Outpost/OutlineKit/Sources/OutlineKit/Caching/CachingOutlineAPIClient.swift

import Foundation

/// Decorates `LiveOutlineAPIClient` (or any `OutlineAPIClient`) with offline
/// support at the existing protocol boundary, so no view model needs to know
/// the network exists:
///
/// - **Reads** (`documentInfo`, `listDocuments`, `documentsList`,
///   `listViewedDocuments`, `listCollections`, `collectionInfo`): read-through
///   cache. Always tries live first — never pre-checks reachability, since
///   "did this specific request just fail" is a more honest signal than a
///   reachability monitor, and the two can disagree (captive portals,
///   flaky Wi-Fi). Falls back to the cache only on failure; a live success
///   always overwrites the cache, so staleness is bounded by "last time this
///   endpoint actually worked."
/// - **A small set of writes** (`updateDocument`, `updateCollection`,
///   pin/star/subscribe create+delete): applied optimistically against the
///   cache and queued in `OfflineCacheStore`'s `PendingOperation` table on
///   failure, then replayed in order by `flushPendingOperations()` once back
///   online. Deliberately doesn't include anything that creates new tree
///   structure (`createDocument`, `moveDocument`, `archiveDocument`,
///   `deleteDocument`, `deleteCollection`, `duplicateDocument`) — those need
///   real server-assigned ids to stay consistent with the rest of the tree,
///   and reconciling a locally-invented id with the one the server hands
///   back on sync is a much bigger problem than this pass takes on. Sharing,
///   permissions, search, and export also stay live-only — read the request,
///   they need someone else's server session, not just a network.
/// - **Manual offline mode** (`offlineModeDefaultsKey`): when set, skips
///   attempting `live` entirely — same fallback/queue paths as a real
///   failure, just chosen on purpose instead of discovered.
public actor CachingOutlineAPIClient: OutlineAPIClient {
    public static let offlineModeDefaultsKey = "outpost.offlineModeEnabled"

    private let live: OutlineAPIClient
    private let cache: OfflineCacheStore
    private let defaults: UserDefaults
    private let encoder: JSONEncoder
    private let decoder: JSONDecoder
    private let keyEncoder: JSONEncoder

    public init(live: OutlineAPIClient, cache: OfflineCacheStore, defaults: UserDefaults = .standard) {
        self.live = live
        self.cache = cache
        self.defaults = defaults

        let encoder = JSONEncoder()
        encoder.dateEncodingStrategy = .iso8601
        self.encoder = encoder

        let decoder = JSONDecoder()
        decoder.dateDecodingStrategy = .iso8601
        self.decoder = decoder

        let keyEncoder = JSONEncoder()
        keyEncoder.outputFormatting = .sortedKeys
        self.keyEncoder = keyEncoder
    }

    private var isManualOfflineModeEnabled: Bool {
        defaults.bool(forKey: Self.offlineModeDefaultsKey)
    }

    // MARK: - Cached reads

    public func documentInfo(id: String) async throws -> OutlineDocument {
        try await cachedFetch(key: "document:\(id)") { try await self.live.documentInfo(id: id) }
    }

    public func listDocuments(
        collectionId: String?,
        parentDocumentId: String?,
        offset: Int,
        limit: Int
    ) async throws -> [OutlineDocument] {
        let key = "documents:\(collectionId ?? "-"):\(parentDocumentId ?? "-"):\(offset):\(limit)"
        return try await cachedFetch(key: key) {
            try await self.live.listDocuments(
                collectionId: collectionId,
                parentDocumentId: parentDocumentId,
                offset: offset,
                limit: limit
            )
        }
    }

    public func documentsList(_ request: DocumentsListRequest) async throws -> [OutlineDocument] {
        try await cachedFetch(key: requestKey("documentsList", request)) { try await self.live.documentsList(request) }
    }

    public func listViewedDocuments(offset: Int, limit: Int) async throws -> [OutlineDocument] {
        try await cachedFetch(key: "documentsViewed:\(offset):\(limit)") {
            try await self.live.listViewedDocuments(offset: offset, limit: limit)
        }
    }

    public func listCollections(offset: Int, limit: Int) async throws -> [OutlineCollection] {
        try await cachedFetch(key: "collections:\(offset):\(limit)") {
            try await self.live.listCollections(offset: offset, limit: limit)
        }
    }

    public func collectionInfo(id: String) async throws -> OutlineCollection {
        try await cachedFetch(key: "collection:\(id)") { try await self.live.collectionInfo(id: id) }
    }

    // MARK: - Queueable writes

    /// The one exception to "no new tree structure while offline" —
    /// synthesizes a document under a `pending-<uuid>` id (same scheme as
    /// pin/star/subscribe), caches it so it's immediately readable/editable,
    /// and queues the real create. On sync, the server-assigned id replaces
    /// the placeholder in the cache; anything still referencing the old id
    /// directly (a currently-open reader, most likely) won't follow that
    /// rename automatically — a known, narrow limitation, not something this
    /// pass tries to solve generally.
    public func createDocument(_ request: CreateDocumentRequest) async throws -> OutlineDocument {
        if !isManualOfflineModeEnabled {
            do {
                let result = try await live.createDocument(request)
                await cacheDocument(result)
                return result
            } catch {
                return await queueDocumentCreate(request)
            }
        }
        return await queueDocumentCreate(request)
    }

    public func updateDocument(_ request: UpdateDocumentRequest) async throws -> OutlineDocument {
        if !isManualOfflineModeEnabled {
            do {
                let result = try await live.updateDocument(request)
                await cacheDocument(result)
                return result
            } catch {
                return try await queueDocumentUpdate(request, dueTo: error)
            }
        }
        return try await queueDocumentUpdate(request, dueTo: nil)
    }

    public func updateCollection(_ request: UpdateCollectionRequest) async throws -> OutlineCollection {
        if !isManualOfflineModeEnabled {
            do {
                let result = try await live.updateCollection(request)
                await cacheCollection(result)
                return result
            } catch {
                return try await queueCollectionUpdate(request, dueTo: error)
            }
        }
        return try await queueCollectionUpdate(request, dueTo: nil)
    }

    public func createPin(_ request: CreatePinRequest) async throws -> OutlinePin {
        if !isManualOfflineModeEnabled {
            do { return try await live.createPin(request) } catch { return await queuePinCreate(request) }
        }
        return await queuePinCreate(request)
    }

    public func deletePin(id: String) async throws {
        if await cancelIfNeverSynced(id: id) { return }
        if !isManualOfflineModeEnabled {
            do {
                try await live.deletePin(id: id)
                return
            } catch {
                await enqueue(.deletePin, payload: IDPayload(id: id), id: "delete-pin-\(id)")
                return
            }
        }
        await enqueue(.deletePin, payload: IDPayload(id: id), id: "delete-pin-\(id)")
    }

    public func createSubscription(_ request: CreateSubscriptionRequest) async throws -> OutlineSubscription {
        if !isManualOfflineModeEnabled {
            do { return try await live.createSubscription(request) } catch { return await queueSubscriptionCreate(request) }
        }
        return await queueSubscriptionCreate(request)
    }

    public func deleteSubscription(id: String) async throws {
        if await cancelIfNeverSynced(id: id) { return }
        if !isManualOfflineModeEnabled {
            do {
                try await live.deleteSubscription(id: id)
                return
            } catch {
                await enqueue(.deleteSubscription, payload: IDPayload(id: id), id: "delete-subscription-\(id)")
                return
            }
        }
        await enqueue(.deleteSubscription, payload: IDPayload(id: id), id: "delete-subscription-\(id)")
    }

    public func starDocument(_ request: StarDocumentRequest) async throws -> OutlineStar {
        if !isManualOfflineModeEnabled {
            do { return try await live.starDocument(request) } catch { return await queueStarDocumentCreate(request) }
        }
        return await queueStarDocumentCreate(request)
    }

    public func starCollection(_ request: StarCollectionRequest) async throws -> OutlineStar {
        if !isManualOfflineModeEnabled {
            do { return try await live.starCollection(request) } catch { return await queueStarCollectionCreate(request) }
        }
        return await queueStarCollectionCreate(request)
    }

    public func deleteStar(id: String) async throws {
        if await cancelIfNeverSynced(id: id) { return }
        if !isManualOfflineModeEnabled {
            do {
                try await live.deleteStar(id: id)
                return
            } catch {
                await enqueue(.deleteStar, payload: IDPayload(id: id), id: "delete-star-\(id)")
                return
            }
        }
        await enqueue(.deleteStar, payload: IDPayload(id: id), id: "delete-star-\(id)")
    }

    // MARK: - Pass-through

    public func authInfo() async throws -> OutlineAuthInfo {
        try await live.authInfo()
    }

    public func searchDocuments(_ request: DocumentSearchRequest) async throws -> [OutlineDocumentSearchResult] {
        try await live.searchDocuments(request)
    }

    public func searchDocumentTitles(_ request: DocumentSearchTitlesRequest) async throws -> [OutlineDocument] {
        try await live.searchDocumentTitles(request)
    }

    public func templatizeDocument(_ request: TemplatizeDocumentRequest) async throws -> OutlineTemplate {
        try await live.templatizeDocument(request)
    }

    public func duplicateDocument(_ request: DuplicateDocumentRequest) async throws -> [OutlineDocument] {
        try await live.duplicateDocument(request)
    }

    public func unpublishDocument(_ request: UnpublishDocumentRequest) async throws -> OutlineDocument {
        try await live.unpublishDocument(request)
    }

    public func archiveDocument(id: String) async throws -> OutlineDocument {
        try await live.archiveDocument(id: id)
    }

    public func moveDocument(_ request: MoveDocumentRequest) async throws {
        try await live.moveDocument(request)
    }

    public func deleteDocument(_ request: DeleteDocumentRequest) async throws {
        try await live.deleteDocument(request)
    }

    public func documentInsights(_ request: DocumentInsightsRequest) async throws -> [OutlineDocumentInsight] {
        try await live.documentInsights(request)
    }

    public func listRevisions(_ request: ListRevisionsRequest) async throws -> [OutlineRevision] {
        try await live.listRevisions(request)
    }

    public func exportDocument(id: String) async throws -> String {
        try await live.exportDocument(id: id)
    }

    public func createShare(_ request: CreateShareRequest) async throws -> OutlineShare {
        try await live.createShare(request)
    }

    public func shareInfo(documentId: String) async throws -> OutlineShare? {
        try await live.shareInfo(documentId: documentId)
    }

    public func updateShare(_ request: UpdateShareRequest) async throws -> OutlineShare {
        try await live.updateShare(request)
    }

    public func listShares(_ request: ListSharesRequest) async throws -> [OutlineShare] {
        try await live.listShares(request)
    }

    public func revokeShare(id: String) async throws {
        try await live.revokeShare(id: id)
    }

    public func listPins(_ request: ListPinsRequest) async throws -> [OutlinePin] {
        try await live.listPins(request)
    }

    public func listSubscriptions(_ request: ListSubscriptionsRequest) async throws -> [OutlineSubscription] {
        try await live.listSubscriptions(request)
    }

    public func listViews(_ request: ListViewsRequest) async throws -> [OutlineView] {
        try await live.listViews(request)
    }

    public func addDocumentUser(_ request: AddDocumentUserRequest) async throws -> OutlineMembership {
        try await live.addDocumentUser(request)
    }

    public func removeDocumentUser(_ request: RemoveDocumentUserRequest) async throws {
        try await live.removeDocumentUser(request)
    }

    public func documentUsers(_ request: ListDocumentUsersRequest) async throws -> [OutlineDocumentMember] {
        try await live.documentUsers(request)
    }

    public func listUsers(_ request: ListUsersRequest) async throws -> [OutlineUser] {
        try await live.listUsers(request)
    }

    public func deleteCollection(id: String) async throws {
        try await live.deleteCollection(id: id)
    }

    public func exportCollection(_ request: ExportCollectionRequest) async throws -> OutlineFileOperation {
        try await live.exportCollection(request)
    }

    public func listStars(_ request: ListStarsRequest) async throws -> [OutlineStar] {
        try await live.listStars(request)
    }

    public func currentUser() async throws -> OutlineUser {
        try await live.currentUser()
    }

    public func createAttachment(_ request: CreateAttachmentRequest) async throws -> CreateAttachmentResult {
        try await live.createAttachment(request)
    }

    public func uploadAttachmentFile(_ result: CreateAttachmentResult, fileData: Data) async throws {
        try await live.uploadAttachmentFile(result, fileData: fileData)
    }

    public func deleteAttachment(id: String) async throws {
        try await live.deleteAttachment(id: id)
    }

    public func updateUserAvatar(_ request: UpdateUserAvatarRequest) async throws -> OutlineUser {
        try await live.updateUserAvatar(request)
    }

    public func updateUserName(_ request: UpdateUserNameRequest) async throws -> OutlineUser {
        try await live.updateUserName(request)
    }

    public func updateUserLanguage(_ request: UpdateUserLanguageRequest) async throws -> OutlineUser {
        try await live.updateUserLanguage(request)
    }

    public func updateUserPreferences(_ request: UpdateUserPreferencesRequest) async throws -> OutlineUser {
        try await live.updateUserPreferences(request)
    }

    public func deleteAccount() async throws {
        try await live.deleteAccount()
    }

    public func subscribeToNotifications(eventType: NotificationEventType?) async throws -> OutlineUser {
        try await live.subscribeToNotifications(eventType: eventType)
    }

    public func unsubscribeFromNotifications(eventType: NotificationEventType?) async throws -> OutlineUser {
        try await live.unsubscribeFromNotifications(eventType: eventType)
    }

    public func listApiKeys(_ request: ListApiKeysRequest) async throws -> [OutlineAPIKey] {
        try await live.listApiKeys(request)
    }

    public func createApiKey(_ request: CreateApiKeyRequest) async throws -> OutlineAPIKey {
        try await live.createApiKey(request)
    }

    public func deleteApiKey(id: String) async throws {
        try await live.deleteApiKey(id: id)
    }

    public func installationInfo() async throws -> OutlineInstallationInfo {
        try await live.installationInfo()
    }

    // MARK: - Sync management (Settings surface)

    public func pendingOperations() async -> [PendingOperationSummary] {
        await cache.pendingOperations().map {
            PendingOperationSummary(id: $0.id, kind: $0.kind, createdAt: $0.createdAt, attemptCount: $0.attemptCount, lastError: $0.lastError)
        }
    }

    public func cacheStorageSummary() async -> CacheStorageSummary {
        CacheStorageSummary(itemCount: await cache.itemCount(), totalBytes: await cache.totalBytes())
    }

    public func clearCache() async {
        await cache.clearAll()
    }

    /// Replays every queued operation against `live`, in the order they were
    /// queued. Each is independent — one failing doesn't block the rest.
    public func flushPendingOperations() async -> SyncFlushSummary {
        let operations = await cache.pendingOperations()
        var succeeded = 0
        var failed = 0
        for operation in operations {
            do {
                try await replay(operation)
                await cache.removeOperation(id: operation.id)
                succeeded += 1
            } catch {
                await cache.recordFailure(id: operation.id, error: errorDescription(error))
                failed += 1
            }
        }
        return SyncFlushSummary(succeeded: succeeded, failed: failed)
    }

    /// "Full Local Sync": eagerly walks every collection and caches every
    /// document's full content (not just whatever's been opened), so
    /// browsing offline works for the whole workspace, not only what was
    /// already viewed. Goes through `self`, not `live`, directly — the
    /// existing cached-read methods already do the caching as a side effect,
    /// this just has to drive the walk and separately cache each document by
    /// id (`listDocuments`'s cache key is the list, not the individual doc).
    ///
    /// Recurses into every document's children, not just collections' own
    /// root-level documents — a document with sub-documents used to leave
    /// them uncached entirely (only reachable if something else happened to
    /// open them individually first). Also caches each collection under its
    /// own `"collection:<id>"` key (previously only cached as part of the
    /// paginated list blob), so both are individually enumerable afterward
    /// via `OfflineCacheStore.loadAll(keyPrefix:)` — see
    /// `cachedDocumentsIndex()`/`cachedCollectionsIndex()`.
    public func performFullSync() async -> FullSyncSummary {
        var documentsCount = 0
        var errors: [String] = []
        var collections: [OutlineCollection] = []
        var collectionsOffset = 0
        let collectionsLimit = 100
        // Outline rejects any `limit` over 100 outright — page in increments
        // of that instead of guessing a total up front (the protocol doesn't
        // expose `pagination`'s total count, only the page itself); a page
        // shorter than the limit is what signals "that was the last one".
        while true {
            let page: [OutlineCollection]
            do {
                page = try await listCollections(offset: collectionsOffset, limit: collectionsLimit)
            } catch {
                errors.append(errorDescription(error))
                break
            }
            collections.append(contentsOf: page)
            guard page.count == collectionsLimit else { break }
            collectionsOffset += collectionsLimit
        }

        for collection in collections {
            await cacheCollection(collection)
            let result = await cacheDocumentTree(collectionId: collection.id, parentDocumentId: nil, collectionName: collection.name)
            documentsCount += result.count
            errors.append(contentsOf: result.errors)
        }

        return FullSyncSummary(collectionsCount: collections.count, documentsCount: documentsCount, errors: errors, finishedAt: Date())
    }

    /// Caches every document under `parentDocumentId` (`nil` = a
    /// collection's root level) and recurses into each one's own children,
    /// depth-first, until a branch runs out of sub-documents. Returns a
    /// plain `(count, errors)` pair rather than mutating shared state across
    /// `await` boundaries, since this calls itself recursively.
    private func cacheDocumentTree(
        collectionId: String,
        parentDocumentId: String?,
        collectionName: String
    ) async -> (count: Int, errors: [String]) {
        var count = 0
        var errors: [String] = []
        var offset = 0
        let limit = 100
        while true {
            let documents: [OutlineDocument]
            do {
                documents = try await listDocuments(collectionId: collectionId, parentDocumentId: parentDocumentId, offset: offset, limit: limit)
            } catch {
                errors.append("\(collectionName): \(errorDescription(error))")
                break
            }
            for document in documents {
                await cacheDocument(document)
                count += 1
                let childResult = await cacheDocumentTree(collectionId: collectionId, parentDocumentId: document.id, collectionName: collectionName)
                count += childResult.count
                errors.append(contentsOf: childResult.errors)
            }
            guard documents.count == limit else { break }
            offset += limit
        }
        return (count, errors)
    }

    /// Every individually cached document from the last Full Local Sync —
    /// empty if a sync has never run (or found nothing). Purely a local
    /// SwiftData read, no network involved.
    public func cachedDocumentsIndex() async -> [OutlineDocument] {
        let payloads = await cache.loadAll(keyPrefix: "document:")
        return payloads.compactMap { try? decoder.decode(OutlineDocument.self, from: $0) }
    }

    /// Every individually cached collection from the last Full Local Sync.
    public func cachedCollectionsIndex() async -> [OutlineCollection] {
        let payloads = await cache.loadAll(keyPrefix: "collection:")
        return payloads.compactMap { try? decoder.decode(OutlineCollection.self, from: $0) }
    }

    // MARK: - Helpers

    private func cachedFetch<T: Codable>(key: String, fetch: () async throws -> T) async throws -> T {
        // Manual offline mode means "skip the network entirely," not just
        // "prefer it" — without this check, a read would still hit `live`
        // (and succeed, showing content beyond whatever's cached) any time
        // the device actually had a connection, defeating the point of
        // deliberately testing/working as if offline.
        if isManualOfflineModeEnabled {
            if let data = await cache.load(forKey: key), let cached = try? decoder.decode(T.self, from: data) {
                return cached
            }
            throw OutlineAPIError.transport(URLError(.notConnectedToInternet))
        }
        do {
            let result = try await fetch()
            if let data = try? encoder.encode(result) {
                await cache.save(data, forKey: key)
            }
            return result
        } catch {
            if let data = await cache.load(forKey: key), let cached = try? decoder.decode(T.self, from: data) {
                return cached
            }
            throw error
        }
    }

    private func requestKey(_ prefix: String, _ request: some Encodable) -> String {
        guard let data = try? keyEncoder.encode(request), let json = String(data: data, encoding: .utf8) else {
            return prefix
        }
        return "\(prefix):\(json)"
    }

    private func cacheDocument(_ document: OutlineDocument) async {
        if let data = try? encoder.encode(document) {
            await cache.save(data, forKey: "document:\(document.id)")
        }
    }

    private func cacheCollection(_ collection: OutlineCollection) async {
        if let data = try? encoder.encode(collection) {
            await cache.save(data, forKey: "collection:\(collection.id)")
        }
    }

    private func enqueue(_ kind: PendingOperationKind, payload: some Encodable, id: String) async {
        guard let data = try? encoder.encode(payload) else { return }
        await cache.enqueueOperation(id: id, kind: kind.rawValue, payload: data)
    }

    /// A delete targeting a `pending-*` id can only mean "cancel the create
    /// still sitting in the queue" — the server has never heard of that id,
    /// so queuing the delete would just fail once synced. Returns whether it
    /// found (and removed) a matching create, meaning the caller is done.
    private func cancelIfNeverSynced(id: String) async -> Bool {
        guard id.hasPrefix("pending-") else { return false }
        return await cache.removeOperation(id: id)
    }

    private func queueDocumentCreate(_ request: CreateDocumentRequest) async -> OutlineDocument {
        let pendingId = "pending-\(UUID().uuidString)"
        let now = Date()
        let synthesized = OutlineDocument(
            id: pendingId,
            title: request.title,
            text: request.text,
            emoji: nil,
            collectionId: request.collectionId,
            parentDocumentId: request.parentDocumentId,
            url: "/doc/\(pendingId)",
            revision: nil,
            fullWidth: nil,
            createdAt: now,
            updatedAt: now,
            publishedAt: request.publish ? now : nil,
            archivedAt: nil,
            deletedAt: nil
        )
        await cacheDocument(synthesized)
        await enqueue(.createDocument, payload: request, id: pendingId)
        return synthesized
    }

    private func queueDocumentUpdate(_ request: UpdateDocumentRequest, dueTo error: Error?) async throws -> OutlineDocument {
        guard let baseData = await cache.load(forKey: "document:\(request.id)"),
              let base = try? decoder.decode(OutlineDocument.self, from: baseData) else {
            throw error ?? OutlineAPIError.transport(URLError(.notConnectedToInternet))
        }
        let mergedText = request.append == true ? base.text + (request.text ?? "") : (request.text ?? base.text)
        let merged = OutlineDocument(
            id: base.id,
            title: request.title ?? base.title,
            text: mergedText,
            emoji: base.emoji,
            collectionId: base.collectionId,
            parentDocumentId: base.parentDocumentId,
            url: base.url,
            revision: base.revision,
            fullWidth: request.fullWidth ?? base.fullWidth,
            createdAt: base.createdAt,
            updatedAt: Date(),
            publishedAt: base.publishedAt,
            archivedAt: base.archivedAt,
            deletedAt: base.deletedAt
        )
        await cacheDocument(merged)

        // Still-unsynced create for this exact document — fold the edit into
        // the pending create's payload instead of queuing a separate update.
        // A separate update would target `merged.id`, which is still the
        // `pending-*` placeholder at replay time; the server has never heard
        // of it and the update would just fail every retry.
        if merged.id.hasPrefix("pending-"),
           let createOp = await cache.pendingOperations().first(where: { $0.id == merged.id && $0.kind == PendingOperationKind.createDocument.rawValue }),
           let createRequest = try? decoder.decode(CreateDocumentRequest.self, from: createOp.payload) {
            let resolvedCreate = CreateDocumentRequest(
                title: merged.title,
                text: merged.text,
                collectionId: createRequest.collectionId,
                parentDocumentId: createRequest.parentDocumentId,
                publish: createRequest.publish
            )
            await enqueue(.createDocument, payload: resolvedCreate, id: merged.id)
            return merged
        }

        // Fully resolved (not the original partial request) so replaying just
        // this one queued operation reproduces `merged` exactly — that's what
        // makes coalescing a second edit onto the same queued id safe.
        let resolved = UpdateDocumentRequest(id: merged.id, title: merged.title, text: merged.text, fullWidth: merged.fullWidth)
        await enqueue(.updateDocument, payload: resolved, id: "update-document-\(merged.id)")
        return merged
    }

    private func queueCollectionUpdate(_ request: UpdateCollectionRequest, dueTo error: Error?) async throws -> OutlineCollection {
        guard let baseData = await cache.load(forKey: "collection:\(request.id)"),
              let base = try? decoder.decode(OutlineCollection.self, from: baseData) else {
            throw error ?? OutlineAPIError.transport(URLError(.notConnectedToInternet))
        }
        let merged = OutlineCollection(
            id: base.id,
            name: request.name ?? base.name,
            description: request.description ?? base.description,
            color: base.color,
            icon: base.icon,
            createdAt: base.createdAt,
            updatedAt: Date()
        )
        await cacheCollection(merged)
        let resolved = UpdateCollectionRequest(id: merged.id, name: merged.name, description: merged.description)
        await enqueue(.updateCollection, payload: resolved, id: "update-collection-\(merged.id)")
        return merged
    }

    private func queuePinCreate(_ request: CreatePinRequest) async -> OutlinePin {
        let pendingId = "pending-\(UUID().uuidString)"
        await enqueue(.createPin, payload: request, id: pendingId)
        return OutlinePin(id: pendingId, documentId: request.documentId, collectionId: request.collectionId, index: nil)
    }

    private func queueSubscriptionCreate(_ request: CreateSubscriptionRequest) async -> OutlineSubscription {
        let pendingId = "pending-\(UUID().uuidString)"
        await enqueue(.createSubscription, payload: request, id: pendingId)
        return OutlineSubscription(id: pendingId, documentId: request.documentId, collectionId: nil, event: request.event)
    }

    private func queueStarDocumentCreate(_ request: StarDocumentRequest) async -> OutlineStar {
        let pendingId = "pending-\(UUID().uuidString)"
        await enqueue(.starDocument, payload: request, id: pendingId)
        return OutlineStar(id: pendingId, index: nil, documentId: request.documentId, collectionId: nil)
    }

    private func queueStarCollectionCreate(_ request: StarCollectionRequest) async -> OutlineStar {
        let pendingId = "pending-\(UUID().uuidString)"
        await enqueue(.starCollection, payload: request, id: pendingId)
        return OutlineStar(id: pendingId, index: nil, documentId: nil, collectionId: request.collectionId)
    }

    private func replay(_ operation: PendingOperation) async throws {
        guard let kind = PendingOperationKind(rawValue: operation.kind) else {
            throw OutlineAPIError.decoding(DecodingError.dataCorrupted(
                DecodingError.Context(codingPath: [], debugDescription: "Unknown pending operation kind: \(operation.kind)")
            ))
        }
        switch kind {
        case .createDocument:
            let request = try decoder.decode(CreateDocumentRequest.self, from: operation.payload)
            let result = try await live.createDocument(request)
            await cacheDocument(result)
            // The placeholder id (== operation.id) is now a dead orphan —
            // nothing server-side will ever answer to it again.
            await cache.removeCacheEntry(forKey: "document:\(operation.id)")
        case .updateDocument:
            let request = try decoder.decode(UpdateDocumentRequest.self, from: operation.payload)
            let result = try await live.updateDocument(request)
            await cacheDocument(result)
        case .updateCollection:
            let request = try decoder.decode(UpdateCollectionRequest.self, from: operation.payload)
            let result = try await live.updateCollection(request)
            await cacheCollection(result)
        case .createPin:
            let request = try decoder.decode(CreatePinRequest.self, from: operation.payload)
            _ = try await live.createPin(request)
        case .deletePin:
            let request = try decoder.decode(IDPayload.self, from: operation.payload)
            try await live.deletePin(id: request.id)
        case .createSubscription:
            let request = try decoder.decode(CreateSubscriptionRequest.self, from: operation.payload)
            _ = try await live.createSubscription(request)
        case .deleteSubscription:
            let request = try decoder.decode(IDPayload.self, from: operation.payload)
            try await live.deleteSubscription(id: request.id)
        case .starDocument:
            let request = try decoder.decode(StarDocumentRequest.self, from: operation.payload)
            _ = try await live.starDocument(request)
        case .deleteStar:
            let request = try decoder.decode(IDPayload.self, from: operation.payload)
            try await live.deleteStar(id: request.id)
        case .starCollection:
            let request = try decoder.decode(StarCollectionRequest.self, from: operation.payload)
            _ = try await live.starCollection(request)
        }
    }

    private func errorDescription(_ error: Error) -> String {
        if let apiError = error as? OutlineAPIError {
            switch apiError {
            case .unauthorized: return "Sign-in expired."
            case .notFound: return "Not found on the server."
            case .server(let status, let message): return message ?? "Server error (\(status))."
            case .decoding: return "Unexpected response shape."
            case .transport: return "Couldn't reach the server."
            case .tokenUnavailable: return "Couldn't access the saved sign-in."
            }
        }
        return String(describing: error)
    }
}