//

//  DataStore.swift

//  USB Meter

//

//  Created by Bogdan Timofte on 03/03/2020.

//  Copyright © 2020 Bogdan Timofte. All rights reserved.

//

import SwiftUI

import Combine

import CoreBluetooth

import UIKit

import Foundation

// MARK: - Device Name Helper

private func getDeviceName() -> String {

    let hostname = ProcessInfo.processInfo.hostName

    return hostname.trimmingCharacters(in: .whitespacesAndNewlines)

}

final class AppData : ObservableObject {

    static let myDeviceName: String = getDeviceName()

    private static let cloudStoreRebuildVersion = 3

    private var icloudDefaultsNotification: AnyCancellable?

    private var cloudSettingsRefreshTimer: AnyCancellable?

    private var cloudDeviceSettingsStore: CloudDeviceSettingsStore?

    private var hasMigratedLegacyDeviceSettings = false

    private var persistedMeterNames: [String: String] = [:]

    private var persistedTC66TemperatureUnits: [String: String] = [:]

        persistedTC66TemperatureUnits = legacyTC66TemperatureUnits

        icloudDefaultsNotification = NotificationCenter.default.publisher(for: NSUbiquitousKeyValueStore.didChangeExternallyNotification).sink(receiveValue: handleLegacyICloudDefaultsChange)

    let bluetoothManager = BluetoothManager()

    @Published var enableRecordFeature: Bool = true

    @ICloudDefault(key: "TC66TemperatureUnits", defaultValue: [:]) private var legacyTC66TemperatureUnits: [String:String]

    func activateCloudDeviceSync(context: NSManagedObjectContext) {

        guard cloudDeviceSettingsStore == nil else {

            return

        }

        context.automaticallyMergesChangesFromParent = true

        // Prefer incoming/store values on conflict so frequent local discovery updates

        // do not wipe remote connection claims from other devices.

        context.mergePolicy = NSMergeByPropertyStoreTrumpMergePolicy

        cloudDeviceSettingsStore = CloudDeviceSettingsStore(context: context)

        cloudDeviceSettingsStore?.rebuildCanonicalStoreIfNeeded(version: Self.cloudStoreRebuildVersion)

        cloudDeviceSettingsStore?.compactDuplicateEntriesByMAC()

        coreDataSettingsChangeNotification = NotificationCenter.default.publisher(for: .NSManagedObjectContextObjectsDidChange, object: context)

            .sink { [weak self] _ in

                self?.reloadSettingsFromCloudStore(applyToMeters: true)

            }

        cloudSettingsRefreshTimer = Timer.publish(every: 10, on: .main, in: .common)

            .autoconnect()

            .sink { [weak self] _ in

                self?.reloadSettingsFromCloudStore(applyToMeters: true)

            }

        reloadSettingsFromCloudStore(applyToMeters: false)

        migrateLegacySettingsIntoCloudIfNeeded()

        cloudDeviceSettingsStore?.clearAllConnections(byDeviceID: Self.myDeviceID)

        reloadSettingsFromCloudStore(applyToMeters: true)

    }

    func persistedMeterName(for macAddress: String) -> String? {

        persistedMeterNames[macAddress]

    }

    func publishMeterConnection(macAddress: String, modelType: String) {

        cloudDeviceSettingsStore?.setConnection(

            macAddress: macAddress,

            deviceID: Self.myDeviceID,

            deviceName: Self.myDeviceName,

            modelType: modelType

        )

    }

    func registerMeterDiscovery(macAddress: String, modelType: String, peripheralName: String?) {

        cloudDeviceSettingsStore?.recordDiscovery(

            macAddress: macAddress,

            modelType: modelType,

            peripheralName: peripheralName,

            seenByDeviceID: Self.myDeviceID,

            seenByDeviceName: Self.myDeviceName

        )

    }

    func clearMeterConnection(macAddress: String) {

        cloudDeviceSettingsStore?.clearConnection(macAddress: macAddress, byDeviceID: Self.myDeviceID)

    }

    func persistMeterName(_ name: String, for macAddress: String) {

        let normalized = name.trimmingCharacters(in: .whitespacesAndNewlines)

        persistedMeterNames[macAddress] = normalized

        var legacyValues = legacyMeterNames

        legacyValues[macAddress] = normalized

        legacyMeterNames = legacyValues

        cloudDeviceSettingsStore?.upsert(macAddress: macAddress, meterName: normalized, tc66TemperatureUnit: nil)

    }

    func persistedTC66TemperatureUnitRawValue(for macAddress: String) -> String? {

        persistedTC66TemperatureUnits[macAddress]

    }

    func persistTC66TemperatureUnit(rawValue: String, for macAddress: String) {

        persistedTC66TemperatureUnits[macAddress] = rawValue

        var legacyValues = legacyTC66TemperatureUnits

        legacyValues[macAddress] = rawValue

        legacyTC66TemperatureUnits = legacyValues

        cloudDeviceSettingsStore?.upsert(macAddress: macAddress, meterName: nil, tc66TemperatureUnit: rawValue)

    }

    private func handleLegacyICloudDefaultsChange(notification: NotificationCenter.Publisher.Output) {

                switch changedKey {

                case "MeterNames":

                    requiresMeterRefresh = true

                    requiresMeterRefresh = true

                    track("Unknown key: '\(changedKey)' changed in iCloud)")

                }

            }

            if requiresMeterRefresh {

                migrateLegacySettingsIntoCloudIfNeeded(force: true)

                applyPersistedSettingsToKnownMeters()

        }

    }

        guard let cloudDeviceSettingsStore else {

            return

        }

        if hasMigratedLegacyDeviceSettings && !force {

            return

        }

        let cloudRecords = cloudDeviceSettingsStore.fetchByMacAddress()

        for (macAddress, meterName) in legacyMeterNames {

            let cloudName = cloudRecords[macAddress]?.meterName

            if cloudName == nil || cloudName?.isEmpty == true {

                cloudDeviceSettingsStore.upsert(macAddress: macAddress, meterName: meterName, tc66TemperatureUnit: nil)

            }

        }

        for (macAddress, unitRawValue) in legacyTC66TemperatureUnits {

            let cloudUnit = cloudRecords[macAddress]?.tc66TemperatureUnit

            if cloudUnit == nil || cloudUnit?.isEmpty == true {

                cloudDeviceSettingsStore.upsert(macAddress: macAddress, meterName: nil, tc66TemperatureUnit: unitRawValue)

            }

        }

        hasMigratedLegacyDeviceSettings = true

    }

    private func reloadSettingsFromCloudStore(applyToMeters: Bool) {

        guard let cloudDeviceSettingsStore else {

            return

        }

        let records = cloudDeviceSettingsStore.fetchAll()

        var names = persistedMeterNames

        var temperatureUnits = persistedTC66TemperatureUnits

        var knownMeters: [String: KnownMeterCatalogItem] = [:]

        for record in records {

            if let meterName = record.meterName, !meterName.isEmpty {

                names[record.macAddress] = meterName

            }

            if let unitRawValue = record.tc66TemperatureUnit, !unitRawValue.isEmpty {

                temperatureUnits[record.macAddress] = unitRawValue

            }

            let displayName: String

            if let meterName = record.meterName?.trimmingCharacters(in: .whitespacesAndNewlines), !meterName.isEmpty {

                displayName = meterName

            } else if let peripheralName = record.lastSeenPeripheralName?.trimmingCharacters(in: .whitespacesAndNewlines), !peripheralName.isEmpty {

                displayName = peripheralName

            } else {

                displayName = record.macAddress

            }

            knownMeters[record.macAddress] = KnownMeterCatalogItem(

                macAddress: record.macAddress,

                displayName: displayName,

                modelType: record.modelType,

                connectedByDeviceID: record.connectedByDeviceID,

                connectedByDeviceName: record.connectedByDeviceName,

                connectedAt: record.connectedAt,

                connectedExpiryAt: record.connectedExpiryAt,

                lastSeenByDeviceID: record.lastSeenByDeviceID,

                lastSeenByDeviceName: record.lastSeenByDeviceName,

                lastSeenAt: record.lastSeenAt,

                lastSeenPeripheralName: record.lastSeenPeripheralName

            )

        }

        persistedMeterNames = names

        persistedTC66TemperatureUnits = temperatureUnits

        knownMetersByMAC = knownMeters

        if applyToMeters {

            applyPersistedSettingsToKnownMeters()

            scheduleObjectWillChange()

        }

    }

    private func applyPersistedSettingsToKnownMeters() {

        for meter in meters.values {

            let macAddress = meter.btSerial.macAddress.description

            if let newName = persistedMeterNames[macAddress], meter.name != newName {

                meter.name = newName

            }

            if meter.supportsManualTemperatureUnitSelection {

                meter.reloadTemperatureUnitPreference()

            }

        }

    }

        DispatchQueue.main.async { [weak self] in

            self?.objectWillChange.send()

        }

    }

struct KnownMeterCatalogItem: Identifiable, Hashable {

    var id: String { macAddress }

    let macAddress: String

    let displayName: String

    let modelType: String?

    let connectedByDeviceID: String?

    let connectedByDeviceName: String?

    let connectedAt: Date?

    let connectedExpiryAt: Date?

    let lastSeenByDeviceID: String?

    let lastSeenByDeviceName: String?

    let lastSeenAt: Date?

    let lastSeenPeripheralName: String?

}

private struct CloudDeviceSettingsRecord {

    let macAddress: String

    let meterName: String?

    let tc66TemperatureUnit: String?

    let modelType: String?

    let connectedByDeviceID: String?

    let connectedByDeviceName: String?

    let connectedAt: Date?

    let connectedExpiryAt: Date?

    let lastSeenAt: Date?

    let lastSeenByDeviceID: String?

    let lastSeenByDeviceName: String?

    let lastSeenPeripheralName: String?

}

private final class CloudDeviceSettingsStore {

    private let entityName = "DeviceSettings"

    private let context: NSManagedObjectContext

    private static let rebuildDefaultsKeyPrefix = "CloudDeviceSettingsStore.RebuildVersion"

    init(context: NSManagedObjectContext) {

        self.context = context

    }

    private func refreshContextObjects() {

        context.processPendingChanges()

    }

    private func normalizedMACAddress(_ value: String) -> String {

        value.trimmingCharacters(in: .whitespacesAndNewlines).uppercased()

    }

    private func fetchObjects(for macAddress: String) throws -> [NSManagedObject] {

        let request = NSFetchRequest<NSManagedObject>(entityName: entityName)

        request.predicate = NSPredicate(format: "macAddress == %@", macAddress)

        return try context.fetch(request)

    }

    private func hasValue(_ value: String?) -> Bool {

        guard let value else { return false }

        return !value.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty

    }

    private func preferredObject(from objects: [NSManagedObject]) -> NSManagedObject? {

        guard !objects.isEmpty else { return nil }

        let now = Date()

        return objects.max { lhs, rhs in

            let lhsHasOwner = hasValue(lhs.value(forKey: "connectedByDeviceID") as? String)

            let rhsHasOwner = hasValue(rhs.value(forKey: "connectedByDeviceID") as? String)

            if lhsHasOwner != rhsHasOwner {

                return !lhsHasOwner && rhsHasOwner

            }

            let lhsOwnerLive = ((lhs.value(forKey: "connectedExpiryAt") as? Date) ?? .distantPast) > now

            let rhsOwnerLive = ((rhs.value(forKey: "connectedExpiryAt") as? Date) ?? .distantPast) > now

            if lhsOwnerLive != rhsOwnerLive {

                return !lhsOwnerLive && rhsOwnerLive

            }

            let lhsUpdatedAt = (lhs.value(forKey: "updatedAt") as? Date) ?? .distantPast

            let rhsUpdatedAt = (rhs.value(forKey: "updatedAt") as? Date) ?? .distantPast

            if lhsUpdatedAt != rhsUpdatedAt {

                return lhsUpdatedAt < rhsUpdatedAt

            }

            let lhsConnectedAt = (lhs.value(forKey: "connectedAt") as? Date) ?? .distantPast

            let rhsConnectedAt = (rhs.value(forKey: "connectedAt") as? Date) ?? .distantPast

            return lhsConnectedAt < rhsConnectedAt

        }

    }

    private func record(from object: NSManagedObject, macAddress: String) -> CloudDeviceSettingsRecord {

        let ownerID = stringValue(object, key: "connectedByDeviceID")

        return CloudDeviceSettingsRecord(

            macAddress: macAddress,

            meterName: object.value(forKey: "meterName") as? String,

            tc66TemperatureUnit: object.value(forKey: "tc66TemperatureUnit") as? String,

            modelType: object.value(forKey: "modelType") as? String,

            connectedByDeviceID: ownerID,

            connectedByDeviceName: ownerID == nil ? nil : stringValue(object, key: "connectedByDeviceName"),

            connectedAt: ownerID == nil ? nil : dateValue(object, key: "connectedAt"),

            connectedExpiryAt: ownerID == nil ? nil : dateValue(object, key: "connectedExpiryAt"),

            lastSeenAt: object.value(forKey: "lastSeenAt") as? Date,

            lastSeenByDeviceID: object.value(forKey: "lastSeenByDeviceID") as? String,

            lastSeenByDeviceName: object.value(forKey: "lastSeenByDeviceName") as? String,

            lastSeenPeripheralName: object.value(forKey: "lastSeenPeripheralName") as? String

        )

    }

    private func stringValue(_ object: NSManagedObject, key: String) -> String? {

        guard let value = object.value(forKey: key) as? String else { return nil }

        let normalized = value.trimmingCharacters(in: .whitespacesAndNewlines)

        return normalized.isEmpty ? nil : normalized

    }

    private func dateValue(_ object: NSManagedObject, key: String) -> Date? {

        object.value(forKey: key) as? Date

    }

    private func mergeBestValues(from source: NSManagedObject, into destination: NSManagedObject) {

        if stringValue(destination, key: "meterName") == nil, let value = stringValue(source, key: "meterName") {

            destination.setValue(value, forKey: "meterName")

        }

        if stringValue(destination, key: "tc66TemperatureUnit") == nil, let value = stringValue(source, key: "tc66TemperatureUnit") {

            destination.setValue(value, forKey: "tc66TemperatureUnit")

        }

        if stringValue(destination, key: "modelType") == nil, let value = stringValue(source, key: "modelType") {

            destination.setValue(value, forKey: "modelType")

        }

        let sourceConnectedExpiry = dateValue(source, key: "connectedExpiryAt") ?? .distantPast

        let destinationConnectedExpiry = dateValue(destination, key: "connectedExpiryAt") ?? .distantPast

        let destinationOwner = stringValue(destination, key: "connectedByDeviceID")

        let sourceOwner = stringValue(source, key: "connectedByDeviceID")

        if sourceOwner != nil && (destinationOwner == nil || sourceConnectedExpiry > destinationConnectedExpiry) {

            destination.setValue(sourceOwner, forKey: "connectedByDeviceID")

            destination.setValue(stringValue(source, key: "connectedByDeviceName"), forKey: "connectedByDeviceName")

            destination.setValue(dateValue(source, key: "connectedAt"), forKey: "connectedAt")

            destination.setValue(dateValue(source, key: "connectedExpiryAt"), forKey: "connectedExpiryAt")

        }

        let sourceLastSeen = dateValue(source, key: "lastSeenAt") ?? .distantPast

        let destinationLastSeen = dateValue(destination, key: "lastSeenAt") ?? .distantPast

        if sourceLastSeen > destinationLastSeen {

            destination.setValue(dateValue(source, key: "lastSeenAt"), forKey: "lastSeenAt")

            destination.setValue(stringValue(source, key: "lastSeenByDeviceID"), forKey: "lastSeenByDeviceID")

            destination.setValue(stringValue(source, key: "lastSeenByDeviceName"), forKey: "lastSeenByDeviceName")

            destination.setValue(stringValue(source, key: "lastSeenPeripheralName"), forKey: "lastSeenPeripheralName")

        }

        let sourceUpdatedAt = dateValue(source, key: "updatedAt") ?? .distantPast

        let destinationUpdatedAt = dateValue(destination, key: "updatedAt") ?? .distantPast

        if sourceUpdatedAt > destinationUpdatedAt {

            destination.setValue(sourceUpdatedAt, forKey: "updatedAt")

        }

    }

    func compactDuplicateEntriesByMAC() {

        context.performAndWait {

            refreshContextObjects()

            let request = NSFetchRequest<NSManagedObject>(entityName: entityName)

            do {

                let allObjects = try context.fetch(request)

                var groupedByMAC: [String: [NSManagedObject]] = [:]

                for object in allObjects {

                    guard let macAddress = object.value(forKey: "macAddress") as? String, !macAddress.isEmpty else {

                        continue

                    }

                    groupedByMAC[macAddress, default: []].append(object)

                }

                var removedDuplicates = 0

                for (_, objects) in groupedByMAC {

                    guard objects.count > 1, let winner = preferredObject(from: objects) else { continue }

                    for duplicate in objects where duplicate.objectID != winner.objectID {

                        mergeBestValues(from: duplicate, into: winner)

                        context.delete(duplicate)

                        removedDuplicates += 1

                    }

                }

                if context.hasChanges {

                    try context.save()

                }

                if removedDuplicates > 0 {

                    track("Compacted \(removedDuplicates) duplicate DeviceSettings row(s)")

                }

            } catch {

                track("Failed compacting duplicate device settings: \(error)")

            }

        }

    }

    func fetchAll() -> [CloudDeviceSettingsRecord] {

        var results: [CloudDeviceSettingsRecord] = []

        context.performAndWait {

            refreshContextObjects()

            let request = NSFetchRequest<NSManagedObject>(entityName: entityName)

            do {

                let allObjects = try context.fetch(request)

                var groupedByMAC: [String: [NSManagedObject]] = [:]

                for object in allObjects {

                    guard let macAddress = object.value(forKey: "macAddress") as? String, !macAddress.isEmpty else {

                        continue

                    }

                    groupedByMAC[normalizedMACAddress(macAddress), default: []].append(object)

                }

                results = groupedByMAC.compactMap { macAddress, objects in

                    guard let preferred = preferredObject(from: objects) else {

                        return nil

                    }

                    return record(from: preferred, macAddress: macAddress)

                }

            } catch {

                track("Failed loading cloud device settings: \(error)")

            }

        }

        return results

    }

    func fetchByMacAddress() -> [String: CloudDeviceSettingsRecord] {

        Dictionary(uniqueKeysWithValues: fetchAll().map { ($0.macAddress, $0) })

    }

    func upsert(macAddress: String, meterName: String?, tc66TemperatureUnit: String?) {

        let macAddress = normalizedMACAddress(macAddress)

        guard !macAddress.isEmpty else {

            return

        }

        context.performAndWait {

            do {

                refreshContextObjects()

                let objects = try fetchObjects(for: macAddress)

                let object = preferredObject(from: objects) ?? NSManagedObject(entity: NSEntityDescription.entity(forEntityName: entityName, in: context)!, insertInto: context)

                for duplicate in objects where duplicate.objectID != object.objectID {

                    context.delete(duplicate)

                }

                object.setValue(macAddress, forKey: "macAddress")

                if let meterName {

                    object.setValue(meterName, forKey: "meterName")

                }

                if let tc66TemperatureUnit {

                    object.setValue(tc66TemperatureUnit, forKey: "tc66TemperatureUnit")

                }

                object.setValue(Date(), forKey: "updatedAt")

                if context.hasChanges {

                    try context.save()

                }

            } catch {

                track("Failed persisting cloud device settings for \(macAddress): \(error)")

            }

        }

    }

    func setConnection(macAddress: String, deviceID: String, deviceName: String, modelType: String) {

        let macAddress = normalizedMACAddress(macAddress)

        guard !macAddress.isEmpty, !deviceID.isEmpty else { return }

        context.performAndWait {

            do {

                refreshContextObjects()

                let objects = try fetchObjects(for: macAddress)

                let object = preferredObject(from: objects) ?? NSManagedObject(entity: NSEntityDescription.entity(forEntityName: entityName, in: context)!, insertInto: context)

                for duplicate in objects where duplicate.objectID != object.objectID {

                    context.delete(duplicate)

                }

                object.setValue(macAddress, forKey: "macAddress")

                object.setValue(deviceID, forKey: "connectedByDeviceID")

                object.setValue(deviceName, forKey: "connectedByDeviceName")

                let now = Date()

                object.setValue(now, forKey: "connectedAt")

                object.setValue(Date().addingTimeInterval(120), forKey: "connectedExpiryAt")

                object.setValue(modelType, forKey: "modelType")

                object.setValue(now, forKey: "updatedAt")

                if context.hasChanges { try context.save() }

            } catch {

                track("Failed publishing connection for \(macAddress): \(error)")

            }

        }

    }

    func recordDiscovery(macAddress: String, modelType: String, peripheralName: String?, seenByDeviceID: String, seenByDeviceName: String) {

        let macAddress = normalizedMACAddress(macAddress)

        guard !macAddress.isEmpty else { return }

        context.performAndWait {

            do {

                refreshContextObjects()

                let objects = try fetchObjects(for: macAddress)

                let object = preferredObject(from: objects) ?? NSManagedObject(entity: NSEntityDescription.entity(forEntityName: entityName, in: context)!, insertInto: context)

                for duplicate in objects where duplicate.objectID != object.objectID {

                    context.delete(duplicate)

                }

                let now = Date()

                // to avoid constant conflicts between devices on frequent BT advertisements

                   let previousSeenBy = object.value(forKey: "lastSeenByDeviceID") as? String,

                   previousSeenBy == seenByDeviceID,

                }

                object.setValue(macAddress, forKey: "macAddress")

                object.setValue(modelType, forKey: "modelType")

                object.setValue(now, forKey: "lastSeenAt")

                object.setValue(seenByDeviceID, forKey: "lastSeenByDeviceID")

                object.setValue(seenByDeviceName, forKey: "lastSeenByDeviceName")

                if let peripheralName, !peripheralName.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty {

                    object.setValue(peripheralName, forKey: "lastSeenPeripheralName")

                }

                object.setValue(now, forKey: "updatedAt")

                if context.hasChanges { try context.save() }

            } catch {

                track("Failed recording discovery for \(macAddress): \(error)")

            }

        }

    }

    func clearConnection(macAddress: String, byDeviceID deviceID: String) {

        let macAddress = normalizedMACAddress(macAddress)

        guard !macAddress.isEmpty else { return }

        context.performAndWait {

            let request = NSFetchRequest<NSManagedObject>(entityName: entityName)

            request.predicate = NSPredicate(format: "macAddress == %@ AND connectedByDeviceID == %@", macAddress, deviceID)

            do {

                let objects = try context.fetch(request)

                guard !objects.isEmpty else { return }

                for object in objects {

                    context.refresh(object, mergeChanges: true)

                    object.setValue(nil, forKey: "connectedByDeviceID")

                    object.setValue(nil, forKey: "connectedByDeviceName")

                    object.setValue(nil, forKey: "connectedAt")

                    object.setValue(nil, forKey: "connectedExpiryAt")

                    object.setValue(Date(), forKey: "updatedAt")

                }

                if context.hasChanges { try context.save() }

            } catch {

                track("Failed clearing connection for \(macAddress): \(error)")

            }

        }

    }

    func clearAllConnections(byDeviceID deviceID: String) {

        guard !deviceID.isEmpty else { return }

        context.performAndWait {

            refreshContextObjects()

            let request = NSFetchRequest<NSManagedObject>(entityName: entityName)

            request.predicate = NSPredicate(format: "connectedByDeviceID == %@", deviceID)

            do {

                let objects = try context.fetch(request)

                guard !objects.isEmpty else { return }

                for object in objects {

                    context.refresh(object, mergeChanges: true)

                    object.setValue(nil, forKey: "connectedByDeviceID")

                    object.setValue(nil, forKey: "connectedByDeviceName")

                    object.setValue(nil, forKey: "connectedAt")

                    object.setValue(nil, forKey: "connectedExpiryAt")

                    object.setValue(Date(), forKey: "updatedAt")

                }

                if context.hasChanges { try context.save() }

                track("Cleared \(objects.count) stale connection claim(s) for this device")

            } catch {

                track("Failed clearing stale connections: \(error)")

            }

        }

    }

    func rebuildCanonicalStoreIfNeeded(version: Int) {

        let defaultsKey = "\(Self.rebuildDefaultsKeyPrefix).\(version)"

        if UserDefaults.standard.bool(forKey: defaultsKey) {

            return

        }

        context.performAndWait {

            refreshContextObjects()

            let request = NSFetchRequest<NSManagedObject>(entityName: entityName)

            do {

                let allObjects = try context.fetch(request)

                var groupedByMAC: [String: [NSManagedObject]] = [:]

                for object in allObjects {

                    guard let rawMAC = object.value(forKey: "macAddress") as? String else { continue }

                    let macAddress = normalizedMACAddress(rawMAC)

                    guard !macAddress.isEmpty else { continue }

                    groupedByMAC[macAddress, default: []].append(object)

                }

                var removedDuplicates = 0

                for (macAddress, objects) in groupedByMAC {

                    guard let winner = preferredObject(from: objects) else { continue }

                    winner.setValue(macAddress, forKey: "macAddress")

                    for duplicate in objects where duplicate.objectID != winner.objectID {

                        mergeBestValues(from: duplicate, into: winner)

                        context.delete(duplicate)

                        removedDuplicates += 1

                    }

                }

                if context.hasChanges {

                    try context.save()

                }

                UserDefaults.standard.set(true, forKey: defaultsKey)

                track("Rebuilt DeviceSettings store in-place: \(removedDuplicates) duplicate(s) removed")

            } catch {

                track("Failed canonical rebuild for DeviceSettings: \(error)")

            }

        }

    }

}