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

import UIKit

class AvatarCache {
    
    static let shared = AvatarCache()
    
    let cache = NSCache<NSString, UIImage>()
    
    var requests = [URL: URLSessionDataTask]()
    var requestCallbacks = [URL: [(UIImage?) -> Void]]()
    
    
    
    private init() {
    }
    
    func get(_ url: URL, completion: @escaping (UIImage?) -> Void) {
        let key = url.absoluteString as NSString
        if let image = cache.object(forKey: key) {
            completion(image)
        } else if var callbacks = requestCallbacks[url] {
            callbacks.append(completion)
            requestCallbacks[url] = callbacks
        } else {
            requestCallbacks[url] = [completion]
            let task = URLSession.shared.dataTask(with: url) { data, response, error in
                guard error == nil, let data = data, let image = UIImage(data: data) else {
                        let callbacks = self.requestCallbacks.removeValue(forKey: url)
                        callbacks?.forEach({ callback in
                            // todo: default avatar for failed requests
                            callback(nil)
                        })
                        return
                }
                
                let callbacks = self.requestCallbacks.removeValue(forKey: url)
                callbacks?.forEach({ callback in
                    callback(image)
                })
                self.cache.setObject(image, forKey: key)
            }
            task.resume()
            requests[url] = task
        }
    }
    
    func cancel(_ url: URL) {
        requests[url]?.cancel()
        requests.removeValue(forKey: url)
        requestCallbacks.removeValue(forKey: url)
    }
    
}