CGImageSourceCreateThumbnailAtIndex 활용하는 이미지 크기 변경

URL+ImageResize.swift

import UIKit
import ImageIO

enum ImageResizeError: Error {
    case invalidMaxDimension
    case cannotCreateImageSource
    case cannotReadImageProperties
    case cannotCreateThumbnail
    case cannotEncodeJPEG
}

extension URL {
    func thumbnail(maxDimension: CGFloat = 1123.0) async throws -> URL {
        
        let imageSource = try await makeImageSource(from: self)
        
        guard let properties = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, nil) as? [CFString: Any] else {
            throw ImageResizeError.cannotReadImageProperties
        }
        
        guard
            let pixelWidth = properties[kCGImagePropertyPixelWidth] as? CGFloat,
            let pixelHeight = properties[kCGImagePropertyPixelHeight] as? CGFloat
        else {
            throw ImageResizeError.cannotReadImageProperties
        }
        
        let longestSide = max(pixelWidth, pixelHeight)
        let thumbnailMaxPixelSize = max(1, min(Int(maxDimension.rounded(.down)), Int(longestSide.rounded(.down))))
        
        let thumbnailOptions: [CFString: Any] = [
            kCGImageSourceCreateThumbnailFromImageAlways: true,
            kCGImageSourceCreateThumbnailWithTransform: true,
            kCGImageSourceShouldCache: false,
            kCGImageSourceThumbnailMaxPixelSize: thumbnailMaxPixelSize
        ]
        
        guard let thumbnail = CGImageSourceCreateThumbnailAtIndex(imageSource, 0, thumbnailOptions as CFDictionary) else {
            throw ImageResizeError.cannotCreateThumbnail
        }
        
        let image = UIImage(cgImage: thumbnail)
        
        guard let jpegData = image.jpegData(compressionQuality: 0.9) else {
            throw ImageResizeError.cannotEncodeJPEG
        }
        
        let tempURL = FileManager.default.temporaryDirectory
            .appendingPathComponent(UUID().uuidString)
            .appendingPathExtension("jpg")
        
        try jpegData.write(to: tempURL, options: .atomic)
        return tempURL
    }
    
    private func makeImageSource(from url: URL) async throws -> CGImageSource {
        if url.isFileURL {
            guard let source = CGImageSourceCreateWithURL(url as CFURL, nil) else {
                throw ImageResizeError.cannotCreateImageSource
            }
            return source
        }
        
        let (data, _) = try await URLSession.shared.data(from: url)
        
        guard let source = CGImageSourceCreateWithData(data as CFData, nil) else {
            throw ImageResizeError.cannotCreateImageSource
        }
        return source
    }
}