conversations-classic-ios/ConversationsClassic/AppCore/Files/FileProcessing.swift

import Foundation
import UIKit

final class FileProcessing {
    static let shared = FileProcessing()

    static var fileFolder: URL {
        // swiftlint:disable:next force_unwrapping
        let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
        let subdirectoryURL = documentsURL.appendingPathComponent(Const.fileFolder)
        if !FileManager.default.fileExists(atPath: subdirectoryURL.path) {
            try? FileManager.default.createDirectory(at: subdirectoryURL, withIntermediateDirectories: true, attributes: nil)
        }
        return subdirectoryURL
    }

    func createThumbnail(localName: String) -> String? {
        let thumbnailFileName = "thumb_\(localName)"
        let thumbnailUrl = FileProcessing.fileFolder.appendingPathComponent(thumbnailFileName)
        let localUrl = FileProcessing.fileFolder.appendingPathComponent(localName)

        // check if thumbnail already exists
        if FileManager.default.fileExists(atPath: thumbnailUrl.path) {
            return thumbnailFileName
        }

        // create thumbnail if not exists
        switch localName.attachmentType {
        case .image:
            guard let image = UIImage(contentsOfFile: localUrl.path) else { return nil }
            let targetSize = CGSize(width: Const.attachmentPreviewSize, height: Const.attachmentPreviewSize)
            guard let thumbnail = scaleAndCropImage(image, targetSize) else { return nil }
            guard let data = thumbnail.pngData() else { return nil }
            do {
                try data.write(to: thumbnailUrl)
                return thumbnailFileName
            } catch {
                return nil
            }

        default:
            return nil
        }
    }
}

func scaleAndCropImage(_ img: UIImage, _ size: CGSize) -> UIImage? {
    let aspect = img.size.width / img.size.height
    let targetAspect = size.width / size.height
    var newWidth: CGFloat
    var newHeight: CGFloat
    if aspect < targetAspect {
        newWidth = size.width
        newHeight = size.width / aspect
    } else {
        newHeight = size.height
        newWidth = size.height * aspect
    }

    UIGraphicsBeginImageContextWithOptions(size, false, 0.0)
    img.draw(in: CGRect(x: (size.width - newWidth) / 2, y: (size.height - newHeight) / 2, width: newWidth, height: newHeight))
    let newImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return newImage
}