ImageFetcher

ImageFetcher.swift

import UIKit

public class ImageSizeFetcher: NSObject, URLSessionDataDelegate {
	
	/// Callback type alias
	public typealias Callback = ((Error?, ImageSizeFetcherParser?) -> (Void))
	
	/// URL Session used to download data
	private var session: URLSession!
	
	/// Queue of active operations
	private var queue = OperationQueue()
	
	/// Built-in in memory cache
	private var cache = NSCache<NSURL,ImageSizeFetcherParser>()
	
	/// Request timeout
	public var timeout: TimeInterval
	
	/// Initialize a new fetcher with in memory cache.
	///
	/// - Parameters:
	///   - configuration: url session configuration
	///   - timeout: timeout for request, by default is 5 seconds.
	public init(configuration: URLSessionConfiguration = .ephemeral, timeout: TimeInterval = 5) {
		self.timeout = timeout
		super.init()
		self.session = URLSession(configuration: configuration, delegate: self, delegateQueue: nil)
	}
	
	/// Request for image info at given url.
	///
	/// - Parameters:
	///   - url: url of the image you want to analyze.
	///   - force: true to skip cache and force download.
	///   - callback: completion callback called to give out the result.
	public func sizeFor(atURL url: URL, force: Bool = false, _ callback: @escaping Callback) {
		guard force == false, let entry = cache.object(forKey: (url as NSURL)) else {
			// we don't have a cached result or we want to force download
			let request = URLRequest(url: url, cachePolicy: .useProtocolCachePolicy, timeoutInterval: self.timeout)
			let op = ImageSizeFetcherOp(self.session.dataTask(with: request), callback: callback)
			queue.addOperation(op)
			return
		}
		// return result from cache
		callback(nil,entry)
	}
	
	//MARK: - Helper Methods
	
	private func operation(forTask task: URLSessionTask?) -> ImageSizeFetcherOp? {
		return (self.queue.operations as! [ImageSizeFetcherOp]).first(where: { $0.url == task?.currentRequest?.url })
	}
	
	//MARK: - URLSessionDataDelegate
	
	public func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
		operation(forTask: dataTask)?.onReceiveData(data)
	}
	
	public func urlSession(_ session: URLSession, task dataTask: URLSessionTask, didCompleteWithError error: Error?) {
		operation(forTask: dataTask)?.onEndWithError(error)
	}
	
}