metatext/View Models/EditFilterViewModel.swift

// Copyright © 2020 Metabolist. All rights reserved.

import Foundation
import Combine

class EditFilterViewModel: ObservableObject {
    @Published var filter: Filter
    @Published var saving = false
    @Published var alertItem: AlertItem?
    let saveCompleted: AnyPublisher<Void, Never>

    var date: Date {
        didSet { filter.expiresAt = date }
    }

    private let identityService: IdentityService
    private let saveCompletedInput = PassthroughSubject<Void, Never>()
    private var cancellables = Set<AnyCancellable>()

    init(filter: Filter, identityService: IdentityService) {
        self.filter = filter
        self.identityService = identityService
        date = filter.expiresAt ?? Date()
        saveCompleted = saveCompletedInput.eraseToAnyPublisher()
    }
}

extension EditFilterViewModel {
    var isNew: Bool { filter.id == Filter.newFilterID }

    var isSaveDisabled: Bool { filter.phrase == "" || filter.context.isEmpty }

    func toggleSelection(context: Filter.Context) {
        if filter.context.contains(context) {
            filter.context.removeAll { $0 == context }
        } else {
            filter.context.append(context)
        }
    }

    func save() {
        (isNew ? identityService.createFilter(filter) : identityService.updateFilter(filter))
            .assignErrorsToAlertItem(to: \.alertItem, on: self)
            .handleEvents(
                receiveSubscription: { [weak self] _ in self?.saving = true },
                receiveCompletion: { [weak self] in
                    guard let self = self else { return }

                    self.saving = false

                    if case .finished = $0 {
                        self.saveCompletedInput.send(())
                    }
                })
            .sink { _ in }
            .store(in: &cancellables)
    }
}