GifExporter.swift

//
//  GifExporter.swift
//  Flipbook
//
//  Created by Matthias Buchetics on 02.12.20.
//  Copyright © 2020 Tinkado. All rights reserved.
//

import Foundation
import UIKit
import ImageIO
import MobileCoreServices

struct GifExporterSettings {

    var size: CGSize
    var fps: Int
    var loop: Bool
    var filename: String
    var filenameExt = "gif"
    
    init(size: CGSize, fps: Int, loop: Bool, fileName: String = "flipbook") {
        self.size = size
        self.fps = fps
        self.loop = loop
        self.filename = fileName
    }
    
    var outputURL: URL {
        cacheURL(filename: filename, ext: filenameExt)
    }
}

class GifExporter: Exporter {
    
    let settings: GifExporterSettings

    init(settings: GifExporterSettings) {
        self.settings = settings
    }
    
    func export(frames: [LazyFrame], completion: @escaping (Result<URL, ExportError>) -> Void) {
        try? FileManager.default.removeItem(atPath: settings.outputURL.path)

        let fileProperties: CFDictionary = [kCGImagePropertyGIFDictionary as String: [
            kCGImagePropertyGIFLoopCount as String: settings.loop ? 0 : 1
        ]] as CFDictionary
        
        let frameProperties: CFDictionary = [kCGImagePropertyGIFDictionary as String: [
            kCGImagePropertyGIFDelayTime as String: 1.0 / Double(settings.fps)
        ]] as CFDictionary
    
        guard
            let url = settings.outputURL as CFURL?,
            let destination = CGImageDestinationCreateWithURL(url, kUTTypeGIF, frames.count, nil)
        else {
            return
        }
        
        CGImageDestinationSetProperties(destination, fileProperties)

        for frame in frames {
            autoreleasepool {
                if let cgImage = frame.computeImage(settings.size).cgImage {
                    CGImageDestinationAddImage(destination, cgImage, frameProperties)
                }
            }
        }
        
        if CGImageDestinationFinalize(destination) {
            completion(.success(self.settings.outputURL))
        } else {
            completion(.failure(.undefined))
        }
    }
}