passepartout-apple/PassepartoutLibrary/Sources/PassepartoutUtils/Reusable/FetchedValueHolder.swift

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//
// FetchedValueHolder.swift
// Passepartout
//
// Created by Davide De Rosa on 4/8/22.
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// Copyright (c) 2023 Davide De Rosa. All rights reserved.
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//
// https://github.com/passepartoutvpn
//
// This file is part of Passepartout.
//
// Passepartout is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Passepartout is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Passepartout. If not, see <http://www.gnu.org/licenses/>.
//
import Foundation
import CoreData
import Combine
public class FetchedValueHolder<V>: NSObject, ValueHolder, NSFetchedResultsControllerDelegate {
@Published public var value: V
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private let controller: NSFetchedResultsController<NSFetchRequestResult>
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private let mapping: ([NSFetchRequestResult]) -> V?
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public convenience init(
context: NSManagedObjectContext,
request: NSFetchRequest<NSFetchRequestResult>,
mapping: @escaping ([NSFetchRequestResult]) -> V?,
initial: V
) {
let controller = NSFetchedResultsController(
fetchRequest: request,
managedObjectContext: context,
sectionNameKeyPath: nil,
cacheName: nil
)
self.init(controller: controller, mapping: mapping, initial: initial)
}
public init(
controller: NSFetchedResultsController<NSFetchRequestResult>,
mapping: @escaping ([NSFetchRequestResult]) -> V?,
initial: V
) {
self.controller = controller
self.mapping = mapping
value = initial
super.init()
controller.delegate = self
do {
try controller.performFetch()
} catch {
pp_log.error("Unable to perform initial fetch: \(error)")
}
mapResults()
}
public func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
mapResults()
}
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private func mapResults() {
guard let results = controller.fetchedObjects else {
return
}
pp_log.verbose("Results: \(results)")
guard let newValue = mapping(results) else {
return
}
value = newValue
}
}