Tusker/Tusker/Views/CachedImageView.swift

//
//  CachedImageView.swift
//  Tusker
//
//  Created by Shadowfacts on 10/4/22.
//  Copyright © 2022 Shadowfacts. All rights reserved.
//

import UIKit

class CachedImageView: UIImageView {
    
    private let cache: ImageCache
    private var url: URL?
    private var isGrayscale = false
    private var fetchTask: Task<Void, Error>?
    
    init(cache: ImageCache) {
        self.cache = cache
        
        super.init(frame: .zero)
        
        NotificationCenter.default.addObserver(self, selector: #selector(preferencesChanged), name: .preferencesChanged, object: nil)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    func update(for url: URL?) {
        if url != self.url {
            self.url = url
            updateImage()
        }
    }
    
    @objc private func preferencesChanged() {
        if isGrayscale != Preferences.shared.grayscaleImages {
            updateImage()
        }
    }
    
    private func updateImage() {
        fetchTask?.cancel()
        fetchTask = Task(priority: .high) {
            self.image = nil
            guard let url else {
                return
            }
            let (_, image) = await cache.get(url)
            guard let image else {
                return
            }
            try Task.checkCancellation()
            // TODO: check that this isn't on the main thread
            guard let transformedImage = ImageGrayscalifier.convertIfNecessary(url: url, image: image) else {
                return
            }
            try Task.checkCancellation()
            self.image = transformedImage
        }
    }
    
}