iOS/Sources/Shared/API/Webhook/Request&Response/WebhookManager.swift

import Foundation
import PromiseKit
import UserNotifications
import ObjectMapper

internal enum WebhookError: Error, Equatable {
    case noApi
    case unregisteredIdentifier
    case unexpectedType(given: String, desire: String)
    case unacceptableStatusCode(Int)
    case unmappableValue
}

// swiftlint:disable file_length
// swiftlint:disable type_body_length

public class WebhookManager: NSObject {
    public static func isManager(forSessionIdentifier identifier: String) -> Bool {
        return identifier.starts(with: baseURLSessionIdentifier)
    }
    private static let baseURLSessionIdentifier = "webhook-"
    private static var currentURLSessionIdentifier: String {
        baseURLSessionIdentifier + Bundle.main.bundleIdentifier!
    }
    private static var currentRegularURLSessionIdentifier: String {
        "non-background"
    }

    internal var sessionInfos = Set<WebhookSessionInfo>()
    internal var currentBackgroundSessionInfo: WebhookSessionInfo {
        sessionInfo(forIdentifier: Self.currentURLSessionIdentifier)
    }
    internal var currentRegularSessionInfo: WebhookSessionInfo {
        sessionInfo(forIdentifier: Self.currentRegularURLSessionIdentifier)
    }

    // must be accessed on appropriate queue
    private let dataQueue: DispatchQueue
    private let dataQueueSpecificKey: DispatchSpecificKey<Bool>
    // underlying queue is the dataQueue
    private let dataOperationQueue: OperationQueue

    private var pendingDataForTask: [TaskKey: Data] = [:] {
        willSet {
            assert(DispatchQueue.getSpecific(key: dataQueueSpecificKey) == true)
        }
    }
    private var resolverForTask: [TaskKey: Resolver<Void>] = [:] {
        willSet {
            assert(DispatchQueue.getSpecific(key: dataQueueSpecificKey) == true)
        }
    }

    private var responseHandlers = [WebhookResponseIdentifier: WebhookResponseHandler.Type]()

    // MARK: - Lifecycle

    override internal init() {
        let specificKey = DispatchSpecificKey<Bool>()
        let underlyingQueue = DispatchQueue(label: "webhookmanager-data")
        underlyingQueue.setSpecific(key: specificKey, value: true)

        self.dataQueue = underlyingQueue
        self.dataQueueSpecificKey = specificKey
        self.dataOperationQueue = with(OperationQueue()) {
            $0.underlyingQueue = underlyingQueue
        }

        super.init()

        // cause the current sessions to be created
        dataQueue.sync {
            _ = self.currentBackgroundSessionInfo
            _ = self.currentRegularSessionInfo
        }

        register(responseHandler: WebhookResponseUnhandled.self, for: .unhandled)
    }

    internal func register(
        responseHandler: WebhookResponseHandler.Type,
        for identifier: WebhookResponseIdentifier
    ) {
        precondition(responseHandlers[identifier] == nil)
        responseHandlers[identifier] = responseHandler
    }

    private func sessionInfo(for session: URLSession) -> WebhookSessionInfo {
        assert(DispatchQueue.getSpecific(key: dataQueueSpecificKey) == true || Current.isRunningTests)

        guard let identifier = session.configuration.identifier else {
            if let sameSession = sessionInfos.first(where: { $0.session == session }) {
                return sameSession
            }

            Current.Log.error("asked for session \(session) but couldn't identify info for it")
            return currentBackgroundSessionInfo
        }

        return sessionInfo(forIdentifier: identifier)
    }

    private func sessionInfo(forIdentifier identifier: String) -> WebhookSessionInfo {
        assert(DispatchQueue.getSpecific(key: dataQueueSpecificKey) == true || Current.isRunningTests)

        if let sessionInfo = sessionInfos.first(where: { $0.identifier == identifier }) {
            return sessionInfo
        }

        let sessionInfo = WebhookSessionInfo(
            identifier: identifier,
            delegate: self,
            delegateQueue: dataOperationQueue,
            background: identifier != Self.currentRegularURLSessionIdentifier
        )
        sessionInfos.insert(sessionInfo)
        return sessionInfo
    }

    public func handleBackground(for identifier: String, completionHandler: @escaping () -> Void) {
        precondition(Self.isManager(forSessionIdentifier: identifier))
        Current.Log.notify("handleBackground started for \(identifier)")

        dataQueue.async { [dataQueue] in
            let sessionInfo = self.sessionInfo(forIdentifier: identifier)
            Current.Log.info("created or retrieved: \(sessionInfo)")

            // enter before setting finish, in case we had another leave/enter pair set up, we want to prevent notifying
            sessionInfo.eventGroup.enter()
            sessionInfo.setDidFinish {
                // this is wrapped via a block -- rather than being invoked directly -- because iOS 14 (at least b1/b2)
                // sends `urlSessionDidFinishEvents` when it didn't send `handleEventsForBackgroundURLSession`
                sessionInfo.eventGroup.leave()
            }

            sessionInfo.eventGroup.notify(queue: DispatchQueue.main) {
                Current.Log.notify("final completion for \(identifier)")
                completionHandler()
            }

            if self.currentBackgroundSessionInfo != sessionInfo {
                sessionInfo.eventGroup.notify(queue: dataQueue) { [weak self] in
                    Current.Log.info("removing session info \(sessionInfo)")
                    self?.sessionInfos.remove(sessionInfo)
                }
            }
        }
    }

    // MARK: - Sending Ephemeral

    public func sendEphemeral(request: WebhookRequest) -> Promise<Void> {
        let promise: Promise<Any> = sendEphemeral(request: request)
        return promise.asVoid()
    }

    public func sendEphemeral<MappableResult: BaseMappable>(request: WebhookRequest) -> Promise<MappableResult> {
        let promise: Promise<Any> = sendEphemeral(request: request)
        return promise.map {
            if let result = Mapper<MappableResult>().map(JSONObject: $0) {
                return result
            } else {
                throw WebhookError.unmappableValue
            }
        }
    }

    public func sendEphemeral<MappableResult: BaseMappable>(request: WebhookRequest) -> Promise<[MappableResult]> {
        let promise: Promise<Any> = sendEphemeral(request: request)
        return promise.map {
            if let result = Mapper<MappableResult>(shouldIncludeNilValues: false).mapArray(JSONObject: $0) {
                return result
            } else {
                throw WebhookError.unmappableValue
            }
        }
    }

    public func sendEphemeral<ResponseType>(request: WebhookRequest) -> Promise<ResponseType> {
        Current.backgroundTask(withName: "webhook-send-ephemeral") { [self, dataQueue] _ in
            attemptNetworking {
                firstly {
                    Self.urlRequest(for: request)
                }.get { _, _ in
                    Current.Log.info("sending: \(request)")
                }.then(on: dataQueue) { urlRequest, data in
                    self.currentRegularSessionInfo.session.uploadTask(.promise, with: urlRequest, from: data)
                }
            }
        }.then { data, response in
            Promise.value(data).webhookJson(
                on: DispatchQueue.global(qos: .utility),
                statusCode: (response as? HTTPURLResponse)?.statusCode
            )
        }.map { possible in
            if let value = possible as? ResponseType {
                return value
            } else {
                throw WebhookError.unexpectedType(
                    given: String(describing: type(of: possible)),
                    desire: String(describing: ResponseType.self)
                )
            }
        }.tap { result in
            switch result {
            case .fulfilled(let response):
                Current.Log.info("got successful response for \(request.type): \(response)")
            case .rejected(let error):
                Current.Log.error("got failure for \(request.type): \(error)")
            }
        }
    }

    // MARK: - Sending Persistent

    public func send(
        identifier: WebhookResponseIdentifier = .unhandled,
        request: WebhookRequest
    ) -> Promise<Void> {
        let (promise, seal) = Promise<Void>.pending()

        dataQueue.async { [dataQueue] in
            let sendRegular: () -> Promise<Void> = { [self] in
                self.send(on: self.currentRegularSessionInfo, identifier: identifier, request: request)
            }

            let sendBackground: () -> Promise<Void> = { [self] in
                self.send(on: self.currentBackgroundSessionInfo, identifier: identifier, request: request)
            }

            let promise: Promise<Void>

            if Current.isBackgroundRequestsImmediate() {
                promise = sendBackground()
            } else {
                Current.Log.info("in background, choosing to not use background session")
                promise = sendRegular().recover(on: dataQueue) { error -> Promise<Void> in
                    Current.Log.error("in-background non-background failed: \(error)")
                    if error is HomeAssistantAPI.APIError {
                        // not worth retrying, since we got a real response that we didn't like
                        throw error
                    } else {
                        return sendBackground()
                    }
                }
            }

            promise.pipe(to: { seal.resolve($0) })
        }

        return promise
    }

    // swiftlint:disable:next function_body_length
    private func send(
        on sessionInfo: WebhookSessionInfo,
        identifier: WebhookResponseIdentifier,
        request: WebhookRequest
    ) -> Promise<Void> {
        guard let handlerType = responseHandlers[identifier] else {
            Current.Log.error("no existing handler for \(identifier), not sending request")
            return .init(error: WebhookError.unregisteredIdentifier)
        }

        let (promise, seal) = Promise<Void>.pending()

        // wrap this in a background task, but don't let the expiration cause the resolve chain to be aborted
        // this is important because we may be woken up later and asked to continue the same request, even if timed out
        // since, you know, background execution and whatnot
        Current.backgroundTask(withName: "webhook-send") { _ in promise }.cauterize()

        firstly {
            Self.urlRequest(for: request)
        }.done(on: dataQueue) { urlRequest, data in
            let task: URLSessionUploadTask
            let filesToRemove: [URL]

            if sessionInfo.isBackground {
                let temporaryDirectory = URL(fileURLWithPath: NSTemporaryDirectory(), isDirectory: true)
                let temporaryFile = temporaryDirectory
                    .appendingPathComponent(UUID().uuidString)
                    .appendingPathExtension("json")
                try data.write(to: temporaryFile, options: [])

                task = sessionInfo.session.uploadTask(with: urlRequest, fromFile: temporaryFile)

                filesToRemove = [temporaryFile]
            } else {
                // not writing to disk so we don't have to deal with the cleanup logic across sessions
                task = sessionInfo.session.uploadTask(with: urlRequest, from: data)
                filesToRemove = []
            }

            let persisted = WebhookPersisted(request: request, identifier: identifier)
            task.webhookPersisted = persisted

            let taskKey = TaskKey(sessionInfo: sessionInfo, task: task)

            self.evaluateCancellable(
                by: task,
                type: handlerType,
                persisted: persisted,
                with: promise
            )
            self.resolverForTask[taskKey] = seal
            task.resume()

            Current.Log.info {
                let values = [
                    "\(taskKey)",
                    "type(\(handlerType))",
                    "request(\(persisted.request))"
                ]
                return "starting request: " + values.joined(separator: ", ")
            }

            for file in filesToRemove {
                // the background session takes over ownership of the files, so that code path needs these cleaned up
                try FileManager.default.removeItem(at: file)
            }
        }.catch { error in
            self.invoke(
                sessionInfo: sessionInfo,
                handler: handlerType,
                request: request,
                result: .init(error: error),
                resolver: seal
            )
        }

        return promise
    }

    // MARK: - Testing Connection Info
    public func sendTest(baseURL: URL) -> Promise<Void> {
        return firstly {
            Self.urlRequest(
                for: .init(type: "get_config", data: [:]),
                baseURL: baseURL
            )
        }.then(on: dataQueue) { urlRequest, data in
            self.currentRegularSessionInfo.session.uploadTask(.promise, with: urlRequest, from: data)
        }.then { data, response in
            Promise.value(data).webhookJson(
                on: DispatchQueue.global(qos: .utility),
                statusCode: (response as? HTTPURLResponse)?.statusCode
            )
        }.asVoid()
    }

    // MARK: - Private

    private func evaluateCancellable(
        by newTask: URLSessionTask,
        type newType: WebhookResponseHandler.Type,
        persisted newPersisted: WebhookPersisted,
        with newPromise: Promise<Void>
    ) {
        currentBackgroundSessionInfo.session.getAllTasks { tasks in
            tasks.filter { thisTask in
                guard let (thisType, thisPersisted) = self.responseInfo(from: thisTask) else {
                    Current.Log.error("cancelling request without persistence info: \(thisTask)")
                    thisTask.cancel()
                    return false
                }

                if thisType == newType, thisTask != newTask {
                    return newType.shouldReplace(request: newPersisted.request, with: thisPersisted.request)
                } else {
                    return false
                }
            }.forEach { existingTask in
                let taskKey = TaskKey(sessionInfo: self.currentBackgroundSessionInfo, task: existingTask)
                if let existingResolver = self.resolverForTask[taskKey] {
                    // connect the task we're about to cancel's promise to the replacement
                    newPromise.pipe { existingResolver.resolve($0) }
                }
                existingTask.cancel()
            }
        }
    }

    private static func urlRequest(
        for request: WebhookRequest,
        baseURL: URL? = nil
    ) -> Promise<(URLRequest, Data)> {
        return Promise { seal in
            guard let connectionInfo = Current.settingsStore.connectionInfo else {
                seal.reject(WebhookError.noApi)
                return
            }

            let webhookURL: URL

            if let baseURL = baseURL {
                webhookURL = baseURL.appendingPathComponent(connectionInfo.webhookPath, isDirectory: false)
            } else {
                webhookURL = connectionInfo.webhookURL
            }

            var urlRequest = try URLRequest(url: webhookURL, method: .post)
            urlRequest.setValue("application/json", forHTTPHeaderField: "Content-Type")

            let jsonObject = Mapper<WebhookRequest>(context: WebhookRequestContext.server).toJSON(request)
            let data = try JSONSerialization.data(withJSONObject: jsonObject, options: [.sortedKeys])

            // httpBody is ignored by URLSession but is made available in tests
            urlRequest.httpBody = data

            seal.fulfill((urlRequest, data))
        }
    }

    private func handle(result: WebhookResponseHandlerResult) {
        if let notification = result.notification {
            UNUserNotificationCenter.current().add(notification) { error in
                if let error = error {
                    Current.Log.error("failed to add notification for result \(result): \(error)")
                }
            }
        }
    }

    private func responseInfo(from task: URLSessionTask) -> (WebhookResponseHandler.Type, WebhookPersisted)? {
        guard let persisted = task.webhookPersisted else {
            Current.Log.error("no persisted info for \(task) \(task.taskDescription ?? "(nil)")")
            return nil
        }

        guard let handlerType = responseHandlers[persisted.identifier] else {
            Current.Log.error("unknown response identifier \(persisted.identifier) for \(task)")
            return nil
        }

        return (handlerType, persisted)
    }
}

extension WebhookManager: URLSessionDelegate {
    public func urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) {
        Current.Log.notify("event delivery ended")
        sessionInfo(for: session).fireDidFinish()
    }
}

extension WebhookManager: URLSessionDataDelegate {
    public func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
        let taskKey = TaskKey(sessionInfo: sessionInfo(for: session), task: dataTask)
        pendingDataForTask[taskKey, default: Data()].append(data)
    }

    public func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
        let sessionInfo = self.sessionInfo(for: session)
        let taskKey = TaskKey(sessionInfo: sessionInfo, task: task)
        let statusCode = (task.response as? HTTPURLResponse)?.statusCode

        guard error?.isCancelled != true else {
            Current.Log.info("ignoring cancelled task \(taskKey)")
            pendingDataForTask.removeValue(forKey: taskKey)
            return
        }

        let result = Promise<Data?> { seal in
            let data = self.pendingDataForTask[taskKey]
            self.pendingDataForTask.removeValue(forKey: taskKey)
            seal.resolve(error, data)
        }.webhookJson(
            on: DispatchQueue.global(qos: .utility),
            statusCode: statusCode
        )

        // dispatch
        if let (handlerType, persisted) = responseInfo(from: task) {
            // logging
            result.done(on: dataQueue) { body in
                Current.Log.info {
                    let values = [
                        "\(taskKey)",
                        "type(\(handlerType))",
                        "request(\(persisted.request))",
                        "statusCode(\(statusCode.flatMap { String(describing: $0) } ?? "none"))",
                        "body(\(body))"
                    ]

                    return "got response: " + values.joined(separator: ", ")
                }
            }.catch { error in
                Current.Log.error("failed request for \(handlerType): \(error)")
            }

            invoke(
                sessionInfo: sessionInfo,
                handler: handlerType,
                request: persisted.request,
                result: result,
                resolver: resolverForTask[taskKey]
            )

            resolverForTask.removeValue(forKey: taskKey)
        } else {
            Current.Log.notify("no handler for background task")
            Current.Log.error("couldn't find appropriate handler for \(task)")
        }
    }

    private func invoke(
        sessionInfo: WebhookSessionInfo,
        handler handlerType: WebhookResponseHandler.Type,
        request: WebhookRequest,
        result: Promise<Any>,
        resolver: Resolver<Void>?
    ) {
        guard let api = Current.api() else {
            Current.Log.error("no api")
            return
        }

        Current.Log.notify("starting \(request.type) (\(handlerType))")
        sessionInfo.eventGroup.enter()

        let handler = handlerType.init(api: api)
        let handlerPromise = firstly {
            handler.handle(request: .value(request), result: result)
        }.done { [weak self] result in
            // keep the handler around until it finishes
            withExtendedLifetime(handler) {
                self?.handle(result: result)
            }
        }

        firstly {
            when(fulfilled: [handlerPromise.asVoid(), result.asVoid()])
        }.tap {
            resolver?.resolve($0)
        }.ensure {
            Current.Log.notify("finished \(request.type) \(handlerType)")
            sessionInfo.eventGroup.leave()
        }.cauterize()
    }
}

internal class WebhookSessionInfo: CustomStringConvertible, Hashable {
    let identifier: String
    let eventGroup: DispatchGroup
    let session: URLSession
    let isBackground: Bool
    private var pendingDidFinishHandler: (() -> Void)?

    var description: String {
        "sessionInfo(identifier: \(identifier))"
    }

    func setDidFinish(_ block: @escaping () -> Void) {
        pendingDidFinishHandler?()
        pendingDidFinishHandler = block
    }

    func fireDidFinish() {
        pendingDidFinishHandler?()
        pendingDidFinishHandler = nil
    }

    init(
        identifier: String,
        delegate: URLSessionDelegate,
        delegateQueue: OperationQueue,
        background: Bool
    ) {
        let configuration: URLSessionConfiguration = {
            let configuration: URLSessionConfiguration

            if NSClassFromString("XCTest") != nil {
                // ^ cannot reference Current here because we're being created inside Current as it is made
                // we cannot mock http requests in a background session, so this code path has to differ
                configuration = .ephemeral
            } else if background {
                configuration = .background(withIdentifier: identifier)
            } else {
                configuration = .ephemeral
            }

            return with(configuration) {
                $0.sharedContainerIdentifier = Constants.AppGroupID
                $0.httpCookieStorage = nil
                $0.httpCookieAcceptPolicy = .never
                $0.httpShouldSetCookies = false
                $0.requestCachePolicy = .reloadIgnoringLocalAndRemoteCacheData

                $0.httpAdditionalHeaders = [
                    "User-Agent": HomeAssistantAPI.userAgent
                ]

                // how long should this request be retried in the background?
                // default is 7days, but our background requests do not need to live that long
                let timeout = Measurement<UnitDuration>(value: 2, unit: .hours)
                $0.timeoutIntervalForResource = timeout.converted(to: .seconds).value
            }
        }()

        self.isBackground = background
        self.identifier = identifier
        self.session = URLSession(configuration: configuration, delegate: delegate, delegateQueue: delegateQueue)
        self.eventGroup = DispatchGroup()

        session.getAllTasks { tasks in
            Current.Log.info("\(identifier) initial tasks: \(tasks.map(\.taskIdentifier))")
        }
    }

    static func == (lhs: WebhookSessionInfo, rhs: WebhookSessionInfo) -> Bool {
        lhs.identifier == rhs.identifier
    }

    func hash(into hasher: inout Hasher) {
        hasher.combine(identifier)
    }
}

private struct TaskKey: Hashable, CustomStringConvertible {
    private let sessionIdentifier: String
    private let taskIdentifier: Int

    init(sessionInfo: WebhookSessionInfo, task: URLSessionTask) {
        self.sessionIdentifier = sessionInfo.identifier
        self.taskIdentifier = task.taskIdentifier
    }

    var description: String {
        "taskKey(session: \(sessionIdentifier), task: \(taskIdentifier))"
    }
}