Kingfisher/Sources/Cache/CacheSerializer.swift

//
//  CacheSerializer.swift
//  Kingfisher
//
//  Created by Wei Wang on 2016/09/02.
//
//  Copyright (c) 2018 Wei Wang <onevcat@gmail.com>
//
//  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 Foundation

/// An `CacheSerializer` is used to convert some data to an image object after
/// retrieving it from disk storage, and vice versa, to convert an image to data object
/// for storing to the disk storage.
public protocol CacheSerializer {
    
    /// Gets the serialized data from a provided image
    /// and optional original data for caching to disk.
    ///
    /// - Parameters:
    ///   - image: The image needed to be serialized.
    ///   - original: The original data which is just downloaded.
    ///               If the image is retrieved from cache instead of
    ///               downloaded, it will be `nil`.
    /// - Returns: The data object for storing to disk, or `nil` when no valid
    ///            data could be serialized.
    func data(with image: Image, original: Data?) -> Data?
    
    /// Gets an image deserialized from provided data.
    ///
    /// - Parameters:
    ///   - data: The data from which an image should be deserialized.
    ///   - options: Options for deserialization.
    /// - Returns: An image deserialized or `nil` when no valid image
    ///            could be deserialized.
    func image(with data: Data, options: KingfisherOptionsInfo?) -> Image?
}

/// Represents a basic and default `CacheSerializer` used in Kingfisher disk cache system.
/// It could serialize and deserialize images in PNG, JEPG and GIF format. For
/// image other than these formats, a normalized `pngRepresentation` will be used.
public struct DefaultCacheSerializer: CacheSerializer {
    
    /// The default general cache serializer used across Kingfisher's cache.
    public static let `default` = DefaultCacheSerializer()
    private init() {}
    
    /// - Parameters:
    ///   - image: The image needed to be serialized.
    ///   - original: The original data which is just downloaded.
    ///               If the image is retrieved from cache instead of
    ///               downloaded, it will be `nil`.
    /// - Returns: The data object for storing to disk, or `nil` when no valid
    ///            data could be serialized.
    ///
    /// - Note:
    /// Only when `original` contains valid PNG, JEPG and GIF format data, the `image` will be
    /// converted to the corresponding data type. Otherwise, if the `original` is provided but it is not
    /// a valid format, the `original` data will be used for cache.
    ///
    /// If `original` is `nil`, the input `image` will be encoded as PNG data.
    public func data(with image: Image, original: Data?) -> Data? {
        let imageFormat = original?.kf.imageFormat ?? .unknown

        let data: Data?
        switch imageFormat {
        case .PNG: data = image.kf.pngRepresentation()
        case .JPEG: data = image.kf.jpegRepresentation(compressionQuality: 1.0)
        case .GIF: data = image.kf.gifRepresentation()
        case .unknown: data = original ?? image.kf.normalized.kf.pngRepresentation()
        }

        return data
    }
    
    /// Gets an image deserialized from provided data.
    ///
    /// - Parameters:
    ///   - data: The data from which an image should be deserialized.
    ///   - options: Options for deserialization.
    /// - Returns: An image deserialized or `nil` when no valid image
    ///            could be deserialized.
    public func image(with data: Data, options: KingfisherOptionsInfo?) -> Image? {
        let options = options ?? .empty
        return KingfisherClass.image(data: data, options: options.imageCreatingOptions)
    }
}