// ImageCache.swift
//
// Copyright (c) 2015-2016 Alamofire Software Foundation (http://alamofire.org/)
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

import Alamofire
import Foundation

#if os(iOS) || os(tvOS) || os(watchOS)
import UIKit
#elseif os(OSX)
import Cocoa
#endif

// MARK: ImageCache

/// The `ImageCache` protocol defines a set of APIs for adding, removing and fetching images from a cache.
public protocol ImageCache {
    /// Adds the image to the cache with the given identifier.
    func addImage(image: Image, withIdentifier identifier: String)

    /// Removes the image from the cache matching the given identifier.
    func removeImageWithIdentifier(identifier: String) -> Bool

    /// Removes all images stored in the cache.
    func removeAllImages() -> Bool

    /// Returns the image in the cache associated with the given identifier.
    func imageWithIdentifier(identifier: String) -> Image?
}

/// The `ImageRequestCache` protocol extends the `ImageCache` protocol by adding methods for adding, removing and
/// fetching images from a cache given an `NSURLRequest` and additional identifier.
public protocol ImageRequestCache: ImageCache {
    /// Adds the image to the cache using an identifier created from the request and additional identifier.
    func addImage(image: Image, forRequest request: NSURLRequest, withAdditionalIdentifier identifier: String?)

    /// Removes the image from the cache using an identifier created from the request and additional identifier.
    func removeImageForRequest(request: NSURLRequest, withAdditionalIdentifier identifier: String?) -> Bool

    /// Returns the image from the cache associated with an identifier created from the request and additional identifier.
    func imageForRequest(request: NSURLRequest, withAdditionalIdentifier identifier: String?) -> Image?
}

// MARK: -

/// The `AutoPurgingImageCache` in an in-memory image cache used to store images up to a given memory capacity. When 
/// the memory capacity is reached, the image cache is sorted by last access date, then the oldest image is continuously 
/// purged until the preferred memory usage after purge is met. Each time an image is accessed through the cache, the 
/// internal access date of the image is updated.
public class AutoPurgingImageCache: ImageRequestCache {
    private class CachedImage {
        let image: Image
        let identifier: String
        let totalBytes: UInt64
        var lastAccessDate: NSDate

        init(_ image: Image, identifier: String) {
            self.image = image
            self.identifier = identifier
            self.lastAccessDate = NSDate()

            self.totalBytes = {
                #if os(iOS) || os(tvOS) || os(watchOS)
                    let size = CGSize(width: image.size.width * image.scale, height: image.size.height * image.scale)
                #elseif os(OSX)
                    let size = CGSize(width: image.size.width, height: image.size.height)
                #endif

                let bytesPerPixel: CGFloat = 4.0
                let bytesPerRow = size.width * bytesPerPixel
                let totalBytes = UInt64(bytesPerRow) * UInt64(size.height)

                return totalBytes
            }()
        }

        func accessImage() -> Image {
            lastAccessDate = NSDate()
            return image
        }
    }

    // MARK: Properties

    /// The current total memory usage in bytes of all images stored within the cache.
    public var memoryUsage: UInt64 {
        var memoryUsage: UInt64 = 0
        dispatch_sync(synchronizationQueue) { memoryUsage = self.currentMemoryUsage }

        return memoryUsage
    }

    /// The total memory capacity of the cache in bytes.
    public let memoryCapacity: UInt64

    /// The preferred memory usage after purge in bytes. During a purge, images will be purged until the memory 
    /// capacity drops below this limit.
    public let preferredMemoryUsageAfterPurge: UInt64

    private let synchronizationQueue: dispatch_queue_t
    private var cachedImages: [String: CachedImage]
    private var currentMemoryUsage: UInt64

    // MARK: Initialization

    /**
        Initialies the `AutoPurgingImageCache` instance with the given memory capacity and preferred memory usage 
        after purge limit.

        Please note, the memory capacity must always be greater than or equal to the preferred memory usage after purge.

        - parameter memoryCapacity:                 The total memory capacity of the cache in bytes. `100 MB` by default.
        - parameter preferredMemoryUsageAfterPurge: The preferred memory usage after purge in bytes. `60 MB` by default.

        - returns: The new `AutoPurgingImageCache` instance.
    */
    public init(memoryCapacity: UInt64 = 100_000_000, preferredMemoryUsageAfterPurge: UInt64 = 60_000_000) {
        self.memoryCapacity = memoryCapacity
        self.preferredMemoryUsageAfterPurge = preferredMemoryUsageAfterPurge

        precondition(
            memoryCapacity >= preferredMemoryUsageAfterPurge,
            "The `memoryCapacity` must be greater than or equal to `preferredMemoryUsageAfterPurge`"
        )

        self.cachedImages = [:]
        self.currentMemoryUsage = 0

        self.synchronizationQueue = {
            let name = String(format: "com.alamofire.autopurgingimagecache-%08%08", arc4random(), arc4random())
            return dispatch_queue_create(name, DISPATCH_QUEUE_CONCURRENT)
        }()

        #if os(iOS)
            NSNotificationCenter.defaultCenter().addObserver(
                self,
                selector: "removeAllImages",
                name: UIApplicationDidReceiveMemoryWarningNotification,
                object: nil
            )
        #endif
    }

    deinit {
        NSNotificationCenter.defaultCenter().removeObserver(self)
    }

    // MARK: Add Image to Cache

    /**
        Adds the image to the cache using an identifier created from the request and optional identifier.

        - parameter image:      The image to add to the cache.
        - parameter request:    The request used to generate the image's unique identifier.
        - parameter identifier: The additional identifier to append to the image's unique identifier.
    */
    public func addImage(image: Image, forRequest request: NSURLRequest, withAdditionalIdentifier identifier: String? = nil) {
        let requestIdentifier = imageCacheKeyFromURLRequest(request, withAdditionalIdentifier: identifier)
        addImage(image, withIdentifier: requestIdentifier)
    }

    /**
        Adds the image to the cache with the given identifier.

        - parameter image:      The image to add to the cache.
        - parameter identifier: The identifier to use to uniquely identify the image.
    */
    public func addImage(image: Image, withIdentifier identifier: String) {
        dispatch_barrier_async(synchronizationQueue) {
            let cachedImage = CachedImage(image, identifier: identifier)

            if let previousCachedImage = self.cachedImages[identifier] {
                self.currentMemoryUsage -= previousCachedImage.totalBytes
            }

            self.cachedImages[identifier] = cachedImage
            self.currentMemoryUsage += cachedImage.totalBytes
        }

        dispatch_barrier_async(synchronizationQueue) {
            if self.currentMemoryUsage > self.memoryCapacity {
                let bytesToPurge = self.currentMemoryUsage - self.preferredMemoryUsageAfterPurge

                var sortedImages = [CachedImage](self.cachedImages.values)
                sortedImages.sortInPlace {
                    let date1 = $0.lastAccessDate
                    let date2 = $1.lastAccessDate

                    return date1.timeIntervalSinceDate(date2) < 0.0
                }

                var bytesPurged = UInt64(0)

                for cachedImage in sortedImages {
                    self.cachedImages.removeValueForKey(cachedImage.identifier)
                    bytesPurged += cachedImage.totalBytes

                    if bytesPurged >= bytesToPurge {
                        break
                    }
                }

                self.currentMemoryUsage -= bytesPurged
            }
        }
    }

    // MARK: Remove Image from Cache

    /**
        Removes the image from the cache using an identifier created from the request and optional identifier.

        - parameter request:    The request used to generate the image's unique identifier.
        - parameter identifier: The additional identifier to append to the image's unique identifier.

        - returns: `true` if the image was removed, `false` otherwise.
    */
    public func removeImageForRequest(request: NSURLRequest, withAdditionalIdentifier identifier: String?) -> Bool {
        let requestIdentifier = imageCacheKeyFromURLRequest(request, withAdditionalIdentifier: identifier)
        return removeImageWithIdentifier(requestIdentifier)
    }

    /**
        Removes the image from the cache matching the given identifier.

        - parameter identifier: The unique identifier for the image.

        - returns: `true` if the image was removed, `false` otherwise.
    */
    public func removeImageWithIdentifier(identifier: String) -> Bool {
        var removed = false

        dispatch_barrier_async(synchronizationQueue) {
            if let cachedImage = self.cachedImages.removeValueForKey(identifier) {
                self.currentMemoryUsage -= cachedImage.totalBytes
                removed = true
            }
        }

        return removed
    }

    /**
        Removes all images stored in the cache.

        - returns: `true` if images were removed from the cache, `false` otherwise.
    */
    @objc public func removeAllImages() -> Bool {
        var removed = false

        dispatch_sync(synchronizationQueue) {
            if !self.cachedImages.isEmpty {
                self.cachedImages.removeAll()
                self.currentMemoryUsage = 0

                removed = true
            }
        }

        return removed
    }

    // MARK: Fetch Image from Cache

    /**
        Returns the image from the cache associated with an identifier created from the request and optional identifier.

        - parameter request:    The request used to generate the image's unique identifier.
        - parameter identifier: The additional identifier to append to the image's unique identifier.

        - returns: The image if it is stored in the cache, `nil` otherwise.
    */
    public func imageForRequest(request: NSURLRequest, withAdditionalIdentifier identifier: String? = nil) -> Image? {
        let requestIdentifier = imageCacheKeyFromURLRequest(request, withAdditionalIdentifier: identifier)
        return imageWithIdentifier(requestIdentifier)
    }

    /**
        Returns the image in the cache associated with the given identifier.

        - parameter identifier: The unique identifier for the image.

        - returns: The image if it is stored in the cache, `nil` otherwise.
    */
    public func imageWithIdentifier(identifier: String) -> Image? {
        var image: Image?

        dispatch_sync(synchronizationQueue) {
            if let cachedImage = self.cachedImages[identifier] {
                image = cachedImage.accessImage()
            }
        }

        return image
    }

    // MARK: Private - Helper Methods

    private func imageCacheKeyFromURLRequest(
        request: NSURLRequest,
        withAdditionalIdentifier identifier: String?)
        -> String
    {
        var key = request.URLString

        if let identifier = identifier {
            key += "-\(identifier)"
        }

        return key
    }
}