Tusker/Tusker/Caching/ImageCache.swift

//
//  ImageCache.swift
//  Tusker
//
//  Created by Shadowfacts on 8/21/18.
//  Copyright © 2018 Shadowfacts. All rights reserved.
//

import UIKit
import Cache

class ImageCache {
    
    static let avatars = ImageCache(name: "Avatars", memoryExpiry: .seconds(60 * 60), diskExpiry: .seconds(60 * 60 * 24))
    static let headers = ImageCache(name: "Headers", memoryExpiry: .seconds(60 * 60), diskExpiry: .seconds(60 * 60 * 24))
    static let attachments = ImageCache(name: "Attachments", memoryExpiry: .seconds(60 * 2))

    let cache: Cache<UIImage>
    
    var requests = [URL: Request]()
    
    init(name: String, memoryExpiry expiry: Expiry) {
        let storage = MemoryStorage<UIImage>(config: MemoryConfig(expiry: expiry))
        self.cache = .memory(storage)
    }
    
    init(name: String, diskExpiry expiry: Expiry) {
        let storage = try! DiskStorage<UIImage>(config: DiskConfig(name: name, expiry: expiry), transformer: TransformerFactory.forImage())
        self.cache = .disk(storage)
    }
    
    init(name: String, memoryExpiry: Expiry, diskExpiry: Expiry) {
        let memory = MemoryStorage<UIImage>(config: MemoryConfig(expiry: memoryExpiry))
        let disk = try! DiskStorage<UIImage>(config: DiskConfig(name: name, expiry: diskExpiry), transformer: TransformerFactory.forImage())
        self.cache = .hybrid(HybridStorage(memoryStorage: memory, diskStorage: disk))
    }
    
    func get(_ url: URL, completion: ((UIImage?) -> Void)?) {
        let key = url.absoluteString
        if (try? cache.existsObject(forKey: key)) ?? false,
            let image = try? cache.object(forKey: key) {
            completion?(image)
        } else {
            if let completion = completion, let request = requests[url] {
                request.callbacks.append(completion)
            } else {
                let request = Request(url: url, completion: completion)
                requests[url] = request
                request.run { (image) in
                    try? self.cache.setObject(image, forKey: key)
                }
            }
        }
    }
    
    func get(_ url: URL) -> UIImage? {
        return try? cache.object(forKey: url.absoluteString)
    }
    
    func cancel(_ url: URL) {
        requests[url]?.cancel()
    }
    
    class Request {
        let url: URL
        var task: URLSessionDataTask?
        var callbacks: [(UIImage?) -> Void]
        
        init(url: URL, completion: ((UIImage?) -> Void)?) {
            if let completion = completion {
                self.callbacks = [completion]
            } else {
                self.callbacks = []
            }
            self.url = url
        }
        
        func run(cache: @escaping (UIImage) -> Void) {
            task = URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in
                guard error == nil, let data = data, let image = UIImage(data: data) else {
                    self.complete(with: nil)
                    return
                }
                cache(image)
                self.complete(with: image)
            })
            task!.resume()
        }
        
        func cancel() {
            task?.cancel()
            complete(with: nil)
        }
        
        func complete(with image: UIImage?) {
            callbacks.forEach { $0(image) }
        }
    }
    
}