//Kingfisher.swift
public final class Kingfisher<Base> {
    public let base: Base
    public init(_ base: Base) {
        self.base = base
    }
}
/**
 A type that has Kingfisher extensions.
 */
public protocol KingfisherCompatible {
    associatedtype CompatibleType
    var kf: CompatibleType { get }
}

public extension KingfisherCompatible {
    public var kf: Kingfisher<Self> {
        return Kingfisher(self)
    }
}

extension Image: KingfisherCompatible { }

#if !os(watchOS)
extension ImageView: KingfisherCompatible { }
extension Button: KingfisherCompatible { }
#else
extension WKInterfaceImage: KingfisherCompatible { }
#endif

open class AnimatedImageView: UIImageView {
    
    /// Proxy object for prevending a reference cycle between the CADDisplayLink and AnimatedImageView.
    class TargetProxy {
        private weak var target: AnimatedImageView?
        
        init(target: AnimatedImageView) {
            self.target = target
        }
        
        @objc func onScreenUpdate() {
            target?.updateFrame()
        }
    }
    
    /// A display link that keeps calling the `updateFrame` method on every screen refresh.
    private lazy var displayLink: CADisplayLink = {
        self.isDisplayLinkInitialized = true
        let displayLink = CADisplayLink(target: TargetProxy(target: self), selector: #selector(TargetProxy.onScreenUpdate))
        displayLink.add(to: .main, forMode: self.runLoopMode)
        displayLink.isPaused = true
        return displayLink
    }()
    
    
}

// MARK: - Image format
private struct ImageHeaderData {
    static var PNG: [UInt8] = [0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A]
    static var JPEG_SOI: [UInt8] = [0xFF, 0xD8]
    static var JPEG_IF: [UInt8] = [0xFF]
    static var GIF: [UInt8] = [0x47, 0x49, 0x46]
}

public enum ImageFormat {
    case unknown, PNG, JPEG, GIF
}
extension DataProxy {
    public var imageFormat: ImageFormat {
        var buffer = [UInt8](repeating: 0, count: 8)
        (base as NSData).getBytes(&buffer, length: 8)
        if buffer == ImageHeaderData.PNG {
            return .PNG
        } else if buffer[0] == ImageHeaderData.JPEG_SOI[0] &&
            buffer[1] == ImageHeaderData.JPEG_SOI[1] &&
            buffer[2] == ImageHeaderData.JPEG_IF[0]
        {
            return .JPEG
        } else if buffer[0] == ImageHeaderData.GIF[0] &&
            buffer[1] == ImageHeaderData.GIF[1] &&
            buffer[2] == ImageHeaderData.GIF[2]
        {
            return .GIF
        }

        return .unknown
    }
}

private var animatedImageDataKey: Void?
private var imageSourceKey: Void?


// MARK: - Image Properties
extension Kingfisher where Base: Image {
    fileprivate(set) var animatedImageData: Data? {
        get {
            return objc_getAssociatedObject(base, &animatedImageDataKey) as? Data
        }
        set {
            objc_setAssociatedObject(base, &animatedImageDataKey, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }
      
    fileprivate(set) var imageSource: ImageSource? {
        get {
            return objc_getAssociatedObject(base, &imageSourceKey) as? ImageSource
        }
        set {
            objc_setAssociatedObject(base, &imageSourceKey, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }

}

/// Main manager class of Kingfisher. It connects Kingfisher downloader and cache.
/// You can use this class to retrieve an image via a specified URL from web or cache.
public class KingfisherManager {
    
    /// Shared manager used by the extensions across Kingfisher.
    public static let shared = KingfisherManager()
    
    /// Cache used by this manager
    public var cache: ImageCache
    
    /// Downloader used by this manager
    public var downloader: ImageDownloader

    fileprivate let processQueue: DispatchQueue
    
    convenience init() {
        self.init(downloader: .default, cache: .default)
    }
    
    init(downloader: ImageDownloader, cache: ImageCache) {
        self.downloader = downloader
        self.cache = cache

        let processQueueName = "com.onevcat.Kingfisher.KingfisherManager.processQueue.\(UUID().uuidString)"
        processQueue = DispatchQueue(label: processQueueName, attributes: .concurrent)
    }
      /**
    Get an image with resource.
    If KingfisherOptions.None is used as `options`, Kingfisher will seek the image in memory and disk first.
    If not found, it will download the image at `resource.downloadURL` and cache it with `resource.cacheKey`.
    These default behaviors could be adjusted by passing different options. See `KingfisherOptions` for more.
    
    - parameter resource:          Resource object contains information such as `cacheKey` and `downloadURL`.
    - parameter options:           A dictionary could control some behaviors. See `KingfisherOptionsInfo` for more.
    - parameter progressBlock:     Called every time downloaded data changed. This could be used as a progress UI.
    - parameter completionHandler: Called when the whole retrieving process finished.
    
    - returns: A `RetrieveImageTask` task object. You can use this object to cancel the task.
    */
    @discardableResult
    public func retrieveImage(with resource: Resource,
        options: KingfisherOptionsInfo?,
        progressBlock: DownloadProgressBlock?,
        completionHandler: CompletionHandler?) -> RetrieveImageTask
    {
        let task = RetrieveImageTask()
        let options = currentDefaultOptions + (options ?? KingfisherEmptyOptionsInfo)
        if options.forceRefresh {
            _ = downloadAndCacheImage(
                with: resource.downloadURL,
                forKey: resource.cacheKey,
                retrieveImageTask: task,
                progressBlock: progressBlock,
                completionHandler: completionHandler,
                options: options)
        } else {
            tryToRetrieveImageFromCache(
                forKey: resource.cacheKey,
                with: resource.downloadURL,
                retrieveImageTask: task,
                progressBlock: progressBlock,
                completionHandler: completionHandler,
                options: options)
        }
        
        return task
    }

}