// 1. Check iCloud account status
func checkICloudStatus() async {
    let status = FileManager.default.ubiquityIdentityToken

    if status == nil {
        print("❌ Not signed into iCloud")
        print("Settings → [Name] → iCloud → Sign in")
        return
    }

    print("✅ Signed into iCloud")

    // For CloudKit specifically
    let container = CKContainer.default()
    do {
        let status = try await container.accountStatus()
        switch status {
        case .available:
            print("✅ CloudKit available")
        case .noAccount:
            print("❌ No iCloud account")
        case .restricted:
            print("❌ iCloud restricted (parental controls?)")
        case .couldNotDetermine:
            print("⚠️ Could not determine status")
        case .temporarilyUnavailable:
            print("⚠️ Temporarily unavailable (retry)")
        @unknown default:
            print("⚠️ Unknown status")
        }
    } catch {
        print("Error checking CloudKit: \(error)")
    }
}

// 2. Check entitlements
func checkEntitlements() {
    // Verify iCloud container exists
    if let containerURL = FileManager.default.url(
        forUbiquityContainerIdentifier: nil
    ) {
        print("✅ iCloud container: \(containerURL)")
    } else {
        print("❌ No iCloud container")
        print("Check Xcode → Signing & Capabilities → iCloud")
    }
}

// 3. Check network connectivity
func checkConnectivity() {
    // Use NWPathMonitor or similar
    print("Network: Check if device has internet")
    print("Try on different networks (WiFi, cellular)")
}

// 4. Check device storage
func checkStorage() {
    let homeURL = FileManager.default.homeDirectoryForCurrentUser
    if let values = try? homeURL.resourceValues(forKeys: [
        .volumeAvailableCapacityKey
    ]) {
        let available = values.volumeAvailableCapacity ?? 0
        print("Available space: \(available / 1_000_000) MB")

        if available < 100_000_000 {  // <100 MB
            print("⚠️ Low storage may prevent sync")
        }
    }
}

CloudKit data not syncing?

├─ Account unavailable?
│   ├─ Check: await container.accountStatus()
│   ├─ .noAccount → User not signed into iCloud
│   ├─ .restricted → Parental controls or corporate restrictions
│   └─ .temporarilyUnavailable → Network issue or iCloud outage
│
├─ CKError.quotaExceeded?
│   └─ User exceeded iCloud storage quota
│       → Prompt user to purchase more storage
│       → Or delete old data
│
├─ CKError.networkUnavailable?
│   └─ No internet connection
│       → Check WiFi/cellular
│       → Test on different network
│
├─ CKError.serverRecordChanged (conflict)?
│   └─ Concurrent modifications
│       → Implement conflict resolution
│       → Use savePolicy correctly
│
└─ SwiftData not syncing?
    ├─ Check ModelConfiguration CloudKit setup
    ├─ Verify private database only (no public/shared)
    └─ Check for @Attribute(.unique) (not supported with CloudKit)

iCloud Drive files not syncing?

├─ File not uploading?
│   ├─ Check: url.resourceValues(.ubiquitousItemIsUploadingKey)
│   ├─ Check: url.resourceValues(.ubiquitousItemUploadingErrorKey)
│   └─ Error details will indicate issue
│
├─ File not downloading?
│   ├─ Not requested? → startDownloadingUbiquitousItem(at:)
│   ├─ Check: url.resourceValues(.ubiquitousItemDownloadingErrorKey)
│   └─ May need manual download trigger
│
├─ File has conflicts?
│   ├─ Check: url.resourceValues(.ubiquitousItemHasUnresolvedConflictsKey)
│   └─ Resolve with NSFileVersion
│
└─ Files not appearing on other device?
    ├─ Check iCloud account on both devices (same account?)
    ├─ Check entitlements match on both
    ├─ Wait (sync not instant, can take minutes)
    └─ Check Settings → iCloud → iCloud Drive → [App] is enabled

if error.code == .accountTemporarilyUnavailable {
    // Retry with exponential backoff
    try await Task.sleep(for: .seconds(5))
    try await retryOperation()
}

if error.code == .quotaExceeded {
    // Show alert to user
    showAlert(
        title: "iCloud Storage Full",
        message: "Please free up space in Settings → [Name] → iCloud → Manage Storage"
    )
}

if error.code == .serverRecordChanged,
   let serverRecord = error.serverRecord,
   let clientRecord = error.clientRecord {
    // Merge records
    let merged = mergeRecords(server: serverRecord, client: clientRecord)

    // Retry with merged version
    try await database.save(merged)
}

if error.code == .networkUnavailable {
    // Queue for retry when online
    queueOperation(for: .whenOnline)

    // Or show offline indicator
    showOfflineIndicator()
}

// ✅ Check upload error
func checkUploadError(url: URL) {
    let values = try? url.resourceValues(forKeys: [
        .ubiquitousItemUploadingErrorKey
    ])

    if let error = values?.ubiquitousItemUploadingError {
        print("Upload error: \(error.localizedDescription)")

        if (error as NSError).code == NSFileWriteOutOfSpaceError {
            print("iCloud storage full")
        }
    }
}

// ✅ Check download error
func checkDownloadError(url: URL) {
    let values = try? url.resourceValues(forKeys: [
        .ubiquitousItemDownloadingErrorKey
    ])

    if let error = values?.ubiquitousItemDownloadingError {
        print("Download error: \(error.localizedDescription)")

        // Common errors:
        // - Network unavailable
        // - Account unavailable
        // - File deleted on server
    }
}

// Add timeout
Task {
    try await withTimeout(seconds: 30) {
        try await database.save(record)
    }
}

// Log operation lifecycle
operation.database = database
operation.completionBlock = {
    print("Operation completed")
}
operation.qualityOfService = .userInitiated

// Check if operation was cancelled
if operation.isCancelled {
    print("Operation was cancelled")
}

// 1. Verify CloudKit configuration
let config = ModelConfiguration(
    cloudKitDatabase: .private("iCloud.com.example.app")
)

// 2. Check for incompatible attributes
// ❌ @Attribute(.unique) not supported with CloudKit
@Model
class Task {
    @Attribute(.unique) var id: UUID  // ← Remove this
    var title: String
}

// 3. Check all properties have defaults or are optional
@Model
class Task {
    var title: String = ""  // ✅ Has default
    var dueDate: Date?      // ✅ Optional
}

// ❌ WRONG: Nested coordination can deadlock
coordinator.coordinate(writingItemAt: url, options: [], error: nil) { newURL in
    // Don't create another coordinator here!
    anotherCoordinator.coordinate(...)  // ← Deadlock risk
}

// ✅ CORRECT: Single coordinator per operation
coordinator.coordinate(writingItemAt: url, options: [], error: nil) { newURL in
    // Direct file operations only
    try data.write(to: newURL)
}

// ❌ WRONG: Not marking as resolved
let conflicts = NSFileVersion.unresolvedConflictVersionsOfItem(at: url)
for conflict in conflicts ?? [] {
    // Missing: conflict.isResolved = true
}

// ✅ CORRECT: Mark resolved and remove
for conflict in conflicts ?? [] {
    conflict.isResolved = true
}
try NSFileVersion.removeOtherVersionsOfItem(at: url)

// ✅ Log all CloudKit operations
extension CKDatabase {
    func saveWithLogging(_ record: CKRecord) async throws {
        print("Saving record: \(record.recordID)")
        let start = Date()

        do {
            try await self.save(record)
            let duration = Date().timeIntervalSince(start)
            print("✅ Saved in \(duration)s")
        } catch let error as CKError {
            print("❌ Save failed: \(error.code), \(error.localizedDescription)")
            throw error
        }
    }
}

func diagnoseCloudSyncIssue() async {
    print("=== Cloud Sync Diagnosis ===")

    // 1. Account
    await checkICloudStatus()

    // 2. Entitlements
    checkEntitlements()

    // 3. Network
    checkConnectivity()

    // 4. Storage
    checkStorage()

    // 5. For CloudKit
    let container = CKContainer.default()
    do {
        let status = try await container.accountStatus()
        print("CloudKit status: \(status)")
    } catch {
        print("CloudKit error: \(error)")
    }

    // 6. For iCloud Drive
    if let url = getICloudContainerURL() {
        let values = try? url.resourceValues(forKeys: [
            .ubiquitousItemDownloadingErrorKey,
            .ubiquitousItemUploadingErrorKey
        ])
        print("Download error: \(values?.ubiquitousItemDownloadingError?.localizedDescription ?? "none")")
        print("Upload error: \(values?.ubiquitousItemUploadingError?.localizedDescription ?? "none")")
    }

    print("=== End Diagnosis ===")
}