mark NAS offline
             snapshot.connectionState = .offline
             snapshot.lastCheckedAt = Date()
             saveSnapshot()
@@ -73,98 +119,150 @@ final class BackupStatusService: NSObject, ObservableObject {
         isRefreshing = false
     }
 
+    // MARK: — Reconciliation
+
     private func reconcile() async throws {
         let store = ConnectionStore.shared
         guard let conn = store.savedConnection else { return }
 
-        // 1. Count phone assets (fast, no network)
+        // ── Step 1: Phone count — metadata only, no image data, no thumbnails ──
         let filter = store.backupFilter
-        let assets = photoService.fetchAssets(filter: filter)
-        let phoneTotal = assets.count
+        let fetchResult = photoService.fetchResultForReconciliation(filter: filter)
+        let phoneTotal = fetchResult.count
+        log.info("PHFetchResult count: \(phoneTotal)")
 
         try Task.checkCancellation()
 
-        // 2. Connect to NAS
+        // ── Step 2: NAS connection ──
         let transfer: any NASTransferProtocol = conn.nasProtocol == .smb ? SMBService() : SFTPService()
-
         do {
             try await transfer.connect(
                 to: conn.host, port: conn.port,
                 username: conn.username, password: conn.password
             )
         } catch {
-            // NAS offline — update phone count only, enforce invariant on cached safe count
+            // NAS offline — keep cached safe count, enforce invariant
             snapshot.phoneTotal = phoneTotal
             snapshot.alreadySafe = min(snapshot.alreadySafe, phoneTotal)
             snapshot.connectionState = .offline
             snapshot.lastCheckedAt = Date()
             saveSnapshot()
+            log.warning("NAS offline — cached numbers retained")
             return
         }
-
         defer { transfer.disconnect() }
         try Task.checkCancellation()
 
-        // 3. Load or bootstrap the manifest
+        // ── Step 3: Load ManifestIndex — Data + BackupManifest released after this call ──
         let manifestPath = "\(conn.remotePath)/\(BackupManifest.remoteFilename)"
-        let manifest: BackupManifest
-
-        do {
-            let data = try await transfer.downloadData(at: manifestPath)
-            if let decoded = try? JSONDecoder().decode(BackupManifest.self, from: data) {
-                manifest = decoded
-            } else {
-                let items = (try? await transfer.listDirectory(at: conn.remotePath)) ?? []
-                manifest = BackupManifest.buildFromNASListing(items)
-            }
-        } catch {
-            // Manifest not found — bootstrap from directory listing
-            let items = (try? await transfer.listDirectory(at: conn.remotePath)) ?? []
-            manifest = BackupManifest.buildFromNASListing(items)
-        }
+        let index = await buildManifestIndex(transfer: transfer, path: manifestPath, conn: conn)
+        log.info("Manifest index built — \(index.totalCount) NAS entries, filename-only=\(index.isFilenameOnly)")
 
         try Task.checkCancellation()
 
-        // 4. Compare — localIdentifier first, filename fallback for legacy entries
-        var safe = 0
-        for asset in assets {
-            if manifest.contains(localIdentifier: asset.localIdentifier)
-                || manifest.containsByFilename(asset.filename) {
-                safe += 1
-            }
-        }
+        // ── Step 4: Count safe assets — PHFetchResult enumerated in batches, no [PhotoAsset] kept ──
+        let safe = try await countSafe(in: fetchResult, against: index)
+        log.info("Comparison complete — \(safe)/\(phoneTotal) already safe")
 
-        // 5. NAS archive count (excludes hidden manifest file)
-        let nasArchive = manifest.entries.filter { !$0.filename.hasPrefix(".") }.count
-
-        // 6. Commit — enforce invariant
+        // ── Step 5: Commit — enforce invariant (alreadySafe ≤ phoneTotal) ──
         var updated = BackupStatusSnapshot()
-        updated.phoneTotal = phoneTotal
-        updated.alreadySafe = min(safe, phoneTotal)   // invariant: never > phoneTotal
-        updated.nasArchiveTotal = nasArchive
+        updated.phoneTotal     = phoneTotal
+        updated.alreadySafe    = min(safe, phoneTotal)
+        updated.nasArchiveTotal = index.totalCount
         updated.connectionState = .connected
-        updated.lastCheckedAt = Date()
+        updated.lastCheckedAt  = Date()
         snapshot = updated
         saveSnapshot()
     }
 
-    // Fast phone-only update used when debouncing NAS round-trips
-    private func updatePhoneCountOnly() {
-        let filter = ConnectionStore.shared.backupFilter
-        let assets = photoService.fetchAssets(filter: filter)
-        let phoneTotal = assets.count
-        if phoneTotal != snapshot.phoneTotal {
-            snapshot.phoneTotal = phoneTotal
-            snapshot.alreadySafe = min(snapshot.alreadySafe, phoneTotal)
-            saveSnapshot()
+    /// Builds a ManifestIndex from NAS. Data and BackupManifest are scoped inside
+    /// this function — they are released before the caller's comparison step begins.
+    private func buildManifestIndex(
+        transfer: any NASTransferProtocol,
+        path: String,
+        conn: NASConnection
+    ) async -> ManifestIndex {
+        do {
+            let data = try await transfer.downloadData(at: path)
+            if let manifest = try? JSONDecoder().decode(BackupManifest.self, from: data) {
+                // `data` and `manifest` released when this scope exits
+                return ManifestIndex(manifest: manifest)
+            }
+        } catch {
+            // File not found — fall through to directory listing bootstrap
         }
+        // Bootstrap from directory listing
+        let items = (try? await transfer.listDirectory(at: conn.remotePath)) ?? []
+        log.info("Manifest not found — bootstrapping from \(items.count) NAS items")
+        return ManifestIndex(nasListing: items)
     }
 
-    // MARK: — Manifest write (non-blocking background operation)
+    /// Enumerates a PHFetchResult in batches using autoreleasepool.
+    /// Never builds a full [PHAsset] or [PhotoAsset] array.
+    private func countSafe(
+        in result: PHFetchResult<PHAsset>,
+        against index: ManifestIndex,
+        batchSize: Int = 150
+    ) async throws -> Int {
+        var safe = 0
+        let total = result.count
+        var processed = 0
+
+        while processed < total {
+            try Task.checkCancellation()
+
+            let batchEnd = min(processed + batchSize, total)
+
+            // autoreleasepool releases PHAsset objects and PHAssetResource arrays
+            // created during this batch before moving to the next
+            let batchSafe: Int = autoreleasepool {
+                var count = 0
+                for i in processed..<batchEnd {
+                    let asset = result.object(at: i)
+
+                    if index.matches(localIdentifier: asset.localIdentifier) {
+                        // Fast path — O(1) Set lookup, no resource inspection
+                        count += 1
+                    } else if index.isFilenameOnly {
+                        // Bootstrap path — manifest was built from NAS directory listing,
+                        // no localIdentifiers available, must look up filename
+                        let resources = PHAssetResource.assetResources(for: asset)
+                        if let name = resources.first?.originalFilename,
+                           index.matches(filename: name) {
+                            count += 1
+                        }
+                    }
+                }
+                return count
+            }
+
+            safe += batchSafe
+            processed = batchEnd
+            await Task.yield() // yield between batches to keep main thread responsive
+        }
+
+        return safe
+    }
+
+    // MARK: — Phone-only lightweight update (no NAS connection)
+
+    private func updatePhoneCountOnly() {
+        // Returns PHFetchResult — no array allocation
+        let result = photoService.fetchResultForReconciliation(
+            filter: ConnectionStore.shared.backupFilter
+        )
+        let phoneTotal = result.count
+        guard phoneTotal != snapshot.phoneTotal else { return }
+        snapshot.phoneTotal = phoneTotal
+        snapshot.alreadySafe = min(snapshot.alreadySafe, phoneTotal)
+        saveSnapshot()
+        log.debug("Phone-only update: \(phoneTotal) assets")
+    }
+
+    // MARK: — Manifest write (non-blocking, background only)
 
     func writeManifest(entries: [ManifestEntry], connection: NASConnection) async {
         guard !entries.isEmpty else { return }
-
         let transfer: any NASTransferProtocol = connection.nasProtocol == .smb ? SMBService() : SFTPService()
         do {
             try await transfer.connect(
@@ -175,6 +273,7 @@ final class BackupStatusService: NSObject, ObservableObject {
 
             let manifestPath = "\(connection.remotePath)/\(BackupManifest.remoteFilename)"
 
+            // Load existing, merge new entries, write back
             var manifest: BackupManifest
             do {
                 let data = try await transfer.downloadData(at: manifestPath)
@@ -188,9 +287,11 @@ final class BackupStatusService: NSObject, ObservableObject {
             let encoder = JSONEncoder()
             encoder.dateEncodingStrategy = .iso8601
             let data = try encoder.encode(manifest)
+            // manifest released here before write
             try await transfer.writeData(data, to: manifestPath)
+            log.info("Manifest written — \(manifest.entries.count) entries")
         } catch {
-            // Manifest write failure is non-fatal — reconciliation rebuilds it next time
+            log.error("Manifest write failed (non-fatal): \(error.localizedDescription)")
         }
     }
 
@@ -215,9 +316,21 @@ final class BackupStatusService: NSObject, ObservableObject {
 // MARK: — PHPhotoLibraryChangeObserver
 
 extension BackupStatusService: PHPhotoLibraryChangeObserver {
+    /// Called on an arbitrary background thread by Photos.
+    /// Debounced: schedules a refresh after a short delay, cancels any pending debounce.
     nonisolated func photoLibraryDidChange(_ changeInstance: PHChange) {
         Task { @MainActor [weak self] in
-            self?.refresh()  // debounced — won't hit NAS more than once per 30s
+            guard let self else { return }
+            // Cancel pending debounce and start a new one
+            self.debounceTask?.cancel()
+            self.debounceTask = Task {
+                do {
+                    try await Task.sleep(nanoseconds: UInt64(BackupStatusService.debounceInterval * 1_000_000_000))
+                    self.refresh()  // non-forced: respects minRefreshInterval
+                } catch {
+                    // Cancelled — a newer change event took over
+                }
+            }
         }
     }
 }

Services/PhotoLibraryService.swift

@@ -68,6 +68,39 @@ final class PhotoLibraryService: PhotoLibraryProtocol {
         return assets
     }
 
+    /// Returns a raw PHFetchResult for memory-safe reconciliation.
+    /// No PhotoAsset array is created — caller enumerates in batches.
+    func fetchResultForReconciliation(filter: BackupFilter) -> PHFetchResult<PHAsset> {
+        let options = PHFetchOptions()
+        options.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: true)]
+
+        var subpredicates: [NSPredicate] = []
+        var mediaTypes: [PHAssetMediaType] = []
+        if filter.includePhotos { mediaTypes.append(.image) }
+        if filter.includeVideos { mediaTypes.append(.video) }
+
+        if !mediaTypes.isEmpty {
+            subpredicates.append(NSPredicate(
+                format: "mediaType IN %@",
+                mediaTypes.map(\.rawValue)
+            ))
+        }
+        if !filter.includeScreenshots {
+            subpredicates.append(NSPredicate(
+                format: "NOT ((mediaSubtype & %d) != 0)",
+                PHAssetMediaSubtype.photoScreenshot.rawValue
+            ))
+        }
+
+        if subpredicates.count > 1 {
+            options.predicate = NSCompoundPredicate(andPredicateWithSubpredicates: subpredicates)
+        } else {
+            options.predicate = subpredicates.first
+        }
+
+        return PHAsset.fetchAssets(with: options)
+    }
+
     func exportAsset(_ asset: PhotoAsset) async throws -> URL {
         let fetchResult = PHAsset.fetchAssets(
             withLocalIdentifiers: [asset.localIdentifier],