Kisani/Services/ThumbnailCache.swift

import UIKit

final class ThumbnailCache {
    static let shared = ThumbnailCache()

    private let memory = NSCache<NSString, UIImage>()
    private let diskDir: URL

    private init() {
        let caches = FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask)[0]
        diskDir = caches.appendingPathComponent("NASThumb", isDirectory: true)
        try? FileManager.default.createDirectory(at: diskDir, withIntermediateDirectories: true)
        memory.countLimit = 300
        memory.totalCostLimit = 80 * 1024 * 1024 // 80 MB
    }

    func get(for path: String) -> UIImage? {
        let key = cacheKey(path)
        if let img = memory.object(forKey: key as NSString) { return img }
        let url = diskDir.appendingPathComponent(key)
        guard let data = try? Data(contentsOf: url),
              let img = UIImage(data: data) else { return nil }
        memory.setObject(img, forKey: key as NSString, cost: data.count)
        return img
    }

    func set(_ image: UIImage, for path: String) {
        let key = cacheKey(path)
        let data = image.jpegData(compressionQuality: 0.7) ?? Data()
        memory.setObject(image, forKey: key as NSString, cost: data.count)
        let url = diskDir.appendingPathComponent(key)
        try? data.write(to: url, options: .atomic)
    }

    private func cacheKey(_ path: String) -> String {
        path
            .replacingOccurrences(of: "/", with: "_")
            .replacingOccurrences(of: ":", with: "-")
    }
}

extension ThumbnailCache {
    static func decodeOffThread(data: Data, size: CGFloat) async -> UIImage? {
        await Task.detached(priority: .userInitiated) {
            UIImage(data: data)?.thumbnailScaled(to: size)
        }.value
    }
}

extension UIImage {
    func thumbnailScaled(to size: CGFloat) -> UIImage {
        let scale = min(size / self.size.width, size / self.size.height)
        guard scale < 1 else { return self }
        let newSize = CGSize(width: self.size.width * scale, height: self.size.height * scale)
        let renderer = UIGraphicsImageRenderer(size: newSize)
        return renderer.image { _ in self.draw(in: CGRect(origin: .zero, size: newSize)) }
    }
}