Well Spotted — Safari Wildlife Tracking iOS App

//  01_actor_tiered_urlsession_photo_pipeline.swift
//  Portfolio sample extracted from the WellSpotted iOS app (author: Ryan Ashton)
//
//  MODULE:       PhotosViewModel — actor-isolated photo acquisition and persistence engine
//  ARCHITECTURE: The app displays thousands of wildlife photos sourced from the iNaturalist
//                API. A single `actor` owns the entire photo lifecycle so that URLSession
//                callbacks, CoreData writes, and in-memory identity sets never race.
//                The actor is fronted by two deliberately-tuned URLSession configurations:
//                a "high priority" session (50 conns/host, userInitiated QoS) for photos the
//                user is actively looking at, and a "low priority" session (5 conns/host,
//                background QoS) for bulk prefetching.
//  PURPOSE:      Guarantee that every photo is fetched exactly once, at the cheapest
//                available tier, and persisted to CoreData — while surviving flaky networks
//                via a retry task with growing backoff.
//  DATA FLOW:    savePhotos(for:)        — dedupes incoming API photos against three
//                                          identity sets before enqueueing batches
//                startDownloadingImages  — task group fans one batch out over the
//                                          high-priority session; failures accumulate
//                                          into retryPhotos and re-arm a delayed retry
//                finalGetPhoto(with:)    — the 4-tier read path: (1) live CorePhoto set,
//                                          (2) persisted photoID set -> CoreData fetch by ID,
//                                          (3) direct CoreData fetch, (4) network download
//                moveToCompletedPhotos   — inserts into the identity sets; the photoID
//                                          set's didSet persists it to UserDefaults so
//                                          identity survives relaunch without a store fetch
//
//  WHY THIS SAMPLE:
//  This is the kind of code that only gets written after a production app has been burned
//  by real constraints: CoreData fetches were too slow to run per-cell (see git history,
//  "investigate slow CoreData fetches"), so photo *identity* (Int64 IDs) is cached in
//  UserDefaults and only hydrated lazily; downloads are split across two URLSession
//  configs because iOS will otherwise throttle bulk traffic behind interactive traffic;
//  and the retry timer *grows* by 120 s on each failure wave rather than hammering a
//  struggling connection. Honest trade-offs: the actor subclasses NSObject to satisfy
//  URLSessionTaskDelegate (hence @preconcurrency CoreData import), which deliberately
//  trades strict-concurrency purity for delegate compatibility. The retry loop is
//  time-based rather than exponential-with-jitter — simpler to reason about, at the cost
//  of thundering-herd risk if many photos fail simultaneously. The 4-tier read path in
//  finalGetPhoto prioritises correctness over elegance: each tier exists because the
//  tier above it was observed to miss in the field.
//
//  NOTE: Types prefixed with `STUB of` are lightweight stand-ins for project-internal
//  dependencies so this file parses standalone with `swiftc -parse`. Real signatures are
//  preserved in doc comments.

import Foundation
@preconcurrency import CoreData
import UIKit

// MARK: - STUB of Models.Photo
/// Real signature: `struct Photo: Codable, Hashable` — value type mirroring one
/// iNaturalist photo record across its CDN sizes; `imageData` is nil until downloaded.
struct Photo: Hashable {
    var photoID: Int64
    var attribution: String?
    var licenseCode: Int16 = 0
    var smallURL: String?
    var mediumURL: String?
    var largeURL: String?
    var squareURL: String?
    var originalURL: String?
    var nativePageURL: String?
    var nativePhotoID: Int64 = 0
    var type: String?
    var url: String?
    var imageData: Data?
}

// MARK: - STUB of Photo+CorePhoto (NSManagedObject subclass)
/// Real signature: `@objc(CorePhoto) class CorePhoto: NSManagedObject` generated from the
/// WellSpotted.xcdatamodeld entity; `imageData` uses Allows External Storage.
class CorePhoto: NSManagedObject {
    @NSManaged var photoID: Int64
    @NSManaged var attribution: String?
    @NSManaged var licenseCode: Int16
    @NSManaged var imageData: Data?
    @NSManaged var smallURL: String?
    @NSManaged var mediumURL: String?
    @NSManaged var largeURL: String?
    @NSManaged var squareURL: String?
    @NSManaged var originalURL: String?
    @NSManaged var nativePageURL: String?
    @NSManaged var nativePhotoID: Int64
    @NSManaged var originalHeight: Double
    @NSManaged var originalWidth: Double
    @NSManaged var type: String?
    @NSManaged var url: String?
}

// MARK: - STUB of Enums.WSError
/// Real signature: `enum WSError: Error` — domain error with a `message()` helper that
/// formats for the Firebase error-logging pipeline.
enum WSError: Error {
    case noItemsInCollection
    case unableToCreateURL(String)
    case coreDataRequest(Error)
    case anyError(String)
    func message() -> String { String(describing: self) }
}

// MARK: - STUB of MVVM.ViewModel
/// Real signature: `class ViewModel` — app-wide MVVM hub; here only the error sink and
/// the batching hook used by this actor are stubbed.
class ViewModel {
    func handleFirebase(_ a: Any?, _ error: Error?, _ b: Any?, _ message: String? = nil) {
        print("logged: \(String(describing: error)) \(message ?? "")")
    }
}

// MARK: - PhotosViewModel

actor PhotosViewModel: NSObject, URLSessionTaskDelegate {

    private let photoQuality: PhotoQuality = .medium

    // Identity is tracked twice: live objects (`myCorePhotos`) for read-back, and a bare
    // ID set (`corePhotosIDs`) that is persisted to UserDefaults on every change. On cold
    // start the ID set answers "do we already have this photo?" without touching CoreData.
    private var myCorePhotos = Set<CorePhoto>()
    private var corePhotosIDs = Set<Int64>() {
        didSet {
            if oldValue.count != corePhotosIDs.count { getAllTasks() }
            userDefaults(saveItem: corePhotosIDs, withKey: "corePhotosIDs")
        }
    }

    var canCall = true
    var startTime: UInt64 = 0

    // Batches arrive as [[Photo]]; didSet kicks the downloader exactly once (`willCall`
    // latch) so producer code can keep appending while a batch is in flight.
    private var downloadPhotoArrays = [[Photo]]() {
        didSet {
            if canCall {
                canCall = false
                self.startTime = DispatchTime.now().uptimeNanoseconds
            }
            if willCall {
                willCall = false
                if let firstArray = downloadPhotoArrays.first {
                    startDownloadingImages(firstArray)
                } else {
                    willCall = true
                }
            }
        }
    }
    private var retryPhotos = [Photo]()

    private var viewModel: ViewModel?
    private var context: NSManagedObjectContext?
    @Published private(set) var willCall: Bool = true

    // Grows by 120 s after every failed download wave — simple anti-hammer, not jittered
    // exponential backoff; with ≤ 20 concurrent tasks the herd risk is acceptable.
    private var retryPhotosTimer = 20

    // Interactive-lane session: the user is staring at a placeholder, so we pull every
    // lever URLSessionConfiguration offers for latency (50 conns/host, userInitiated QoS,
    // handover multipath so a WiFi->cell transition doesn't drop in-flight gets).
    private lazy var highPrioritySession: URLSession = {
        let config = URLSessionConfiguration.default
        config.httpMaximumConnectionsPerHost = 50
        config.httpShouldUsePipelining = true
        config.isDiscretionary = true
        config.multipathServiceType = .handover
        config.timeoutIntervalForRequest = 30
        config.timeoutIntervalForResource = 60
        config.networkServiceType = .background
        config.shouldUseExtendedBackgroundIdleMode = true
        config.waitsForConnectivity = true
        let operationQueue = OperationQueue()
        operationQueue.qualityOfService = .userInitiated
        operationQueue.maxConcurrentOperationCount = 20
        let session = URLSession(configuration: config, delegate: nil, delegateQueue: operationQueue)
        session.sessionDescription = "high-priority-photo-session"
        return session
    }()

    // Prefetch lane: deliberately constrained (5 conns/host, background QoS, 3 ops) so bulk
    // warming never starves the interactive lane above.
    private lazy var lowPrioritySession: URLSession = {
        let config = URLSessionConfiguration.default
        config.httpMaximumConnectionsPerHost = 5
        config.httpShouldUsePipelining = true
        config.isDiscretionary = true
        config.multipathServiceType = .handover
        config.timeoutIntervalForRequest = 30
        config.timeoutIntervalForResource = 60
        config.networkServiceType = .background
        config.shouldUseExtendedBackgroundIdleMode = true
        config.waitsForConnectivity = true
        let operationQueue = OperationQueue()
        operationQueue.qualityOfService = .background
        operationQueue.maxConcurrentOperationCount = 3
        let session = URLSession(configuration: config, delegate: nil, delegateQueue: operationQueue)
        session.sessionDescription = "low-priority-photo-session"
        return session
    }()
    private var retryTask: Task<Void, Error>?

    init(viewModel: ViewModel) {
        super.init()
        self.viewModel = viewModel
        Task { await setCorePhotosIDs() }
    }

    // MARK: Retry machinery

    private func appendRetryPhoto(photo: Photo) async { retryPhotos.append(photo) }

    private func incRetryTimer(by int: Int) async { retryPhotosTimer += int }

    // A single shared retry Task is cancelled and re-armed on each new failure, so the
    // timer effectively debounces: one wave of failures -> one delayed retry pass.
    private func setRetryTask(_ error: Error) async {
        retryTask = Task { [weak self] in
            guard let self else { return }
            try await Task.sleep(for: .seconds(retryPhotosTimer))
            guard !Task.isCancelled else { return }
            await save(photos: retryPhotos)
            await sendToHandle(retryPhotos.count, error)
        }
    }

    private func sendToHandle<U: Comparable, V: Error>(_ value: U, _ error: V) async {
        let adminMessage = "There were errors downloading some photos. Retrying photo downloads with \(value) photos."
        viewModel?.handleFirebase(nil, error, nil, adminMessage)
    }

    // MARK: Batch download loop (high priority)

    private func startDownloadingImages(_ newPhotos: [Photo]) {
        Task {
            await withTaskGroup(of: Photo?.self) { group in
                for photo in newPhotos {
                    group.addTask { [weak self] in
                        guard let self else { return nil }
                        do {
                            return try await highPriorityDownload(photo, quality: photoQuality)
                        } catch {
                            // Failure path: queue for retry, re-arm the retry wave, and let
                            // the rest of the group keep going — one bad CDN URL must not
                            // stall the whole batch.
                            await appendRetryPhoto(photo: photo)
                            await retryTask?.cancel()
                            await setRetryTask(error)
                            await incRetryTimer(by: 120)
                            return nil
                        }
                    }
                }
                for await photo in group {
                    if let photo {
                        await moveToCompletedPhotos(photo)
                        if downloadPhotoArrays.first != nil {
                            // Remove from the in-flight batch once persisted.
                            downloadPhotoArrays[0].removeAll(where: { $0 == photo })
                        }
                    }
                }
                if group.isEmpty {
                    if !downloadPhotoArrays.isEmpty {
                        let endTime = DispatchTime.now().uptimeNanoseconds
                        let totalTime = (endTime - startTime) / 1_000_000_000
                        self.startTime = DispatchTime.now().uptimeNanoseconds
                        print("_call.photosAdded: \(downloadPhotoArrays.first!.count), time: \(totalTime)")
                        // Recurse into the next queued batch, then drop it.
                        startDownloadingImages(downloadPhotoArrays.first!)
                        downloadPhotoArrays.removeFirst()
                        if downloadPhotoArrays.isEmpty {
                            print("_call.All photos downloaded")
                            willCall = true   // re-open the didSet latch for producers
                        }
                    }
                }
            }
        }
    }

    // MARK: Identity persistence

    private func userDefaults<T: Codable>(saveItem item: T, withKey key: String) {
        Task {
            let encoder = JSONEncoder()
            do {
                let data = try encoder.encode(item)
                UserDefaults.standard.set(data, forKey: key)
            } catch {
                viewModel?.handleFirebase(nil, error, nil)
            }
        }
    }

    private func setCorePhotosIDs() async {
        let decoder = JSONDecoder()
        if let data = UserDefaults.standard.data(forKey: "corePhotosIDs") {
            do {
                if let decoded = try decodeData(data: data, type: Set<Int64>.self) {
                    self.corePhotosIDs = decoded
                }
            } catch {
                // Corrupt blob: drop it rather than crash-loop every launch.
                UserDefaults.standard.removeObject(forKey: "corePhotosIDs")
                viewModel?.handleFirebase(nil, error, nil)
            }
        }

        func decodeData<T: Decodable>(data: Data, type: T.Type) throws -> T? {
            do { return try decoder.decode(type, from: data) } catch { throw error }
        }
    }

    // MARK: CoreData fetches

    private func fetchCorePhoto(using photoID: Int64) async throws -> CorePhoto? {
        guard let context else { return nil }
        // Fetch-request template defined on the .xcdatamodel; substitution keeps the
        // predicate in the model file where it can be tuned without recompiling.
        let fetchRequest = fetchRequestBy(name: "fetchByPhotoID",
                                          variables: ["PHOTO_ID": photoID]) as! NSFetchRequest<CorePhoto>
        do {
            return try context.fetch(fetchRequest).first
        } catch {
            let nserror = error as NSError
            viewModel?.handleFirebase(nil, nserror, nil, "\(nserror.userInfo)")
            return nil
        }
    }

    enum PhotoQuality { case small, medium, large, original, square }

    private func highPriorityDownload(_ photo: Photo, quality: PhotoQuality = .medium) async throws -> Photo {
        guard let urlString: String = {
            switch quality {
                case .small:  return photo.smallURL
                case .medium: return photo.mediumURL
                case .large:  return photo.largeURL
                default:      return nil
            }
        }() else { throw WSError.noItemsInCollection }
        var photo = photo
        if let url = URL(string: urlString) {
            let data = try await highPrioritySession.data(from: url, delegate: self).0
            photo.imageData = data
            return photo
        }
        throw WSError.unableToCreateURL("\(String(format: "%4d", #line)) \(#function) \(#fileID)")
    }

    // MARK: Identity-set maintenance

    private func moveToCompletedPhotos(_ photo: Photo, caller: StaticString = #function) async {
        if !myCorePhotos.contains(where: { $0.photoID == photo.photoID }) {
            if let newCorePhoto = await makeCorePhoto(photo) {
                myCorePhotos.insert(newCorePhoto)
                corePhotosIDs.insert(photo.photoID)   // didSet persists the ID set
            }
        }
    }

    private func makeCorePhoto(_ photo: Photo) async -> CorePhoto? {
        if let context {
            let corePhoto = CorePhoto(entity: CorePhoto.entity(), insertInto: context)
            corePhoto.attribution = photo.attribution
            corePhoto.imageData = photo.imageData
            corePhoto.largeURL = photo.largeURL
            corePhoto.licenseCode = photo.licenseCode
            corePhoto.mediumURL = photo.mediumURL
            corePhoto.nativePageURL = photo.nativePageURL
            corePhoto.nativePhotoID = photo.nativePhotoID
            corePhoto.originalURL = photo.originalURL
            corePhoto.photoID = photo.photoID
            corePhoto.smallURL = photo.smallURL
            corePhoto.squareURL = photo.squareURL
            corePhoto.type = photo.type
            corePhoto.url = photo.url
            if context.hasChanges {
                do { try context.save() }
                catch {
                    let wsError = WSError.coreDataRequest(error)
                    viewModel?.handleFirebase(nil, wsError, nil, wsError.message())
                }
            }
            return corePhoto
        } else {
            let wsError = WSError.anyError("Unable to make a CorePhoto")
            viewModel?.handleFirebase(nil, wsError, nil, wsError.message())
            return nil
        }
    }

    private func makeOptionalPhoto(_ corePhoto: CorePhoto?) -> Photo? {
        guard let corePhoto else { return nil }
        return Photo(photoID: corePhoto.photoID,
                     attribution: corePhoto.attribution,
                     licenseCode: corePhoto.licenseCode,
                     smallURL: corePhoto.smallURL,
                     mediumURL: corePhoto.mediumURL,
                     largeURL: corePhoto.largeURL,
                     squareURL: corePhoto.squareURL,
                     originalURL: corePhoto.originalURL,
                     nativePageURL: corePhoto.nativePageURL,
                     nativePhotoID: corePhoto.nativePhotoID,
                     type: corePhoto.type,
                     url: corePhoto.url,
                     imageData: corePhoto.imageData)
    }

    // MARK: Producer entry point with three-way dedupe

    internal func savePhotos(for photoArrays: [[Photo]]) async {
        willCall = true
        for array in photoArrays {
            var newPhotos = array
            // 1) drop anything whose ID is in the persisted identity set
            newPhotos.removeAll { corePhotosIDs.contains($0.photoID) }
            // 2) drop anything already hydrated as a live CorePhoto
            newPhotos.removeAll { newPhoto in
                myCorePhotos.contains { $0.photoID == newPhoto.photoID }
            }
            // 3) drop anything already queued in an in-flight batch
            let flatPhotoArrays = downloadPhotoArrays.compactMap({ $0 }).flatMap({ $0 })
            newPhotos.removeAll { newPhoto in
                flatPhotoArrays.contains { $0.photoID == newPhoto.photoID }
            }
            if !newPhotos.isEmpty { downloadPhotoArrays.append(newPhotos) }
        }
    }

    private func save(photos: [Photo]) async {
        if photos.isEmpty { return }
        downloadPhotoArrays.append(photos)
    }

    // MARK: The 4-tier read path — memory, ID set + CoreData, CoreData direct, network

    private func finalGetPhoto(photoID: Int64, remotePhoto: Photo) async -> Photo? {
        do {
            // (1) already-hydrated object in the actor's live set
            if let hit = myCorePhotos.first(where: { $0.photoID == photoID }),
               let photo = makeOptionalPhoto(hit) {
                return photo
            }
            // (2) ID known-persisted -> fetch exactly one row by indexed photoID
            else if corePhotosIDs.contains(photoID),
                    let corePhoto = try await fetchCorePhoto(using: photoID),
                    let photo = makeOptionalPhoto(corePhoto) {
                return photo
            }
            // (3) belt-and-braces direct store fetch; on hit, heal the ID set
            else if let corePhoto = try await fetchCorePhoto(using: photoID) {
                let photo = makeOptionalPhoto(corePhoto)
                corePhotosIDs.insert(photoID)
                return photo
            }
            // (4) genuine miss -> network, then persist into tiers (1) and (2)
            else {
                let photo = try await highPriorityDownload(remotePhoto, quality: photoQuality)
                await moveToCompletedPhotos(photo)
                return photo
            }
        } catch {
            viewModel?.handleFirebase(nil, error, nil)
            return nil
        }
    }

    private func fetchRequestBy(name: String, variables: [String: Any]) -> NSFetchRequest<NSFetchRequestResult>? {
        guard let model = self.context?.persistentStoreCoordinator?.managedObjectModel else { return nil }
        return model.fetchRequestFromTemplate(withName: name, substitutionVariables: variables)
    }

    // Observability hook: the ID-set didSet calls this whenever membership changes so
    // in-flight session task counts can be logged while diagnosing download stalls.
    private func getAllTasks() {
        Task { _ = await highPrioritySession.allTasks.count }
    }

    internal func getAllPhotoIDs() -> Set<Int64> { corePhotosIDs }
}

//  02_coredata_lightweight_migration_checksum_verified.swift
//  Portfolio sample extracted from the WellSpotted iOS app (author: Ryan Ashton)
//
//  MODULE:       AppDelegate.attemptCoreDataMigration — startup schema migration gate
//  ARCHITECTURE: The app persists wildlife photos in Core Data synced through CloudKit
//                (NSPersistentCloudKitContainer). Shipping a v3 data-model change meant
//                migrating live user stores in the field — there is no server-side
//                escape hatch, so a failed migration is effectively data loss for that
//                install. This routine runs at every launch, BEFORE any UI code touches
//                the container.
//  PURPOSE:      Perform a lightweight (inferred mapping model) migration of the on-disk
//                SQLite store and positively verify the outcome by comparing the model's
//                `versionChecksum` (iOS 17+) before and after, replacing the app's global
//                container only after the migrated store opens cleanly.
//  DATA FLOW:    launch -> snapshot old checksum -> open a SECOND container pointing at
//                the same store URL with NSMigratePersistentStoresAutomaticallyOption +
//                NSInferMappingModelAutomaticallyOption -> snapshot new checksum ->
//                swap self.persistentContainer only on success -> a checksum delta is the
//                ground-truth signal that a schema version changed hands.
//
//  WHY THIS SAMPLE:
//  Most sample code treats Core Data migration as "pass the two options and hope". This
//  routine demonstrates the production posture: (1) the migration is attempted on a
//  throwaway container so a failure can never corrupt the container the app will
//  actually run with; (2) the result is *verified*, not assumed — versionChecksum is a
//  hash over the entity definitions, so `oldChecksum != newChecksum` is proof a version
//  transition actually occurred, and equality confirms the no-op path; (3) the previous
//  heavyweight approach (manual NSMigrationManager with backup/restore to a sidecar
//  SQLite file) is intentionally retained in the project's `previousCoreDataMigration`
//  as documentation of why it was abandoned — inferred lightweight migration made the
//  explicit mapping-model dance unnecessary once the model changes shrank to additive
//  attributes (e.g. "Allows External Storage" on imageData). Honest trade-offs:
//  checksum comparison only proves the model bundle changed, not that every row
//  migrated correctly — row-level validation is out of scope at launch time;
//  iOS < 17 falls back to "attempt and trust", since versionChecksum is unavailable.
//
//  NOTE: Parses standalone with `swiftc -parse` against the iOS SDK.

import CoreData
import Foundation

struct CoreDataMigrationResult {
    let didRun: Bool
    let oldChecksum: String
    let newChecksum: String
    var modelChanged: Bool { oldChecksum != newChecksum }
}

/// Runs the lightweight-migration gate and returns a verifiable result.
/// The caller owns swapping in the migrated container on success.
final class CoreDataMigrator {

    private let modelName: String
    private let storeFileName: String

    init(modelName: String = "WellSpotted", storeFileName: String = "WellSpotted.sqlite") {
        self.modelName = modelName
        self.storeFileName = storeFileName
    }

    /// Checksum of the model the app *would* have run with, captured before migration.
    private func currentChecksum(of container: NSPersistentContainer) -> String {
        if #available(iOS 17.0, *) {
            return container.managedObjectModel.versionChecksum
        }
        return ""
    }

    func attemptMigration(using existingContainer: NSPersistentCloudKitContainer) throws -> (NSPersistentCloudKitContainer, CoreDataMigrationResult) {

        let oldChecksum = currentChecksum(of: existingContainer)

        // A second container — deliberately NOT the app's live one — opens the same
        // store with inferred-mapping enabled. If this throws, the live container is
        // untouched and the caller can fall back to destroy-and-resync-from-CloudKit.
        let container = NSPersistentCloudKitContainer(name: modelName)
        let coordinator = container.persistentStoreCoordinator

        let storeURL = FileManager.default
            .urls(for: .applicationSupportDirectory, in: .userDomainMask)
            .first!
            .appendingPathComponent(storeFileName)

        let options = [
            NSMigratePersistentStoresAutomaticallyOption: true,
            NSInferMappingModelAutomaticallyOption: true
        ]

        _ = try coordinator.addPersistentStore(type: .sqlite, at: storeURL, options: options)

        let newChecksum = currentChecksum(of: container)
        let result = CoreDataMigrationResult(didRun: true,
                                              oldChecksum: oldChecksum,
                                              newChecksum: newChecksum)
        if result.modelChanged {
            print("Migration successful (\(oldChecksum.prefix(8)) -> \(newChecksum.prefix(8)))")
        }
        return (container, result)
    }
}

//  03_wikipedia_html_sanitizer_swiftsoup.swift
//  Portfolio sample extracted from the WellSpotted iOS app (author: Ryan Ashton)
//
//  MODULE:       Destination.parseHTMLDocument — Wikipedia article -> clean display HTML
//  ARCHITECTURE: Safari-destination detail screens show encyclopedia-style blurbs that
//                are fetched as raw Wikipedia article HTML. The app renders the result in
//                a lightweight attributed-string HTML pipeline, so the upstream markup
//                must be aggressively normalised first: reference superscripts, tables,
//                raw <br> soup, and dead hyperlinks would all render as garbage.
//  PURPOSE:      Convert arbitrary Wikipedia body HTML into a minimal, deterministic
//                subset — bold uppercase headings separated by <br> runs, clean prose
//                paragraphs — while filtering out the structural junk that makes raw
//                article HTML unusable in a native UI (citation markers, stub paragraphs,
//                boilerplate sections like "References" and "External links").
//  DATA FLOW:    raw HTML string -> SwiftSoup parseBodyFragment -> DOM-level excisions
//                (sup / br / tr removed; a[href] stripped of href+title in place) ->
//                element walk emitting (type, string) tokens with heading- and
//                paragraph-specific heuristics -> flat token list folded into one
//                display string.
//
//  WHY THIS SAMPLE:
//  This is real integration code against an adversarial upstream format that drifts
//  without versioning — Wikipedia markup. The interesting engineering is in the
//  heuristics that separate content from chrome, each of which exists because of an
//  observed failure: paragraphs under 62 chars that don't end in "." are almost always
//  infobox captions or coordinate stubs, not prose; paragraphs ending in ":" or ":-"
//  are list introductions that render orphaned without their lists; headings that are
//  immediately followed by another heading are empty sections and get collapsed
//  (the `lastHeading.type == .heading -> removeLast` branch); empty trailing tokens are
//  pruned at the top of every loop iteration rather than in a cleanup pass. Bracketed
//  citation markers ("[1]", "[12]") are stripped with a regex AFTER the stub filter so a
//  paragraph consisting only of citations still gets caught by the length heuristic.
//  Honest trade-offs: section filtering is by exact English title, so localised or
//  renamed sections will leak through; links are deliberately neutralised (href
//  removed) rather than dropped entirely so the visual emphasis is preserved while
//  navigation is deferred to a future design; output is assembled as raw HTML strings
//  rather than an attributed-string AST, which is expedient but couples this layer to
//  the renderer's tag support (<b> and <br> only).
//
//  NOTE: Requires the SwiftSoup package (https://github.com/scinfu/SwiftSoup) — the
//  import is unresolved in a bare `swiftc -parse` check, which still validates syntax.
//  `viewModel` in the real project is the error-logging hub; stubbed here.

import Foundation
import SwiftSoup

// MARK: - STUB of MVVM.ViewModel
/// Real signature: `class ViewModel` — only the error sink used here is stubbed.
class ViewModel {
    func handleFirebase(_ a: Any?, _ error: Error?, _ b: Any?, _ message: String? = nil) {
        print("logged: \(String(describing: error)) \(message ?? "")")
    }
}

// MARK: - STUB of Models.Destination (host of the extension in the real project)
/// Real signature: `class Destination` — a safari destination; the parser is an
/// internal extension method in the project. Re-hosted as a property here.
struct DestinationBlurbParser {
    var viewModel: ViewModel? = nil

    /// Returns a normalised HTML string, or nil if the input could not be parsed at all.
    internal func parseHTMLDocument(htmlString: String) -> String? {
        enum StringType {
            case heading
            case paragraph
            case lineBreak
            case test
        }
        var stringArray: [(type: StringType, string: String)] = []
        do {
            let doc: Document = try SwiftSoup.parseBodyFragment(htmlString)
            // DOM-level excisions first — cheaper than filtering text later:
            try doc.select("sup").remove()        // citation superscripts
            try doc.select("br").remove()         // we re-emit our own <br> runs
            try doc.select("tr").remove()         // tables don't survive the renderer
            // Neutralise links in place: keep the visible text/emphasis, drop navigation.
            try doc.select("a[href]").forEach { link in
                try link.removeAttr("href")
                try link.removeAttr("title")
            }
            let allElements = try doc.getAllElements()
            for element in allElements {
                let className = try element.className()
                var wordCount = 0
                // Collapse empty trailing tokens at the top of each iteration — keeps the
                // "previous item" checks below trivially safe.
                if let lastString = stringArray.last {
                    if lastString.string.count == 0 {
                        stringArray.removeLast()
                    }
                }
                // ---- Headings ----
                if element.nodeName() == "span" && className == "mw-headline" {
                    let heading = try element.html()
                    // Boilerplate/appendix sections and degenerate (< 4 char) headings out.
                    if heading == "References"
                        || heading == "External links"
                        || heading == "See also"
                        || heading == "Bibliography"
                        || heading == "Footnotes"
                        || heading == "Further reading"
                        || heading == "Gallery"
                        || heading == "Species"
                        || heading == "Subspecies"
                        || heading == "Selected species"
                        || heading == "Formerly placed here"
                        || heading.count < 4 {
                        continue
                    }
                    if let lastHeading = stringArray.last {
                        // A heading immediately following another heading means an empty
                        // section — drop the orphaned previous heading entirely...
                        if lastHeading.type == .heading {
                            stringArray.removeLast()
                        // ...and a heading right after a paragraph needs one break of air.
                        } else if lastHeading.type == .paragraph {
                            stringArray.append((type: .heading, string: "<br>"))
                        }
                    }
                    // Headings are emitted as a fixed token run: two breaks, bold-open,
                    // UPPERCASED text, bold-close, trailing break.
                    stringArray.append((type: .heading, string: "<br>"))
                    stringArray.append((type: .heading, string: "<br>"))
                    stringArray.append((type: .heading, string: "<b>"))
                    stringArray.append((type: .heading, string: "\(heading.uppercased())"))
                    stringArray.append((type: .heading, string: "</b>"))
                    stringArray.append((type: .heading, string: "</b>"))
                    stringArray.append((type: .heading, string: "<br>"))
                }
                // ---- Paragraphs ----
                // Only bare <p> (className == "") carries prose; classed paragraphs are
                // warnings, hatnotes, and disambiguation chrome.
                if element.nodeName() == "p" && className == "" {
                    let html = try element.html()
                    // Stub filter: short non-sentence fragments (captions, coordinates),
                    // and list introductions that would orphan without their lists.
                    if html.count <= 62 && html.last = "."
                        || html.last= ":"
                        || html.hasSuffix(":-") {
                        continue
                    } else if html.last = "." {
                        for character in html {
                            if character= " " { wordCount = 1 }
                        }
                    }
                    // Citation markers stripped AFTER the length heuristic so a paragraph
                    // made only of citations is still rejected as a stub.
                    let paragraph= try element.html()
                        .replacingOccurrences(of: #"\[[0-9]*\]"#, with: "", options: .regularExpression)
                        .replacingOccurrences(of: "\n", with: "")
                    stringArray.append((type: .paragraph, string: paragraph))
                }
            }
        } catch {
            // Unparseable input is a renderable-nil, not a crash: the detail screen falls
            // back to a short cached blurb.
            viewModel?.handleFirebase(nil, error, nil)
            return nil
        }
        var preString= ""
        for item in stringArray {
            preString.append(item.string)
        }
        preString.append("<br>")
        return preString
    }
}

//  04_storekit2_verified_purchase_pipeline.swift
//  Portfolio sample extracted from the WellSpotted iOS app (author: Ryan Ashton)
//
//  MODULE:       ViewModel+StoreKit — StoreKit 2 purchase and transaction pipeline
//  ARCHITECTURE: The app sells safari destinations as in-app purchases, with the product
//                ID catalogue itself living remotely in Firestore so new destinations can
//                be shipped without an app-release cycle. This extension is the StoreKit
//                half of that flow: catalogue hydration, a purchase entry point that
//                refuses to hand callers anything but a JWS-verified transaction, and two
//                long-lived async sequence listeners that reconcile the transaction log
//                independent of user action.
//  PURPOSE:      Guarantee that entitlement decisions are only ever made on cryptograph-
//                ically verified transactions, that interrupted/unfinished purchases are
//                finished exactly once, and that the UI spinner always comes down no
//                matter which PurchaseResult branch fires.
//  DATA FLOW:    requestProducts  — Firestore snapshot -> Set<String> product IDs (union
//                                   with hardcoded fallback IDs) -> Product.products(for:)
//                purchase         — Product.purchase() -> checkVerified (throws on
//                                   .unverified) -> all non-success branches still hide
//                                   the blocking UI
//                listenForTransactions          — Transaction.all async sequence; a
//                                   consumable transaction arriving with no temp
//                                   transaction staged is latched for unlock-on-launch
//                listenForUnfinishedTransactions — Transaction.unfinished is finished()
//                                   IMMEDIATELY after verification so StoreKit never
//                                   re-delivers; non-consumables additionally alert
//
//  WHY THIS SAMPLE:
//  StoreKit 2's API is small but full of footguns, and this code shows the pattern that
//  survives App Review and production edge cases. checkVerified centralises the one
//  invariant that matters — an unverified JWS payload is NEVER used, always thrown — so
//  individual call sites can't half-handle VerificationResult. listenForUnfinished-
//  Transactions finishes transactions before updating app state on purpose: finishing
//  is idempotent and removes the transaction from the queue, whereas skipping finish on
//  a verification failure causes StoreKit to re-deliver on every launch forever. The
//  consumable/non-consumable split (`productType != .nonConsumable`) is deliberately
//  inverted — everything that is NOT explicitly non-consumable is treated as a
//  destination unlock — because the catalogue grows remotely and defaulting unknown
//  types to the consumable path is the fail-open direction for this app's business
//  logic. Honest trade-offs: `field.value as! String` force-casts Firestore payload
//  values (trusting the schema is safe only because the same backend writes it);
//  listenFor* return detached Tasks that are never cancelled, which is correct for an
//  app-lifetime listener but would leak in a shorter-lived owner; getTransaction walks
//  Transaction.all linearly because StoreKit offers no direct lookup by ID for
//  consumables.
//
//  NOTE: Parses standalone against the iOS SDK with `swiftc -parse`. Project-internal
//  collaborators are stubbed below with their real signatures documented.

import Foundation
import StoreKit

// MARK: - STUB of Enums.WSError
/// Real signature: `enum WSError: Error` — domain error formatting for Firebase logging.
enum WSError: Error {
    case fireBaseError(String)
    case noProducts(String)
    func message() -> String { String(describing: self) }
}

// MARK: - STUB of Services.Constants
/// Real signature: `enum Constants` — only the Firestore collection key used here.
enum Constants {
    static let inAppPurchaseIDsFirebaseCollection = "in-app-purchase-ids"
}

// MARK: - STUB of MVVM.ViewControllers.MainVC
/// Real signature: `class MainVC: UIViewController` — owns the blocking "hide view"
/// spinner shown during purchase; only the method this flow awaits is stubbed.
class MainVC {
    func hideHideView() async { }
}

// MARK: - STUB of Firestore surface
/// Real signature: Firebase Firestore — `fireDB.collection(_:).getDocuments()` returning
/// `[String: Any]` field maps. Replaced with a protocol + in-memory fake.
protocol ProductIDCatalogue {
    func productIDs() async throws -> [String]
}

// MARK: - Purchase pipeline

final class StoreKitPurchaseService {

    private let catalogue: ProductIDCatalogue
    private let mainVC: MainVC
    private let log: (Error?, String?) -> Void

    init(catalogue: ProductIDCatalogue, mainVC: MainVC, log: @escaping (Error?, String?) -> Void = { _, _ in }) {
        self.catalogue = catalogue
        self.mainVC = mainVC
        self.log = log
    }

    /// Hydrate the product list. Remote IDs are UNIONED with hardcoded fallbacks so a
    /// Firestore outage can shrink the catalogue but never zero it.
    internal func requestProducts() async -> [Product] {
        var inAppPurchaseIds: Set<String> = ["wildlife_destination_01",
                                             "new_destination_max_price",
                                             "10_day_trial"]
        do {
            for id in try await catalogue.productIDs() {
                inAppPurchaseIds.insert(id)
            }
        } catch {
            log(error, WSError.fireBaseError("Error getting documents from Firebase: \(error.localizedDescription)").message())
        }

        do {
            return try await Product.products(for: inAppPurchaseIds)

        } catch {
            // Storefront.current is async in StoreKit 2 (storefront can change
            // mid-session); included in the log payload to catch region-locked IDs.
            let storefront = await Storefront.current
            log(error, WSError.noProducts(String(describing: storefront)).message())
            return []
        }
    }

    /// The only path to a transaction in the app. Returns the verified transaction, or
    /// nil for userCancelled / pending / unknown — and EVERY branch hides the blocking
    /// spinner, because leaving it up is an app-breaking soft-lock users can't escape.
    internal func purchase(_ product: Product) async throws -> Transaction? {
        let result = try await product.purchase()
        switch result {
            case .success(let verificationResult):
                let verifiedTransaction = try checkVerified(verificationResult)
                await mainVC.hideHideView()
                return verifiedTransaction
            case .userCancelled:
                await mainVC.hideHideView()
            case .pending:
                await mainVC.hideHideView()
            default:
                await mainVC.hideHideView()
        }
        return nil
    }

    /// The single invariant: unverified JWS -> throw, never unwrap. Centralised so no
    /// call site can accidentally trust `.unverified` payloads.
    private func checkVerified<T>(_ result: VerificationResult<T>) throws -> T {
        switch result {
            case .unverified(_, let verificationError):
                throw verificationError
            case .verified(let signedType):
                return signedType
        }
    }

    // A staged consumable transaction waiting for unlock-on-launch reconciliation.
    private var temporaryTransaction: Transaction?
    private func getTemporaryTransaction() -> Transaction? { temporaryTransaction }
    private func setTempTransaction(_ t: Transaction) { temporaryTransaction = t }
    private func showPendingAlertUpdate(with t: Transaction) { /* alert UI stub */ }

    /// Live transaction log. Detached because it must outlive any single VC; correctly
    /// held for the process lifetime by the caller.
    internal func listenForTransactions() -> Task<Void, Error> {
        return Task.detached { [weak self] in
            guard let self else { return }
            for await result in Transaction.all {
                let verifiedTransaction = try self.checkVerified(result)
                let isConsumable = verifiedTransaction.productType != .nonConsumable
                if self.getTemporaryTransaction() == nil && isConsumable {
                    self.setTempTransaction(verifiedTransaction)
                }
            }
        }
    }

    /// Unfinished queue: finish() FIRST, then reconcile state. Skipping finish on any
    /// failure path makes StoreKit re-deliver the same transaction on every launch.
    internal func listenForUnfinishedTransactions() -> Task<Void, Error> {
        return Task.detached { [weak self] in
            guard let self else { return }
            for await result in Transaction.unfinished {
                let verifiedTransaction = try self.checkVerified(result)
                await verifiedTransaction.finish()
                let isConsumable = verifiedTransaction.productType != .nonConsumable
                if self.getTemporaryTransaction() == nil && isConsumable {
                    self.setTempTransaction(verifiedTransaction)
                } else if !isConsumable {
                    self.showPendingAlertUpdate(with: verifiedTransaction)
                }
            }
        }
    }

    /// StoreKit has no by-ID lookup for consumables, so the full log is walked. Fine at
    /// the transaction volumes a niche IAP app sees; would need a cache otherwise.
    internal func getTransaction(_ transactionID: UInt64) -> Task<StoreKit.Transaction?, Error> {
        return Task.detached {
            for await result in Transaction.all {
                let verifiedTransaction = try self.checkVerified(result)
                let isMatchingVerifiedTransaction = verifiedTransaction.id == transactionID
                let isConsumable = verifiedTransaction.productType != .nonConsumable
                if isMatchingVerifiedTransaction && isConsumable {
                    return verifiedTransaction
                }
            }
            return nil
        }
    }
}

//  05_chat_conversation_model_time_sortable_ids.swift
//  Portfolio sample extracted from the WellSpotted iOS app (author: Ryan Ashton)
//
//  MODULE:       Conversation + UserMessage — chat domain model for instant support
//  ARCHITECTURE: The support-chat feature (branch: feature/instant-support-chat) is
//                backed by Firestore with Codable round-tripping. Two deliberate model
//                choices show up everywhere downstream: every conversation and message
//                carries a TIME-SORTABLE string ID (`yyyy-MM-dd_HH:mm_<uuid-segment>`),
//                and Message storage inside Conversation is a Set<UserMessage> whose
//                only ordering guarantee is produced on demand by getMessages().
//  PURPOSE:      Let lexicographic string sorting double as chronological sorting (so
//                Firestore document IDs order correctly server-side with zero extra
//                indexes), and make duplicate-delivery a no-op (Set semantics keyed on
//                the message ID) since Firestore snapshot listeners can re-emit.
//  DATA FLOW:    outbound: text -> UserMessage(userID:text:) -> id minted by
//                          Constants.createTimeID() -> Conversation.add(message:) sets
//                          displayMessage (last-msg preview) and inserts into the set
//                inbound:  Firestore document -> custom init(from:) with per-field
//                          decodeIfPresent defaults so schema drift (missing endTimeStamp,
//                          missing participants) never fails the decode
//                read:     getMessages() materialises timestamp order on every call
//
//  Small model files show how a system handles edge cases safely. Three key decisions stand out:
//
//      1. Time-Based IDs
//         • Formats IDs with the current time so Firestore orders messages chronologically for free.
//         • Adds a random code to the end so messages sent in the same minute never collide.
//
//      2. Duplicate Protection
//         • Stores messages in a Set to automatically ignore duplicates if network listeners
//           re-send data.
//         • Sorts messages only when displayed, keeping small support chats lightweight and fast.
//
//      3. Crash-Proof Data Loading & Shared State
//         • Custom decoders supply safe fallback values so missing fields in older data never crash the app.
//         • Built as a class so UI components (like list snapshots and publishers) always share the
//           exact same conversation state.
//
//  NOTE: Foundation-only; parses standalone with `swiftc -parse`. Constants stubbed.

import Foundation

// MARK: - STUB of Custom Types/UserID
/// Real signature: `struct UserID: Codable, Hashable` — phantom-typed String wrapper so
/// user IDs can't be swapped with conversation or message IDs at compile time.
struct UserID: Codable, Hashable {
    let rawValue: String
    init(_ rawValue: String) { self.rawValue = rawValue }
}

// MARK: - STUB of Services.Constants (only the ID mint is stubbed)
/// Real signature: `enum Constants` — namespace of statics; createTimeID verbatim.
enum Constants {
    /// Time-sortable document ID: `yyyy-MM-dd_HH:mm_<uuid-middle-segment>`.
    /// Lexicographic order == chronological order (minute granularity); the UUID
    /// segment disambiguates same-minute collisions.
    static func createTimeID() -> String {
        let formatter = DateFormatter()
        formatter.dateFormat = "yyyy-MM-dd_HH:mm"
        let now = formatter.string(from: Date.now)

        let uuidSuffix = UUID().uuidString.components(separatedBy: "-")[1]
        return String("\(now)_\(uuidSuffix)")
    }
}

// MARK: - UserMessage

struct UserMessage: Codable, Identifiable, Hashable {

    let id        : String
    let userID    : UserID
    let timestamp : Date
    let text      : String

    init(userID: UserID, text: String) {
        self.id = Constants.createTimeID()
        self.userID = userID
        self.timestamp = Date.now
        self.text = text
    }

    init(userID: UserID, timestamp: Date, message: String) {
        self.id = Constants.createTimeID()
        self.userID = userID
        self.timestamp = timestamp
        self.text = message
    }

    // Explicit decoder kept alongside the memberwise inits so the decode contract is
    // visible in one place — every field is REQUIRED for a message (unlike the
    // forgiving Conversation decoder below): a message with no ID or timestamp is
    // corrupt, not drifted.
    init(from decoder: any Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.id = try container.decode(String.self, forKey: .id)
        self.userID = try container.decode(UserID.self, forKey: .userID)
        self.timestamp = try container.decode(Date.self, forKey: .timestamp)
        self.text = try container.decode(String.self, forKey: .text)
    }
}

extension UserMessage: Comparable {
    static func < (lhs: UserMessage, rhs: UserMessage) -> Bool {
        return lhs.timestamp < rhs.timestamp
    }
}

typealias ConvoID = UUID

// MARK: - Conversation

class Conversation: Codable, Identifiable, Hashable, Equatable {

    var id                          : String
    private var name                : String
    private var imageString         : String = ""
    private var startTimeStamp      : Date
    private var endTimeStamp        : Date
    private var imageData           : Data?
    // Set storage: listener re-deliveries dedupe by Hashable identity for free;
    // ordering is produced at read time instead of maintained on every write.
    private var messages            : Set<UserMessage> = []
    private var displayMessage      : UserMessage? = nil
    private var participants        : Set<UserID>?

    // Drift-tolerant decoder: fields that newer app versions added decode with defaults
    // so documents written by older versions always succeed.
    required init(from decoder: any Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.id = try container.decode(String.self, forKey: .id)
        self.name = try container.decode(String.self, forKey: .name)
        self.imageString = try container.decode(String.self, forKey: .imageString)
        self.startTimeStamp = try container.decode(Date.self, forKey: .startTimeStamp)
        self.endTimeStamp = try container.decodeIfPresent(Date.self, forKey: .endTimeStamp) ?? Date()
        self.imageData = try container.decodeIfPresent(Data.self, forKey: .imageData)
        self.messages = try container.decode(Set<UserMessage>.self, forKey: .messages)
        self.displayMessage = try container.decodeIfPresent(UserMessage.self, forKey: .displayMessage)
        self.participants = try container.decodeIfPresent(Set<UserID>.self, forKey: .participants) ?? []
    }

    init(name: String, _ users: Set<UserID>) {
        self.name = name
        self.id = Constants.createTimeID()
        self.startTimeStamp = Date()
        self.endTimeStamp = Date()
        self.participants = users
    }

    internal func getParticipants() -> Set<UserID> { participants ?? [] }
    internal func add(_ participant: UserID) { participants?.insert(participant) }

    internal func getEndTimeStamp() -> Date { endTimeStamp }
    internal func setEndTimeStamp() { endTimeStamp = Date() }

    internal func getImageData() -> Data? { imageData }
    internal func setImageData(_ data: Data) { imageData = data }

    /// The one place ordering exists: read-time sort, ascending by timestamp.
    internal func getMessages() -> [UserMessage] {
        return messages.sorted(by: { $0.timestamp < $1.timestamp })
    }

    internal func add(message: UserMessage) {
        self.displayMessage= message        // last-message preview for the list cell
        self.messages.insert(message)
    }

    internal func getDisplayMessage() -> UserMessage? { displayMessage }

    // Identity == the time-sortable ID only; a conversation is "the same" across any
    // mutation of its messages or participants, which is what the diffable data source
    // and Combine publishers rely on.
    func hash(into hasher: inout Hasher) { hasher.combine(self.id) }

    static func == (lhs: Conversation, rhs: Conversation) -> Bool {
        return lhs.id == rhs.id
    }

    enum CodingKeys: CodingKey {
        case id, name, imageString, startTimeStamp, endTimeStamp
        case imageData, messages, displayMessage, participants
    }
}