frenzy-ios/Reader/Screens/Home/HomeCollectionViewCell.swift

//
//  HomeCollectionViewCell.swift
//  Reader
//
//  Created by Shadowfacts on 1/9/22.
//

import UIKit
import Fervor
import Persistence
import OSLog

private let signposter = OSSignposter(subsystem: "net.shadowfacts.Reader", category: "HomeCollectionViewCell")

class HomeCollectionViewCell: UICollectionViewListCell {
    
    private var currentItemCountTask: Task<Void, Never>?
    private var itemCount: Int?
    
    #if !targetEnvironment(macCatalyst)
    override func updateConfiguration(using state: UICellConfigurationState) {
        var backgroundConfig = UIBackgroundConfiguration.listGroupedCell().updated(for: state)
        if state.isHighlighted || state.isSelected {
            backgroundConfig.backgroundColor = .appCellHighlightBackground
        } else {
            backgroundConfig.backgroundColor = .appBackground
        }
        self.backgroundConfiguration = backgroundConfig
    }
    #endif
    
    override func prepareForReuse() {
        super.prepareForReuse()
        currentItemCountTask?.cancel()
        itemCount = nil
    }
    
    func updateUI(item: ItemListType, persistentContainer: PersistentContainer) {
        var config = UIListContentConfiguration.valueCell()
        config.text = item.title
        if let itemCount {
            config.secondaryText = itemCount.formatted(.number)
        }
        config.secondaryTextProperties.color = .tintColor
        self.contentConfiguration = config
        
        currentItemCountTask = Task(priority: .userInitiated) {
            let state = signposter.beginInterval("fetch count", id: signposter.makeSignpostID(), "\(String(item.hashValue, radix: 16), privacy: .public)")
            if let count = await fetchCount(item: item, in: persistentContainer),
               !Task.isCancelled {
                self.itemCount = count
                config.secondaryText = count.formatted(.number)
                self.contentConfiguration = config
            }
            signposter.endInterval("fetch count", state)
        }
    }
    
    private func fetchCount(item: ItemListType, in persistentContainer: PersistentContainer) async -> Int? {
        guard let request = item.countFetchRequest else {
            return nil
        }
        return await withCheckedContinuation({ continuation in
            let state = signposter.beginInterval("waiting to perform", id: signposter.makeSignpostID(), "\(String(item.hashValue, radix: 16), privacy: .public)")
            persistentContainer.performBackgroundTask { context in
                signposter.endInterval("waiting to perform", state)
                let state = signposter.beginInterval("count", id: signposter.makeSignpostID(), "\(String(item.hashValue, radix: 16), privacy: .public)")
                let count = try? context.count(for: request)
                signposter.endInterval("count", state)
                continuation.resume(returning: count)
            }
        })
    }
    
}