metatext/ViewModels/Sources/ViewModels/CompositionViewModel.swift

// Copyright © 2020 Metabolist. All rights reserved.

import Combine
import Foundation
import Mastodon
import ServiceLayer

public final class CompositionViewModel: ObservableObject {
    public let composition: Composition
    @Published public private(set) var isPostable = false
    @Published public private(set) var identification: Identification
    @Published public private(set) var attachmentUpload: AttachmentUpload?

    private let eventsSubject: PassthroughSubject<Event, Never>
    private var cancellables = Set<AnyCancellable>()

    init(composition: Composition,
         identification: Identification,
         identificationPublisher: AnyPublisher<Identification, Never>,
         eventsSubject: PassthroughSubject<Event, Never>) {
        self.composition = composition
        self.identification = identification
        self.eventsSubject = eventsSubject
        identificationPublisher.assign(to: &$identification)
        composition.$text.map { !$0.isEmpty }.removeDuplicates().assign(to: &$isPostable)
    }
}

public extension CompositionViewModel {
    enum Event {
        case insertAfter(CompositionViewModel)
        case presentMediaPicker(CompositionViewModel)
        case error(Error)
    }

    struct AttachmentUpload {
        public let progress: Progress
        public let data: Data
        public let mimeType: String
    }

    func presentMediaPicker() {
        eventsSubject.send(.presentMediaPicker(self))
    }

    func insert() {
        eventsSubject.send(.insertAfter(self))
    }

    func attach(itemProvider: NSItemProvider) {
        let progress = Progress(totalUnitCount: 1)

        MediaProcessingService.dataAndMimeType(itemProvider: itemProvider)
            .flatMap { [weak self] data, mimeType -> AnyPublisher<Attachment, Error> in
                guard let self = self else { return Empty().eraseToAnyPublisher() }

                DispatchQueue.main.async {
                    self.attachmentUpload = AttachmentUpload(progress: progress, data: data, mimeType: mimeType)
                }

                return self.identification.service.uploadAttachment(data: data, mimeType: mimeType, progress: progress)
            }
            .print()
            .sink { [weak self] in
                DispatchQueue.main.async {
                    self?.attachmentUpload = nil
                }

                if case let .failure(error) = $0 {
                    self?.eventsSubject.send(.error(error))
                }
            } receiveValue: { [weak self] in
                self?.composition.attachments.append($0)
            }
            .store(in: &cancellables)
    }
}