ProductImageUploader.swift

import Combine
import UIKit
import Foundation
import struct Yosemite.ProductImage
import enum Yosemite.ProductAction
import protocol Yosemite.StoresManager
import enum Yosemite.ProductImageStatus
import enum Yosemite.ProductImageAssetType
import enum Yosemite.ProductOrVariationID
import class Networking.ProductImageStatusStorage
import protocol Experiments.FeatureFlagService

/// Information about a background product image upload error.
struct ProductImageUploadErrorInfo {
    let siteID: Int64
    let productOrVariationID: ProductOrVariationID
    let error: ProductImageUploaderError
}

/// Identifiable information about a specific product or product variation of different sites for image upload.
struct ProductImageUploaderKey: Equatable, Hashable {
    let siteID: Int64
    let productOrVariationID: ProductOrVariationID
    let isLocalID: Bool
}

/// Handles product image upload to support background image upload.
protocol ProductImageUploaderProtocol {

    /// Emits active image uploads
    var activeUploads: AnyPublisher<[ProductImageUploaderKey], Never> { get }

    /// Emits product image upload errors.
    var errors: AnyPublisher<ProductImageUploadErrorInfo, Never> { get }

    /// Called for product image upload use cases (e.g. product/variation form, downloadable product list).
    /// - Parameters:
    ///   - key: identifiable information about the product.
    ///   - originalStatuses: the current image statuses of the product for initialization.
    func actionHandler(key: ProductImageUploaderKey, originalStatuses: [ProductImageStatus]) -> ProductImageActionHandler

    /// Replaces the local ID of the product with the remote ID from API.
    ///
    /// Called in "Add product" flow as soon as the product is saved in the API.
    ///
    /// Replacing product ID is necessary to update the product with the images that are already uploaded without product ID.
    /// Note that the images start uploading even before the product is created in API.
    ///
    /// - Parameters:
    ///   - siteID: The ID of the site to which images are uploaded to.
    ///   - localID: A temporary local ID of the product.
    ///   - remoteID: Remote product ID received from API.
    func replaceLocalID(siteID: Int64, localID: ProductOrVariationID, remoteID: Int64)

    /// Saves the product remotely with the images after none is pending upload.
    /// - Parameters:
    ///   - key: identifiable information about the product.
    ///   - onProductSave: called after the product is saved remotely with the uploaded images.
    func saveProductImagesWhenNoneIsPendingUploadAnymore(key: ProductImageUploaderKey,
                                                         onProductSave: @escaping (Result<[ProductImage], Error>) -> Void)

    /// Stops the emission of errors when the user is in the product form to edit a specific product.
    /// - Parameters:
    ///   - key: identifiable information about the product.
    func stopEmittingErrors(key: ProductImageUploaderKey)

    /// Starts the emission of errors when the user leaves the product form.
    /// - Parameters:
    ///   - key: identifiable information about the product.
    func startEmittingErrors(key: ProductImageUploaderKey)

    /// Triggers a notice about background image upload for a product if needed.
    /// - Parameter key: identifiable information about the product.
    ///
    func sendBackgroundUploadNoticeIfNeeded(key: ProductImageUploaderKey, using noticePresenter: NoticePresenter)

    /// Determines whether there are unsaved changes on a product's images.
    /// If the product had any save request before, it checks whether the image statuses to save match the latest image statuses.
    /// Otherwise, it checks whether there is any pending upload or the image statuses match the given original image statuses.
    /// - Parameters:
    ///   - key: identifiable information about the product.
    ///   - originalImages: the image statuses before any edits.
    func hasUnsavedChangesOnImages(key: ProductImageUploaderKey, originalImages: [ProductImage]) -> Bool

    /// Resets all internal states and tracking of image uploads for connected stores.
    /// Called when the user is logged out.
    func reset()
}

/// Supports background image upload and product images update after the user leaves the product form.
final class ProductImageUploader: ProductImageUploaderProtocol {

    let imageStatusStorage: ProductImageStatusStorage

    var errors: AnyPublisher<ProductImageUploadErrorInfo, Never> {
        if featureFlagService.isFeatureFlagEnabled(.backgroundProductImageUpload) {
            return imageStatusStorage.errorsPublisher
                .flatMap { errorItems in
                    errorItems.publisher
                        .compactMap { errorItem in
                            guard let productOrVariationID = errorItem.productOrVariationID,
                                  let assetType = errorItem.assetType else { return nil }
                            return ProductImageUploadErrorInfo(
                                siteID: errorItem.siteID,
                                productOrVariationID: productOrVariationID,
                                error: .failedUploadingImage(asset: assetType, error: errorItem.error)
                            )
                        }
                }
                .eraseToAnyPublisher()
        } else {
            return errorsSubject.eraseToAnyPublisher()
        }
    }

    var activeUploads: AnyPublisher<[ProductImageUploaderKey], Never> {
        if featureFlagService.isFeatureFlagEnabled(.backgroundProductImageUpload) {
            return imageStatusStorage.statusesPublisher
                .map { statuses in
                    statuses.compactMap { status -> ProductImageUploaderKey? in
                        if status.isUploading {
                            return ProductImageUploaderKey(siteID: status.siteID,
                                                           productOrVariationID: status.productOrVariationID,
                                                           isLocalID: status.isLocalID)
                        }
                        return nil
                    }
                }
                .eraseToAnyPublisher()
        } else {
            return $activeUploadsPublisher.eraseToAnyPublisher()
        }
    }

    typealias Key = ProductImageUploaderKey

    private let errorsSubject: PassthroughSubject<ProductImageUploadErrorInfo, Never> = .init()
    private var statusUpdatesExcludedProductKeys: Set<Key> = []
    private var statusUpdatesSubscriptions: Set<AnyCancellable> = []
    private var imageUploadSubscriptions: Set<AnyCancellable> = []

    private var actionHandlersByProduct: [Key: ProductImageActionHandler] = [:]
    private var imagesSaverByProduct: [Key: ProductImagesSaver] = [:]

    @Published private var activeUploadsPublisher: [ProductImageUploaderKey] = []

    private let stores: StoresManager
    private let featureFlagService: FeatureFlagService
    private let imagesProductIDUpdater: ProductImagesProductIDUpdaterProtocol

    private var cancellables = Set<AnyCancellable>()

    init(stores: StoresManager = ServiceLocator.stores,
         featureFlagService: FeatureFlagService = ServiceLocator.featureFlagService,
         imagesProductIDUpdater: ProductImagesProductIDUpdaterProtocol = ProductImagesProductIDUpdater(),
         imageStatusStorage: ProductImageStatusStorage = ProductImageStatusStorage()) {
        self.stores = stores
        self.featureFlagService = featureFlagService
        self.imagesProductIDUpdater = imagesProductIDUpdater
        self.imageStatusStorage = imageStatusStorage

        // Observe when the app enters background.
        NotificationCenter.default.addObserver(self,
                                               selector: #selector(appDidEnterBackground),
                                               name: UIApplication.didEnterBackgroundNotification,
                                               object: nil)
    }

    deinit {
        NotificationCenter.default.removeObserver(self)
    }

    func actionHandler(key: ProductImageUploaderKey, originalStatuses: [ProductImageStatus]) -> ProductImageActionHandler {
        let actionHandler: ProductImageActionHandler
        if let handler = actionHandlersByProduct[key] {
            actionHandler = handler
        } else {
            actionHandler = ProductImageActionHandler(siteID: key.siteID, productID: key.productOrVariationID, imageStatuses: originalStatuses, stores: stores)
            actionHandlersByProduct[key] = actionHandler
            observeStatusUpdates(key: key, actionHandler: actionHandler)
            observeImageUploads(key: key, actionHandler: actionHandler)
        }

        return actionHandler
    }

    func replaceLocalID(siteID: Int64, localID: ProductOrVariationID, remoteID: Int64) {
        let key = Key(siteID: siteID,
                      productOrVariationID: localID,
                      isLocalID: true)
        guard let handler = actionHandlersByProduct[key] else {
            return
        }

        // Update the product ID of handler to make sure that future product image uploads use the `remoteProductID` instead of `localProductID`
        let remoteProductOrVariationID = localID.replacingID(remoteID)
        handler.updateProductID(remoteProductOrVariationID)

        actionHandlersByProduct.removeValue(forKey: key)
        let keyWithRemoteProductID = Key(siteID: siteID,
                                         productOrVariationID: remoteProductOrVariationID,
                                         isLocalID: false)
        actionHandlersByProduct[keyWithRemoteProductID] = handler

        statusUpdatesExcludedProductKeys.remove(key)
        statusUpdatesExcludedProductKeys.insert(keyWithRemoteProductID)
    }

    func stopEmittingErrors(key: ProductImageUploaderKey) {
        statusUpdatesExcludedProductKeys.insert(key)
    }

    func startEmittingErrors(key: ProductImageUploaderKey) {
        statusUpdatesExcludedProductKeys.remove(key)
    }

    func sendBackgroundUploadNoticeIfNeeded(key: ProductImageUploaderKey, using noticePresenter: NoticePresenter) {
        if featureFlagService.isFeatureFlagEnabled(.backgroundProductImageUpload) {
            let statuses = imageStatusStorage.getAllStatuses(for: key.siteID, productID: key.productOrVariationID)
            if statuses.contains(where: { $0.isUploading }) {
                let notice = Notice(title: Localization.backgroundUploadNoticeTitle)
                noticePresenter.enqueue(notice: notice)
            }
        } else {
            if activeUploadsPublisher.contains(key) {
                let notice = Notice(title: Localization.backgroundUploadNoticeTitle)
                noticePresenter.enqueue(notice: notice)
            }
        }
    }

    func hasUnsavedChangesOnImages(key: ProductImageUploaderKey, originalImages: [ProductImage]) -> Bool {
        guard let handler = actionHandlersByProduct[key] else {
            return false
        }
        let productImagesSaver = imagesSaverByProduct[key]

        if let productImagesSaver, productImagesSaver.imageStatusesToSave.isNotEmpty {
            // If there are images scheduled to be saved, there are no unsaved changes if the image statuses to save match the latest image statuses.
            return handler.productImageStatuses.images != productImagesSaver.imageStatusesToSave.images
        } else {
            if handler.productImageStatuses.hasPendingUpload {
                return true
            }

            /// If there's a product saved in background, compare the images to determine unsaved changes.
            if let savedProduct = productImagesSaver?.savedProduct {
                return handler.productImageStatuses.images.map { $0.imageID } != savedProduct.images.map { $0.imageID }
            }

            // Otherwise, there are unsaved changes if there is any difference in the remote image IDs between the
            // original and latest product.
            return handler.productImageStatuses.images.map { $0.imageID } != originalImages.map { $0.imageID }
        }
    }

    func saveProductImagesWhenNoneIsPendingUploadAnymore(key: ProductImageUploaderKey,
                                                         onProductSave: @escaping (Result<[ProductImage], Error>) -> Void) {
        // The product has to exist remotely in order to save its images remotely.
        // In product creation, this save function should be called after a new product is saved remotely for the first time.
        guard key.isLocalID == false else {
            return onProductSave(.failure(ProductImageUploaderError.noRemoteProductIDFound))
        }

        guard let handler = actionHandlersByProduct[key] else {
            return onProductSave(.failure(ProductImageUploaderError.noActionHandlerFound))
        }

        let imagesSaver: ProductImagesSaver
        if let productImagesSaver = imagesSaverByProduct[key] {
            imagesSaver = productImagesSaver
        } else {
            imagesSaver = ProductImagesSaver(siteID: key.siteID,
                                             productOrVariationID: key.productOrVariationID,
                                             stores: stores)
            imagesSaverByProduct[key] = imagesSaver
        }

        imagesSaver.saveProductImagesWhenNoneIsPendingUploadAnymore(imageActionHandler: handler) { [weak self] result in
            guard let self = self else { return }
            onProductSave(result)
            if case let .failure(error) = result {
                self.errorsSubject.send(.init(siteID: key.siteID,
                                              productOrVariationID: key.productOrVariationID,
                                              error: .failedSavingProductAfterImageUpload(error: error)))
            }
            self.updateProductIDOfImagesUploadedUsingLocalProductID(siteID: key.siteID,
                                                                    productOrVariationID: key.productOrVariationID,
                                                                    images: handler.productImageStatuses.images)
        }
    }

    func reset() {
        statusUpdatesExcludedProductKeys = []
        statusUpdatesSubscriptions = []
        imageUploadSubscriptions = []
        activeUploadsPublisher = []

        imageStatusStorage.clearAllStatuses()

        actionHandlersByProduct = [:]
        imagesSaverByProduct = [:]
    }

    private func scheduleUploadInProgressNotificationIfNeeded() {
        if featureFlagService.isFeatureFlagEnabled(.backgroundProductImageUpload) {
            let statuses = imageStatusStorage.getAllStatuses()
            let hasUploadingStatuses = statuses.contains { $0.isUploading }

            if hasUploadingStatuses {
                let notification = LocalNotification(scenario: .productImageBackgroundUpload)
                let trigger = UNTimeIntervalNotificationTrigger(timeInterval: 1, repeats: false)
                Task {
                    await LocalNotificationScheduler(pushNotesManager: ServiceLocator.pushNotesManager).schedule(notification: notification,
                                                                                                                trigger: trigger, remoteFeatureFlag: nil)
                }
            }
        } else {
            guard !activeUploadsPublisher.isEmpty else { return }

            let notification = LocalNotification(scenario: .productImageBackgroundUpload)
            let trigger = UNTimeIntervalNotificationTrigger(timeInterval: 1, repeats: false)
            Task {
                await LocalNotificationScheduler(pushNotesManager: ServiceLocator.pushNotesManager).schedule(notification: notification,
                                                                                                             trigger: trigger, remoteFeatureFlag: nil)
            }
        }
    }

    @objc private func appDidEnterBackground() {
        self.scheduleUploadInProgressNotificationIfNeeded()
    }
}

private extension ProductImageUploader {
    /// Called to replace the local product ID with remote product ID for the previously uploaded images
    ///
    func updateProductIDOfImagesUploadedUsingLocalProductID(siteID: Int64,
                                                            productOrVariationID: ProductOrVariationID,
                                                            images: [ProductImage]) {
        images.forEach { image in
            Task {
                _ = try? await imagesProductIDUpdater.updateImageProductID(siteID: siteID,
                                                                           productID: productOrVariationID.id,
                                                                           productImage: image)
            }
        }
    }

    func observeStatusUpdates(key: Key, actionHandler: ProductImageActionHandler) {
        let observationToken = actionHandler.addUpdateObserver(self) { [weak self] productImageStatuses in
            guard let self = self else { return }

            if featureFlagService.isFeatureFlagEnabled(.backgroundProductImageUpload) {
                // Update the states in userDefaultsStatuses
                self.imageStatusStorage.appendStatuses(productImageStatuses, for: key.siteID, productID: key.productOrVariationID)
            }
            else {
                if !activeUploadsPublisher.contains(key), productImageStatuses.hasPendingUpload {
                    activeUploadsPublisher.append(key)
                } else if activeUploadsPublisher.contains(key), !productImageStatuses.hasPendingUpload {
                    /// When all pending uploads are completed or removed,
                    /// remove the key from active uploads
                    removeProductFromActiveUploads(key: key)
                }
            }
        }
        statusUpdatesSubscriptions.insert(observationToken)
    }

    func observeImageUploads(key: Key, actionHandler: ProductImageActionHandler) {
        let observationToken = actionHandler.addAssetUploadObserver(self) { [weak self] asset, result in
            guard let self else { return }

            if case .failure(let error) = result {
                let infoError = ProductImageUploadErrorInfo(siteID: key.siteID,
                                                            productOrVariationID: key.productOrVariationID,
                                                            error: .failedUploadingImage(asset: asset, error: error))
                if statusUpdatesExcludedProductKeys.contains(key) == false {
                    if !self.featureFlagService.isFeatureFlagEnabled(.backgroundProductImageUpload) {
                        // Only send the error directly if `backgroundProductImageUpload` feature flag is disabled
                        errorsSubject.send(infoError)
                    }
                    // To keep in mind
                    // Do not update storage here as the action handler will update its status
                    // which will trigger `observeStatusUpdates` to do the storage update
                }
            }
        }
        imageUploadSubscriptions.insert(observationToken)
    }

    func removeProductFromActiveUploads(key: Key) {
        if featureFlagService.isFeatureFlagEnabled(.backgroundProductImageUpload) {
            imageStatusStorage.removeStatus(where: { status in
                status.siteID == key.siteID &&
                status.productOrVariationID == key.productOrVariationID &&
                status.isUploading
            })
        } else {
            activeUploadsPublisher.removeAll(where: { $0 == key })
        }
    }
}

private extension ProductOrVariationID {
    func replacingID(_ id: Int64) -> ProductOrVariationID {
        switch self {
        case .product:
            return .product(id: id)
        case .variation(let productID, _):
            return .variation(productID: productID, variationID: id)
        }
    }
}

/// Possible errors from background image upload.
enum ProductImageUploaderError: Error {
    case noActionHandlerFound
    case noRemoteProductIDFound
    case failedSavingProductAfterImageUpload(error: Error)
    case failedUploadingImage(asset: ProductImageAssetType, error: Error)
}

private enum Localization {
    static let backgroundUploadNoticeTitle = NSLocalizedString(
        "productImageUploader.backgroundUploadNotice.title",
        value: "Image uploading will continue in the background",
        comment: ""
    )
}