Make a GIF from a list of UIImages

GifBuilder.swift

//
//  GifBuilder.swift
//  Landscape
//
//  Created by Cameron Deardorff on 6/10/20.
//  Copyright © 2020 Cameron Deardorff. All rights reserved.
//

import UIKit
import ImageIO
import MobileCoreServices

struct GifBuilder {
    
    var frames: Int
    var duration: Float
    var fps: Float { return Float(frames) / duration }
    
    private var url: URL
    private var destination: CGImageDestination
    
    init?(frames: Int, duration: Float, name: String) {
        self.frames = frames
        self.duration = duration
        
        guard let documentsDirectoryURL = try? FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
            else { return nil }
        let filename = "\(name.replacingOccurrences(of: " ", with: "-")).gif"
        self.url = documentsDirectoryURL.appendingPathComponent(filename)

        guard let cfUrl = self.url as CFURL?,
            let destination = CGImageDestinationCreateWithURL(cfUrl, kUTTypeGIF, frames, nil)
            else { return nil }
        self.destination = destination
        
        let fileProperties: CFDictionary = [
            kCGImagePropertyGIFDictionary as String: [
                kCGImagePropertyGIFLoopCount as String: 0,
                kCGImagePropertyGIFHasGlobalColorMap as String: false]
            ] as CFDictionary
        CGImageDestinationSetProperties(destination, fileProperties)
    }
    
    func add(image: UIImage) {
        autoreleasepool {
            let frameProperties: CFDictionary = [
                kCGImagePropertyGIFDictionary as String: [
                    (kCGImagePropertyGIFDelayTime as String): 1.0 / fps, // spf
                    kCGImagePropertyGIFHasGlobalColorMap as String: false]
                ] as CFDictionary
            guard let cg = image.cgImage else { return }
            CGImageDestinationAddImage(destination, cg, frameProperties)
        }
    }
    
    func cancel() {
        autoreleasepool {
            CGImageDestinationFinalize(destination)
            try? FileManager.default.removeItem(at: url)
        }
    }
    
    func finish() -> URL? {
        guard CGImageDestinationFinalize(destination) else { return nil }
        return url
    }
}