A tiny and still kinda work in progress Image Cache along with convenient loader class DataService

ImageCache-iOS.swift

//
//  ImageCache.swift
//  HMTestApp
//
//  Created by Daniel Bonates on 05/12/21.
//  Modified by Daniel Bonates on 05/12/21.

import UIKit

final class ImageCache {

    private static let appImageFolder = "images"

    private static var cacheURL: URL {
        return FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!.appendingPathComponent("cache")
    }

    static func getImage(for url: URL, completion: @escaping (UIImage?) -> ()) throws {

        let destinationPath = cacheURL.appendingPathComponent(url.lastPathComponent)

        if FileManager.default.fileExists(atPath: destinationPath.path) {

            if let image = UIImage(contentsOfFile: destinationPath.path) {
                completion(image)
                return
            } else {
                throw APIError.invalidData
            }

        }

        let imgResource = Resource<UIImage>(request: URLRequest(url: url), parse: { data in

            let destinationURL = cacheURL.appendingPathComponent(url.lastPathComponent)

            try? FileManager.default.createDirectory(
                atPath: self.cacheURL.path,
                withIntermediateDirectories: true,
                attributes: [:])

            do {
                try data.write(to: destinationURL)
            } catch let error {
                print(error.localizedDescription)
            }

            return UIImage(data: data)
        })

        WebService.load(resource: imgResource, completion: { image in
            completion(image)
        })

    }

    // util - clear the cache
    static func clearCache() {
        let fileManager = FileManager.default

        var isDir = ObjCBool(false)
        guard fileManager.fileExists(atPath: cacheURL.path, isDirectory: &isDir) else {
            print("nothing to clear")
            return
        }

        do {
            let files = try fileManager.contentsOfDirectory(atPath: cacheURL.path)
            for file in files {

                try fileManager.removeItem(atPath: cacheURL.path + "/" + file)
            }
        } catch let error as NSError {
            print("Could not clear temp folder: \(error.debugDescription)")
        }
    }
}

ImageCache-macos.swift

//
//  ImageCache.swift
//  Listing0
//
//  Created by Daniel Bonates on 05/03/17.
//  Copyright © 2017 Daniel Bonates. All rights reserved.
//

import Cocoa

final class ImageCache {

    private static let appImageFolder = "images"

    private static var cacheURL: URL {
        return FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!.appendingPathComponent("cache")
    }

    static func getImage(for url: URL, completion: @escaping (NSImage?) -> ()) throws {

        let destinationPath = cacheURL.appendingPathComponent(url.lastPathComponent)

        if FileManager.default.fileExists(atPath: destinationPath.path) {

            if let image = NSImage(contentsOfFile: destinationPath.path) {
                completion(image)
                return
            } else {
                throw APIError.invalidData
            }

        }

        let imgResource = Resource<NSImage>(request: URLRequest(url: url), parse: { data in

            let destinationURL = cacheURL.appendingPathComponent(url.lastPathComponent)

            try? FileManager.default.createDirectory(
                atPath: self.cacheURL.path,
                withIntermediateDirectories: true,
                attributes: [:])

            do {
                try data.write(to: destinationURL)
            } catch let error {
                print(error.localizedDescription)
            }

            return NSImage(data: data)
        })

        WebService.load(resource: imgResource, completion: { image in
            completion(image)
        })

    }

    // util - clear the cache
    static func clearCache() {
        let fileManager = FileManager.default

        var isDir = ObjCBool(false)
        guard fileManager.fileExists(atPath: cacheURL.path, isDirectory: &isDir) else {
            print("nothing to clear")
            return
        }

        do {
            let files = try fileManager.contentsOfDirectory(atPath: cacheURL.path)
            for file in files {

                try fileManager.removeItem(atPath: cacheURL.path + "/" + file)
            }
        } catch let error as NSError {
            print("Could not clear temp folder: \(error.debugDescription)")
        }
    }
}

WebService.swift

//
//  WebService.swift
//  Listing0
//
//  Created by Daniel Bonates on 05/03/17.
//  Copyright © 2017 Daniel Bonates. All rights reserved.
//

import Foundation

enum APIError: Error {
    case invalidURL
    case invalidData
    case invalidResponseFormat
    case unknown

    var errorMessage: String {
        switch self {
        case .invalidURL:
            return "invalid URL"
        case .invalidData:
            return "no data or invalid format to decode"
        case .invalidResponseFormat:
            return "response format unexpected"
        case .unknown:
            return "network error, not known"
        }
    }
}

struct Resource<T> {
    var request: URLRequest
    var parse: (Data) -> T?
}

final class WebService {
    static func load<T>(resource: Resource<T>, completion: @escaping (T?) -> ()) {
        (URLSession.shared.dataTask(with: resource.request, completionHandler: { data, response, error in
            guard error == nil else { print(error.debugDescription); return }
            guard
                let response = response as? HTTPURLResponse,
                response.statusCode == 200
            else {
                print("request failed.")
                return
            }
            guard let data = data else { completion(nil); return }
            completion(resource.parse(data))
        })).resume()
    }
}

TODO: this cache system could be upgraded and work as storage for any type. For download videos for offline viewing, for example. This could be accomplished by implementing a justDownload kind of function, with a Bool to return the status of the operation.